Copyright by Brook Colleen Daun Riley 2004
242
Copyright by Brook Colleen Daun Riley 2004
Transcript of Copyright by Brook Colleen Daun Riley 2004
Copyright
by
Brook Colleen Daun Riley
2004
The Dissertation Committee for Brook Colleen Daun Riley Certifies that this is the
approved version of the following dissertation:
LARAMIDE EXHUMATION AND HEATING IN SOUTHEASTERN ARIZONA:
LOW-TEMPERATURE THERMAL HISTORY AND IMPLICATIONS FOR ZIRCON FISSION-TRACK
SYSTEMATICS
Committee:
Mark Cloos, Supervisor
John I. Garver
Earle F. McBride
Randall Marrett
Raymond V. Ingersoll
George H. Davis
LARAMIDE EXHUMATION AND HEATING IN SOUTHEASTERN ARIZONA:
LOW-TEMPERATURE THERMAL HISTORY AND IMPLICATIONS FOR ZIRCON FISSION-TRACK
SYSTEMATICS
by
Brook Colleen Daun Riley, B.S.
Dissertation
Presented to the Faculty of the Graduate School of
The University of Texas at Austin
in Partial Fulfillment
of the Requirements
for the Degree of
Doctor of Philosophy
The University of Texas at Austin
May, 2004
Dedication
This dissertation is dedicated to Robert K. Goldhammer…he wouldn’t let me quit.
v
Acknowledgements
“…exhumin’ things that’s better left alone.”
—Randy Travis, Storms of Life, 1986
That’s what this dissertation and this degree have been about: bringing up questions
that don’t have ready answers, figuring out the best way (or at least one way) to answer them,
and continually expanding one’s horizons in order to do that. But of course this did not happen
in a vacuum.
Geologic expertise and considerable financial assistance were contributed by Mark
Cloos. I am continually impressed by the extent of Mark’s knowledge of geology, and his
support of projects and ideas outside the general realm of tectonics, structure, and petrology.
When I first came to UT, and confessed that I had this idea about the Laramide of SE Arizona
that I wished to pursue, I was floored by Mark’s response: it was something along the lines of
“It’s your Ph.D….you should make it what you want.” I hadn’t ever experienced such open-
minded willingness to let me pursue what a friend once called the “last best chance to do what
you really want to do.” Mark always supported my research, both financially and in spirit. He
also recognized my ability to self-direct, and I was given my head very early in my course of
study.
vi
Of course that kind of freedom opened me up to a whole new world (and trouble!), some
of which I was ill-prepared to realize. Enter John Garver. I’ll bet that when he met me over a
beer in Lorne, Australia, he never would have realized the fundamental (‘crucial’ he might call it)
role he would play in this work. Simply put, there is no way that this dissertation would be what it
is without John, and it likely would not even have been possible in it’s current form without his
tremendous effort and patience. John is a talented mind, capable of seeing the best in
everything, and picking up on the thread that links seemingly disparate observations. This goes
a long way in your third year when you’re just about ready to throw in the towel should things not
begin to go your way. Perhaps the best thing about an advisor like John is having someone who
you can call, whenever, and they’re always ready to talk, about whatever. I always liked picking
up the phone in our office and hearing “Dude, John Garver here…this plot is cool!” I think one of
my acquaintances put it best after she met John at a GSA meeting recently: she gave him a hug
and said “Man, I wish you were my advisor!”
I must also thank my committee, each of whom was carefully selected for their expertise
in sedimentary petrology and diagenesis, brittle deformation, ‘the Laramide’ of southeastern
Arizona, and tectonics and sandstone petrology. Profs. Earle McBride, Randy Marrett, George
Davis, and Ray Ingersoll always proved available when needed, never blinked when my papers
didn’t come out on schedule, and were understanding as things took a turn for the unknown. I
could not have crafted a better committee.
Technical assistance was provided willingly and cheerfully by many people. Raman
spectroscopy proved to be one of the turning points in my work, and without the direction and
encouragement of Dr. Lutz Nasdala (University of Mäinz), breakthroughs might never have been
made. The road to crystallization ages and REE chemistries for The Holy Sample was paved by
vii
John Lansdown, Jim Connelly, and Kathy Manser, all from the University of Texas. Kitty
Milliken, also of UT, provided assistance with the SEM and CL, which laid the groundwork for the
Raman spectroscopy and laser analyses. Finally, Eric James always provided a ready ear for
some off-the-wall sedimentologist’s idea on recycling of Sierran arc-derived zircons or what Ce
anomalies really mean…subjects far outside my normal frame of reference.
Without the efforts of Philip Guerrero, Debra Sue Trinque, and Bill Woods, I wouldn’t
have been able to register, defend, graduate, pay my bills, or get anything administrative done.
A Ph.D. is a time-consuming, selfish, expensive, and strange thing to do, albeit
rewarding in the end. And many of us forget while we’re here that it is a choice: we choose this
path, whereas most people would turn tail when they realized what it was all about. And so I
must thank the following people for putting up with me while I did this to myself: Matthias Bernet,
Donna Cathro, Kara Dotter, Rob Forkner, Tim Gibbons, Kristin Goddard, Fabienne Grellet-
Tinner, Chris Hare, Dan Harrington, Jeff Harrison, Kim High, Brian Knight, Cori Lambert,
Graham Moss, J. Terrill Paterson, Barbara Tillotson, Keith Woodburne, and Richard Weiland. In
particular, when I was probably at my worst, Jason Poe saw me as ‘the best.’
Most deserving of thanks are Bill and Dianne Riley, who provided field assistance, home
base, encouragement, food, and who listened intently as I explained how a mass spec works
(sorry, Ma!).
Some of the most important people in my life while I’ve been at UT have been my
students. While in theory they have no choice but to pay attention to the person in front of them
and what that person tells them how to do, the truth is that learning and engaging are always a
viii
choice. It was often my refuge to enter the classroom or go into the field and discuss plunging
folds, cross-cutting relationships, and trough cross-strata, and always my pleasure to be a part of
that process. I thank each student with whom I had contact for that opportunity.
In parallel with this are the people for whom I taught. I learned more than I can express
about teaching field geology, mapping, structure, sedimentology, and field logistics from Mark
Helper, Earle McBride, Randy Marrett, Jim Connelly, and Bob Goldhammer. I very much
appreciate the opportunity to learn from and teach with these consummate professionals.
Projects like mine, which seed in the blurry head of an undergrad at the U of A, typically
are not funded by large NSF-style grants, and rely on many smaller contributions to complete
field work and analyses, in addition to the daily routine of eating and paying rent. Funding was
provided by the following entities: Department of Geological Sciences; Chevron Merit Fellowship
Program; Getty Oil Company Centennial Chair/Mark Cloos; Laura Thomson Barrow Graduate
Fellowship/Dr. Thomas D. Barrow; Gulf Coast Association of Geological Societies; Atlantic-
Richfield Company (ARCO); Society of Independent Professional Earth Scientists; Department
of Energy Reactor Use Sharing Program (DOE-RUS)/Steve Binney; BP-Amoco; Austin
Geological Society; Bowman Endowed Presidential Scholarship/Mr. John B. Payne; Geological
Society of America; University of Texas at Austin Continuing Fellowship Program; Wendler
Professional Development Fund.
Access was provided by the following: Fort Huachuca Army Intelligence Base, Fort
Huachuca, Arizona; KG Ranch, Canelo Hills, Arizona; Tom Hunt, Foreman, Rail X Ranch,
Patagonia, Arizona.
ix
LARAMIDE EXHUMATION AND HEATING IN SOUTHEASTERN ARIZONA:
LOW-TEMPERATURE THERMAL HISTORY AND IMPLICATIONS FOR ZIRCON FISSION-TRACK
SYSTEMATICS
Publication No._____________
Brook Colleen Daun Riley, Ph.D.
The University of Texas at Austin, 2004
Supervisor: Mark Cloos
Fission-track (FT) ages of zircon from Mesozoic sandstones were analyzed to address
provenance and post-depositional thermal history of Laramide synorogenic strata. Upper
Cretaceous samples show a complex provenance, with significant recycling from underlying
rocks. FT peak ages from 14 Jura-Cretaceous sandstones include populations of 570-165, 140-
82, and 68-42 Ma. Older single-grain ages (1000-600 Ma) indicate long-term sub-annealing
temperatures (<180°C, up to 260°C, depending on single-grain response to heating) for portions
of the source area. Older FT ages present in all sampled units indicate little burial of the Jura-
Cretaceous rocks prior to recycling into the Upper Cretaceous; record little variation in the
thermal signature of recycled crustal detritus; and show that the older Jurassic and Cretaceous
rocks likely provided an important source for the Fort Crittenden Formation. The uniformity of FT
ages necessitates that source rocks all record essentially the same thermal signatures.
Accordingly, the relative abundance of rock units in the source terrane was rather uniform, and
there was no preferential exhumation of one source area over another.
x
Some zircons show evidence for significant post-depositional thermal annealing; these
strata reached temperatures sufficient to anneal fission tracks in some grains (c. 180°C-260°C).
Thicknesses of overlying units was likely less than 2 km; as such, the FT age structure is not
purely the result of burial. Regionally, samples with Paleocene-Eocene reset peak ages
coincide with proximity to magmatic bodies (75-40 Ma). Besides conductive heating, a
hydrothermal system may have locally modified these rocks, causing preferential resetting of
certain zircons. This setting provides an opportunity to investigate controls on single-grain
thermal response. Geochemical and crystallinity data indicate a correlation between old
crystallization ages, high U+Th concentrations, elevated alpha-damage, and young reset FT
ages. Resetting occurred in grains with higher radiation damage, and less damaged grains have
a higher temperature of track retention and therefore retain a primary detrital signature. Zircon
color is related in part to increasing radiation damage, and can be used for identifying different
thermal events in both the pre- and post-depositional history of individual zircons. In this study,
honey and colorless grains essentially behave as one population in all data sets. Based on
these data, this study establishes criteria for identifying reset grains in detrital populations, and
suggests revisions in the current methodology.
xi
Table of Contents
List of Tables .................................................................................................................... xiv
List of Figures.................................................................................................................... xv
List of Figures.................................................................................................................... xv
Chapter 1—Laramide exhumation and heating in southeastern Arizona: Low- temperature thermal history and provenance............................................................1
Abstract......................................................................................................................1
Introduction................................................................................................................3
Background/Methods/Sampling ................................................................................7
Early Laramide Sedimentation—Existing Age Constraints .............................7
Santa Rita Mountains/Canelo Hills ........................................................8
Huachuca Mountains ...........................................................................15
Sample Suite .................................................................................................16
Fission-track Analysis ....................................................................................17
Vitrinite Reflectance.......................................................................................19
Data/Observations...................................................................................................26
Fission-track Data..........................................................................................26
Young Reset Peak Ages......................................................................26
Provenance Ages.................................................................................29
Pb-Pb Geochronology ...................................................................................31
Mineralogic Provenance ................................................................................32
Diagenetic Overprint ......................................................................................33
Discussion ...............................................................................................................34
Age Data—Young Reset Peak Ages.............................................................34
Age Data—Static Peaks ................................................................................35
Pb-Pb Ages....................................................................................................38
Provenance of FT Samples, Prior Work ........................................................40
Diagenesis of Fort Crittenden Formation Samples, and Prior Work .............42
Regional versus Local Heating......................................................................42
Implications for Provenance of Fort Crittenden Formation and Changes in Thermal Structure through Time..........................................................47
Provenance..........................................................................................48
xii
Structural Constraints ..........................................................................49
Conclusions .............................................................................................................55
Chapter 2—Controls on the low-temperature thermal response of single detrital zircons: Temperature, crystallinity, and chemistry .................................................57
Abstract....................................................................................................................57
Introduction..............................................................................................................59
Methods...................................................................................................................62
Field Setting...................................................................................................62
Fission-track Analysis ....................................................................................64
Cathodoluminescence ...................................................................................65
Crystallinity.....................................................................................................69
Rare-Earth-Element Geochemistry and Pb-Pb Ages ....................................69
Data/Observations...................................................................................................71
Fission-track Data..........................................................................................71
Vitrinite-Reflectance Data ..............................................................................82
Pb-Pb Data from Color/Morphology Fractions...............................................85
Raman Microscopy Data ...............................................................................88
Effective Dose/Effective Dose Factor ..................................................96
FT Ages versus Minimum Damage Storage Ages.............................101
REE Data.....................................................................................................108
Discussion .............................................................................................................113
FT Age Data ................................................................................................113
Raman Crystallinity Data .............................................................................114
Overlapping Behavior: Honey vs. Colorless Zircons ..................................116
Activation Energy for Damage Annealing....................................................117
Criteria for Recognizing Reset Grains .........................................................118
Conclusions ...........................................................................................................123
Appendix 1—Age data for Upper Cretaceous and key post-Upper Cretaceous igneous rocks in southeastern Arizona ...............................................................127
Appendix 2—Sample suite field descriptions for fission-track work, Santa Rita and Huachuca Mountains, southeastern Arizona.........................................................131
Appendix 3—Description of techniques used in this study .............................................149
Fission-track Thermochronology ...........................................................................149
Cathodoluminescence...........................................................................................153
xiii
Raman Microscopy................................................................................................154
U-Th-Pb and Rare-earth-element Analysis ...........................................................156
Appendix 4—Complete fission-track data for Jura-Cretaceous sandstone samples, Santa Rita and Huachuca Mountains, southeastern Arizona................................159
Appendix 5—Compositional data for Upper Cretaceous Fort Crittenden Formation sandstones, Santa Rita and Huachuca Mountains, southeastern Arizona ...........208
Appendix 6—Electron-microprobe analyses of 57 zircons from Station 23, Huachuca Mountains ..............................................................................................................209
References ......................................................................................................................213
Vita.…..............................................................................................................................222
xiv
List of Tables
Table 1-1. Binomial fitted and χ2 fission-track peak ages for Mesozoic sandstone
samples from the Santa Rita and Huachuca Mountains, southeastern
Arizona. ......................................................................................................22
Table 2-1. Zircon color and morphology fractions, Station 23, Huachuca Mountains. ....66
Table 2-2. Single-grain fission-track ages (FTGA), Pb-Pb ages, effective uranium
concentrations (eU), and Raman crystallinity data (bandwidth and position)
for color fraction zircons from Station 23, Huachuca Mountains................67
Table 2-3. Fission-track peak ages from Station 23, Huachuca Mountains. ...................78
Table 2-4. Radiation damage dose data for color fraction zircons from Station 23,
Huachuca Mountains..................................................................................98
Table 2-5. Rare earth element concentration data (ppm) for color fraction zircons from
Station 23, Huachuca Mountains. ............................................................109
xv
List of Figures
Figure 1-1. Regional geologic map of southeastern Arizona (after Reynolds, 1988),
showing study areas in the Santa Rita and Huachuca Mountains)..............5
Figure 1-2. Generalized time-stratigraphic column for the Middle Jurassic-Paleogene
section, southeastern Arizona (column and lithologies after Hayes, 1970a,
1970b; Inman, 1982; Hayes, 1986, 1987; Inman, 1987; Dickinson and
others, 1989; Bassett and Busby, 1996). .....................................................6
Figure 1-3. Geologic map of the Huachuca Mountains (generalized after Hayes and
Raup, 1968) showing sample locations as part of the regional study..........9
Figure 1-4. Geologic map of the eastern flank of the Santa Rita Mountains,
southeastern Arizona (after Drewes, 1971a). ............................................10
Figure 1-5. Geologic map of the northern part of the Canelo Hills, southeastern
Arizona (after Drewes, 1980; Kluth, 1982; Reynolds, 1988). .....................13
Figure 1-6a. Qm-P-K, Qm-F-Lt, and Qp-Lv-Ls ternary plots from Inman (1987) for 10
Fort Crittenden Formation samples (shale member) from the Adobe
Canyon area, eastern Santa Rita Mountains. ............................................20
Figure 1-6b. Qm-P-K, Qm-F-Lt, and Qp-Lv-Ls ternary plots from Hayes (1987).............20
Figure 1-6c. Qm-P-K, Qm-F-Lt, and Qp-Lv-Ls ternary plots for 10 Fort Crittenden
Formation samples from the Huachuca and Santa Rita mountains from
this study. ...................................................................................................20
Figure 1-7. Pb-Pb age versus fission-track grain age (FTGA) for the same zircon
grains from Station 23, Huachuca Mountains. ...........................................25
xvi
Figure 1-8. Huachuca and Santa Rita Mountains geologic maps (after Hayes and
Raup, 1968; Drewes, 1971) showing zircon fission-track peak ages (χ2
ages as noted; binomial fitted ages elsewhere) for sample sites included
in this study.................................................................................................28
Figure 1-9. Compositional ternary diagram for conglomerates in the Fort Crittenden
Formation (N = 27 clast counts; from Hayes, 1987)...................................51
Figure 1-10a. Idealized structural-sedimentologic scenario for the Fort Crittenden
Formation depositional period. ...................................................................53
Figure 1-10b. Evolution of 200°C isotherm during post-depositional magmatic activity
and subsequent burial by uppermost Cretaceous and younger volcanic
and sedimentary rocks. ..............................................................................53
Figure 2-1a. Generalized time-stratigraphic column for the Upper Jurassic-Upper
Cretaceous section, Huachuca Mountains, showing approximate
stratigraphic position of sample from Station 23 (column and lithologies
after Hayes, 1970a; Hayes, 1970b; Palmer, 1983; Hayes, 1986; Hayes,
1987; Dickinson and others, 1989).............................................................63
Figure 2-1b. Huachuca Mountains geologic map (generalized after Hayes and Raup,
1968) showing location of Station 23, sample locations as part of the
regional study. ............................................................................................63
Figure 2-2. Cumulative probability density (PD) plot and fitted for bulk zircon from
Station 23, Huachuca Mountains; peak ages fitted after Brandon (1996). 72
Figure 2-3. Cumulative probability density (PD) curves for zircon fractions from Station
23, Huachuca Mountains............................................................................73
xvii
Figure 2-4. Cumulative probability distribution (PD) plot and fitted peaks for all counted
grains (bulk plus color fractions), Station 23, Huachuca Mountains; peak
ages fitted after Brandon (1996).................................................................74
Figure 2-5. Huachuca Mountains geologic map (generalized after Hayes and Raup,
1968) showing representative zircon fission-track peak ages from the
regional study. ............................................................................................77
Figure 2-6. Pb-Pb age versus fission-track age (FTGA) for the same zircon grains
from Station 23, Huachuca Mountains. ......................................................86
Figure 2-7. Full-width at half maximum (FWHM) versus Raman wave number for
color fractions from Station 23, Huachuca Mountains................................90
Figure 2-8. Full-width at half maximum (FWHM) versus U+Th concentration (effective
uranium, or eU (= U+Th in ppm)) for color fractions from Station 23,
Huachuca Mountains..................................................................................93
Figure 2-9. Full-width at half maximum (FWHM) versus fission-track grain age (FTGA)
for color fractions from Station 23, Huachuca Mountains. .........................95
Figure 2-10a. Comparison of color fractions from Station 23, Huachuca Mountains
with 'complete storage' line and analyses of 33 zircons considered to
have remained at sub-annealing temperatures since crystallization
(Nasdala and others, 2001)........................................................................97
Figure 2-10b. Comparison of effective dose factor with eU from color fraction zircons
from Station 23. ..........................................................................................97
Figure 2-10c. Effective dose factor compared to fission-track age of color fraction
zircons from Station 23...............................................................................97
Figure 2-10d. Effective dose compared to eU concentration for color fraction zircons
from Station 23. ..........................................................................................97
xviii
Figure 2-10e. Comparison of effective dose to FT age for color fraction zircons from
Station 23. ..................................................................................................97
Figure 2-11a. Comparison of effective doses using those calculated from the fission-
track ages, and those calculated based on present crystallinities (from
Raman microprobe data, FWHM). ...........................................................102
Figure 2-11b. Comparison of minimum damage storage ages (based on Raman
microprobe data, FWHM) with fission-track ages. ...................................102
Figure 2-12. Normalized rare-earth-element data for color fraction zircons from
Station 23, Huachuca Mountains. ............................................................111
Figure 2-13. Qualitative relationship between time, alpha-damage, and effective
uranium (eU) concentration......................................................................119
Figure 2-14. Inferred relationship between annealing of fission tracks, annealing
temperature, and accumulated alpha-damage. .......................................124
1
Chapter 1—Laramide exhumation and heating in southeastern Arizona: Low-temperature thermal history and provenance
ABSTRACT
Disagreement regarding patterns of Laramide deformation and basin development in SE
Arizona underlies the lack of a clear picture of exhumation and sediment recycling for
syntectonic basins in this area. Fission-track (FT) ages of zircon from Mesozoic sandstones
were analyzed to address the provenance and post-depositional thermal history of the
synorogenic strata. Samples from strike-normal transects across the Laramide basin boundary
within the Upper Jurassic-Upper Cretaceous section show a complex provenance, with
significant recycling from the underlying rocks. FT peak ages from 14 Jura-Cretaceous
sandstones include populations of 570-165, 140-82, and 68-42 Ma. Numerous older single-
grain ages (1000-600 Ma) are also present, indicating long-term sub-annealing temperatures
(less than perhaps 180°C, up to 260°C, depending on single-grain response to heating) for
portions of the source area. While most samples show a range of provenance ages, a small
fraction of grains shows evidence for significant post-depositional thermal annealing. Burial
depths were highly variable, but the cumulative thicknesses of units overlying the Jura-
Cretaceous section was likely less than 2 km. Accordingly, the zircon FT age structure present
in sandstone samples included in this study is not just the result of burial. Regionally, samples
with Paleocene-Eocene reset peak ages coincide with proximity to magmatic bodies ranging
from 75-40 Ma in age. Besides conductive heating, a hydrothermal system may have locally
modified these rocks, and caused preferential resetting of certain zircons. Older grain ages
present in all sampled units indicate little burial of the older Jurassic and Cretaceous rocks prior
to recycling into the Fort Crittenden Formation (Upper Cretaceous); record little variation in the
thermal signature of the recycled crustal detritus; and show that the older Jurassic and
2
Cretaceous rocks likely provided an important sediment source for the Fort Crittenden
Formation. Prior work on the provenance of early Laramide sedimentary rocks in this area
documented the presence of primarily volcanic and granitic source rocks. The uniformity of FT
ages necessitates that source rocks, no matter their composition or age of
deposition/crystallization, all record essentially the same thermal signatures. Accordingly, during
the perhaps 10 m.y. of deposition of the Fort Crittenden Formation, the relative abundance of
different rock units in the source terrane was rather uniform, and it is likely that there was no
preferential exhumation of one source area over another.
3
INTRODUCTION
Structural development and basin formation in the Laramide orogen in southeastern
Arizona present a longstanding problem in the regional geology of the southwestern U.S.
(Eardley, 1963; Coney, 1976; Krantz, 1989). Uncertain structural, kinematic, and sedimentologic
ties between the southern Laramide province and the classic Laramide province in Colorado and
Wyoming have led to contradictory tectonic models, as discussed in detail by Coney (1976) and
Krantz (1989). Two fundamental questions are basin-formation mechanisms and source-rock
exhumation histories. Additionally, confusion arises simply from terminology. Some workers
use the term ‘Laramide’ as a time descriptor (e.g. Coney, 1972; Davis, 1979), as a region (e.g.
Coney, 1972; Dickinson and Snyder, 1978), or as a structural style (e.g. Drewes, 1978, 1981,
1988a, 1988b; Dickinson and Snyder, 1978; Dickinson and others, 1988). In addition, the
spatially and temporally transgressive nature of deformation from west to east across western
North America, and across southern Arizona in particular, as well as different basement
anisotropies from place to place, should have caused variations in the style of Laramide
deformation. Consequently, no one style adequately describes structures in all areas (Dickinson
and Snyder, 1978).
In the context of this work, the term Laramide is broadly defined as the structural
development associated with ‘shallow-slab’ subduction beneath western North America
(Dickinson and Snyder, 1978). In concert with subduction-driven shortening, laterally restricted
foreland basins developed adjacent to locally uplifted and exhumed blocks along high- and low-
angle reverse faults. Deformation and magmatic activity associated with the progressive
decrease in the dip of the subducting slab were both temporally and spatially transgressive
(Dickinson and Snyder, 1978). However, as the area included in this study is relatively small,
4
the time-transgressive nature of Laramide deformation is limited. Nonetheless, the superposition
of structures, and dating of these features, remains a problem.
Understanding basin formation and attendant processes must be based on knowledge
of relationships among fault activation and movement, exhumation of adjacent source areas, and
basin initiation and evolution. Modification of Laramide strata by subsequent deformation and
magmatism has complicated the picture, and seeing through that deformation proves difficult,
particularly where the major Laramide structures also have a younger history of movement (e.g.,
Sawmill Canyon fault zone, Santa Rita Mountains; Drewes, 1981). In general, these
relationships are more clearly defined for basins and associated source rocks in the classic
Laramide province (i.e. Chapin and Cather, 1983; Dickinson and others, 1988; Yin and Ingersoll,
1997), and in portions of the New Mexico segment of the belt (Seager and Mack, 1986; Mack
and Clemons, 1988). Understanding of these problems in southeastern Arizona is fragmentary,
and few studies within the southern Laramide province are linked regionally.
To better address thermal evolution and basin development in southeastern Arizona
during early Laramide sedimentation and subsequent magmatism, this study presents new
thermal and timing information obtained from zircon fission-track (FT) analysis with new and
existing provenance data for the Santa Rita and Huachuca mountains (Figure 1-1). Sample
suites from sandstones of Middle Jurassic through Late Cretaceous age (Figure 1-2) provide
new thermochronologic data, and traditional provenance analysis complements the
geochronology. Key factors in understanding Laramide thermal, tectonic, and basin
development in southeastern Arizona include the age of initial sedimentation; the timing of basin
subsidence; and the thermochronology of detrital grains which record the exhumation history of
the source areas.
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rocks, in
terc
ala
ted
vo
lca
nic
ro
cks
Ju
rassic
se
dim
en
tary
, vo
lca
nic
ro
cks
Ju
rassic
gra
nito
id r
ocks (
gra
nite
to
dio
rite
, lo
ca
l a
lka
line
ro
cks)
Pa
leo
zo
ic s
ed
ime
nta
ry r
ocks,
un
diffe
ren
tia
ted
Pe
nn
sylv
an
ian
-Pe
rmia
n s
ed
ime
nta
ry
rocks
Ca
mb
ria
n-M
issis
sip
pia
n s
ed
ime
nta
ry
rocks
M. P
rote
rozo
ic g
ran
ito
id r
ocks (
~1
40
0
Ma
)
L. P
rote
rozo
ic m
eta
se
dim
en
tary
ro
cks,
un
diffe
ren
tia
ted
me
tam
orp
hic
ro
cks
Jg
Tsn
Tsp
Tv Ti
KT
g
Kv
JK
s
Jsv
Pzu
IPP
Yg
Xm
s
CM
CM
JK
s
Fig
ure
1-1
. R
eg
ion
al g
eo
log
ic m
ap
of so
uth
ea
ste
rn A
rizo
na
(a
fte
r R
eyn
old
s, 1
98
8),
sh
ow
ing
stu
dy a
rea
s in
th
e S
an
ta
S A N T A R I T A M O U N T A I N S
C A N
E L O
H I
L L S
H U A
C H
U C
A
M O
U N
T A
I N S
Rita a
nd H
uachuca M
ounta
ins. F
ield
are
a for
this
stu
dy inclu
des e
xposure
s o
f th
e J
ura
-
Cre
tace
ou
s s
ectio
n (
port
ion
s o
f Jsv,
JK
s).
5
PATAGONIA
MOUNTAINS
Sa
nta
Rit
a
Mo
un
tain
s
W E S T
E A S T
Hu
ac
hu
ca
Mo
un
tain
s
Apache C
anyon
Form
ation (
~250 m
)
Will
ow
Ca
nyo
nF
orm
ation (
~1300 m
)
Fort
Crittenden
Form
ation (
~1500 m
)
Sa
lero
Fm
.
vo
lca
nic
s
Turn
ey R
anch
Form
ation (
~1500 m
)
? ?
Sh
elle
nb
erg
er
Ca
nyo
nF
orm
ation (
~1000 m
)
Gla
nce
Co
ng
lom
era
te (
0-2
00
0 m
)
?
Te
mp
ora
l/B
ath
tub
Fo
rma
tio
ns
?
Helv
etia s
tocks/q
uart
z latite
plu
gs
Gre
ate
rvill
e p
lugs/q
uart
z latite
porp
hyry
Re
dM
ounta
inco
mp
lex
Grin
go
Gu
lch
plu
ton
/vo
lca
nic
s
Pa
tag
on
ia
Mo
un
tain
s
Ca
ne
lo
Hills
ce
ntr
al S
an
ta R
ita
hyd
roth
erm
al a
lte
ratio
n
Ele
ph
an
t H
ea
d/M
ad
era
Ca
nyo
n/
Jo
se
ph
ine
Ca
nyo
n in
tru
siv
es
Coro
na s
tock/q
uart
z d
iorite
E o
f M
t.F
agan R
anch
vo
lca
nic
s o
fD
ove
Ca
nyo
n/
tra
ch
ya
nd
esite
of M
ea
do
wV
alle
y
Cin
tura
Form
ation
(Bis
bee G
roup)
Fort
Crittenden
Form
ation
(~1200 m
)
?? ?
vo
lca
nic
s o
f
Jo
ne
s M
esa
Ju
rassic
vo
lca
nic
s o
f
Jo
ne
s M
esa
?
Cin
tura
Form
ation
(~2
90
m)
Fort
Crittenden
Form
ation (
~660 m
)
Mu
ral F
orm
atio
n(~
210 m
)
Gla
nce
co
ng
lom
era
te,
an
de
site
(0-6
30 m
)
?? ?
Morita
Form
ation
(~1270 m
)
Ca
ne
lo H
ills
vo
lca
nic
s
qu
art
z m
on
zo
nite
,ce
ntr
al H
ua
ch
uca
s??
50 M
a
60 M
a
70 M
a
80 M
a
90 M
a
110 M
a
120 M
a
130 M
a
163 M
a
150 M
a
140 M
a
100 M
a
APTIANALBIANCENOMANIAN
TU
RO
NIA
N
CO
NIA
CIA
N
SA
NT
ON
IAN
CAMPANIANMAASTRICHTIAN
LATE EARLY
CRETACEOUSE
AR
LY
LA
TE
EA
RLY
EOCENE PALEOCENE
PALEOGENETERTIARY
NEOCOMIAN
JURASSIC
LATE
Co
rra
l C
an
yo
nvo
lca
nic
s
?
Fig
ure
1-2
. G
enera
lized tim
e-s
tratigra
phic
colu
mn for
the M
iddle
Jura
ssic
-Pale
ogene s
ection,
south
easte
rn A
rizona
up
pe
r co
ng
lom
era
te
su
bu
nit
low
er
co
ng
lom
era
te
su
bu
nit
sh
ale
me
mb
er
tuff/u
pp
er
red
co
ng
lom
era
te m
em
be
r
low
er
red
co
ng
lom
era
te m
em
be
r
bro
wn
co
ng
lom
era
te m
em
be
r
sh
ale
me
mb
er
(colu
mn a
nd litholo
gie
s a
fter
Hayes, 1970a, 1970b; In
man, 1982; H
ayes, 1986, 1987; In
man, 1987;
Dic
kin
son a
nd o
thers
, 1989; B
assett a
nd B
usby,
1996).
T
imescale
of
Palm
er
(1983).
N
ote
that
these
are
com
posite c
olu
mns for
the e
ntire
are
a, and that all
form
ation a
nd intr
a-f
orm
ational boundaries a
re
tim
e-t
ransgre
ssiv
e in d
eta
il.
6
Bis
bee G
roup
Bis
be
e G
rou
p
7
Most crucial is to define the source area for Laramide basin sediments, in terms of both
the thermal signature (low-temperature cooling histories of source terranes), as well as the
petrologic provenance. The focus of this study is the Upper Cretaceous Fort Crittenden
Formation (Figure 1-2), as it records the onset of Laramide sedimentation in this area (Dickinson
and others, 1989). It will be shown that the thermal signature and the provenance of sandstones
in the Fort Crittenden Formation can be related to that of the Jurassic and Lower Cretaceous
section.
BACKGROUND/METHODS/SAMPLING
Early Laramide Sedimentation—Existing Age Constraints
The depositional age of the Fort Crittenden Formation in the study area is 85-75 Ma
based on limited terrestrial faunal records and K-Ar dating of volcanic rocks stratigraphically
above and below the formation (Drewes, 1968; Hayes, 1970a; Hayes, 1970b; Inman, 1982;
Hayes, 1986; Dickinson and others, 1989). Based on measured sections and regional mapping
in the Santa Rita and Huachuca Mountains, early Laramide sedimentation is thought to have
ceased by the time of deposition of the Salero Formation volcanic rocks (Dickinson and others,
1989), dated at about 75 Ma (± 4 m.y.; K-Ar on biotite from multiple members of the formation,
detailed in Appendix 1; Drewes, 1968; Inman, 1982; Keith and Wilt, 1986).
Previous work on the regional depositional and stratigraphic relationships of the Fort
Crittenden Formation includes that of Inman (1982, 1987) and Hayes (1986, 1987). At the
regional scale in the Fort Crittenden Formation, Hayes’ work (1986) suggests the presence of
two separate depositional systems: one in the Santa Rita Mountains and Canelo Hills, which is
distinct from other Fort Crittenden Formation deposits in the Huachuca Mountains (Figure 1-1).
Lithologies in most sections define overall fining-upward sequences, which Hayes (1986)
8
attributed to the destruction of tectonic relief. According to Hayes (1986), depositional
environments in the Santa Rita Mountains and Canelo Hills include middle alluvial fans, with
deposition by streamflood, sheet flood, and debris flow processes. In contrast, depositional
elements in the Huachuca Mountains section, best expressed at Brushy Canyon in the north-
central part of the range (Figure 1-3), show an evolution from alluvial fans to coarse braidplains,
capped at the top by marginal lacustrine mudflat deposits.
Santa Rita Mountains/Canelo Hills
The Fort Crittenden Formation (Upper Cretaceous) in the Santa Rita Mountains includes
five members defined by Drewes (1968). From oldest to youngest, these include the shale,
lower red conglomerate, brown conglomerate, upper red conglomerate, and tuff members
(Figure 1-2). The uppermost Cretaceous section unconformably overlies the Lower Cretaceous
Bisbee Group in the Santa Rita Mountains, but in many exposures, the formation is faulted
against Lower Cretaceous sedimentary and volcanic, Triassic-Jurassic igneous, Paleozoic
sedimentary, and Precambrian granitic rocks (Drewes, 1971a; Kluth, 1982). In the Adobe
Canyon area on the east flank of the range (Figure 1-4), there is a disconformity between the
Turney Ranch Formation (uppermost Bisbee Group) and the basal Fort Crittenden Formation
shale member (Inman, 1982; Hayes, 1986; Inman, 1987). According to Inman’s work (1982,
1987), the contact lacks the structural discordance suggested in previous studies (i.e. Drewes,
1971a, 1971b). In the Santa Rita Mountains, the Fort Crittenden Formation is locally
conformably overlain by the Maastrichtian Salero Formation (Drewes, 1971a, 1971b), composed
predominantly of dacitic volcanic and associated sedimentary rocks. The igneous rocks are
considered by most to reflect the encroachment of arc activity into southeastern Arizona during
the eastward sweep of magmatism associated with slab flattening (Hayes, 1970b; Coney,
Kfc
Kc
Kc
Kg
aJh
?
Km
oK
ga
Kc
23
Kfc
Kc
Km
o
Km
u
Kc
Km
o
Km
o
Km
o
Km
u
Kg
Kg
Kg
aP
zu
Pzu
Kga
Kg
eK
ga
Pzu
e
Pzu
Pzu
Jh
Km
o
Kg
Pzu
Km
o
Kg
Kga
Kg
Km
oK
g
Km
u
Kc
Kfc
TQ
uK
b?
TQ
u
Km
o?
Tg
Tg
TQ
u
TQ
u
TQ
u
TQ
uTi
Ti
Km
o
pC
g
Tg
TQ
u
KfcTi
Pzu
eQg
Tg
Qal
TQ
u
Km
o
Km
u
Kc
Kg
a
Kg
Kb
pC
g
Jh
TJc
Te
rtia
ry a
nd
Qu
ate
rna
ry g
rave
ls,
allu
viu
m
Tert
iary
intr
usiv
es (
quart
z
mo
nzo
nite
, a
laskite
, g
ran
o-
dio
rite
, a
lka
li d
iorite
); in
tern
al
ag
e r
ela
tio
nsh
ips u
nce
rta
in
Up
pe
r C
reta
ce
ou
s F
ort
Critt
en
de
n
Fo
rma
tio
n (
ea
rly L
ara
mid
e b
asin
fill
)
Lo
we
r C
reta
ce
ou
s B
isb
ee
Gro
up
Ju
rassic
Ca
ne
lo H
ills
Vo
lca
nic
s a
nd
asso
cia
ted
rocks
Pa
leo
zo
ic s
ed
ime
nta
ry
rocks, e
xo
tic b
locks o
f
Pa
leo
zo
ic w
ith
in o
the
r u
nits
Pre
ca
mb
ria
n g
ran
ite
01
kilo
me
ters
mile
s0
1
fissio
n tra
ck s
am
ple
; S
tation 2
3 d
enote
d
vitrin
ite
sa
mp
le
Ro =
3.0
0%
(N
= 4
4)
Tm
ax 2
25
-30
0°C
Ro =
2.0
3%
(N
= 5
0)
Tm
ax 1
50
-25
0°C
fau
lt;
da
sh
ed
wh
ere
in
ferr
ed
an
ticlin
al tr
ace
; d
ash
ed
wh
ere
in
ferr
ed
,
plu
ng
ing
wh
ere
in
dic
ate
d
syn
clin
al tr
ace
; d
ash
ed
wh
ere
in
ferr
ed
,
plu
ng
ing
an
d/o
r o
ve
rtu
rne
d w
he
re in
dic
ate
d
co
nta
ct;
da
sh
ed
wh
ere
in
ferr
ed
Map
Un
its
Map
Sym
bo
ls
pC
g
pC
g
pC
g
pC
g
pC
g
Fig
ure
1-3
. G
eo
log
ic m
ap
of th
e H
ua
ch
uca
Mo
un
tain
s (
ge
ne
raliz
ed
aft
er
Ha
ye
s a
nd
Ra
up
, 1
96
8)
sh
ow
ing
sa
mp
le
Bru
sh
y C
an
yo
n
are
a
9
locations a
s p
art
of th
e r
egio
nal stu
dy.
V
itrinite-r
eflecta
nce d
ata
show
n a
dja
cent
to s
am
ple
loca
tio
ns (
Tm
ax e
stim
ate
s b
ased o
n v
itrinite-r
eflecta
nce d
ata
fro
m F
ort
Critt
enden F
orm
ation
silt
sto
ne
/sh
ale
sa
mp
les, in
terp
rete
d a
fte
r H
éro
ux a
nd
oth
ers
, 1
97
9; S
tap
lin, 1
98
2; B
urn
ha
m
an
d S
we
en
ey,
19
89
; B
ark
er
an
d P
aw
lew
icz, 1
99
4).
TJh
TJc?
TJc?
TJc
TJc
TJh
TJc
TJh
TJh
TJc
TJh
TJh
11
4°
113°
112
°111°
110
°3
7°
36
°
35
°
34
°
33
°
32
°114°
113
°
112
°
111°
110°
37
°
36
°
35°
34
°
33
°
32
°
pCg
Kbw
KbaTQg
Ti
Kba
Kbt
Kbw
Kbg
Pzu
pCg
Kfs
Kflr
Kfb
Kfur
Kft
Jbu
Jbm
Jbl
Jtu
Jtm
Jtl
Js
Tp
Tg
Tw
Tqd
Tg
Kiu
Jtlm
Kbt
Pzu
Kfb
Tg
Tw
Tw
Tqd
TQg
Jtu
Jtu
Jbl
Jbm Jbu
Tp
Js
Tp
Jtm
Jtlm
Jtl
Jbl
Ti Tg
Jtm
Kbt
Kflr
Kfur
KbtKflr
KfbTertiary-Quaternary gravel and conglomerate,
undifferentiated
Paleocene? Gringo Gulch Volcanics
Tertiary intrusive rocks (associated with Gringo
Gulch Volcanics, Oligocene Grosvenor Hills
Volcanics)
uppermost Cretaceous intrusive rocks
(associated with Elephant Head Quartz Monzonite)
Upper Cretaceous
Fort Crittenden
Formation (early
Laramide basin
fill)
Lower Cretaceous
Bisbee Group
Middle Jurassic
Bathtub Formation
Middle Jurassic
Temporal Formation
Triassic? Mount Wrightson Formation
Jurassic Squaw Gulch Granite (Lower Jurassic?)
Triassic? quartz diorite
Triassic? Piper Gulch Monzonite
Triassic? Gardner Canyon Formation
Paleozoic sedimentary rocks, undifferentiated
Precambrian granite
0 1
kilometers
miles0 1
Ti
upper red conglomerate member/
tuff member
brown conglomerate member
lower red conglomerate member
shale member
TQg
Figure 1-4. Geologic map of the eastern flank of the southern Santa Rita Mountains, south-
fission track sample
vitrinite sample
fault; dashed where inferred
anticlinal trace; dashed where inferred,
plunging where indicated
synclinal trace; dashed where inferred,
plunging and/or overturned where indicated
contact; dashed where inferredMap Symbols
quartz vein
Map Units
mine location
eastern Arizona (after Drewes, 1971a). Vitrinite-reflectance (VR) datashown adjacent to sample locations (Tmax estimates based on vitrinite-
reflectance data from Fort Crittenden Formation siltstone/shale samples,
interpreted after Héroux and others, 1979; Staplin, 1982; Burnham and
Sweeney, 1989; Barker and Pawlewicz, 1994).
10
Adobe
Canyon
area
Sa
wm
ill
Ro = 2.26% (N = 50)
Tmax 200-250°C
Ro = 0.77% (N = 7)
Tmax 85-135°C
Fa
ult
Ca
nyo
nZ
on
e
114° 113° 112° 111° 110°37°
36°
35°
34°
33°
32°114°
113°
112°
111° 110°
37°
36°
35°
34°
33°
32°
xx x
x
x x
x
x
x
xxx
x
x
xx
xx
x
11
1978; Dickinson and others, 1978). In most locations, however, Tertiary and Quaternary gravels
rest in angular unconformity atop the Fort Crittenden Formation.
The shale member represents deposition in a lacustrine setting, with gradual
progradation of fan deltas into the lacustrine basin (Inman, 1982). The lowermost 55 meters of
the shale member is a volcaniclastic pebble to boulder conglomerate (referred to as the basal
conglomerate by Inman (1982)), reflecting availability of volcanic detritus early in the depositional
history of the Fort Crittenden Formation. The abundance of recycled volcanic material contrasts
with the upper portions of the Bisbee Group that record a source with significant monocrystalline
quartz, and increasing but minor recycled volcanic detritus upsection (Inman, 1987). The
remaining ~180 meters of the shale member are interbedded channel sandstone, and
interdistributary and lacustrine mudstone and shale. A lack of structural discordance (Inman,
1982) has led some workers to suggest that the hiatus between the Bisbee Group and the Fort
Crittenden Formation lasted at most 10-15 m.y. (Inman, 1987; Dickinson and others, 1989).
The contact between the shale member and the lower red conglomerate member (~485
meters thick; Hayes, 1986) is gradational, where lacustrine deposits grade vertically into alluvial-
fan facies deposited as the basin filled (Inman, 1982; Hayes, 1986). The brown conglomerate
(~660 meters thick; Hayes, 1986) intertongues with both the lower red conglomerate member
and the upper red conglomerate member (Drewes, 1968). Both the brown and lower red
conglomerates have similar composition, texture, sedimentary structures, and scales and styles
of interbedding (Hayes, 1986), although the brown conglomerate is coarser toward the top than
the lower red conglomerate, and is overall finer grained throughout the rest of the section.
12
Additionally, both conglomerates show an increase in recycled sedimentary detritus, as well as
intercalated volcanic tuff, toward the top of the respective sections.
The brown and upper red conglomerate members (minimum 355 m; Hayes, 1986)
intertongue along the eastern flank of the Santa Rita Mountains. The upper red conglomerate is
composed almost entirely of recycled sedimentary material, including clasts of muddy to pebbly
sandstone, sandy mudstone, and pebble to cobble conglomerate (Hayes, 1986, 1987); the
interpreted source for this recycled sedimentary material is the Lower Cretaceous Bisbee Group.
Hayes (1986) also stated that the upper red conglomerate coarsens upward, and appears to
display upward-thickening and coarsening trends low in the section. Hayes (1986) considered
facies of all the conglomerate members to be similar, and inferred that the upper portions of the
brown conglomerate member, and entirety of the upper red conglomerate member tapped
mainly sedimentary sources. Intercalated tuffs (<5 meters thick) are increasingly common
upsection into the upper tuff member. Both Drewes (1971b) and Hayes (1986) observed that
tuffs within the section thicken to the west, suggesting that these locations were closer to the
source.
In the Canelo Hills (Figure 1-5), the Fort Crittenden section is more faulted and very
limited in exposure (Kluth, 1982; Hayes, 1986), leading to difficulty in correlation of adjacent
sections along the flanks of the range and with sections in the Santa Rita and Huachuca
Mountains. Individual members, as defined in the Santa Rita or Huachuca Mountains sections
(Figure 1-2), have not been identified here. Mapping by Kluth (1982) indicates that limited
exposures of the Fort Crittenden Formation crop out in two separate major fault blocks, along the
northeastern and northwestern flanks of the range (Figure 1-5). The formation rests in
disconformity atop the Lower Cretaceous Cintura Formation (part of Kbu on Figure 1-5) in the
Kr?
TQu
Pzu
TJu
TJu
Kr?
Kbu
Ka
Klvs TJu
Klvs?Ks
Pzu
TQu
KTi
TJu
TJu
TJu
TQu KTi
Pzu
Pzu
Pzu
Pzu
Pzu
Pzu
Pzu
Kbu
TQuPzu
Ks
KTi
Pzu
TQu
Ka
Kbu
Tertiary and Quaternary gravels and
alluvium, undifferentiated
Cretaceous-Tertiary volcanic and
intrusive rocks (rhyolite, andesite flows;
intercalated pyroclastic/epiclastic
rocks; associated quartz monzonite and
granodiorite stocks, latite porphyries)
Upper Cretaceous Fort Crittenden
Formation (early Laramide basin fill)
Lower Cretaceous Bisbee Group,
undifferentiated
Triassic and Jurassic volcanic and
clastic rocks; includes portions of the
Canelo Hills Volcanics
Paleozoic sedimentary
rocks, undivided
fault; dashed where inferred
anticlinal trace; dashed where
inferred
synclinal trace; dashed where
inferred
contact; dashed where inferred
Map Units
Map Symbols
TJu
Kr
andesitic volcanic rocks; includes
portions of Salero Formation
rhyodacite, welded tuff; includes
portions of Salero Formation
TQuTQu
Kbu
Ks
TQu
Lower Cretaceous andesitic to rhyolitic
volcanic rocks, conglomerate,
sandstone
Klvs
0 1kilometers
miles0 1
TQu
TQu
Ks
Ks
Figure 1-5. Geologic map of the northern part of the Canelo Hills, southeastern Arizona (after
Drewes, 1980; Kluth, 1982; Reynolds, 1988).
13
114° 113° 112° 111° 110°37°
36°
35°
34°
33°
32°114°
113°
112°
111° 110°
37°
36°
35°
34°
33°
32°
14
O’Donnell Canyon area (east side of range; Figure 1-5). The Fort Crittenden Formation
conformably overlies the Corral Canyon andesite (part of Klvs on Figure 1-5; 75 Ma; K-Ar on
biotite; Hayes, 1987; all cited ages from sources prior to 1976 have been corrected after
Dalrymple (1979; refer to Appendix 1)) along the west flank of the range, and is interbedded
with volcanic and volcaniclastic rocks at the base of this section (Hayes, 1987). Hayes (1987)
pointed out that the Corral Canyon section is very similar in composition and depositional style to
the lower red conglomerate member of the Fort Crittenden Formation in the Santa Rita
Mountains. Volcanic activity is also indicated toward the end of, and immediately following, the
Fort Crittenden depositional period in the Canelo Hills, similar to the relationships documented in
the Huachuca Mountains. In the area of Jones Mesa, a unit informally termed the Jones Mesa
volcanics (Hayes, 1970b; part of Kr, Ks on Figure 1-5) overlies the Fort Crittenden Formation and
has been dated at 72 Ma (K-Ar on biotite; Hayes, 1970b). Additional evidence for volcanism
during the same period includes the Dove Canyon volcanics (73 Ma; K-Ar on biotite; Marvin and
others, 1973; Marvin and others, 1978) and the Meadow Valley trachyandesite (74 Ma; K-Ar on
biotite; Marvin and others, 1973; Marvin and others, 1978). Outside the Jones Mesa area, the
exposed top of the section is a fault contact with Jurassic Canelo Hills volcanics, or is overlain by
Tertiary and Quaternary gravels (Figure 1-5). The ages of overlying and underlying volcanic
rocks suggest that deposition of the Fort Crittenden Formation may have been short-lived in the
Canelo Hills. It is also possible that this is the case elsewhere, as there are no radiometric ages
other than those in the Canelo Hills section that constrain the age of the base of the formation
more accurately than post-Albian (the cited age for Bisbee Group sediments younger than the
Mural Formation; Figure 2; Hayes (1986), Dickinson and others (1989)). Because of the lack of
complete sections, and highly faulted nature of Canelo Hills sections and exposures, Fort
Crittenden Formation samples are not included in this discussion. The preceding discussion
15
serves to provide a more complete picture for the Fort Crittenden Formation in the central part of
the field area.
Huachuca Mountains
Partial sections of the Fort Crittenden Formation are exposed along the western flank of
the Huachuca Mountains (Figure 1-3); the most complete section lies along Brushy Canyon, in
the north-central part of the range, where the section is 675 meters thick (Hayes, 1986). Two
informal members were assigned to the Fort Crittenden section in this area by Hayes (1970a);
these include the basal conglomerate (divided into a lower and upper conglomerate) and shale
members. The basal contact is locally an angular unconformity with the Lower Cretaceous
Cintura Formation, and regionally a poorly exposed disconformity. The lower subunit of the
basal conglomerate member is present only in the northwestern Huachuca Mountains and, along
with the upper red conglomerate in the Santa Rita Mountains, is the only part of the section rich
in recycled sedimentary detritus (Hayes, 1986, 1987). The upper part of the basal conglomerate
is similar in character to the lower conglomerate subunit, but tends to display better rounding and
sorting, suggestive of increasing textural maturity up-section. The upper conglomerate subunit
contains approximately equal portions of recycled sedimentary, volcanic, and granitic clasts.
The contact between the basal member and the shale member is gradational.
As discussed above, the Fort Crittenden Formation marks the onset of sedimentation
associated with Laramide deformation. In general, the textural and sedimentologic
characteristics of the Fort Crittenden Formation are in marked contrast to older synorogenic
rocks such as the Lower Cretaceous Glance conglomerate (Bilodeau, 1978; Vedder, 1984), the
Upper Jurassic Temporal and Bathtub formations (Drewes, 1968, 1971b; Bassett and Busby,
1996), and the Upper Jurassic red bed deposits of the Canelo Hills volcanics (Davis and others,
16
1979). The Fort Crittenden Formation is texturally and compositionally more mature than the
older Cretaceous and Jurassic synorogenic basin fill (Bilodeau, 1978; Davis and others, 1979;
Inman, 1982; Hayes, 1986). Additionally, there is no evidence for direct fault control on
sedimentation in terms of clast size, composition, or mechanism of derivation, as present in the
Glance conglomerate, the Temporal and Bathtub formations, and the Canelo Hills volcanics
(Bilodeau, 1978; Davis and others, 1979; Bassett and Busby, 1996). The finer and more mature
nature of the Fort Crittenden Formation requires that new approaches be taken to understand its
provenance.
Sample Suite
Samples from the Middle Jurassic Temporal and Bathtub formations, the Lower
Cretaceous Bisbee Group, and the Upper Cretaceous Fort Crittenden Formation (Figure 1-2)
comprise the basis for the geochronology, provenance, and vitrinite-reflectance data sets
included in this study (Appendix 2). Most samples are composed of approximately 10 kg of
sandstone with little to no pebble content; rarely, samples contained a granule to pebble fraction
up to 20% of the total volume where this is representative of the sample interval. Key sampling
areas are adjacent to the fault zones along the western flank of the Huachuca Mountains, and
the Sawmill Canyon fault zone along the eastern flank of the Santa Rita Mountains (Figure 1-3;
Figure 1-4), in addition to other control points throughout the region. Where possible, a
complete Middle Jurassic through Cretaceous section was sampled along a strike-normal
transect.
The Jura-Cretaceous section in this part of southeastern Arizona records the
progression from arc volcanism associated with Sevier deformation through backarc region
extension associated with deposition of the Bisbee Group, through segmentation of the Sevier
17
foreland and development of smaller basins associated with Laramide contraction (Dickinson
and others, 1989). These transitions in tectonic setting are demonstrated within the
clastic/volcaniclastic and minor carbonate rocks in the form of changes in sedimentation
style/volume, depositional environment, and provenance, both mineralogic and thermal. The
Jura-Cretaceous section was deformed and intruded during the Laramide (Figure 1-3 and 1-4).
The area chosen for this study is the best possible for determining the thermal state of the crust
prior to exhumation and recycling of the upper crust and accumulation of Laramide basin fill.
Laramide basin-fill rocks are relatively well-exposed here, and fairly complete Jura-Cretaceous
sections are present (c.f. Inman, 1982; Hayes, 1986). These two factors enable the petrologic
and thermal character of the Fort Crittenden Formation to be thoroughly evaluated and
compared to potential source terranes. Additionally, the study area lies within the uplift/basin-
bounding fault zone recognized by Davis (1979), thus providing the most direct record of the
evolution of these sediment-source couples. It was discovered that some samples show
evidence for post-depositional heating such that a few zircons were reset by annealing.
Consequently, a derivative study was undertaken to document fission-track response of zircons
to post-depositional heating (Chapter 2).
Fission-track Analysis
Thermal and temporal information, critical to the understanding of source area
exhumation and recycling and central to the understanding of subsequent thermal events, is
provided by fission-track analysis. The closure temperature for the FT chronometer in zircon has
been proposed to be 235°C ± 25°C (Brandon and Vance, 1992), but as shown in Chapter 2, may
be as low as ~180°C or so, depending on single-grain response to heating due primarily to
radiation damage. The temporal information obtained from the FT data at temperatures between
180°C-260°C is unique to this system. In concert with FT samples from the Laramide basin fill
18
(Fort Crittenden Formation), traditional mineralogic provenance from these sandstones was used
to evaluate the nature of source rocks. Point counts (300 counts per section) were made on thin
sections impregnated with blue epoxy and stained for potassium feldspar for each of the Fort
Crittenden Formation samples (Figure 1-3, 1-4), and ternary plots of these data appear in Figure
1-6.
Each sandstone sample (~10 kg of material) was crushed and milled, then separated
using a Wilfley table, heavy liquids, and a Frantz magnetic separator. The zircon separate was
obtained from the methylene iodide sinks, 1.7 A non-magnetic fraction. A small portion of this
material was prepared for fission-track dating, with approximately 2000-3000 grains per mount in
two Teflon mounts. All zircon fractions were mounted and etched according to the procedures in
Garver and others (2000). Mounts were etched in a KOH:NaOH eutectic at 228°C for between 5
and 17 hours to adequately represent the widest possible spectrum of grain types, ages, and U
contents (i.e. Naeser and others, 1987). All zircon mounts were irradiated at the Oregon State
University Reactor Facility, with a requested thermal neutron fluence of 2 x 1015 n/cm2.
According to methods described in Naeser (1976) and Garver and Brandon (1994), pre-
annealed mica sheets were attached to grain mounts prior to irradiation, and were removed and
etched to reveal induced fission tracks following irradiation. All mounts were counted at 1250x
using a dry 100x objective (10x oculars, 1.25x tube factor) on a Zeiss Axioskop microscope fitted
with an automated stage/digitizing tablet. Refer to Appendix 3 for further procedure and data
reduction information. Zircon FT peak ages and 95% confidence intervals for data from 30-60
dated zircon grains per sample appear in Table 1-1. Peak ages were fitted using the binomial
fitting method of Brandon (1996).
19
For the Station 23, Huachuca Mountains sample (Figure 1-3), a small portion of the zircon
separate was prepared for traditional fission-track dating as described above, with approximately
2000-3000 grains in each of two Teflon mounts (bulk sample). The remaining zircons were then
hand-picked into three distinct color fractions. Fractions include light to dark pink and purple
zircons (fraction p; ~5% of total yield), colorless zircons (fraction c; ~20% of total yield), and
honey zircons (fraction h; ~75% of total yield); refer to Chapter 2, Table 1-1 for further detail.
Zircon fractions from this sample, as well as the original bulk zircon material, were mounted and
etched as described above. The original bulk mounts were etched for 17 hours (long etch) and
12 hours (short etch); the pink/purple fraction was etched under the conditions described above
for 5 hours. The colorless and honey fraction yield was high enough to allow two mounts each,
for which the long etch was 10 hours, and the short etch was 5 hours. All suitable grains in each
of the color mounts were counted, yielding a total of 57 single-grain FT ages for color mounts,
combined with the 60 single-grain ages from the unpicked bulk sample. For the zircon color
grain mounts, other analyses shed light on single-grain response to modest heating (150°C-
225°C), and the control of accumulated α-damage on the FT closure temperature (Chapter 2).
Pertinent to the present discussion are Pb-Pb ages from these FT-dated zircons, which appear
plotted versus corresponding FT grain ages in Figure 1-7. This detailed study is described
here only to the extent that these data bear on the exhumation and recycling histories for these
rocks.
Vitrinite Reflectance
To independently estimate the maximum temperatures reached by these sandstones,
interbedded Fort Crittenden Formation mudrocks were sampled where possible for analysis of
vitrinite reflectance (VR; analyses made by D. O’Connor at Baseline DGSI, The Woodlands,
craton interiortransitional continental
quartzose recycled
mixed
transitional recycled
lithic recycled
undissected arctransitional arc
basement uplift
dissected arc
Qm
F Lt
Qm
LtF
Figure 1-6a. Qm-P-K, Qm-F-Lt, and Qp-Lv-Ls ternary plots from Inman (1987) for 10 Fort
a.
b.
Qm
F Lt
Qm
P K
Qp
LsLv
c.
Santa Rita Mountains samples Huachuca Mountains samples
Qp
Lv Ls
Qm
P K
Inman (1987)
n = 10
Hayes (1987)
n = 70
this study
n = 10
Crittenden Formation samples (shale member) from the Adobe Canyon area,
eastern Santa Rita Mountains. Qm = monocrystalline quartz; P =
plagioclase; K = potassium feldspar; F = plagioclase + potassium feldspar;
Lt = total lithic fragments; Qp = polycrystalline quartz (excluding micro-
crystalline quartz); Lv = volcanic lithic fragments; Ls = sedimentary lithic
Figure 1-6b. Qm-P-K, Qm-F-Lt, and Qp-Lv-Ls ternary plots from Hayes (1987). Compositional
ranges for Fort Crittenden Formation samples from the Huachuca
Mountains Brushy Canyon section (n = 24) and Santa Rita Mountains
(n = 46) are plotted.
samples from the Huachuca and Santa Rita mountains from this study.
fragments. Key from Dickinson and others (1983).
Figure 1-6c. Qm-P-K, Qm-F-Lt, and Qp-Lv-Ls ternary plots for 10 Fort Crittenden Formation
20
Map locations on Figures 1-3, 1-4.
0 10 20 30 40 50 60 70 80 90 100
0
10
20
30
40
50
60
70
80
90
100
K
Qm
P
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90 100
0
10
20
30
40
50
60
70
80
90
100
Ls
Qp
Lv
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90 100
0
10
20
30
40
50
60
70
80
90
100
Lt
Qm
F
0
10
20
30
40
50
60
70
80
90
100
21
Texas). As temperature increases, the reflectance of vitrinite fragments also increases, and the
Ro value, or mean reflectance, rises; the relationship between maximum temperature (Tmax) and
Ro is linear or nearly so (Price, 1983). Average Ro values, based on 20-50 measurements
per sample, were used to define maximum temperature bounds for interbedded mudrocks;
these average values are shown adjacent to sample locations in Figures 1-3 and 1-4.
In the northern and central Huachuca Mountains, mudrocks in the lower part of the Upper
Cretaceous Fort Crittenden Formation were sampled at three separate locations adjacent to FT
sampling stations. Unfortunately, siltstone and shale near Station 23 are highly oxidized, and
accordingly a maximum temperature estimate for these rocks was not obtained. Shales and
siltstones farther north at a similar stratigraphic interval contain un-oxidized vitrinite. The
average Ro values for these sites are 3.00% and 2.03%, and correspond to peak temperature
estimates of 225-300°C and 150-250°C, respectively (interpreted after Héroux and others, 1979;
Staplin, 1982; Burnham and Sweeney, 1989; Barker and Pawlewicz, 1994). Because the
estimate of peak temperature from Ro values varies somewhat, a range of peak temperature
values associated with a given Ro measurement is reported here. In the eastern Santa Rita
Mountains, Tmax for interbedded siltstones are available from two sites within the Fort Crittenden
Formation. Station 43, within interbedded siltstone of the brown conglomerate member of the
Fort Crittenden Formation has an Ro value of 2.33%, corresponding to a peak temperature
estimate of 200-250°C. A sample from Station 66 (Fort Crittenden Formation shale member)
yielded only 7 un-oxidized vitrinite fragments, which record an Ro value of 0.77%, corresponding
to a Tmax of 85-135°C.
These estimates provide an independent measure of the maximum paleotemperature,
Tab
le 1
. B
inom
ial fitt
ed a
nd χ
2 f
issio
n t
rack p
eak a
ges f
or
Mesozoic
sandsto
ne s
am
ple
s f
rom
the S
anta
Rita a
nd H
uachuca M
ounta
ins,
south
easte
rn A
rizona.
P1
P2
P3
P4
P5
P6
2 a
ge
(M
a)
SA
NT
A R
ITA
MO
UN
TA
INS
Mid
dle
Ju
ras
sic
Te
mp
ora
l F
orm
atio
n
Sta
tio
n 3
3p
ea
k a
ge
(M
a)
55
—8
21
23
——
—n
= 2
7 (
27
)9
5%
c.i.
(+/-
; m
.y.)
6/5
8/7
10
/10
% o
f g
rain
s2
0.4
37
.44
2.2
Lo
we
r C
reta
ce
ou
s T
urn
ey R
an
ch
Fo
rma
tio
n S
tatio
n 3
8p
ea
k a
ge
(M
a)
——
11
21
75
56
6—
—n
= 4
4 (
14
/30
)9
5%
c.i.
(+/-
; m
.y.)
14
/12
32
/27
18
9/1
43
% o
f g
rain
s4
8.6
43
.48
.0
Up
pe
r C
reta
ce
ou
s F
ort
Cri
tte
nd
en
Fo
rma
tio
n,
up
pe
r re
d c
on
glo
me
rate
me
mb
er
Sta
tio
n 4
2p
ea
k a
ge
(M
a)
52
—1
11
—2
76
——
n =
60
(3
0/3
0)
95
% c
.i.
(+/-
; m
.y.)
23/16
9/9
39
/34
% o
f g
rain
s1.8
65
.53
2.7
Mid
dle
Ju
ras
sic
Ba
thtu
b F
orm
atio
n
Sta
tio
n 4
4p
ea
k a
ge
(M
a)
52
—9
91
67
——
—n
= 5
1 (
30
/21
)9
5%
c.i.
(+/-
; m
.y.)
5/4
12
/11
29
/25
% o
f g
rain
s2
7.2
47
.22
5.6
Up
pe
r C
reta
ce
ou
s F
ort
Cri
tte
nd
en
Fo
rma
tio
n s
ha
le m
em
be
r S
tatio
n 5
2p
ea
k a
ge
(M
a)
——
——
——
15
7
n =
13
(1
3)
95
% c
.i.
(+/-
; m
.y.)
18
/16
% o
f g
rain
s5
4
HU
AC
HU
CA
MO
UN
TA
INS
Up
pe
r C
reta
ce
ou
s F
ort
Cri
tte
nd
en
Fo
rma
tio
n S
tatio
n 9
pe
ak a
ge
(M
a)
42
68
10
7—
——
—n
= 2
9 (
12
/17
)9
5%
c.i.
(+/-
; m
.y.)
12
/98
/71
7/1
5
% o
f g
rain
s7
.26
5.2
27
.6
χ
22
χ
HU
AC
HU
CA
MO
UN
TA
INS
, co
ntin
ue
d
P1
P2
P3
P4
P5
P6
2 a
ge
(M
a)
up
pe
rmo
st
Ju
ras
sic
-Lo
we
r
Cre
tac
eo
us
Gla
nce
co
ng
lom
era
te
Sta
tio
n 1
1p
ea
k a
ge
(M
a)
——
92
12
1317
——
n =
42
(3
0/1
2)
95
% c
.i.
(+/-
; m
.y.)
9/8
13
/12
70/58
% o
f g
rain
s5
1.5
43
.84.8
Up
pe
r C
reta
ce
ou
s F
ort
Cri
tte
nd
en
Fo
rma
tio
n S
tatio
n 1
3p
ea
k a
ge
(M
a)
—6
0—
13
8—
——
n =
31
(2
4/7
)9
5%
c.i.
(+/-
; m
.y.)
6/6
17
/15
% o
f g
rain
s5
6.7
43
.3
Lo
we
r C
reta
ce
ou
s C
intu
ra F
orm
atio
n
Sta
tio
n 1
4p
ea
k a
ge
(M
a)
——
10
6—
23
68
03
—n
= 3
3 (
11
/3/5
/14
)9
5%
c.i.
(+/-
; m
.y.)
13
/12
22
/20
20
1/1
63
% o
f g
rain
s2
0.9
60
.91
8.2
Up
pe
r C
reta
ce
ou
s F
ort
Cri
tte
nd
en
Fo
rma
tio
n S
tatio
n 2
3
bu
lk s
am
ple
pe
ak a
ge
(M
a)
—6
09
11
39
——
—n
= 6
0 (
30
/30
)9
5%
c.i.
(+/-
; m
.y.)
8/7
10
/91
8/1
6
% o
f g
rain
s1
7.3
48
.62
9.1
fra
cti
on
pp
ea
k a
ge
(M
a)
—6
3—
17
5—
——
n =
14
95
% c
.i.
(+/-
; m
.y.)
9/8
19
/17
% o
f g
rain
s2
7.3
72
.7
fra
cti
on
cp
ea
k a
ge
(M
a)
——
78
12
0—
——
n =
30
(1
9/1
1)
95
% c
.i.
(+/-
; m
.y.)
7/7
11
/10
% o
f g
rain
s4
5.6
51
.1
fra
cti
on
hp
ea
k a
ge
(M
a)
—7
0—
11
8—
——
n =
22
(1
6/6
)9
5%
c.i.
(+/-
; m
.y.)
6/5
12
/11
% o
f g
rain
s5
8.8
41
.2
bu
lk +
fra
cti
on
sp
ea
k a
ge
(M
a)
—5
98
01
28
——
—n
= 1
27
95
% c
.i.
(+/-
; m
.y.)
7/6
7/7
10
/9
% o
f g
rain
s1
1.4
37
.24
6.6
23
χ
HU
AC
HU
CA
MO
UN
TA
INS
, co
ntin
ue
d
P1
P2
P3
P4
P5
P6
2 a
ge
(M
a)
Up
pe
r C
reta
ce
ou
s F
ort
Cri
tte
nd
en
Fo
rma
tio
n lo
we
r co
ng
lom
era
te s
ub
un
it
Sta
tio
n 4
5p
ea
k a
ge
(M
a)
——
10
41
71
353
——
n =
26
(6
/3/1
3/4
)9
5%
c.i.
(+/-
; m
.y.)
9/8
17
/16
115/87
% o
f g
rain
s5
0.0
42
.47.6
Up
pe
r C
reta
ce
ou
s F
ort
Cri
tte
nd
en
Fo
rma
tio
n u
pp
er
co
ng
lom
era
te s
ub
un
it
Sta
tio
n 4
6p
ea
k a
ge
(M
a)
——
—1
37
——
—n
= 1
8 (
4/1
3/1
)9
5%
c.i.
(+/-
; m
.y.)
11
/10
% o
f g
rain
s1
00
Up
pe
r C
reta
ce
ou
s F
ort
Cri
tte
nd
en
Fo
rma
tio
n s
ha
le m
em
be
r S
tatio
n 4
7p
ea
k a
ge
(M
a)
——
——
——
19
0
n =
59
5%
c.i.
(+/-
; m
.y.)
32
/27
% o
f g
rain
s8
0
Up
pe
r C
reta
ce
ou
s F
ort
Cri
tte
nd
en
Fo
rma
tio
n S
tatio
n 4
9p
ea
k a
ge
(M
a)
——
——
——
10
9
n =
5 (
1/4
)9
5%
c.i.
(+/-
; m
.y.)
17
/14
% o
f g
rain
s8
0
No
tes:
Bin
om
ial fitt
ed
an
d χ
2 f
issio
n t
rack p
ea
k a
ge
s a
nd
95
% c
on
fid
en
ce
in
terv
als
fo
r zir
co
n f
rom
14
sa
nd
sto
ne
sa
mp
les in
th
e S
an
ta R
ita
an
d H
ua
ch
uca
Mo
un
tain
s.
n =
nu
mb
er
of
gra
ins
co
un
ted
(w
he
re m
ore
th
an
on
e n
um
be
r is
cite
d,
firs
t is
to
tal n
um
be
r co
un
ted
; su
bse
qu
en
t n
um
be
rs a
re n
um
be
rs o
f g
rain
s c
ou
nte
d f
rom
su
cce
ssiv
ely
sh
ort
er
etc
he
s).
Bin
om
ial p
ea
k f
ittin
g m
eth
od
(B
ran
do
n,
19
96
); P
1 =
fitte
d p
ea
k 1
; P
2 =
fitte
d p
ea
k 2
, e
tc.
24
Pb-Pb age vs. Fission-track grain age
100
200
300
400
500
600
700
0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200
Pb-Pb age (Ma)
FT
GA
(M
a)
pink/purple (N = 14 grains)
colorless (N = 22 grains)
honey (N = 20 grains)
Figure 1-7. Pb-Pb age versus fission track grain age (FTGA) for the same zircon grains from
depositional
age of sample
Station 23, Huachuca Mountains. Cited uncertainties for Pb-Pb ages are 1
standard deviation, and 95% confidence intervals for FT ages.
25
26
and indicate that peak temperatures in the northern Huachuca Mountains were higher than
suspected during sampling for FT work (up to ~225°C vs. <120°C). Rock characteristics as seen
in the field did not suggest that these sandstones and conglomerates were thermally altered.
Most samples from this area are only moderately indurated and have almost no quartz cement.
Another notable feature, considering the presence of nearby Tertiary plutons is a lack of veining.
Most importantly, the locations with elevated peak temperature values generally correspond well
with locations of sandstone samples containing young reset FT peak ages and/or reset single-
grain ages throughout the northwestern and west-central parts of the Huachuca Mountains.
Similar relationships occur in the Santa Rita Mountains.
DATA/OBSERVATIONS
Fission-track Data
As discussed in previous sections, the sample suite for this regional study includes
Middle Jurassic through Upper Cretaceous clastic and volcaniclastic rocks (Table 1-1; Appendix
2). The most important feature of these data is that despite the 100 m.y. range in depositional
age or varying location of the studied units, all samples have a similar suite of fission-track peak
ages (Figure 1-8). The following observations are pertinent to this discussion.
Young Reset Peak Ages
Given the range of depositional ages in the study area, FT ages younger than the
depositional age of the sample must be due to annealing and resetting of the fission-track
grain ages (FTGA). In many samples, regardless of depositional age, FT ages younger than
the age of the Fort Crittenden Formation (85-75 Ma; Drewes, 1968; Hayes, 1970a, 1970b;
Inman, 1987; Hayes, 1987; Dickinson and others, 1989) are also common (Figure 1-8). As
discussed in previous sections, partially reset samples in some cases occur in proximity to
27
exposed igneous bodies (e.g. Station 23, Huachuca Mountains; Figure 1-8), but there is no
obvious spatial variation in FTGA with respect to the distribution of exposed Laramide igneous
rocks.
Very young reset peak ages (42-55 Ma) are present in most samples from Santa Rita
Mountains, whereas peaks this young are present in only one sample from the
northern Huachuca Mountains (Fort Crittenden Formation). This younger reset peak age is
composed by as much as 2% to 27% of counted grains in a given sample. An intermediate
young peak age of approximately 65 Ma is common in Huachuca Mountains samples, but not in
samples farther to the west.
Young intermediate peak ages between 85-75 Ma are present in a sample from the
Middle Jurassic Temporal Formation, Santa Rita Mountains and in a sample from the Upper
Cretaceous Fort Crittenden Formation, Huachuca Mountains (Figure 1-8; Table 1-1). In the case
of the Jurassic volcaniclastic sample, this population represents either full resetting of some
zircon FT ages around 82 Ma, or partial resetting of older FTGA associated with heating at ~60
Ma. A peak of this age could be related to any of the following: exhumation at the beginning of
the Laramide; thermal resetting associated with magmatism slightly older than the Fort
Crittenden Formation (i.e. Corral Canyon volcanics, Canelo Hills; 75 Ma, K-Ar on biotite; Hayes,
1987; Appendix 1); or partial resetting of an older FT age by either of the two previously
mentioned mechanisms.
In the case of the Fort Crittenden Formation sample with the 80 Ma peak age, discussed
in greater detail in Chapter 2, there are two possibilities for the significance of this peak age: (1)
a volcanogenic source transitional in age between the Bisbee Group and the Fort Crittenden
pCg
Kbw
Kba
Kbt
Pzu
Kfb
Tg
Tw
Tw
Tqd
QTg
Jtu
Jtu
Jbl
Jbm Jbu
Tp
Js
Tp
Jtm
Jtlm
Jtl
Jbl
Ti Tg
Jtm
KfsKbt
Kflr
Kfur
KbtKflr
Kfb
0 1
kilometers
miles0 1
TiQTg
#942 Ma 68 Ma
107 MaN = 29
#2359 Ma80 Ma
128 MaN = 127
#1192 Ma121 Ma
N = 42
#1360 Ma138 MaN = 31
#49χ2 age:
109 MaN = 5
#46137 Ma
N = 18
#45104 Ma171 Ma
N = 26
#14106 Ma236 Ma803 Ma
N = 33
#47χ2 age:
190 MaN = 5
#38 112 Ma175 Ma566 Ma
N = 44
#40 no countable
grains
#42 111 Ma276 Ma
N = 60
#51 no countable
grains
#61 no countable
grains
#44 52 Ma 99 Ma167 Ma
N = 51
#33 55 Ma 82 Ma 123 Ma
N = 27
#36 no countable
grains
#52χ2 age:
157 MaN = 13
Kfc
Kc
KcKga
Jh?
KmoKga
Kc
Kfc
Kc
Kmo
Kmu
Kc
Kmo
Kmo
Kmo
Kmu
Kg
Kg
Kga Pzu
Pzu
Kga
Kg
eKga
Pzu
Kmo
Kg
KmoKg
Kmu
Kc
Kfc
TQu Kb?
TQu
Tg
Tg
TQu
TQu
TQu
Ti
Ti Kmo
pCg
JTh?
JTc
JTc
JTh
JTh
JTc
JTc?
JTc?
0 1
kilometers
miles0 1
pCg
pCg
pCg
Figure 1-8. Huachuca and Santa Rita Mountains geologic maps (after Hayes and Raup, 1968;
reset FTGA
reset FTGA
Drewes, 1971) showing zircon fission-track peak ages (χ2 ages as noted;
binomial fitted ages elsewhere) for sample sites included in this study.
Statistical peak ages are based on approximately 30-60 dated grains per
sample, except where χ2 age is given. Boxes around sample locations
indicate evidence for resetting in sample. Refer to Appendix 4 for further
28
detail on peak ages, uncertainties, and single-grain age data.
x
xx
xx
x
xxx
x
x
xx
x
xx
xx
29
Formation; and/or (2) partially to fully reset older FT ages. Based on constraints from the Pb-Pb
data for this sample, which indicate that all crystallization ages from the FT-dated zircons are
>170 Ma (Figure 1-7), these grains are not first-cycle volcanic zircons associated with early
Laramide volcanism (i.e. units such as the Corral Canyon volcanics, Canelo Hills; Appendix 1).
Pb-Pb ages of the FT-dated grains instead favor the interpretation that this peak is composed of
partially to fully reset older FT ages, probably associated with burial and heating related to
eastward migration of the arc across southern Arizona during the early Laramide (Coney, 1978;
Dickinson and Snyder, 1978; Keith, 1978). Refer to the next section of this chapter and
Chapter 2 for a complete discussion of this sample.
Provenance Ages
There is clear evidence for Paleogene heating and associated annealing in some
samples (Figure 1-8; Appendix 1, 4). Cooling to sub-annealing temperatures (<180°C) occurred
during the Paleocene and Eocene. As such, there is potential for partial resetting in any of the
samples. Accordingly, peak ages older than the depositional age of the sample are termed
minimum provenance ages, or minimum ages for cooling in the source terrane. As discussed in
detail in Chapter 2, grains with varying levels of radiation damage, and thus different effective
closure temperatures, are present in different populations of zircon from a single sample. This
effect makes certain zircons more susceptible to resetting, allowing for partial resetting of an
older component. However, it is doubtful that these older FT ages have been completely reset.
If older FTGA were dominated by resetting, it is unlikely that these older peak ages would be so
similar throughout all samples, and that older ages would represent such a large proportion of
the total grains counted.
30
Zircon FT ages that comprise these older pre-depositional peaks, as well as very old
single-grain FT ages, generally constitute between 30 and 100% of the total number of grains
counted (Appendix 4). Peaks defined by the older FT ages show a fairly narrow dispersion of
ages among the different samples, all of which are consistent with derivation from similar
sources supplying detritus to the Bisbee basin (i.e. related to arc magmatism, or related to
exhumation associated with formation of the Bisbee basin). Finally, peaks with these older ages,
and older widely varying single-grain FT ages, are present in every sample in the study. In the
case of partially resetting an older age component, as discussed in greater detail in Chapter 2,
one might expect the following: (1) a smaller percentage of grains would have the reset peak
age(s); and (2) a wider spread of partially reset ages within the field area and a lack of
consistency of peak ages among samples (depending on the location and timing of heating, and
the susceptibility of a zircon to resetting; Chapter 2). One would not expect a partially reset FT
peak age to be so consistent and ubiquitous throughout the sample suite and field area. Rather,
partially reset FT peak ages would vary spatially depending on the mechanism of resetting (for
example, resetting by local magmatism/hydrothermal activity, or by burial). The key observation
is that rocks that have remained relatively cool (those without any obvious evidence for resetting,
likely remaining at temperatures <180°C) have similar ages for the pre-depositional peaks as
those rocks with clear evidence for Paleogene resetting. As such it is likely that a significant
amount of provenance information has remained unaffected.
Older peak ages, in the range 90-175 Ma, are common to all samples in varying
abundances, and generally represent most of all grains counted, no matter the depositional age
of the sample (Table 1-1; Figure 1-8). Scattered older peak ages are present in a few samples
(for example, in the Turney Ranch Formation and in the upper red conglomerate member of the
Fort Crittenden Formation in the Santa Rita Mountains; Table 1-1). It is also noteworthy that
31
nearly every sample retains grains with very old FT ages, even those samples that also contain
a young reset peak age (e.g. Stations 13, 38, 44, 45, 46; Table 1-1; Appendix 4). These older
peak ages and older single-grain ages indicate that some portion of the source area for Middle
Jurassic-Cretaceous rocks in this area remained below temperatures of 180-260°C, depending
on single-grain response to heating.
Pb-Pb Geochronology
One of the key questions is whether syn-depositional volcanic zircons are present in the
samples. A lack of such zircons is indicated by the FT ages of samples from Stations 9, 13, 42,
47, 49, 46, and 45. These samples have peak ages that are generally 25-200 m.y. older than
the depositional age of the Fort Crittenden Formation (Table 1-1). Pb-Pb ages for FT-dated
grains from Station 23 in the Huachuca Mountains (Figure 1-3) assist in defining the source of
zircons with a given cooling age, but confirm a lack of syn-depositional volcanic zircon.
Zircons with 90-170 Ma FT ages could be arc-derived first- or second-cycle grains,
having been derived from either the arc or recycled from the Bisbee Group or older Jurassic
volcanogenic strata. Alternatively, if these grains have older crystallization ages their FT ages
could have been reset during arc-related magmatism and/or exhumation and block faulting
associated with formation of the Bisbee basin (Hayes, 1970b; Bilodeau, 1978, 1979; Dickinson
and others, 1986; Klute, 1987). Additionally, crystallization ages help determine the age of
granitic source terranes that supplied detritus to the Fort Crittenden Formation (Inman, 1982;
Hayes, 1986). Precambrian granite or Mesozoic granite are possible sources, in terms of both
exhumation and provenance. This possibility feeds back into the question of understanding what
part of the crust was being exhumed and recycled, and when these sediments were shed into
the basin.
32
Two main groups of Pb-Pb ages occur in FT-dated zircons in the Station 23 sample: the
pink/purple suite is dominantly Proterozoic, ranging from 1200 to 2000 Ma, whereas colorless
and honey-colored zircons from the same sample have a variety of Pb-Pb ages, the majority of
which range from 160 to 720 Ma (Figure 1-7). An older group of both honey and colorless
zircons is also present, with six ages from 1300 to 1800 Ma overlapping with the pink/purple
series. A key discovery from the Pb-Pb data is that syndepositional, probably volcanogenic,
zircons are not present in this particular sample.
Mineralogic Provenance
Sandstones in the Fort Crittenden Formation are typically lithic-rich (Figure 1-6; Inman,
1982; Hayes, 1986). Compositional data for ten Fort Crittenden Formation sandstones from the
current study are compared with compositions of sandstones from the work of Inman (1987) in
the Santa Rita Mountains (shale member, Fort Crittenden Formation), and with sandstone
compositions from Hayes (1987) in the Santa Rita and Huachuca Mountains (including all
members and subunits of the formation in both ranges) (Figure 1-6).
Most Fort Crittenden Formation samples are lithic rich (Figure 1-6; Inman, 1982; Hayes,
1986). Lithic framework components include plutonic rock fragments (PRF), dominant volcanic
rock fragments (VRF), with many unidentified rock fragments (URF) also present. The latter are
problematic in that such grains could be highly altered VRF, sedimentary rock fragments (SRF),
or feldspar. Samples were stained for potassium feldspar, but due to alteration of feldspars to
clays, accurate identification of grain type sometimes proved difficult.
33
Petrographic observations from this study are generally in keeping with those of Hayes
(1986, 1987) and Inman (1982, 1987) (Figure 1-6). However, due to sample size (10 Fort
Crittenden Formation samples included in this study), data presented here vary somewhat from
that of larger sample suites such as those of Inman (1982) and Hayes (1986). Most sandstone
samples are lithic rich, particularly VRF and quartzose PRF, with subordinate to subequal
populations of SRF. Carbonate rock fragments (CRF) are rare. Monocrystalline quartz has
multiple potential sources. Vein quartz, plutonic quartz, and metamorphic quartz were identified,
based on grain properties (extinction character, presence or absence of inclusions).
Polycrystalline quartz likely also has both metamorphic and plutonic provenance.
Microcrystalline quartz is sparse to rare, and where present, relict ghost textures commonly
suggest volcanogenic provenance. Both VRF and PRF are abundant in samples included in this
study, but unaltered plagioclase is rare, and generally subordinate to potassium feldspar (Figure
1-6).
Diagenetic Overprint
Each of the sampled Fort Crittenden Formation units clearly has an extensive, and in
some cases complicated, diagenetic history, also noted in Hayes (1986). The description
included herein is not intended to review burial histories in exhaustive detail, but rather to
highlight those points pertinent to the thermal history of the samples, which is critical to
interpreting the FT data.
The most clear common thread among the FT-dated samples is abundant evidence for
relatively early compaction. This is indicated by a lack of cementation, and by quartz grains and
other competent framework grains indenting less competent grains, such as potassium feldspar,
lithic fragments, plagioclase, and in some cases, other quartz grains. Further evidence exists in
34
samples such as that from sandstone of the lower red conglomerate member in the Santa Rita
Mountains (Figure 1-4), where mudclasts were deformed into pseudomatrix around more
competent framework types. Compaction in the majority of these samples occurred early, prior
to cementation, and generally limited the opportunity for cementing fluids to later infiltrate
remaining primary or secondary pore space. As such, carbonate and quartz cements are poorly
developed, and primary pore space is nearly obliterated. Secondary pore space is generally
limited to dissolution of feldspars. Dissolution of framework, pseudomatrix, and cement on the
whole is uncommon throughout the suite, and porosities are low (on the order of 1-2%).
The most commonly altered framework types are VRFs, PRFs with high feldspar
content, and feldspar grains. Alteration within VRFs includes chloritization, minor dissolution,
and replacement by patchy, fine-grained carbonate cement (calcite ± dolomite). Alteration of
PRFs is generally restricted to the feldspathic portion of the grain, and typically involves
conversion to clays; replacement by calcite along grain rims and cleavage planes, followed by
patchy replacement by calcite within grain interiors; and dissolution. Where replacement by
calcite is more extensive (on the order of 2-5% of total thin section), quartz within PRFs is locally
replaced. Alteration of single-grain feldspars is similar to that demonstrated by feldspar within
PRFs.
DISCUSSION
Age Data—Young Reset Peak Ages
Younger reset peak ages (42-55 Ma; Figure 1-8; Table 1-1) are common in the Santa
Rita Mountains, but are lacking in most of the Huachuca Mountains samples. These peak ages
could document different ages of magmatic activity in the two ranges. However, this cannot be
properly addressed because Tertiary igneous rocks in the Huachuca Mountains are undated.
35
Most importantly, as discussed more completely in Chapter 2, it is possible that there are varying
responses to modest heating (150°-225°C or so), depending on the character of zircons in the
sample. For example, single-grain differences in the amount of accumulated α-damage can
allow certain grains to respond differently to heating. Alternatively, the presence of the younger
reset peak ages in the Santa Rita Mountains could signify contrasting cooling regimes: if one
area cooled more rapidly than the other, or remained at elevated temperatures longer than the
other, this could produce differences in the ages of reset zircons. However, this case is unlikely
as the FT data indicate that thermal annealing and subsequent Paleocene-Eocene cooling of
some portion of most samples was widespread through the study area, and thus that elevated
temperatures of at least 150°C were probably a regional feature (Figure 1-8; Appendix 4).
As a corollary to the preceding discussion, intermediate young reset peak ages of
approximately 65 Ma are present in Huachuca Mountains samples, but not in Santa Rita
Mountains samples (Figure 1-8; Table 1-1). Again, this poses several questions: (1) did the
Santa Rita Mountains samples cool more slowly, thereby producing younger FT peak ages?; (2)
did the Santa Rita Mountains experience higher peak temperatures? (3) does the difference in
FT peak ages indicate different episodes of magmatic activity in the two ranges?; or (4) were
zircons in the Santa Rita Mountains samples more susceptible to resetting? Chapter 2 presents
some methods for determining the answers to questions such as these, specific to the Huachuca
Mountains.
Age Data—Static Peaks
Older peak ages throughout the study area are similar (Table 1-1), ranging from 99 to
175 Ma in the Santa Rita Mountains, and 91-171 Ma in the Huachuca Mountains samples. The
presence of these peak ages throughout the Middle Jurassic-Upper Cretaceous section
36
suggests that an important source of sediment for the Fort Crittenden Formation was the
underlying Middle Jurassic through Lower Cretaceous section, and/or recycling of components
with similar cooling ages from other units. These older peak ages are herein termed static peaks
(Brandon and Vance, 1992), as these are persistent age components in all samples.
There are several likely sources for grains with cooling ages in the 90-120 Ma range in
the Fort Crittenden Formation: (1) recycling of first-cycle volcanogenic detritus shed into the
Bisbee basin during deposition (i.e., magmatic-arc activity associated with basin extension); (2)
recycling of older rocks affected by heating associated with this igneous activity, or exhumed arc
rocks; and/or (3) zircons from rocks exhumed during extensional block faulting associated with
formation of the Bisbee basin. Radiometric ages within the 90-120 Ma range are common in
dated granitoid suites in the Sierra Nevada of California (Chen and Moore, 1982). Similar older
peak ages (90-115 Ma and 120-175 Ma) are present in all sandstones sampled for this study
(Table 1-1), confirming recycling of the older Jura-Cretaceous rocks as a potential source for
these peak ages in the Fort Crittenden Formation. Additionally, previous workers found local
and regional petrologic evidence for recycling of the Bisbee Group and intermediate volcanic
rocks into the Fort Crittenden Formation (Inman, 1982, 1987; Hayes, 1986, 1987; Lindberg,
1987; Mann, 1995). An equally viable source of grains with these FT ages are rocks exhumed
and cooled during normal faulting associated with Late Jurassic-Early Cretaceous formation of
the Bisbee basin (Hayes, 1970b; Bilodeau, 1978, 1979; Klute, 1987; Dickinson and others,
1986); these grains could subsequently have been recycled into the Laramide basin fill. In the
older Lower Cretaceous and Jurassic rocks that contain peak ages in the range 90-115 Ma and
120-175 Ma, the processes mentioned above would generate FT ages such as these in situ.
Alternatively, grains with FT ages in the older portion of this age range might have been recycled
from older rocks into the Bisbee Group sampled for this work.
37
Minimum provenance ages around 170 Ma likely represent a cooling age associated
with Jurassic volcanism, expressed throughout southeastern Arizona (i.e. Jurassic Canelo Hills
volcanics, Late Jurassic ‘rocks of Mount Hughes,’ Juniper Flat granite near Bisbee, and
equivalents; Creasey and Kistler, 1962; Kluth, 1982; Kluth and others, 1982; Vedder, 1984).
Another probable source of similar ages includes rhyolitic-dome deposits and associated
volcaniclastic rocks of the Middle Jurassic Temporal and Bathtub formations. These rocks have
been dated at 182-172 Ma (U-Pb on zircon; Riggs and others, 1993; Bassett and Busby, 1996),
and have a gradational contact with the basal Glance conglomerate in the Santa Rita Mountains.
These strata mark the transition between widespread volcanism and Bisbee basin
sedimentation, and were deposited in trans-tensional basins possibly associated with movement
along the Mojave-Sonora megashear (Bassett and Busby, 1996). Accordingly, grains with FT
ages around 170 Ma may have been derived directly from these Jurassic volcanic and igneous
rocks, from older rocks affected by that thermal event, or from Bisbee Group lithologies which
sourced these Jurassic and older rocks. These observations support a relatively local source for
at least some of the c. 170 Ma provenance ages.
The source for 140 Ma ages might also have been relatively local. Intercalated within
the basal Bisbee Group in the Huachuca Mountains are intermediate volcanic rocks referred to
as the Glance andesite (Hayes and Raup, 1968; Figure 1-3); these rocks remain undated by
radiometric means. However, based on the age of the Canelo Hills Volcanics (185-165 Ma;
Vedder, 1984) and the rocks of Mount Hughes (intercalated tuffs within the basal portion of the
Glance Conglomerate in the Canelo Hills, 150 Ma; Kluth and others, 1982), and their relationship
with the basal Bisbee Group section, these andesites might be 150 Ma or younger. These
Jurassic and Cretaceous rocks might then have been recycled into the Upper Cretaceous
38
synorogenic fill, yielding a similar age component within the Fort Crittenden Formation. It is also
possible that grains with these cooling ages reflect heating associated with the magmatic source
of these andesites, thus yielding similar cooling ages from rocks with older depositional ages.
The Glance andesite may thus provide a source for cooling ages of c. 140 Ma.
Much older peak ages are present throughout the study area, including those from the
upper red conglomerate member of the Fort Crittenden Formation (276 Ma) and the Turney
Ranch Formation (566 Ma) in the Santa Rita Mountains; and the Cintura Formation (236 Ma and
803 Ma) and the basal conglomerate subunit of the Fort Crittenden Formation (353 Ma) in the
Huachuca Mountains (Table 1-1). The presence of these older peak ages and older single-grain
FTGA in most samples brings up the issue of peak temperatures attained for all units in this
study. Clearly in certain zircons, there is tremendous potential for recording and retaining very
old cooling ages, depending on the thermal history of the grain following closure to the FT
system. Because of this dependence on thermal history, as well as other single-grain
characteristics (Chapter 2), the observation of this very old component in the FT data indicates
that portions of the source area remained at sub-annealing temperatures (perhaps 180-260°C,
depending on single-grain response to heating; Chapter 2) through the myriad of tectonic and
thermal events which have affected southeastern Arizona, in some cases since the Proterozoic
(Appendix 4).
Pb-Pb Ages
Pb-Pb ages for Station 23 in the Huachuca Mountains (Figure 1-3) provide further
constraints on sources of zircon in the basal subunit of the Fort Crittenden Formation. Three
observations about this unit are critical (Hayes, 1986, 1987): (1) the basal conglomerate is only
present in the northwestern Huachuca Mountains; (2) this unit is characterized by poor clast
39
sorting and rounding; and (3) there is an up-section change in conglomerate clast composition
within the unit, from approximately equal components of limestone (proposed by Hayes (1986,
1987) to be derived from the Mural Formation, Bisbee Group; Figure 1-2) and intermediate
volcanics, to almost solely volcanic clasts similar in composition to the Glance andesite.
Pb-Pb ages of detrital zircons from Station 23 in the Huachuca Mountains (Figure 1-7)
indicate a lack of input of Mesozoic volcanic detritus at the base of the Laramide sedimentary
section at this location, because greater than 90% of the crystallization ages in FT-dated zircons
are Paleozoic or older (Figure 1-7). Hayes (1986) suggested the following as sources for the
dominantly volcaniclastic sandstones throughout the section, and volcanic-rich conglomerates in
every Upper Cretaceous sedimentary unit except for the upper red conglomerate in the Santa
Rita Mountains: Triassic-Jurassic volcanic rocks in the Santa Rita Mountains, the Jurassic
Canelo Hills Volcanics, the Glance andesite in the Huachuca Mountains, and early Laramide
volcanic rocks in the Canelo Hills and Santa Rita Mountains. For detrital zircons in the basal
part of the section, however, crystallization ages are dominantly Proterozoic and Paleozoic. As
such, if these zircons represent the volcanogenic component of the sandstone, a more likely
source for this detritus in this portion of the basin is older volcanic rocks. In the present
configuration, the nearest Proterozoic volcanic rocks lie in the northern Dos Cabezas Mountains
(Anderson, 1989); additionally, volcanic, volcaniclastic, and metavolcanic rocks of Proterozoic
age exist throughout central and northwestern Arizona (Anderson, 1989). A small fraction of
these zircons, if derived from the volcanic fraction of the sandstone, could also have been
derived from Mesozoic volcanic and volcaniclastic units, given their Pb-Pb ages; source units
might include the Jurassic Canelo Hills volcanics (Figure 1-3; Figure 1-2). Though older volcanic
and/or plutonic rocks may be the ultimate source of most grains with these crystallization ages, a
multi-cycle origin is quite likely.
40
Another issue to consider is that zircons from Station 23 may not be derived from the
volcanic component of the sandstone, suggested by Hayes (1986) to reflect recycling of the
Glance andesite into the basal conglomerate subunit of the Fort Crittenden Formation. Despite
a significant proportion of VRF in the sampled interval at Station 23 (19% total lithics (Lt), 6%
volcanic lithics (Lv); Appendix 5), detrital zircons in this sample are also likely derived from other
component compositions within the framework, and thus not fully represent the source ages of
the recycled volcanics in the lower part of this section. Additionally, because of the constituent
grain size, many VRF and possible VRF (included in URF) might have a negligible contribution
to the dated fraction. As such, the Station 23 sample is probably dominated by zircon derived
from granitic and recycled sedimentary sources.
Provenance of FT Samples, Prior Work
Provenance work for the Fort Crittenden Formation FT samples indicates that source
areas for most samples included both granitic and volcanic rocks, with subordinate recycling of
sedimentary rocks (Figure 1-6). Given that almost the entire Paleozoic section is composed of
carbonates, the overall lack of CRF and chert indicates a paucity of Paleozoic source rocks,
and/or that rock fragments derived from the Paleozoic carbonates were unstable during transport
and diagenesis, and thus make up some portion of the URF.
Prior work by Hayes (1986, 1987) similarly indicates variable mineralogy and textural
maturity among analyzed sandstones. Most samples show evidence for textural and
compositional immaturity, with Huachuca Mountains samples being the most mature of those
studied (lithic arkose, low-quartz feldspathic litharenite), and samples from the Santa Rita
Mountains being somewhat less mature (dominantly lithic arkoses) than sandstones from the
41
Huachuca Mountains. Important observations made by Hayes (1986) include the following: (1)
plutonic quartz is dominant over vein and metamorphic quartz; (2) sodic plagioclase, microcline,
and perthite are the most common feldspar compositions; (3) VRFs are abundant, and document
contribution of andesitic detritus (whereas the composition of the Jurassic Canelo Hills volcanics
tend to be more rhyolitic); and (4) SRFs tend to be mostly shale and siltstone, with subordinate
sandstone, limestone, and chert. Metamorphic rock fragments are rare, but detrital chlorite is
common. Important accessory minerals include muscovite, biotite, iron oxides, and epidote.
Petrographic observations on samples from this work agree on all above points, although this
study documents a greater contribution of SRF, feldspar, and MRF in certain samples.
Ten sandstone samples from the shale member of the Fort Crittenden Formation
described by Inman (1982) reflect an enrichment of volcanic rock fragments relative to
sedimentary and plutonic components, and a relative enrichment in plagioclase over potassium
feldspar. Sandstones interbedded with the basal conglomerate of the shale member plot in the
transitional-arc region on a Qm-F-Lt diagram (where Qm is monocrystalline quartz, F is feldspar,
and Lt is total aphanitic lithic content). Sandstones in the remainder of the shale member plot in
the transitional-recycled regions on a Qm-F-Lt diagram (Figure 1-6; Inman, 1987). These
features suggest a dominantly volcanic source for sandstones in the lower Fort Crittenden
Formation in the Santa Rita Mountains, though the lack of potassium feldspar may also be
reflective of diagenetic modification (Inman, 1982). This is a similar provenance signature to the
upper portion of the Turney Ranch Formation (upper transitional unit of Inman, 1982), which
changes from a dominantly sedimentary source to a mixed volcanic and sedimentary
provenance, and finally to a dominantly volcanic source at the top of the formation.
42
Diagenesis of Fort Crittenden Formation Samples, and Prior Work
Hayes (1986) found evidence for extensive burial diagenetic modification in Fort
Crittenden samples from both the Santa Rita and Huachuca Mountains, including possible
selective replacement/alteration of potassium feldspar; chloritization of biotite; and extensive pre-
cement compaction. This work suggested “rapid, deep burial and/or a high geothermal gradient”
(Hayes, 1986, p. 67) to achieve the diagenetic alteration present, though Hayes (1986) did not
cite a burial depth or maximum peak temperature, and no attempt to constrain these parameters
was made. Evidence for early, extensive compaction and subordinate cementation was also
found in the present study in all FT-dated Fort Crittenden Formation samples. However, without
a more extensive petrographic study, including further X-ray diffraction work on mixed-layer
clays in some samples, the diagenetic character of FT-dated samples remains a qualitative
guide for interpretation of burial temperatures, and hence, inferred depths. Better estimates for
maximum depth of burial are made using the thicknesses of overlying sediments and the FT age
signatures (refer to next section).
Regional versus Local Heating
The question of local versus regional heating is of critical importance to this discussion.
The FT data for the entire study area and sparse vitrinite-reflectance data suggest that, on the
whole, these rocks probably did not exceed 200-225°C (Figure 1-1). In the case of other
samples within the remainder of the study area (Santa Rita Mountains, Fort Crittenden
Formation shale member), vitrinite-reflectance data record temperatures on the order of 150-
250°C, somewhat lower than maximum temperatures recorded elsewhere (this peak
temperature is based on 7 vitrinite measurements). Notably, peak temperature determinations
do not show a clear correlation with proximity to exposed lower Tertiary intrusive rocks, although
the VR data are sparse. Additionally, the presence of reset FT peak ages and/or single-grain
43
reset FT ages does not always coincide with proximity to exposed intrusive rocks (e.g. Station
13, 14; Table 1-1, Appendix 4).
Trends within the FT data suggest that, with the exception of two locations, most
samples experienced sufficient Paleogene heating to reset the FT ages of certain grains
(Appendix 4; Figure 1-8). This observation includes those samples near Tertiary intrusions and
dikes (i.e. Station 9, 23), but also some samples not near any mapped intrusive rocks (e.g.
Station 13). Additionally, there is little consistent spatial variation in peak ages among dated
samples, which indicates that resetting had little if any resetting effect on most grains. These
observations suggest both local and regional controls on peak temperatures. Locally elevated
temperatures are likely related to plutons associated with a deeper-seated magmatic and
hydrothermal system that changed the regional geothermal gradient. Magmatic activity at depth
would provide a regional heat source for thermal reset at the present level of erosion, with locally
higher paleotemperatures directly adjacent to intrusive bodies. Given the magmatic setting
established in this area during the Laramide, local variations in peak temperatures are possible,
if not likely (Titley and Anthony, 1989). The observations fit well with the eastward migration of
arc-related magmatic activity through southeastern Arizona associated with shallowing of the
subducting slab during this time (Snyder and others, 1976; Coney, 1978; Dickinson and Snyder,
1978; Keith and Wilt, 1986).
Additionally, it is possible that the basin-bounding fault zone in the Huachuca Mountains
and farther northwest along the Sawmill Canyon fault zone in the Santa Rita Mountains aided in
the channelization of fluid flow and heat. Fission-track ages from rocks well outside this zone
would be needed to test this idea. There is clear evidence for focused fluid migration along
mapped fractures and fault zones; Pb-Zn-Ag mineralization is scattered throughout the eastern
44
Santa Rita Mountains along the western portions of the Sawmill Canyon fault zone (mines
located with X on Figure 1-4; Drewes, 1971a, 1976; Titley and Anthony, 1989). This
mineralization is associated with nearby calc-alkaline intrusions ranging in age from 75 to 55 Ma
(Appendix 1); locations of established mining activity in the district adjacent to or within
Laramide-associated intrusions are shown in Figures 4 and 8.
The effect of thermal resetting of FT ages by enhanced fluid flow along fault zones, and
movement of hydrothermal fluids within basin strata, has been documented in the Late Triassic-
Early Jurassic Newark basin, New Jersey (Steckler and others, 1993). The Newark basin study
documents the importance of low-temperature (100-250°C) hydrothermal systems active in
sedimentary basins and the effect of heat transport during fluid flow on FT ages in zircon. Along
the border fault of this rift basin, zircon and apatite FT ages are older than reset FT ages from
rocks at the same time-stratigraphic level deposited within the basin, indicating that rocks along
the border fault remained cooler. As there is no evidence for differential subsidence or
intrabasinal exhumation relative to the border fault region, lower temperatures along the fault are
attributed to downwelling of cooler water at the basin bounding fault zone, likely resulting from
the high topography along the flank of the basin combined with an active hydrothermal system.
This hypothesis is corroborated by fluid-inclusion work and authigenic clay mineralogy. To
determine the applicability of this scenario to the current study area, new FT ages both inside
and outside the fault zones would be needed, in addition to other thermal indicators, such as
fluid-inclusion work and information on zeolitic and clay cement development (following the
methods of Steckler and others, 1993).
Lateral migration of fluids far outboard of an advancing deformation front can also occur.
Lateral movement of formation and metamorphic fluids as much as 100-200 km outboard of the
45
contractional deformation front in the Alberta basin has been documented by Machel and Cavell
(1999) and Machel and others (2000). Sr isotopic signatures of cements from Devonian
carbonates and shales indicate lateral migration of extra-basinal fluids associated with burial and
loading during with Laramide deformation (Machel and Cavell, 1999). Additionally, Machel and
others (1999) suggest that subvertical faults played an important role by localizing vertical
movement of fluids through the deeper parts of the section, with subsequent migration into
accumulating sediments of the foreland basin. Such mechanisms could also have played a role
in the development of the hydrothermal system in the Laramide basin in the present study.
Migration of hot fluids along fault zones and lateral movement of fluids through basinal
sediments could have enabled metamorphic and/or magmatic fluids associated with intrusions to
affect strata well outboard of the deformation front.
Another consideration in the present study is the depth of burial of the Jura-Cretaceous
section. Regional map relationships between the Fort Crittenden Formation and older rocks
indicate that the contact is generally a disconformity, or a slight angular unconformity with little
change in dip across the contact (typically <20°; Hayes and Raup, 1968; Drewes, 1971a). As
such, where the section is relatively undeformed, it was likely a nearly horizontal section that
was buried. Where the Jura-Cretaceous section is deformed (i.e. within the Sawmill Canyon
fault zone, Figure 1-4; or along the west flank of the Huachuca Mountains, Figure 1-3), folds are
typically km- to sub-km scale, with meso-scale folding at the outcrop level. Absent overturning
on these larger-scale folds, which is generally not the norm in this area, the Jura-Cretaceous
section was not overturned during burial.
Younger rocks and sediments stratigraphically above the Jura-Cretaceous section
include uppermost Cretaceous and Paleogene volcanic and sedimentary rocks, Tertiary
46
conglomerate and sandstone, and Quaternary conglomerate, sandstone, and unconsolidated
gravels. The maximum preserved thickness of these units is estimated to be 4200 m
(Scarborough, 1989). The distribution of these rocks is highly variable throughout southern
Arizona, and it is unlikely that a 4-km-thick section existed within the field area. The thickness of
strata deposited atop the section of interest is highly variable, resulting from local interaction
between sedimentation and structural development during the Cenozoic (Scarborough, 1989).
Thus, there is no reason to believe that the thickness of units overlying the Upper Cretaceous
Fort Crittenden Formation exceeded 4200 m, and is likely much less, perhaps on the order of
2000 meters within the field area (un-decompacted thicknesses). Assuming an average
continental geothermal gradient of 30°C/km, burial temperatures for the Upper Cretaceous rocks
probably would not have exceeded 125°C.
Accordingly, there is insufficient overlying strata to bury the section deep enough to heat
zircons to partial annealing zone (PAZ) conditions and anneal tracks. Additionally, if the
resetting of FT ages in zircon were purely the result of burial, one would expect to see a
systematic change in FT ages upward through the section. In other words, the Jurassic rocks
should have been buried to the greatest depths, and the Fort Crittenden Formation buried the
least, and the annealing should reflect this difference in maximum temperature. In this case, the
Middle Jurassic rocks from the Santa Rita Mountains would then have a larger proportion of
zircons with reset FT ages, and these ages would be younger overall than FT ages from strata
upsection. Likewise, the Fort Crittenden Formation would have the fewest reset FT ages, as it
would have been buried the least, and these cooling ages would be somewhat older than cooling
ages present in the older Jurassic rocks, depending on exhumation rate and geothermal
gradient. This pattern of FT ages with respect to depositional age is not seen in the FT data
from this study area (Table 1-1; Figure 1-8). Additionally, if the thermal signature of samples in
47
this area were purely the result of burial heating, it would be a major coincidence that reset
samples throughout the section would contain similar Paleocene-Eocene reset peak ages (Table
1-1).
Implications for Provenance of Fort Crittenden Formation and Changes in Thermal Structure through Time
Very similar FT age distributions occur throughout the sample suite (Table 1-1). All
samples contain FT peak ages of 90-170 Ma and older single-grain ages, which in some cases
are sufficient in number to define an older peak age. Many samples also contain a young reset
peak, 68-42 Ma, and single reset FT ages (Appendix 4). For the unreset ages, two important
factors are revealed about the thermal structure of the crust recycled into the Laramide basin:
(1) there was potentially direct recycling of Middle Jurassic and Lower Cretaceous strata into the
Fort Crittenden Formation, or at least erosion of some rocks with a similar thermal signature as
the Middle Jurassic-Lower Cretaceous; and (2) the Jura-Cretaceous section was probably not
ever buried very deeply.
It is clear from prior work on the sedimentology and provenance of the Fort Crittenden
Formation that clastic sediments were derived from the Middle Jurassic through Lower
Cretaceous strata, as well as other units, including granitic sources (Inman, 1982; Hayes, 1986).
However, given the FT data, the age distribution of the source area for the Fort Crittenden
Formation is the same as the signature present in the older Jura-Cretaceous lithologies, and that
signature must also have been present in other units being eroded into the basin. This
observation suggests that at least at the beginning of the Laramide, during basin formation, there
was no preferential uplift of one source area relative to another: granites sourced by the Fort
Crittenden Formation were at the same thermal level as the remainder of the section.
48
Provenance
Certain aspects of prior work on the sedimentology and provenance of the Fort
Crittenden Formation are pertinent to the current discussion of derivation of Laramide basin fill.
Hayes (1986) documented a distinct transition in conglomerate clast compositions in the basal
and upper conglomerate subunits in the Huachuca Mountains. The basal conglomerate subunit
is present only in the northwestern Huachuca Mountains, and is one of the only units for which
Bisbee Group recycling is required by the provenance data (also required in the case of the
upper red conglomerate, Santa Rita Mountains; Hayes, 1986). The basal conglomerate subunit
is characterized by poor size sorting and angular clasts, suggesting textural immaturity,
particularly with respect to the upper conglomerate subunit. Specific to the basal conglomerate
subunit, Hayes (1987) also noted a change in clast composition upsection, from approximately
equal components of limestone and intermediate volcanics to solely volcanic compositions
(clasts similar to composition of Glance andesite; Figure 1-2). This observation may indicate
erosion through the upper part of the Lower Cretaceous section (i.e. limestone component)
through to Glance conglomerate and interbedded Glance andesite. In the upper conglomerate
subunit, clasts are well rounded and well size sorted, indicating greater textural maturity
upsection. Compositions of conglomerates throughout the upper conglomerate subunit are
equal portions of recycled sedimentary, volcanic, and granitic clasts. This pattern suggests
continuing erosion through the Lower Cretaceous section into Jurassic volcanic rocks and
Jurassic intrusions.
Hayes (1986) suggested several different sources for conglomerates in the Upper
Cretaceous section. Compositional fields for Fort Crittenden Formation conglomerates in the
Huachuca and Santa Rita Mountains are shown in Figure 1-9. Most conglomerates in the
section are dominated by volcanic and granitic clasts, with less evidence for recycling of
49
sedimentary rocks. For granite clasts and detritus, sources may include both Precambrian and
Triassic-Jurassic granites. Where conglomerates sourced volcanic rocks, Hayes (1986) cited
essentially every volcanic rock in the pre-Upper Cretaceous section as a potential source:
Triassic-Jurassic volcanics, Mount Wrightson Formation, Canelo Hills volcanics; Glance
andesite; and early Laramide volcanics. Siliciclastic sedimentary detritus may have been
derived from the Lower Cretaceous Bisbee Group, or from the Cambrian Bolsa quartzite. Some
variation in clast composition is noted through the section: the lower red and brown
conglomerate members contain subequal granitic and volcanic clast compositions; the upper red
conglomerate member sourced dominantly sedimentary rocks.
The evolution of clast compositions of conglomerates in the Huachuca Mountains,
including volcanic clasts in all cases, have been discussed above. Based on Hayes’ (1986)
conglomerate clast compositions (Figure 1-9), source areas for Fort Crittenden sediments may
have evolved in either or both of the following ways: (1) recycling into the basin and sourcing in
the conglomerates works through granites and volcanic cover to uncover sedimentary sources;
and/or (2) tapping of different sources in different areas through time. In the northern Huachuca
Mountains in particular, Hayes (1986) suggests that with progressive alluvial fan development,
there is an evolution of recycling first the Lower Cretaceous section (Bisbee Group), and then
continuing down into underlying Mesozoic volcanic rocks and granitic rocks.
Structural Constraints
Most faults that juxtapose the Fort Crittenden Formation with older rocks dip at relatively high
angles to the attitude of the offset strata (Hayes and Raup, 1968; Drewes, 1971a). Drewes
(1981, 1988) suggested multiple periods of movement along the Sawmill Canyon fault zone,
and that this was a major structure reactivated during Laramide contraction. Davis (1979) noted
50
the presence of the Sawmill Canyon fault zone and its along-strike parallel relationship with the
west-flank fault zone in the Huachuca Mountains (Figure 1-1), and suggested that these
structures may have formed the bounding fault zone which separated the Laramide structural
uplift from the adjacent basin. These faults generally have steep dips (>45°) relative to the dip of
bedding in Laramide synorogenic strata.
Given the preceding argument, and considering the suggestion that Jura-Cretaceous
strata were buried as a straight section, Figure 1-10a shows the interpreted configuration for the
sediment-source couple that satisfies critical relationships present in the FT and provenance
data, and Figure 1-10b provides one possibility for post-depositional heating of the section:
(1) This scenario provides a straight stratigraphic section that allows for the unroofing
sequence documented in conglomerate and sandstone compositions by Hayes (1986).
(2) Significant recycling of the Jurassic-Cretaceous section occurs in this configuration,
and granitic material is derived from either Precambrian or Mesozoic granitic rocks that
underlie the Lower Cretaceous Bisbee Group (LK in Figure 1-10; documented by
Bilodeau, 1979), via recycling of granite-clast conglomerates abundant in the Glance
conglomerate (detailed in Bilodeau, 1979), or by tapping Precambrian source rocks as
shown in Figure 1-10a. Granite sourcing in this case does not necessitate preferential
uplift of granitic rocks at basin-bounding faults: trunk streams and tributaries feeding
alluvial fans need only incise into the basal Bisbee Group, or into granitic rocks in
nonconformity with the Bisbee Group. However, the configuration presented in Figure 1-
10a agrees with the present relationship of Precambrian granites to the Phanerozoic
section, and presents the possibility for sourcing of granite by exhumation along reverse
faults. Note that because of the thermal signature in units determined in this study,
juxtaposition of Precambrian and Phanerozoic rocks is not associated with significant
granitic
volcanic sedimentary
Figure 1-9. Compositional ternary diagram for conglomerates in the Fort Crittenden Formation
Santa Rita Mountains samples
Huachuca Mountains samples
(N = 27 clast counts from the Santa Rita and Huachuca mountains; from
51
Hayes, 1987).
52
uplift during the early Laramide.
(3) Volcanic detritus is readily available from at least two sources: the Jurassic Canelo
Hills volcanics, and the Glance andesite (portions of J and LK on Figure 1-10a; Figure 1-
2).
(4) There is a distinct lack of recycling of Paleozoic carbonate units into the Fort
Crittenden Formation samples in this study (Figure 1-6). While Hayes (1986)
documented somewhat greater recycling of sedimentary rocks than found in the current
study, the recycled sedimentary component, including Paleozoic carbonate lithologies, is
overall subordinate to the input of volcanic and granitic detritus. This indicates that the
Paleozoic carbonate section was stripped prior to deposition of the Fort Crittenden
Formation, that Paleozoic carbonate clasts did not survive transport, or that Paleozoic
carbonates were covered and unavailable to the basin during Laramide sedimentation.
(5) Because the FT thermal signature of the underlying section is so similar to that of
the Fort Crittenden Formation, there is no significant differential in the exhumation level
of one source terrane over another.
(6) Because of the similarity of peak ages within the Fort Crittenden Formation,
variations in the thermal signature of the source are minimized by the presence of the
same units along strike, which probably contain similar thermal signatures.
(7) Post-depositional heating of the section is proposed to be a combination of thermal
input from magmatic activity (Drewes, 1976) and limited burial of the section by
uppermost Cretaceous and Cenozoic volcanic and sedimentary rocks (Figure 1-10b).
The maximum thickness of post-Fort Crittenden Formation rocks is 4200 meters
(Scarborough, 1989), but due to local variations in thickness, values on the order of 2
km are present. In combination with deeper-seated magmatic activity, as shown in
SW
NE
4 k
m
?
LK
J
4 k
m
Pz
UK
Pz
J?
20
0°C
/
~65 M
a
20
0°C
/
~55 M
a
20
0°C
/
~4
5 M
a
SW
NE
?
4 k
m
?
Pa
leo
zo
ic(P
z)
Fig
ure
1-1
0a
. I
de
aliz
ed
str
uctu
ral-se
dim
en
tolo
gic
sce
na
rio
fo
r th
e F
ort
Critt
en
de
n F
orm
atio
n d
ep
ositio
na
l p
erio
d.
J
K
pC
g4
km
Pz
a. F
ort
Critten
den
Fo
rma
tio
n (
UK
)
de
po
sitio
na
l p
erio
d
(85
-75
Ma
)
b. p
ost-
de
po
sitio
na
l
therm
al effects
:
magm
atism
and
bu
ria
l
Up
pe
rC
reta
ce
ou
s (
UK
)
burial by ~
2 k
m o
f
post-
Fort
Crittenden
Form
ation v
olc
anic
/
sedim
enta
ry r
ocks
Lo
we
rC
reta
ce
ou
s (
LK
)
Ju
rassic
? (
J)
Pre
ca
mb
ria
ng
ran
ite
(pC
g)
pC
g
pC
g
Fig
ure
1-1
0b
. E
vo
lutio
n o
f 2
00
°C iso
the
rm d
urin
g p
ost-
de
po
sitio
na
l m
ag
ma
tic a
ctivity a
nd
su
bse
qu
en
t b
uria
l b
y u
pp
erm
ost C
reta
ce
ou
s
an
d y
ou
ng
er
vo
lca
nic
an
d s
ed
ime
nta
ry r
ocks.
53
ind
ex m
ap
of stu
dy a
rea
sh
ow
ing
lo
ca
tio
n o
f b
lock
dia
gra
ms
?
pC
g
pC
gp
Cg
pC
gp
Cg
54
Figure 1-10b, the geothermal gradient was elevated and the evolution of the 200°C
isotherm following intrusion at ~65 Ma is shown. This combination allows for the
appropriate scale and timing of heating to achieve the post-depositional annealing found
in the FT data. The scale and relationship of intrusive bodies with the surrounding wall
rocks are in keeping with mapped surficial relationships (i.e. Hayes and Raup, 1968;
Drewes, 1971a), and the scale of thermal effects (as shown by the evolution of the
200°C isotherm) is supported by thermal modeling of Barton and Hanson (1989) and
Hanson (1996).
In terms of direct fault control on sedimentation, the structural and sedimentologic
scenario for the Laramide basin presented in Figure 1-10 is in contrast with sedimentary tectonic
models proposed for older basins in this part of southeastern Arizona. One example of this
contrast is the work of Davis and others (1979), that suggests that extensional faults exerted
marked control on deposition of Permian exotic blocks in Jurassic red-bed deposits in the
Canelo Hills (Figure 1-5). These exotic blocks of Permian carbonates measure up to 400 meters
in thickness, are up to 2 km along strike, and are intercalated with the Jurassic Canelo Hills
volcanics (Figure 1-2) in both the Sawmill Canyon Fault Zone as well as the west-flank fault zone
in the Huachuca Mountains (Davis and others, 1979; Figures 1-4, 1-3). Bedding-parallel faults,
slickenlines, clastic dikes, and breccias near the contact of these blocks are interpreted to have
formed during block emplacement, as the blocks gravitationally glided into unlithified red-bed
sediments. In many cases, emplacement of blocks is related to activity on high-angle north-
northeast- to northeast-striking faults (Davis and others, 1979).
The sedimentologic character of the Fort Crittenden Formation is significantly different
than that of the exotic-block facies of the Canelo Hills volcanics: deposits of the Fort Crittenden
55
Formation are texturally and mineralogically more mature, finer-grained, and less proximal than
the exotic block/red-bed facies described by Davis and others (1979). Additionally, all exotic
blocks intercalated with the Canelo Hills volcanics are Paleozoic, whereas the Fort Crittenden
Formation appears to have either not sourced the Paleozoic at all, or that Paleozoic-derived rock
fragments and clasts did not survive transport within the basin. Based on mapping and
kinematic analysis, Davis and others (1979) concluded that deposition of these exotic Paleozoic
blocks is the result of gravitational gliding associated with normal faulting. Fault control on facies
and emplacement of large exotic blocks in this manner is not documented for the Fort Crittenden
Formation, and this example thus serves to document the relative lack of direct fault control on
derivation of the Fort Crittenden Formation. The relative uniformity of source rocks for the
Laramide basin indicates that unlike in older synorogenic basins in the same area, the deformed
nature of source rocks and the distribution of these older rocks does not exert significant control
on the FT signature of the Laramide basin fill.
CONCLUSIONS
Based primarily on zircon FT data complemented by petrography and existing
provenance studies, the following conclusions may be made:
(1) Young FT ages (Paleocene-Eocene) in many samples indicate that widespread
thermal activity reset some zircons preferentially, whereas a significant fraction has
much older ages. Because of the thickness of the overlying section and the distribution
of young reset FT peak ages in almost every Jurassic-Cretaceous unit sampled, the FT
age structure present in these samples could not have been produced purely by burial
heating.
(2) Samples with young FT ages do not always coincide with the outcrop distribution of
plutons, and the distribution of these samples widespread throughout the data set, with
56
similar peak ages from place to place regardless of depositional ages. As such,
Paleogene heating was regional, potentially related to conductive heating and
hydrothermal circulation associated with magmatic activity at depth.
(3) Older FT grain ages provide minimum provenance ages for Fort Crittenden
Formation sediments. These peak ages show that there has been little burial of the
older Jura-Cretaceous section prior to recycling into the Laramide basin, document little
variation in the thermal signature of the crust being recycled, and suggest that the Jura-
Cretaceous section provided an important sediment source for the Fort Crittenden
Formation. The presence of older peaks of similar ages in the Jurassic, Lower
Cretaceous, and Upper Cretaceous sediments, in combination with petrographic
evidence for recycling, demonstrates that there was probably little exhumation of one
source terrane preferentially to others prior to and during deposition of the Fort
Crittenden Formation. It is likely that some fraction of zircon in a given sample is also
derived from granites (Triassic-Jurassic or Precambrian). Although there clearly was
granite exhumed and recycled into the Fort Crittenden Formation (Hayes, 1986), these
units must have been relatively high in the crustal stack, and cooling ages of zircons
derived from these granites are the result of annealing prior to the Laramide. Granite
sources in this case could be either Precambrian or Mesozoic, or both.
(4) Jura-Cretaceous rocks included in this study likely did not exceed temperatures
greater than 200°C-225°C, depending on single-grain annealing characteristics. Units
that do not display any obvious resetting of the FTGA have probably remained at
temperatures <180°C, but have similar age distributions for older FT ages as rocks with
clear evidence for Paleogene resetting. This observation documents the criticality of
single-grain characteristics as controls on the closure temperature of zircon, the focus of
Chapter 2.
57
Chapter 2—Controls on the low-temperature thermal response of single detrital zircons: Temperature, crystallinity, and chemistry
ABSTRACT
Fission-track (FT) ages of zircon from Mesozoic sandstones were analyzed to address
the provenance and post-depositional thermal history of Laramide synorogenic strata in
southeastern Arizona. Samples from strike-normal transects across the Laramide basin
boundary show a complex provenance, with significant recycling from underlying strata.
Fourteen Jura-Cretaceous sandstones have FT populations with peaks between 570-165, 140-
82, and 68-42 Ma. Numerous older single-grain ages (1000-600 Ma) are also present, indicating
long-term cool conditions (temperatures less than perhaps 180°C, up to 260°C, depending on
single-grain response to heating) for portions of the source area. While most samples show a
range of provenance ages, a small fraction have been affected by post-depositional thermal
annealing. The distribution of samples with reset ages coincides in some locations with
proximity to magmatic bodies 75-40 Ma in age. This setting provides an opportunity to
investigate controls on single-grain response to thermal perturbations. The young component of
reset ages falls between 68 and 42 Ma, and is younger than the depositional age of the Jurassic-
Upper Cretaceous strata in which these ages occur. As such, these strata reached
temperatures sufficient to anneal fission tracks in some grains (c. 180°C-260°C). U-Th-Pb, REE,
and Raman microprobe analyses from these samples indicate a correlation among old
crystallization ages, high U+Th (eU, or effective uranium) concentrations, elevated alpha-
damage dose, and young reset FT ages. Resetting occurred in grains with higher radiation
damage, as determined by FT and Raman microprobe analyses, and total and effective alpha-
dose calculations. Less-damaged grains have a higher temperature of track retention, and
therefore retain a primary detrital signature. Zircon color is related, in part, to increasing
58
radiation damage, and can be used for identifying different thermal events in both the pre- and
post-depositional history of individual zircons. In this study, honey and colorless grains
essentially behave as one population in all data sets.
This study establishes some criteria for identifying reset grains in detrital populations:
(1) the pink/purple color series provides the greatest potential for having the combination of old
crystallization ages and/or high α-damage; (2) honey and colorless grains which have high eU,
i.e. greater than 650 ppm, might also be suspected as being preferentially reset, depending on
thermal history and retention time; and (3) zircons in rocks that attained paleotemperatures of
180°C-260°C may provide information on low-temperature thermal effects. The following
revision of methods is necessary to avoid difficulties in interpreting multi-component detrital-
zircon data sets: (1) separate zircons into color populations, and evaluate FTGA accordingly; (2)
evaluate etch behavior, as fission tracks will etch more rapidly in grains with higher accumulated
alpha damage; (3) evaluate FTGA with respect to eU, as high eU is sometimes correlated with
reset FT ages in honey and colorless zircons; and (4) utilize vitrinite-reflectance data where
possible to constrain maximum paleotemperature.
59
INTRODUCTION
Determining the thermal history of sedimentary strata during diagenesis and burial,
specifically in the temperature range 150-300°C, is critical to the understanding of basin
evolution, and provides important constraints on thermal and tectonic processes that affect
strata. The zircon fission-track system, with closure temperatures in the range of 235°C ± 25°C
(Brandon and Vance, 1992), is a proven means of determining the thermal history of upper-
crustal lithologies as these rocks are eroded and deposited into flanking sedimentary basins.
However, this thermal signature is just one aspect of the picture provided by the zircon FT
system. Where sedimentary strata have reached peak temperatures less than about 200°C,
zircon fission-track data primarily provide information on sediment provenance (i.e. Garver and
others, 1999). Where temperatures were higher, and samples are collected in stratigraphic and
structural context, thermal history and processes involved in basin formation and subsequent
deformation are further elucidated.
This study makes the first quantitative link between cooling age and crystallization age
of single grains. New constraints on the low-temperature response of zircons based on
variations in single-grain radiation damage and crystal chemistry are provided. Developing
relationships among these parameters strengthens our understanding of the low-temperature
behavior of zircons, and yields information critical to source-area evolution and pre- and post-
depositional thermal events for clastic rocks. The most important part of this issue centers on
the potential for radiation damage, specifically α-damage, to decrease the stability of fission
tracks in zircon, thus lowering the effective closure temperature of the system (Kasuya and
Naeser, 1988). This preferential annealing of radiation-damaged zircons, which has also been
noted in two recent studies (Kunlun Mountains of northeast Tibet, and Hudson Valley, New York;
Garver and others, 2002), allows dating of both provenance and post-depositional thermal
60
activity using the same sample if the factors controlling zircon behavior can be identified.
Recognizing and quantifying resetting of α-damaged zircons will more clearly reveal the closure
temperature range, and thus, the conditions under which resetting occurs in damaged zircons.
Finally, recognition of post-depositional thermal events is necessary to prevent the
misinterpretation of young (reset) fission-track ages in synorogenic sandstones, because such
ages can be mistakenly interpreted as indicators of synorogenic magmatic activity.
Radiation damage affects zircon (ZrSiO4) in several ways. Color in zircon changes over
geologic timescales, and is related to accumulation of α-damage and crystal chemistry (e.g.
Gastil and others, 1967). The presence of different color populations in zircon from a sandstone
allows optical separation into populations presumably related to differences in source-rock
histories. Many studies have attributed zircon color and/or morphology to: (a) crystallization age
or fission-track age (e.g. Vitanage, 1957; Gastil and others, 1967; Malcuit and Heimlich, 1972;
Garver and Kamp, 2002; and references therein); (b) source (e.g. Vitanage, 1957; Malcuit and
Heimlich, 1972; Gehrels and others, 2000; Riley and others, 2000); (c) chemical composition of
host rocks (e.g. Turniak, 1997); (d) granite genesis (e.g. Poldervaart, 1956; Forbes, 1969; Arps,
1970; Pupin, 1980); and (e) correlation of lithologies (e.g. Poldervaart, 1956; Vitanage, 1957). In
light of this literature, it is clear that the origin of color in zircon is complex. Though the
relationship among heating, color loss (i.e. annealing of α-damage), and resetting of the FT
system has been discussed (Garver and Kamp, 2002), the effects of accumulated radiation
damage and the single-grain response to heating have not been fully explored. Early
observations noted the general relationship of depth of color to crystallization age (e.g. Gastil
and others, 1967; Nerurkar and others, 1979). It is suspected that accumulated α-damage
results in decreased crystallinity and progressive color change (Garver and Kamp, 2002; Rahn
and others, in press). However, with the exception of a study in the Southern Alps of New
61
Zealand (Garver and Kamp, 2002), there is little information as to how color is altered by heating
at low temperatures (<300°C). It seems clear that a fundamental attribute of color is trace-
element impurities in zircon, but this aspect of color generation is also little studied. Work by
Fielding (1970) on hyacinth (pink/purple/red) series zircons suggests that the development of
“color centers” is related to uranium (U) content, rare-earth-element (REE) chemistry, and the
oxidation state and concentration of niobium (Nb). In a study of detrital-zircon populations in the
Potsdam sandstone (New York State), Gaudette and others (1981) suggested a link between
brown color in grains and positive europium (Eu) anomalies.
Prior to the development of laser ablation enhancement of inductively coupled plasma
mass spectrometry (LA-ICP-MS), it was very difficult to determine crystallization age and FT age
on the same grain. In the few cases where this has been attempted, zircons have been
separated into two fractions, one for U-Pb analysis, and one for FT age determination (i.e.
Hoisch and others, 1997; Carter and Moss, 1999). Likewise, single-crystal geochemistry
involved dissolution and/or ion-microprobe work on yet another separate fraction. In these
cases, the major problem is that the interrelation of attributes is unknown because analysis was
done on separate fractions. Such a cumbersome method obviates key information regarding the
relationship of single-grain provenance ages and thermal history, and the complex and
potentially useful link to the color of zircons.
This study investigates the relations among color, Pb-Pb crystallization age, fission-track
age, crystallinity and radiation damage, and trace-element chemistry of single detrital zircons
from a sample from a Laramide basin in southeastern Arizona. Making these measurements on
single detrital zircons provides new and unique insights into the provenance, thermal history, and
composition of these grains, thus providing a clearer picture of the regional evolution of source
62
and thermal history of rocks in this study. The multi-analysis approach employed here also
provides a basis for other workers to use observations and criteria from these data to better
understand what occurs to zircons at temperatures of 150°C to 250°C. To that end, zircons with
different color and morphology were chosen from a specific sample from a group of thirty-four
samples that are part of a larger study in southeastern Arizona (Chapter 1). This sample was
chosen because the FT data revealed a surprising finding: a small fraction of the grains had
been annealed and the FT ages reset, so the sample contains thermal information for the
sandstone as well as provenance information about the source(s).
Acquisition of Pb-Pb and FT ages on the same grains defines both the age of
crystallization and subsequent cooling to ~235°C of source rocks, providing crucial provenance
information. Working from this finding, important information regarding both provenance and
post-depositional heating should be obtainable from multiple analyses of single grains.
Specifically, understanding how the relationship between radiation damage and thermal
response controls the resetting of fission-track ages helps better define factors that control the
lower end of the fission-track system closure temperature (180°C-235°C) and annealing of
different types of radiation damage. Following on the observations made about this particular
sample, this study provides a basis for future workers by presenting criteria for identification of
reset fission-track grain ages (FTGA) in multi-component populations.
METHODS
Field Setting
The sample selected was 5 kg of coarse-grained lithic arkose from the base of the
Upper Cretaceous Fort Crittenden Formation in the Huachuca Mountains of southeastern
Kfc
Kc
Kc
Kga
Jh
?
Km
oK
ga
Kc
Sta
tio
n 2
3K
fc
Kc
Km
o
Km
u
Kc
Km
o
Km
o
Km
o
Km
u
Kg
Kg
Kg
aP
zu
Pzu
Kga
Kg
eK
ga
Pzu
e
Pzu
Pzu
Jh
Km
o
Kg
Pzu
Km
o
Kg
Kga
Kg
Km
oK
g
Km
u
Kc
Kfc
TQ
uK
b?
TQ
u
Km
o?
Tg
Tg
TQ
u
TQ
u
TQ
u
TQ
uTi
Ti
Km
o
pC
g
Tg
TQ
u
KfcTi
Pzu
e
Qal
Tg
TQ
u
Qg
Km
o
Km
u
Kc
Kga
Kg
Kb
pC
g
Jh
JTc
JT
h
JT
h?
JTc
JTc
JT
h
JT
h
JT
h JTc
JT
h
JTc
JTc?
JTc?
Te
rtia
ry a
nd
Qu
ate
rna
ry g
rave
ls,
allu
viu
m
Tert
iary
intr
usiv
es (
quart
z
mo
nzo
nite
, a
laskite
, g
ran
o-
dio
rite
, a
lka
li d
iorite
); in
tern
al
ag
e r
ela
tio
nsh
ips u
nce
rta
in
Up
pe
r C
reta
ce
ou
s F
ort
Critt
en
de
n
Fo
rma
tio
n (
ea
rly L
ara
mid
e b
asin
fill
)
Lo
we
r C
reta
ce
ou
s
Bis
be
e G
rou
p
Ju
rassic
Ca
ne
lo H
ills
Vo
lca
nic
s a
nd
asso
cia
ted
rocks
Pa
leo
zo
ic s
ed
ime
nta
ry
rocks, exotic b
locks o
f
Pa
leo
zo
ic w
ith
in o
the
r u
nits
Pre
ca
mb
ria
n g
ran
ite
01
kilo
me
ters
mile
s0
1
fissio
n tra
ck s
am
ple
; S
tation 2
3 d
enote
d
vitrin
ite
sa
mp
le
Ro =
3.0
0%
(N
= 4
4)
Tm
ax 2
25
-30
0°C
Ro =
2.0
3%
(N
= 5
0)
Tm
ax 1
50
-25
0°C
fau
lt; d
ash
ed
wh
ere
in
ferr
ed
an
ticlin
al tr
ace
; d
ash
ed
wh
ere
in
ferr
ed
,
plu
ng
ing
wh
ere
in
dic
ate
d
syn
clin
al tr
ace
; d
ash
ed
wh
ere
in
ferr
ed
,
plu
ng
ing
an
d/o
r o
ve
rtu
rne
d w
he
re in
dic
ate
d
co
nta
ct;
da
sh
ed
wh
ere
in
ferr
ed
Map
Un
its
Map
Sym
bo
ls
pC
g
pC
g
pC
g
pC
g
pC
g
a.
b.
Bis
be
e G
rou
p, u
nd
iffe
ren
tia
ted
Cin
tura
Fo
rma
tio
n
Mu
ral F
orm
atio
n
Morita
Form
ation
Gla
nce
an
de
site
Gla
nce
co
ng
lom
era
te
63
Hu
ach
uca
Mo
un
tain
s
Cin
tura
Fo
rma
tio
n
(~2
90
m)
Fo
rt C
ritt
en
de
n
Fo
rma
tio
n (
~6
60
m)
Mu
ral F
orm
atio
n
(~2
10
m)
Gla
nce
Co
ng
lom
era
te
(0-6
30
m)
??
Mo
rita
Fo
rma
tio
n
(~1
27
0 m
)
Ca
ne
lo H
ills
volc
anic
s
qu
art
z m
on
zo
nite
,
ce
ntr
al H
ua
ch
uca
s??
50
Ma
60
Ma
70
Ma
80
Ma
90
Ma
110 M
a
12
0 M
a
13
0 M
a
163 M
a
15
0 M
a
14
0 M
a
10
0 M
a
APTIANALBIANCENOMANIAN
TU
RO
NIA
N
CO
NIA
CIA
N
SA
NT
ON
IAN
CAMPANIANMAASTRICHTIAN
LATE EARLY
CRETACEOUS
EA
RLY
LA
TE
EA
RLY
EOCENE PALEOCENE
PALEOGENETERTIARY
NEOCOMIAN
JURASSIC
LATE
? ?? ??
Sta
tio
n 2
3
sa
mp
ling
in
terv
al
114°
11
3°
112
°111°
11
0°
37
°
36
°
35
°
34
°
33
°
32
°11
4°
11
3°
112°
111°
110
°
37
°
36
°
35
°
34°
33
°
32
°
Figure 2-1a. Generalized time-stratigraphic column for the Upper Jurassic-Upper Cretaceous section, Huachuca Mountains, showing approximate stratigraphic position of sample from Station 23 (column and lithologies after Hayes, 1970a; Hayes, 1970b; Palmer, 1983; Hayes, 1986; Hayes, 1987; Dickinson and others, 1989). Timescale of Palmer, 1983. Note that this is a composite column for the entire range, and that all formation and intraformational boundaries are time-transgressive in detail (shown schematically).
Figure 2-1b. Huachuca Mountains geologic map (generalized after Hayes and Raup, 1968) showing location of Station 23, sample locations as part of the regional study. Vitrinite-reflectance data shown adjacent to sample locations (Tmax estimates based on vitrinite-reflectance data from Fort Crittenden Formation siltstone/shale samples, interpreted after Héroux and others, 1979; Staplin, 1982; Burnham and Sweeney, 1989; Barker and Pawlewicz, 1994).
64
Arizona (Figure 2-1). The Cretaceous sequence is locally intruded by a quartz-monzonite
pluton emplaced sub-parallel to bedding within strata of the Lower Cretaceous Bisbee Group
(Figure 2-1). The sample site is 1 km from the intrusion (map distance). Cross-cutting relations
indicate a Tertiary age for the intrusion, and regional considerations imply that it is related to
other intrusions throughout the study area dated at c. 75-55 Ma (Hayes and Raup, 1968;
Drewes, 1972, 1976). Local structural relationships along the west flank of the range indicate
that this and similar smaller dikes and sills in Cretaceous strata are folded, and thus were
emplaced prior to major Laramide deformation (Hayes and Raup, 1968). Accordingly, this phase
of magmatism would have provided a source of heat for the area around this sample location
approximately 10-15 m.y. after deposition.
The sampled interval is the lowest portion of the Fort Crittenden Formation, just above a
disconformable contact with the Lower Cretaceous Cintura Formation. Strata include medium-
to coarse-grained, subangular to subrounded litharenites, deposited in an alluvial-fan setting
(Hayes, 1986, 1987). Framework grains include plutonic and metamorphic rock fragments (RF),
altered K-feldspar, sand-rich clastic RF, carbonate RF, and volcanic and/or microcrystalline to
mud-sized sedimentary RF, as well as common and vein quartz. The rock is partially cemented
by calcite, but cementation is overall subordinate to extensive compaction (contact index
average value of 6; very little cement is present (<1%), indicating thorough early compaction).
Fission-track Analysis
Zircons were separated with standard techniques using a Wilfley table, heavy liquids,
and a Frantz magnetic separator. A fraction of this material was prepared for traditional fission-
track age dating. From another fraction, zircon was then hand-picked into three distinct color
fractions (Table 2-1). The most appropriate division of the remaining sample was by color rather
65
than by grain morphology. Color is difficult to distinguish once mounted in Teflon, but grain
shape is still readily identified. Color fractions include: (1) light to dark pink and purple
(hyacinth) zircons (fraction p; ~5% of total yield); (2) colorless zircons (fraction c; ~20% of total
yield); and (3) honey-colored zircons (fraction h; ~75% of total yield). Each of the color fractions
includes at least two, and as many as seven, individual morphology groups, as shown in Table
2-1.
All hand-picked zircon fractions, as well as the original bulk zircon, were mounted and
etched for FT analysis (i.e. Garver and others, 2000). Each fraction comprised two mounts
containing approximately 1000 grains in each of two Teflon mounts. Mounts were polished and
then etched in a KOH:NaOH eutectic at 228°C for 17 hours (long etch), 12 hours (short etch), 10
hours (fractions c and h long etch), 8 hours (fractions c and h short etch), and 5 hours (fraction
p). All mounts were irradiated at the Oregon State University Reactor Facility, with a thermal
neutron fluence of 2 x 1015 n/cm2, and etched fission tracks were counted at 1250x magnification
(dry). Grains were analyzed using the external-detector method calibrated to zircons from Fish
Canyon Tuff and Buluk tuff zircons (refer to Table 2-2 for details, and Appendix 3 for a brief
discussion of FT systematics).
Cathodoluminescence
Following preparation and analysis for fission tracks (including irradiation and counting),
the color FT mounts were carbon-coated and cathodoluminescence (CL) images of each dated
grain were taken at the University of Texas using an Oxford Instruments photomultiplier-based
CL detector mounted on a JEOL T330A scanning electron microscope (SEM); accelerating
voltages range from 10-15 kV, as described in Milliken (1994). SEM-CL images assist in
delineating zonation and degree of heterogeneity within individual grains for the region counted
Tab
le 2
-1.
Zircon c
olo
r and m
orp
holo
gy f
ractions,
Sta
tion 2
3,
Huachuca M
ounta
ins.
rela
tive
ab
un
da
nce
co
lor
form
ha
bit/r
ou
nd
ing
cla
rity
inclu
sio
ns
siz
e
fra
cti
on
p
(pin
k/p
urp
le)
ab
un
da
nt
ve
ry lig
ht
pin
k t
o v
ery
lig
ht
pu
rple
elo
ng
ate
(~
2:1
to
4:1
)ro
un
de
d t
o w
ell
rou
nd
ed
cle
ar
rare
to
no
ne
larg
e t
o m
ed
ium
co
mm
on
me
diu
m t
o d
ark
pin
k t
o
pu
rple
eq
ua
nt
we
ll r
ou
nd
ed
cle
ar
rare
larg
e t
o m
ed
ium
co
mm
on
me
diu
m p
ink t
o p
urp
lee
qu
an
tw
ell r
ou
nd
ed
cle
ar
rare
larg
e t
o m
ed
ium
rare
me
diu
m p
ink t
o p
urp
leslig
htly t
o m
od
era
tely
elo
ng
ate
(2:1
to
3:1
)
eu
he
dra
l to
su
bh
ed
ral
cle
ar
rare
me
diu
m
rare
da
rk p
urp
le t
o b
lack
eq
ua
nt
su
bh
ed
ral to
ro
un
de
dfr
actu
red
/clo
ud
yu
nkn
ow
n d
ue
to
da
rk c
olo
r/fr
actu
ring
larg
e
rare
lig
ht
pu
rple
elo
ng
ate
(~
2:1
to
5:1
)e
uh
ed
ral
cle
ar
rare
to
no
ne
larg
e
fra
cti
on
c
(co
lorl
es
s)
ab
un
da
nt
co
lorl
ess
eq
ua
nt
we
ll r
ou
nd
ed
cle
ar
rare
larg
e
sp
ars
eco
lorl
ess
ve
ry e
lon
ga
te (
3:1
an
d g
rea
ter)
to s
lig
htly e
lon
ga
te (
2:1
)
eu
he
dra
lcle
ar
sp
ars
e t
o
co
mm
on
me
diu
m
fra
cti
on
h
(ho
ne
y)
ab
un
da
nt
lig
ht
ho
ne
ye
qu
an
t to
slig
htly e
lon
ga
te (
2:1
)su
bh
ed
ral to
an
he
dra
lcle
ar
sp
ars
em
ed
ium
to
la
rge
co
mm
on
ve
ry lig
ht
to lig
ht
ho
ne
yslig
htly t
o v
ery
elo
ng
ate
(2
:1 t
o
4:1
an
d g
rea
ter)
eu
he
dra
lcle
ar
sp
ars
em
ed
ium
to
la
rge
co
mm
on
lig
ht
am
be
r~
eq
ua
nt
an
he
dra
l to
ro
un
de
dslig
htly t
o h
igh
ly f
ractu
red
un
kn
ow
n d
ue
to
fra
ctu
rin
g
me
diu
m
sp
ars
eve
ry lig
ht
ho
ne
y t
o v
ery
lig
ht
am
be
r
eq
ua
nt
we
ll r
ou
nd
ed
cle
ar
rare
me
diu
m t
o la
rge
sp
ars
em
ed
ium
to
da
rk h
on
ey;
co
mm
on
Fe
oxid
e s
tain
eq
ua
nt
to s
lig
htly e
lon
ga
te t
o
mo
de
rate
l y e
lon
ga
te (
3:1
eu
he
dra
lcle
ar
un
kn
ow
n d
ue
to
co
lor
me
diu
m
sp
ars
elig
ht
ho
ne
y t
o d
ark
am
be
re
qu
an
te
uh
ed
ral to
su
bh
ed
ral
fra
ctu
red
un
kn
ow
n d
ue
to
fra
ctu
rin
g
me
diu
m t
o la
rge
rare
da
rk b
row
n t
o r
ed
~e
qu
an
ta
nh
ed
ral to
ro
un
de
dslig
htly t
o h
igh
ly
fra
ctu
red
/clo
ud
y
un
kn
ow
n d
ue
to
co
lor/
fra
ctu
rin
g
me
diu
m t
o la
rge
No
tes:
ab
un
da
nt
= 2
6-9
9%
; co
mm
on
= 6
-25
%;
sp
ars
e =
2-5
%;
rare
= >
0-1
%;
larg
e =
>1
00
µ m
lo
ng
est
exp
ose
d d
ime
nsio
n;
me
diu
m =
50
-10
0 µ
m lo
ng
est
exp
ose
d d
ime
nsio
n;
sm
all =
<5
0 µ
m lo
ng
est
exp
ose
d
dim
en
sio
n.
Zir
co
ns w
ere
se
pa
rate
d u
sin
g s
tan
da
rd t
ech
niq
ue
s (
Wilfle
y t
ab
le,
he
avy liq
uid
s,
an
d m
ag
ne
tic s
ep
ara
tio
n),
an
d h
an
d p
icke
d in
to c
olo
r a
nd
mo
rph
olo
gy f
ractio
ns u
sin
g a
bin
ocu
lar
mic
rosco
pe
.
66
Tab
le 2
-2.
Sin
gle
-gra
in f
issio
n t
rack a
ges (
FT
GA
), P
b-P
b a
ges,
eff
ective u
raniu
m c
oncentr
ations (
eU
), a
nd R
am
an c
rysta
llinity d
ata
(band
wid
th a
nd
positio
n)
for
colo
r fr
action z
ircons f
rom
Sta
tion 2
3,
Huachuca M
ounta
ins.
gra
in #
FT
GA
(M
a)
err
or
(+/-
; m
.y.)
Pb
-Pb
ag
e (
Ma
)e
rro
r (1
SD
; m
.y.)
eU
(p
pm
)e
rro
r (1
SD
; p
pm
)F
WH
M c
orr
. (c
m-1
)e
rro
r (c
m -1
)s
hif
t (c
m-1
)e
rro
r (c
m -1
)
pin
k/p
urp
le
d1
65
59
11
/91
84
61
59
69
45
78
.60
.86
10
03
.70
.50
d1
61
65
18
/14
13
70
14
01
22
22
02
11
.81
.18
10
03
.40
.50
d0
70
74
27
/20
17
92
98
87
92
04
10
.61
.06
10
03
.30
.50
d1
27
13
43
7/2
91
53
21
50
53
93
68
.40
.84
10
04
.10
.50
d0
05
13
84
9/3
51
77
11
19
70
11
89
7.8
0.7
81
00
3.9
0.5
0
d1
44
14
15
2/3
71
54
11
08
41
93
96
.30
.63
10
04
.70
.50
L0
49
14
36
6/4
31
32
41
50
58
82
87
.90
.79
10
06
.10
.50
d1
95
14
35
8/4
01
72
07
35
28
21
6.1
0.6
11
00
5.1
0.5
0
L0
62
14
94
2/3
31
89
22
17
55
13
66
.10
.61
10
06
.20
.50
d1
31
15
47
1/4
71
94
12
48
57
03
77
.20
.72
10
04
.90
.50
L3
04
18
94
6/3
71
20
74
04
81
52
6.9
0.6
91
00
5.4
0.5
0
d0
12
20
76
2/4
81
74
81
16
37
14
66
.50
.65
10
04
.60
.50
d0
13
31
01
16
/80
19
81
14
93
64
13
8.7
0.8
71
00
4.2
0.5
0
L3
30
50
83
85
/19
81
92
61
60
26
42
46
.80
.68
10
05
.00
.50
co
lorl
ess
c2
_0
31
53
15
/12
44
81
27
10
53
13
54
.10
.50
10
06
.40
.50
c1
_3
00
75
19
/15
33
06
09
06
80
3.8
0.5
01
00
7.1
0.5
0
c2
_2
85
75
31
/22
60
34
51
36
71
42
5.5
0.5
51
00
6.4
0.5
0
c2
_2
50
77
15
/13
54
15
11
06
21
33
4.5
0.5
01
00
6.3
0.5
0
c2
_2
97
78
20
/16
31
33
41
05
21
02
4.4
0.5
01
00
6.7
0.5
0
c1
_7
72
84
25
/19
56
55
21
16
88
34
.90
.50
10
05
.40
.50
c1
_2
16
88
28
/21
58
01
40
97
78
24
.70
.50
10
05
.60
.50
c2
_2
22
90
28
/21
68
51
64
92
15
93
.90
.50
10
06
.50
.50
c2
_0
64
92
31
/23
41
14
37
19
57
3.6
0.5
01
00
7.0
0.5
0
c1
_0
82
10
53
1/2
41
74
23
91
21
02
4.8
0.5
01
00
5.7
0.5
0
c2
_6
95
10
52
9/2
33
23
37
77
32
84
.30
.50
10
06
.70
.50
c2
_0
65
10
73
3/2
55
87
11
46
19
14
3.7
0.5
01
00
6.9
0.5
0
c2
_5
28
10
72
8/2
24
58
57
95
98
34
.30
.50
10
06
.40
.50
c1
_7
28
11
13
5/2
76
72
73
82
18
04
.20
.50
10
06
.10
.50
c1
_3
76
11
32
6/2
12
88
20
97
05
85
.30
.53
10
05
.40
.50
c2
_5
44
11
63
8/2
94
81
44
76
65
95
.10
.51
10
06
.20
.50
c1
_2
23
12
83
4/2
73
72
15
28
54
17
44
.60
.50
10
06
.90
.50
c1
_5
98
13
24
1/3
23
06
26
12
58
15
84
.70
.50
10
04
.80
.50
c1
_4
37
13
32
4/2
04
53
28
83
34
04
.70
.50
10
06
.10
.50
c1
_1
10
14
84
5/3
51
78
21
05
33
71
56
.00
.60
10
06
.20
.50
c2
_0
44
18
78
0/5
31
51
91
05
34
21
86
.50
.65
10
05
.40
.50
c1
_2
91
52
01
68
/12
81
32
81
07
23
52
34
.60
.50
10
06
.70
.50
67
Ta
ble
2-2
, co
ntin
ue
d
gra
in #
FT
GA
(M
a)
err
or
(+/-
; m
.y.)
Pb
-Pb
ag
e (
Ma
)e
rro
r (1
SD
; m
.y.)
eU
(p
pm
)e
rro
r (1
SD
; p
pm
)F
WH
M c
orr
. (c
m-1
)e
rro
r (c
m -1
)s
hif
t (c
m-1
)e
rro
r (c
m -1
)
ho
ne
y
h1
_1
09
57
13
/11
31
38
91
17
54
34
.40
.50
10
06
.10
.50
h2
_3
74
58
15
/12
24
84
91
16
82
83
.50
.50
10
07
.30
.50
h2
_2
40
61
17
/13
36
23
61
22
91
69
4.6
0.5
01
00
6.9
0.5
0
h2
_1
19
62
17
/13
46
64
41
13
86
14
.50
.50
10
05
.90
.50
h2
_2
49
64
20
/15
71
61
01
93
72
46
4.5
0.5
01
00
6.3
0.5
0
h2
_2
48
70
17
/14
19
81
91
08
06
94
.50
.50
10
06
.20
.50
h2
_2
92
71
15
/13
56
86
58
08
64
4.3
0.5
01
00
7.4
0.5
0
h2
_2
76
73
17
/14
24
12
28
87
39
3.7
0.5
01
00
6.6
0.5
0
h1
_4
82
74
17
/14
48
71
05
14
54
57
4.6
0.5
01
00
5.9
0.5
0
h2
_0
31
80
18
/15
33
84
18
83
25
5.4
0.5
41
00
6.1
0.5
0
h1
_1
80
85
21
/17
16
81
61
27
14
15
.90
.59
10
06
.70
.50
h2
_3
90
86
24
/19
39
72
18
77
59
4.8
0.5
01
00
6.8
0.5
0
h1
_2
24
10
32
4/2
04
63
34
10
17
50
4.5
0.5
01
00
6.7
0.5
0
h2
_3
58
10
42
6/2
16
09
53
96
19
45
.70
.57
10
06
.40
.50
h2
_1
89
10
83
2/2
41
48
43
04
92
67
24
.70
.50
10
06
.80
.50
h1
_1
01
10
95
0/3
32
50
37
10
11
13
46
.40
.64
10
05
.40
.50
h2
_5
11
11
63
0/2
41
31
13
29
68
63
36
.80
.68
10
06
.10
.50
h1
_3
00
11
83
4/2
63
47
40
15
04
75
4.7
0.5
01
00
7.0
0.5
0
h2
_0
95
13
43
4/2
75
92
92
11
26
64
4.6
0.5
01
00
7.0
0.5
0
h2
_2
21
15
66
6/4
41
68
72
40
50
05
64
.90
.50
10
06
.40
.50
No
tes:
Fis
sio
n t
rack a
ge
s (
± 2
σ u
nce
rta
inty
) w
ere
de
term
ine
d u
sin
g t
he
Ze
ta m
eth
od
, a
nd
ag
es w
ere
ca
lcu
late
d u
sin
g t
he
co
mp
ute
r p
rog
ram
an
d e
qu
atio
ns in
Bra
nd
on
(1
99
2).
F
or
zir
co
n,
a Z
eta
fa
cto
r o
f 3
52
.74
±
8.0
9 (
± 1
se
) is
ba
se
d o
n d
ete
rmin
atio
ns f
rom
bo
th t
he
Fis
h C
an
yo
n T
uff
an
d t
he
Bu
luk T
uff
. G
lass m
on
ito
rs (
CN
5 f
or
zir
co
n),
pla
ce
d a
t th
e t
op
an
d b
ott
om
of
the
irr
ad
iatio
n p
acka
ge
, w
ere
use
d t
o d
ete
rmin
e
the
flu
en
ce
gra
die
nt.
A
ll s
am
ple
s w
ere
co
un
ted
at
12
50
x u
sin
g a
dry
10
0x o
bje
ctive
(1
0x o
cu
lars
an
d 1
.25
x t
ub
e f
acto
r) o
n a
Ze
iss A
xio
sko
p m
icro
sco
pe
fitte
d w
ith
an
au
tom
ate
d s
tag
e a
nd
a d
igitiz
ing
ta
ble
t.
Etc
hin
g o
f sta
nd
ard
s f
ollo
we
d G
arv
er
an
d o
the
rs (
20
00
).
Pb
-Pb
ag
es (
± 1
σ u
nce
rta
inty
) a
re b
ase
d o
n L
A-I
CP
-MS
da
ta u
sin
g c
ou
nts
pe
r se
co
nd
of
bo
th 2
07P
b a
nd
206P
b,
an
d c
alib
rate
d u
sin
g t
he
UT
-01
zir
co
n
sta
nd
ard
; re
fer
to A
pp
en
dix
1 f
or
furt
he
r d
eta
ils.
Eff
ective
ura
niu
m (
± 1
σ u
nce
rta
inty
) co
nce
ntr
atio
ns a
re c
alc
ula
ted
ba
se
d o
n U
co
nce
ntr
atio
ns f
rom
th
e F
T w
ork
, a
nd
Th
co
nce
ntr
atio
ns a
re c
alc
ula
ted
ba
se
d o
n
a c
om
pa
riso
n o
f L
A-I
CP
-MS
U a
nd
Th
me
asu
rem
en
ts a
nd
FT
U m
ea
su
rem
en
ts,
as d
escri
be
d in
th
e t
ext.
R
am
an
ba
nd
wid
ths a
nd
ba
nd
wid
th s
hifts
we
re m
ea
su
red
with
in t
he
FT
-co
un
ted
are
a a
t th
e U
niv
ers
ity o
f
Ma
inz,
usin
g a
Jo
bin
Yvo
n L
ab
Ra
m-H
R e
qu
ipp
ed
with
an
Oly
mp
us o
ptica
l m
icro
sco
pe
(1
00
x o
bje
ctive
, n
um
eri
ca
l a
pe
rtu
re 0
.9).
S
pe
ctr
a w
ere
excite
d u
sin
g t
he
He
-Ne
63
2.8
nm
lin
e (
3 m
W a
t th
e s
am
ple
su
rfa
ce
),
with
wa
ve
nu
mb
er
accu
racie
s o
f ± 0
.5 c
m-1
, a
nd
sp
ectr
al re
so
lutio
n o
f a
pp
roxim
ate
ly 0
.5 c
m-1
(se
e m
eth
od
s in
Na
sd
ala
an
d o
the
rs,
20
01
).
Cite
d e
rro
rs f
or
Ra
ma
n b
an
dw
idth
(F
WH
M)
an
d p
ositio
n (
sh
ift)
qu
an
tifie
d a
s d
escri
be
d in
Na
sd
ala
an
d o
the
rs (
20
01
).
68
69
for FT analysis. The magnitude of CL response within zircon is the result of the degree of
metamictization (Chuanyi and others, 1992; Nasdala and others, 2002), trace-element
composition (Hanchar and Rudnick, 1995), and other factors. As such, the use of CL remains a
qualitative guide for other quantitative portions of this work.
Crystallinity
In this study, at least one representative Raman measurement was made for the FT-
dated region of each grain. Measurements were also made to capture zonation detected in the
CL images, and in general included 2-6 measurements per grain. Raman microscopy measures
short-range order, or crystallinity, in the areas analyzed (volume resolution = 5 µm3), and the
selection of specific areas avoids the time-consuming process of making full Raman crystallinity
maps for each grain (e.g. Nasdala and others, 2001). Raman measurements were made at the
University of Mäinz (Germany) using a Jobin Yvon LabRam-HR equipped with an Olympus
optical microscope (100x objective, numerical aperture 0.9). Spectra were excited using the He-
Ne 632.8 nm line (3 mW at the sample surface), yielding wave number accuracies of ± 0.5 cm-1,
with spectral resolution of approximately 0.5 cm-1 (see methods in Nasdala and others, 2001).
Rare-Earth-Element Geochemistry and Pb-Pb Ages
Each FT-dated zircon was analyzed for Pb, U, Th, and REE in the FT-counted area
using laser-ablation inductively coupled mass spectrometry (LA-ICP-MS). These destructive
measurements were made using a LA-ICP-MS system (Platform quadrapole ICP-MS) at the
University of Texas at Austin. This system utilizes a LUV 213 Nd:YAG laser, which generates a
200 mJ beam at 1064 nm. The laser beam is polarized and passes through a series of harmonic
resonators, resulting in a final laser beam of up to 5 mJ of 213 nm ultraviolet light. Based on
grain behavior and machine response, the laser was used at 40-50% maximum power with 30-
70
40 µm actual spot sizes. In general, this area is well within the FT-counted area. Ablated
material is injected into the plasma, extracted to the Hexapole cell, ionized, and passed through
the quadrapole mass analyzer to a single Daly-cup detector. For each grain, 78 scans of each
mass were made for 28Si, 91Zr, 96Zr, all REE, 176Hf, 179Hf, 206Pb, 207Pb, 208Pb, 232Th, and 238U.
For calculation of Pb-Pb ages, a ratio of the number of counts per second of 206Pb and
207Pb was made for multiple sequential analyses (up to 78 scans) of each grain during the
sample run. The total number of scans for each grain was divided into three groups, and the
blank-subtracted averages of these groups were used to calculate the concentration ages for the
majority of grains for which FT, crystallinity measurements, and REE compositions were
determined. Precision estimates for the ages were determined by finding the standard deviation
of the three counts-per-second averages over the course of the 78 runs; the standard deviation
of these values was then used as an estimate of the error (one standard deviation shown in
Table 2-2).
232Th, 238U, 235U, and REE concentrations were calculated based on counts-per-second
measurements from the LA-ICP-MS. Reduction of these data for the unknown zircons involves
comparison of counts per second for a given element over the run time with solution-
concentration data for a standard zircon (zircon UT-01, from the University of Texas at Austin
Vargas Mineral Collection; dissolved and analyzed by J. Lansdown, University of Texas, January
2003), and with concentrations of Zr from electron-microprobe analysis of the unknown zircons
(analyzed at Rensselaer Polytechnic Institute, Troy, NY, by K. Becker; JEOL-733; Appendix 6).
The data-reduction procedure for calculation of the concentrations appears in Appendix 3.
71
DATA/OBSERVATIONS
Fission-track Data
As expected, the detrital zircon grains have a wide range of FT ages. These ages can
be resolved into fission-track-component populations or “peak ages” and 95% confidence
intervals, using a binomial peak-fitting routine (Brandon, 1996). Peak ages and confidence
intervals for the bulk sample appear in the first part of Table 2-3. From the sixty grains counted
(thirty from the long etch, thirty from the short etch), three well-defined peaks occur at 60, 91,
and 139 Ma (Figure 2-2). Older single-grain ages are also present in the bulk sample, ranging
from 250 Ma to 800 Ma. Sixty-seven grains were counted from the three color fractions (Table
2-1; Figure 2-3). Fitted peak ages and 95% confidence intervals for the p, c, and h fractions are
listed in Table 2-3. Within the bulk data as well as the color fraction data, there are several
single older ages. Fitted peak ages for the bulk sample plus color fractions do not differ much
from those fitted to the bulk data alone (Figure 2-2 and Figure 2-4). These data show statistical
peaks at 59, 80, and 128 Ma, and older single-grain ages range between 200 Ma and 800 Ma.
Given the 85-75 Ma depositional age of the Fort Crittenden Formation in this area
(Hayes, 1970a, 1970b; Hayes, 1987; Inman, 1987; Dickinson and others, 1989), the ~60 Ma
peak age in both the bulk and the composite sample is younger than deposition, and records
cooling following post-depositional heating. This young reset peak (Paleocene) is present in
varying abundance within many samples in the regional study, regardless of the depositional age
(Middle Jurassic-Upper Cretaceous; Chapter 1). Burial depths may have been on the order of 2
km (refer to Chapter 1), so that heating into the range of annealing probably is due to local
magmatic activity.
Fort Crittenden Formation (Upper Cretaceous)
Huachuca Mountains Station 23
bulk data n = 60 grains
FT grain age (Ma)30 50 300 500 70010 1000
Pro
ba
bili
ty d
en
sity (
%/∆
z=
0.1
)
0
1
2
3
4
5
6
7
8
9
10
11
60 M M
a
139
Ma
depositional age
85-75 Ma
Figure 2-2. Cumulative probability density (PD) plot and fitted peaks for bulk zircon from
Station 23, Huachuca Mountains; peak ages fitted after Brandon (1996).
Heavy line is cumulative PD; histogram of grain ages shown behind curves;
data from 60 counted grains (30 from the 17 h etch, 30 from the 12 h etch).
72
FT grain age (Ma)30 50 70 300 500 70010 100 1000
Pro
ba
bili
ty d
en
sity (
%/∆
z=
0.1
)
Fort Crittenden Formation (Upper Cretaceous)
Huachuca Mountains Station 23
color fraction data30 50 70 300 500 70010 100 1000
depositional age
85-75 Ma
colorless (N = 30 grains)
honey (N = 22 grains)
pink/purple (N = 15 grains)
Figure 2-3. Cumulative probability density (PD) curves for zircon fractions from Station 23,
1
2
3
4
5
1
2
3
4
1
2
3
4
5
6
7
73
Huachuca Mountains. Heavy line is cumulative PD; histogram of grain
ages shown behind curves.
FT grain age (Ma)30 50 300 500 70010 1000
0
2
4
6
8
10
12
14
16
18
Pro
ba
bili
ty d
en
sity (
%/∆
z=
0.1
)Fort Crittenden Formation (Upper Cretaceous)
Huachuca Mountains Station 23
composite data
128
Ma
depositional age
85-75 Ma
n = 127 grains
Figure 2-4. Cumulative probability density (PD) plot and fitted peaks for all counted grains
a
59
(bulk plus color fractions), Station 23, Huachuca Mountains; peak ages fitted
after Brandon (1996). Heavy line is cumulative PD; histogram of grain ages
shown behind curves; data from 127 counted grains (60 from bulk sample,
67 from color fractions).
74
75
The Paleocene-Eocene reset peak age is well defined in the bulk sample from Station
23, which contains abundant and varying proportions of each color population. The reset FT
ages are present in the pink/purple suite, but a relatively large percentage of grains in the honey
fraction also record similar young ages (Figure 2-3). The young reset peak age present in zircon
from Station 23 is probably related to the presence of the Tertiary quartz-monzonite body (Figure
2-1). However, as Paleocene-Eocene reset peak ages and/or single-grain reset FT ages occur
within most samples, whether adjacent to an exposed intrusion or not, resetting may also have
been related to regional heating and establishment of a higher geothermal gradient within the
field area, in addition to local intrusive bodies (Chapter 1).
In sandstones with poor depositional age control, detecting the presence of post-
depositional thermal annealing presents a challenge in the interpretation of multi-component
data. In the absence of other data, such as FT ages from older Jurassic and Cretaceous
sandstones or crystallinity measurements, these ages might have been interpreted incorrectly as
representing volcanic input to the basin during deposition; in this case, the depositional age
would have been inferred to have been younger. Additionally, overlooking the post-depositional
thermal event would have potentially significant implications for the understanding of subsequent
thermal and deformation history during the later Laramide orogeny. Resetting is now discussed
below in terms of grain-specific factors such as peak temperature, crystallization age, crystallinity
and radiation damage, and trace-element geochemistry.
Because deposition occurred at c. 85-75 Ma (Hayes, 1970a, 1970b; Hayes, 1987;
Inman, 1987; Dickinson and others, 1989), all FT ages in this range and older must reflect, in
part, source-rock cooling ages. However, based on FT ages alone, partial annealing of these
grains cannot be ruled out. In other words, it cannot be ruled out that some but not all of the
76
accumulated fossil fission tracks in a grain are shortened or fully annealed. As such, these ages
must represent a minimum age for source-rock cooling. This cooling is either related to: (a)
slow cooling during exhumation of rock from depth; or (b) rapid cooling following high-level
magmatic activity. Grains with these FT ages could have been derived from older rocks
exhumed and cooled during extension associated with formation of the Bisbee basin and
deposition of the Bisbee Group (Hayes, 1970b; Bilodeau, 1978, 1979; Dickinson and others,
1986; Klute, 1987). These grains could have then been recycled into the Fort Crittenden
Formation. Older rocks could have included Precambrian granitoids/metasediments, Paleozoic
sandstones, and Triassic-Jurassic granitoids and volcanic and sedimentary rocks, as rocks of all
these ages were exhumed and shed into the Bisbee basin (Bilodeau, 1978). Alternatively, these
older grains could have been recycled from either volcanogenic detritus shed into the Bisbee
basin during deposition (i.e. magmatic arc activity coeval with extension of the basin), or
recycled from older rocks heated during this time by related magmatic activity. Similar older
peak ages (125-140 Ma) are present in all sandstones sampled from the Bisbee Group and the
older Jurassic volcaniclastic section in the Santa Rita Mountains, Canelo Hills, and Huachuca
Mountains (Chapter 1; Figure 2-5), making this a likely source for grains of these ages.
Additionally, there is ample local and regional petrologic evidence for recycling of both the
Bisbee Group as well as intermediate volcanic rocks into the Fort Crittenden Formation (Inman,
1982, 1987; Hayes, 1986, 1987; Lindberg, 1987; Mann, 1995).
The intermediate peak age (P2) in the bulk sample is 91 Ma, whereas for the composite
sample, the intermediate age is 80 Ma (Table 2-3). Given the depositional age of the Fort
Crittenden Formation (85-75 Ma), and the fact that P2 in both the bulk and composite sample is
close to the depositional age, there are two possibilities for the source of grains that comprise
Kfc
Kc
Kc
Kg
aJh
?
Km
oK
ga
Kc
Sta
tion 2
3
Kfc
Kc
Km
o
Km
u
Kc
Km
o
Km
o
Km
o
Km
u
Kg
Kg
Kga
Pzu
Pzu
Kg
a
Kg
eK
ga
Pzu
e
Pzu
Pzu
Jh
Km
o
Kg
Pzu
Km
o
Kg
Kg
a
Kg
Km
oK
g
Km
u
Kc
Kfc
TQ
uK
b?
TQ
u
Km
o?
Tg
Tg
TQ
u
TQ
u
TQ
u
TQ
uTi
Ti
Km
o
pC
g
Tg
TQ
u
KfcTi
Pzu
e
Qa
l
Tg
TQ
u
Qg
Km
o
Km
u
Kc
Kga
Kg
Kb
pC
g
Jh
JTc
JT
h
JT
h?
JTc
JTc
JT
h
JT
h
JT
h JTc
JT
h
JTc
JTc?
JTc?
Te
rtia
ry a
nd
Qu
ate
rna
ry g
rave
ls,
allu
viu
m
Tert
iary
intr
usiv
es (
quart
z
mo
nzo
nite
, a
laskite
, g
ran
o-
dio
rite
, a
lka
li d
iorite
); in
tern
al
ag
e r
ela
tio
nsh
ips u
nce
rta
in
Up
pe
r C
reta
ce
ou
s F
ort
Critt
en
de
n
Fo
rma
tio
n (
ea
rly L
ara
mid
e b
asin
fill
)
Low
er
Cre
taceous B
isbee
Gro
up
Ju
rassic
Ca
ne
lo H
ills
Vo
lca
nic
s a
nd
asso
cia
ted
rocks
Pa
leo
zo
ic s
ed
ime
nta
ry
rocks, exotic b
locks o
f
Pa
leo
zo
ic w
ith
in o
the
r u
nits
Pre
ca
mb
ria
n g
ran
ite
01
kilo
me
ters
mile
s0
1
fissio
n tra
ck s
am
ple
; S
tation 2
3 d
enote
d
vitrin
ite
sa
mp
le
fau
lt;
da
sh
ed
wh
ere
in
ferr
ed
an
ticlin
al tr
ace
; d
ash
ed
wh
ere
in
ferr
ed
,
plu
ng
ing
wh
ere
in
dic
ate
d
syn
clin
al tr
ace
; d
ash
ed
wh
ere
in
ferr
ed
,
plu
ng
ing
an
d/o
r o
ve
rtu
rne
d w
he
re in
dic
ate
d
co
nta
ct;
da
sh
ed
wh
ere
in
ferr
ed
Map
Un
its
Map
Sym
bo
ls
pC
g
pC
g
pC
g
pC
g
pC
g
Fig
ure
2-5
. H
ua
ch
uca
Mo
un
tain
s g
eo
log
ic m
ap
(g
en
era
lize
d a
fte
r H
aye
s a
nd
Ra
up
, 1
96
8)
sh
ow
ing
re
pre
se
nta
tive
zirco
n fis
sio
n-t
rack
reset F
TG
A
pe
ak a
ge
s f
rom
th
e r
eg
ion
al stu
dy.
S
tatistica
l p
ea
k a
ge
s a
re b
ase
d o
n 3
0-6
0 d
ate
d g
rain
s p
er
sa
mp
le, e
xce
pt a
s
no
ted
. R
efe
r to
Ch
ap
ter
1 a
nd
Ap
pe
nd
ix 4
fo
r fu
rth
er
de
tail
on
pe
ak a
ge
s, u
nce
rta
intie
s, sin
gle
-gra
in a
ge
da
ta.
77
42
Ma
68
Ma
10
7 M
aN
= 2
9
59 M
a
80
Ma
12
8 M
aN
= 1
27
92
Ma
12
1 M
aN
= 4
2
60 M
a
13
8 M
aN
= 3
1
13
7 M
aN
= 1
8
10
4 M
a
17
1 M
aN
= 2
6
10
6 M
a
23
6 M
a
80
3 M
aN
= 3
3
χ2
age:
19
0 M
aN
= 5
χ2
age:
10
9 M
aN
= 5
114
°113
°11
2°
111°
110°
37
°
36
°
35
°
34
°
33
°
32
°114°
113°
11
2°
111
°110
°
37
°
36
°
35
°
34°
33
°
32
°
Tab
le 2
-3.
Fis
sio
n t
rack p
eak a
ges f
rom
Sta
tion 2
3,
Huachuca M
ounta
ins.
P1
P2
P3
bu
lk s
am
ple
pe
ak a
ge
(M
a)
60
91
13
9
n =
60
(3
0/3
0)
95
% c
.i.
(+/-
; m
.y.)
8/7
10
/91
8/1
6
% o
f g
rain
s1
7.3
48
.62
9.1
pin
k/p
urp
le (
fra
cti
on
p)
pe
ak a
ge
(M
a)
63
—1
75
n =
14
95
% c
.i.
(+/-
; m
.y.)
9/8
19
/17
% o
f g
rain
s2
7.3
72
.7
co
lorl
es
s (
fra
cti
on
c)
pe
ak a
ge
(M
a)
—7
81
20
n =
30
(1
9/1
1)
95
% c
.i.
(+/-
; m
.y.)
7/7
11
/10
% o
f g
rain
s4
5.6
51
.1
ho
ne
y
(fr
ac
tio
n h
)p
ea
k a
ge
(M
a)
70
—1
18
n =
22
(1
6/6
)9
5%
c.i.
(+/-
; m
.y.)
6/5
12
/11
% o
f g
rain
s5
8.8
41
.2
bu
lk +
fra
cti
on
sp
ea
k a
ge
(M
a)
59
80
12
8
n =
12
79
5%
c.i.
(+/-
; m
.y.)
7/6
7/7
10
/9
% o
f g
rain
s1
1.4
37
.24
6.6
No
tes:
FT
pe
ak a
ge
s (
± 2
σ u
nce
rta
inty
) fo
r b
ulk
zir
co
n,
fra
ctio
ns,
bu
lk +
fra
ctio
ns f
rom
Sta
tio
n 2
3 w
ere
de
term
ine
d u
sin
g t
he
Ze
ta m
eth
od
, a
nd
ag
es w
ere
ca
lcu
late
d u
sin
g t
he
co
mp
ute
r p
rog
ram
an
d e
qu
atio
ns
in B
ran
do
n (
19
92
).
n =
nu
mb
er
of
gra
ins c
ou
nte
d (
wh
ere
th
ree
nu
mb
ers
are
cite
d,
firs
t is
to
tal n
um
be
r o
f g
rain
s,
se
co
nd
is n
um
be
r fr
om
lo
ng
etc
h,
thir
d is n
um
be
r fr
om
sh
ort
etc
h).
P
1 =
fitte
d p
ea
k 1
; P
2 =
fitte
d p
ea
k 2
; P
3 =
fitt
ed
pe
ak t
hre
e.
Fo
r zir
co
n,
a Z
eta
fa
cto
r o
f 3
52
.74
± 8
.09
(± 1
se
) is
ba
se
d o
n d
ete
rmin
atio
ns f
rom
bo
th t
he
Fis
h C
an
yo
n T
uff
an
d t
he
Bu
luk T
uff
. G
lass m
on
ito
rs (
CN
5 f
or
zir
co
n),
pla
ce
d a
t th
e t
op
an
d b
ott
om
of
the
irra
dia
tio
n p
acka
ge
, w
ere
use
d t
o d
ete
rmin
e t
he
flu
en
ce
gra
die
nt.
A
ll s
am
ple
s w
ere
co
un
ted
at
12
50
x u
sin
g a
dry
10
0x o
bje
ctive
(1
0x o
cu
lars
an
d 1
.25
x t
ub
e f
acto
r) o
n a
Ze
iss A
xio
sko
p m
icro
sco
pe
fitte
d w
ith
an
au
tom
ate
d
sta
ge
an
d a
dig
itiz
ing
ta
ble
t.
Etc
hin
g o
f sta
nd
ard
s f
ollo
we
d G
arv
er
an
d o
the
rs (
20
00
).
78
79
these peak ages. If these grains were derived from rapid exhumation of source rock, there
remain approximately 5-15 m.y. in the case of the 91 Ma peak age to move these zircons from
the partial annealing zone (PAZ, at 8-10 km given an average geothermal gradient of 25°C/km)
to the surface (based on the proposed depositional age of the Fort Crittenden Formation and the
peak age). These estimates suggest exhumation rates of approximately 0.5-1.5 km/m.y.
Although this is fairly rapid, it is in keeping with exhumation related to normal faulting in an
extending backarc tectonic environment.
However, the P2 age in the composite sample, 80 Ma, presents a problem in
considering that these grains were derived by exhumation, because exhumation would have to
have been almost instantaneous to generate a peak age of 80 Ma. Thus, there are two
possibilities for the source of the 80 Ma peak: (a) these grains may have a volcanogenic source
transitional in age between deposition of the Bisbee Group and the Fort Crittenden Formation; or
(b) this peak may represent partially or fully reset ages. This resetting may have occurred at ~80
Ma (full reset in the source), or may have occurred in the basin strata during the thermal event
that produced the 59 Ma peak age (i.e. partial reset for these grains).
If zircons that comprise the 80 Ma P2 age are first-cycle volcanic, this would indicate at
least two distinct provenances for zircon in the Fort Crittenden Formation in this area,
considering both the bulk and composite sample: a synorogenic volcanic component, and an
exhumed source (Lower Cretaceous and older; 91 Ma P2 age). Regionally, volcanic activity is
indicated toward the end of and immediately following Fort Crittenden deposition in the nearby
Santa Rita Mountains (Fort Crittenden Formation, upper tuff member (Drewes, 1968, 1971);
Salero Formation, 79-73 Ma, K-Ar and Ar-Ar on biotite (Drewes, 1968; Keith and Wilt, 1986;
Hayes, 1987); all cited ages from sources prior to 1976 have been corrected after Dalrymple,
80
1979; refer to Appendix 1), and in the Canelo Hills (Jones Mesa volcanics, 72 Ma, K-Ar on biotite
(Hayes, 1970b); Appendix 1). Volcanic activity also occurred at this time in the southern Canelo
Hills as well, although the stratigraphic relationship with the Upper Cretaceous section is
indeterminate (Dove Canyon volcanics, 73 Ma, K-Ar on biotite (Marvin and others, 1973; Marvin
and others, 1978); Meadow Valley trachyandesite, 74 Ma, K-Ar on biotite (Marvin and others,
1973; Marvin and others, 1978); Appendix 1). In the Huachuca Mountains, the upper contact of
the Fort Crittenden Formation is either erosional, with Tertiary gravels resting in angular
unconformity atop the Upper Cretaceous, or is a fault (Hayes and Raup, 1968; Hayes, 1986). As
such, it is difficult to discern whether or not this volcanic activity extended to the east. The only
documented occurrence of Cretaceous volcanic rocks directly underlying the Fort Crittenden
Formation are the Corral Canyon volcanics in the Canelo Hills (75 Ma; K-Ar on biotite; (Hayes,
1987); Appendix 1), which are conformably overlain by Fort Crittenden clastic rocks. If these
rocks were more extensive during deposition, and were subsequently eroded, this might have
provided a nearby source for ~80 Ma FT ages. However, as is shown below, Pb-Pb
crystallization ages demonstrate no synorogenic volcanic source for this particular sample.
In both the bulk sample and the color fractions, there is a population of young grain ages
(comprising P1, 59 Ma in the bulk sample; 60 Ma in the composite sample; Table 2-3) that is 15-
25 m.y. younger than the depositional age of 85-75 Ma. This age coincides with widespread
plutonism in the region (Drewes, 1972). Given the presence of this 60-59 Ma peak age, it is
possible that all older peak ages represent a partially reset older component that is a minimum
cooling age for the source. In other words, the original provenance cooling age may have been
compromised. However, this alternative is considered unlikely based on the following
observations. Single-grain ages which comprise both the 91 Ma and the 80 Ma peaks are
abundant in these data (Table 2-3; 29 of 60 counted grains in the bulk sample (49%), and 47 of
81
127 grains counted in the composite sample (37%)). Peaks in the 91/80 Ma age range are
present in all samples throughout the study area, including heated and annealed Upper Jurassic
volcaniclastic sandstones, as well as Lower Cretaceous Bisbee Group sandstones and Upper
Cretaceous synorogenic rocks (Figure 2-5). Older peak ages (detrital; 110-100 Ma, 125 Ma, and
older ages) are also present in all samples from the larger exhumation study (Chapter 1). These
older ages are characteristic of Mesozoic sandstones within this basin, and the spread of these
ages is relatively narrow (Figure 2-5). In the case of resetting an older age component via post-
depositional thermal disturbance, one might expect the following: an overall smaller percentage
of the total grains would have the reset age (depending on the susceptibility of a grain to being
reset); a wider spread of reset peak ages from one locality to the next, depending on the locus,
duration, and areal extent of thermal disturbance; and a distinct lack of consistency of peak ages
among samples throughout the area (depending on the age of thermal resetting in different
locations). These features are not observed in the older peaks (91/80 Ma and older peaks) in
Station 23, and similar peak ages throughout the study area.
The two older statistical peak ages and older single-grain ages could be interpreted as
reflecting exhumation associated with Bisbee basin formation, and heating associated with
intrusion ± volcanism prior to subsidence of the Laramide basin. This hypothesis allows for the
possibility that the 80 and 91 Ma FT peak ages are either volcanic, or related to thermal resetting
during the transition from Bisbee basin deposition to deposition in the Laramide basin. While a
volcanic source is plausible given the FT data, it was not found in the Pb-Pb ages. The majority
of the analyzed grains have Pb-Pb ages that are significantly older (one group 160-720 Ma, and
a subordinate group 1200-2000 Ma; Table 2-2). The Pb-Pb ages then provide a more distinctive
assignment of the source of the 80 and 91 Ma peaks for this sample: given that all crystallization
ages are much older than Late Cretaceous, the FT peaks encompassing these grains are not
82
directly related to Late Cretaceous volcanism, but potentially are related to thermal resetting
associated with Late Cretaceous magmatism as the arc advanced eastward (Coney, 1978;
Dickinson and Snyder, 1978; Keith, 1978).
Vitrinite-Reflectance Data
As an independent estimate of the peak temperatures reached in the sampling areas,
interbedded mudrocks of the Fort Crittenden Formation were sampled for vitrinite-reflectance
(VR) analysis. At higher absolute temperatures, reflectance of vitrinite fragments in the samples
increases, and Ro (mean reflectance) values rise (see Price, 1983). These thermal maturity
values, based on the average Ro value of 20-50 un-oxidized vitrinite fragments per sample, were
then used to estimate maximum temperatures reached by these rocks. As such, the VR data
complement the fission-track and other thermochronology data, but prove difficult to obtain in
sandstone-rich sections where mudrocks are lacking, and/or where organic material has been
oxidized during diagenesis or weathering. Additionally, the calibration of peak-temperature
estimates for Ro values varies somewhat (e.g. Héroux and others, 1979; Staplin, 1982; Price,
1983; Burnham and Sweeney, 1989, Barker and Pawlewicz, 1994). Accordingly, the range of
peak temperature values associated with a given Ro value must be evaluated using sample
context and field relationships.
Because of the relatively coarse nature of the section, vitrinite-bearing mudrocks occur
at restricted intervals; an additional constraint is the necessity of sampling interbedded mudrock
as close as possible to the interval sampled for FT work. Fresh mudrock in the lower part of the
uppermost Cretaceous section was sampled at three locations in the northern and central
Huachuca Mountains (limited to the Fort Crittenden Formation; Figure 2-1). Siltstone and shale
south of Station 23 were sampled (Figure 2-1), but did not yield usable vitrinite because of
83
oxidation. However, shale and siltstone at a stratigraphically similar position 9.5 km to the north
yielded Ro values of 3.00% and 2.03%, that correspond to peak temperatures of 225-300°C (Ro
= 3.00%), and 150-250°C (Ro = 2.03%) (interpreted after Héroux and others, 1979; Staplin,
1982; Burnham and Sweeney, 1989, and Barker and Pawlewicz, 1994). These values provide a
broad constraint on the local maximum temperature conditions. The vitrinite data indicate that
the present erosional level across the region is such that the strata attained temperatures near
the proposed closure temperature for FT in zircons.
It is important to note that annealing of some grains identified in FT data for this study
occurred at significantly lower Ro value than that proposed by previous workers. Green and
others (1996) stated that no annealing in zircons is detected at Ro values less than 4%
(correlated to maximum temperature of >260°C using the model of Burnham and Sweeney
(1989)). Reflectance values associated with zircon FT annealing in this study are significantly
lower than those reported by Green and others (1996), and this observation suggests that
annealing of fission tracks in radiation-damaged zircons occurs at much lower temperatures than
the temperature required to anneal all grains in a variable population.
The Fort Crittenden Formation here illustrates an important lesson in terms of the field
appearance of thermally modified sedimentary rocks. The character of the samples in the field
did not give rise to any suspicion that these sandstones and conglomerates were heated to
temperatures of 200°C or higher. Most samples from this area are only moderately indurated,
with almost no quartz cement, and no veining. The VR data make it evident that rocks at the
present erosional level were heated to 150°C-225°C. Burial depths of ~2 km (Chapter 1) make it
evident that heating by the nearby Tertiary intrusions was significant. Such heating explains the
84
presence of the Paleocene-Eocene reset FT peak ages in sandstones interbedded with these
mudrocks throughout the northwestern and west-central parts of the range (Figure 2-5).
The issue of local versus regional heating is also pertinent to this discussion. Vitrinite-
reflectance data for the entire study area (refer to Chapter 1) suggest that these rocks did not
exceed ~225°C or so (Figure 2-1). In the case of samples in other parts of the study area (Santa
Rita Mountains, Fort Crittenden Formation shale member; Chapter 1), vitrinite-reflectance data
for one sample indicate peak temperatures of 85-135°C (interpreted after Héroux and others,
1979; Staplin, 1982; Burnham and Sweeney, 1989), which should be well below the temperature
range for annealing in zircons, and lower than maximum temperatures recorded elsewhere in the
Huachuca Mountains (Chapter 1). Vitrinite data are sparse, but suggest that heating effects
caused by Tertiary intrusions were variable because of covered plutons and associated
hydrothermal fluid flow. Consequently, peak-temperature determinations do not always show a
correlation with proximity to lower Tertiary intrusive rocks.
Reset FT peak ages and/or single-grain reset FT ages indicate that, with the exception
of two locations, most samples experienced sufficient Paleogene heating to reset the FT ages of
certain grains (Appendix 4). Samples with reset ages include those samples near Paleogene
intrusions and dikes (i.e. Station 9; Figure 2-5), as well as those not near any obvious heat
source exposed at the surface (Station 11, 13; Figure 2-5). It is thus concluded that heating to
150-225°C occurred on a regional scale at this erosional level. An elevated regional thermal
gradient resulted from the eastward migration of arc-related magmatic activity through
southeastern Arizona associated with shallowing of the subducting slab during this time (Snyder
and others, 1976; Coney, 1978; Dickinson and Snyder, 1978; Keith and Wilt, 1986).
Additionally, it is possible that the basin-bounding fault zone in this area and farther northwest
85
along the Sawmill Canyon fault zone in the Santa Rita Mountains aided the channelization of this
heat flow, although fission-track ages from rocks well outside this fault zone would be needed to
support this. Such controls on the FT ages of zircons in Newark basin fill have been
documented by Steckler and others (1993), as discussed in greater detail in Chapter 1.
Pb-Pb Data from Color/Morphology Fractions
Pb-Pb ages were calculated from LA-ICP-MS data for fifty-six of the FT-dated grains
from Station 23, and unfortunately, during sample handling, eleven FT-dated zircons were lost.
Teflon FT mounts hold zircons by their crystal faces and edges rather than by gluing them in and
as such, zircons easily pop out of the mounts. Pb-Pb ages plotted versus FT ages for the same
zircons appear in Figure 2-6. Uncertainties shown are the 95% confidence intervals for fission-
track ages and one standard deviation for Pb-Pb ages.
Several important findings result from the relationships among crystallization age, color,
and FT age. (1) These data show that a primary difference between the pink/purple suite and
the other zircons in this sample is crystallization age (Pb-Pb): the former are dominantly
Proterozoic, ranging from 1200-2000 Ma, whereas the others show diverse ages, with most
between 160 and 720 Ma (Table 2-2; Figure 2-6). An older group of honey and colorless grains
is also present, with six Pb-Pb ages from 1300 to 1800 Ma. (2) The youngest FT ages (reset)
are from the pink/purple fraction, but a relatively large percentage of young reset grains are also
from the honey fractions. (3) There is a much greater spread of FT ages in the pink/purple
zircons, versus the tighter cluster of both FT and Pb-Pb ages for the majority of the honey and
colorless grains. (4) At Station 23, there is no evidence for coeval volcanism during deposition.
Pb-Pb age vs. Fission track grain age
0
100
200
300
400
500
600
700
0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200
Pb-Pb age (Ma)
FT
GA
(M
a)
pink/purple (N = 14 grains)
colorless (N = 22 grains)
honey (N = 20 grains)
Figure 2-6. Pb-Pb age versus fission-track age (FTGA) for the same zircon grains from Station
depositional
age of sample
86
23, Huachuca Mountains. Cited uncertainties for Pb-Pb ages are 1 standard
deviation, and 95% confidence intervals for FT ages.
87
As the grains with older Pb-Pb ages tend to be pink and purple, these data reaffirm the
previous generalization that the development of pink/purple color is mainly related to time since
crystallization. However, the issue is more complicated than simply time since crystallization, as
demonstrated by Garver and Kamp (2002). The accumulation of radiation damage, more
specifically α-damage, is probably a primary control on the development of color in zircons, and
the level of accumulation is controlled by U + Th concentration and single-grain thermal history.
Older grains from all populations have had more time to accumulate radiation damage, and are
also, of course, more likely to have had a more complicated thermal history.
These data also show that grains with greater amounts of α-damage (calculated from
the crystallization age and U and Th concentrations; see below), are preferentially annealed and
lose fission-track damage (Figure 2-6; Table 2-2). Young reset FT ages are most common in
those grains from all color groups that have older crystallization ages, and/or elevated U+Th
content (Table 2-2). Fission-track age distributions for the pink/purple suite are more dispersed
overall than those of other color fractions. This wider range of FT ages for the older pink/purple
group is probably related to these grains having more complicated thermal histories.
Another important relationship is the similarity between the honey and colorless
populations. These grains have similar age distributions (FT and Pb-Pb), which would suggest
that the difference in color is unrelated to thermal history. It is worth noting that the difference
between these two color populations (honey series versus colorless series) may reflect specific
zircon trace-element composition (REE), as suggested by Gastil and others (1967) and Garver
and Kamp (2002). Following these observations of α-damage in grains with older crystallization
ages and younger reset fission-track ages, the next step is to look at crystallinity in single grains,
and how this relates to track retentivity.
88
Raman Microscopy Data
As radiation damage accumulates in a zircon, there should be a decrease in crystallinity,
because radiation damage causes crystal lattice disruption (Murakami and others, 1991;
Nasdala and others, 1995; Nasdala and others, 2001). Resulting from derivation from multiple
sources, zircons in a detrital suite will likely have U and Th concentrations and thermal histories,
and will accordingly have different crystallinities. As such the spread of individual grain ages
within a fraction would then be a function of different thermal histories and/or U + Th
concentrations. The amount of short-range order of the crystal lattice, and therefore the degree
of crystallinity of a zircon, is related to the amount of radiation damage, with α-damage being the
main contributor (Murakami and others, 1991; Nasdala and others, 1995; Nasdala and others,
2001). The factors controlling the amount of α-damage are U + Th contents and the duration of
α-damage accumulation, the latter being a function of single-grain thermal history. Greater α-
damage and resultant lower crystallinity have been proposed to decrease the effective closure
temperature for the fission-track system (Kasuya and Naeser, 1988), and the more damaged
grains will be preferentially reset by post-depositional heating. Raman microprobe analyses are
here used to determine short-range order in the crystal lattice within the FT-counted area and
among different CL-detected zones in fifty-seven color fraction zircons from the Station 23
sample (Figure 2-1; Table 2-2). Unfortunately, ten FT-dated grains were lost from the p, c, and h
mounts during preparation for this analysis.
With α-decay of 235U, 238U, and 232Th in the zircon, atomic displacements related to the
passage of α-particles and movement of α-recoil nuclei produce changes in atomic positions and
consequent variations in bond lengths and bond angles within the crystal lattice. This process
eventually leads to development of interconnected zones of amorphous or non-crystalline
material, collectively known as α-damage (Murakami and others, 1991). Depending on the
89
parent atom, decay by alpha emission to stable daughter Pb occurs between six and eight times,
whereas a single damage track is produced during spontaneous fission of 238U. Because α-
decay is the dominant mode of decay for U and Th, the contribution of fission tracks to the
overall damage state is negligible relative to α-recoil and α-particle tracks (Murakami and others,
1991). Greater damage in more restricted areas of the lattice is produced by α-recoil, whereas
passage of α-particles tends to produce point defects in the early stages of damage
development (Murakami and others, 1991). As atomic displacements accumulate, the lattice
becomes increasingly disordered, and crystallinity decreases; widths of Raman bands within the
spectrum 200-1010 cm-1 increase, relative intensities decrease, and a shift to overall lower wave
numbers is observed (Nasdala and others, 1995; Nasdala and others, 2001). As such, a highly
metamict grain would exhibit wave numbers less than 1000 cm-1, and Raman bands with full
width at half-maximum intensity (FWHM) of >30 cm-1, whereas a completely crystalline zircon
would yield FWHM of 1.8 cm-1, and wave number of 1008.3 cm-1 (both with 0.5 cm-1 uncertainty;
Nasdala and others, 2002). Broadening of the ν3SiO4 Raman band at ~1000 cm-1 has been
found to demonstrate the strongest response to amorphization, and therefore FWHM is a
relatively sensitive indicator of the crystallinity of the area analyzed (Nasdala and others, 1995).
In the following work, observations based primarily on FWHM data are related to crystallization
and cooling ages and crystal chemistry for individual zircons.
All measurements for grains from the Station 23 sample have the expected correlation of
increasing FWHM with decreasing wave number as grains range from less radiation damaged to
more damaged (Figure 2-7). In particular, the pink/purple zircons (fraction p), with Early to
Middle Proterozoic Pb-Pb ages, have overall wider peaks at lower wave numbers when
compared with all other color fractions. The honey and colorless populations, with much
younger crystallization ages, tend to overlap one another in a broad range from ~3.5 to 6.0 cm-1
Full width at half maximum vs. wave number
1002.0
1003.0
1004.0
1005.0
1006.0
1007.0
1008.0
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
FWHM (cm-1
)
Ra
ma
n w
av
e n
um
be
r (c
m-1
)
pink/purple (N = 14 grains)
colorless (N = 22 grains)
honey (N = 21 grains)
Figure 2-7. Full-width at half maximum (FWHM) versus Raman wave number for color
fractions from Station 23, Huachuca Mountains. Cited uncertainties for
Raman FWHM and wave number quantified as described in Nasdala and
others (2001). FWHM and wave number position are measures of the
crystallinity of the analyzed portion of a zircon. Increased alpha-damage
accumulation results in decreased crystallinity, expressed as wider Raman
peaks (larger FWHM) and shifts to lower wave numbers.
90
91
(FWHM) and 1005.0-1007.5 cm-1 (wave number). The overlapping behavior of the honey and
colorless populations indicates that the generation of honey color is probably unrelated to
differences in crystallinity of zircons from this sample. It is apparent that α-damage in zircons
from all color populations is annealed to some degree, and would be expected as a result of the
Paleogene heating. Despite this partial annealing, differences in behavior among these
populations can still be readily identified.
Another important factor in the accumulation of α-damage is the U and Th content,
termed effective uranium concentration (eU; e.g. Gastil and others, 1967). Model eU
concentrations for each grain were calculated based on both the FT and LA-ICP-MS data, as the
concentrations of U from the mass spectrometry were generally 0.5-1.0 times those derived from
the fission-track work. This disagreement in U concentrations between the two methods may be
due to several factors, including analytical differences resulting from factors such as differing
ablation rate among zircons with different crystallinities (including the standard zircon UT-01). U
concentrations derived from the FT data were used, and effective Th concentrations were
calculated based on the U:Th ratio from the ICP-MS work. Concentrations of U for each grain
based on the fission-track work were compared to those derived from the laser work, and a ratio
was calculated for FT U:laser U concentrations for each zircon. These values were then used to
scale the Th concentrations calculated from the laser work, assuming the machine response for
the two elements to be similar. The ranges of Th concentrations derived in this manner agree
favorably with Garver and Kamp (2002), who stated that the typical Th:U ratio is ~0.5 in zircon.
It is also important to note that in typical zircon (Th<U), the contribution to total α-decay events
by U accounts for 80% or more of the total damage.
92
Trends in bandwidth versus eU reflect the similar behavior of the honey and colorless
populations, which are distinct from the pink/purple grains (Figure 2-8). Pink/purple zircons
retain more α-damage (greater FWHM) than colorless and honey grains. In addition, the
pink/purple series has a shallower positive slope as both bandwidth and eU increase, indicating
that with increasing U+Th, there is an increase in the amount of damage retained in a crystal
regardless of FT cooling age. This is in contrast to the honey and colorless series, which do not
show an increase in accumulated damage with increasing eU concentration.
Ranges of eU values also vary among the color populations. Most honey and colorless
grains range from 600 to 1500 ppm eU, whereas pink/purple grains have overall lower eU (200-
700 ppm, with only a few grains up to 1300 ppm). Note however that a few lower-eU honey and
colorless grains plot with a similar trend to the pink/purple population (Figure 2-8). The common
theme among these lower eU honey and colorless zircons is older Pb-Pb ages, relative to the
other grains from the population (ranging from 1300 to 1790 Ma for those five zircons; Table 2-
2). Despite the fact that eU concentrations for colorless and honey grains are overall higher than
those for pink/purple fraction grains, Raman band widths are narrower and show less dispersion
as compared to the pink/purple zircons (Figure 2-8). In other words, despite higher eU contents
for colorless and honey zircons, these grains are overall less damaged than the pink/purple
fraction. This less damaged character of the colorless and honey populations may reflect two
factors: first, the honey and colorless grains have overall younger crystallization ages than the
pink/purple grains (Table 2-2), allowing less total time to accumulate damage prior to the
Paleogene reheating event, despite the higher eU concentrations. The colorless and honey
populations may also have had less complicated thermal histories owing to their younger
crystallization ages. As such, these zircons could have behaved similarly during the heating
event, and may not have accumulated as much damage as the older pink/purple zircons,
Full width at half maximum (FWHM) vs. eU
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
FWHM (cm-1
)
eU
(p
pm
)
pink/purple UT-01 (N = 14 grains)
colorless UT-01 (N = 22 grains)
honey UT-01 (N = 20 grains)
Figure 2-8. Full-width at half maximum (FWHM) versus U+Th concentration (effective uranium,
or eU (= U+Th in ppm)) for color fractions from Station 23, Huachuca
Mountains. Cited uncertainties for Raman FWHM quantified as described
in Nasdala and others (2001). eU concentrations from fission track and
laser ablation ICP-MS data, with 95% confidence intervals (refer to text for
details). Note that increased alpha-damage accumulation results in
decreased crystallinity, which is expressed as wider Raman peaks (greater
FWHM).
93
94
thereby producing the overall narrower bandwidths and smaller range of values as compared
with the pink/purple zircons. Alternatively, there may have been some homogenization of
bandwidths (and damage states) associated with the heating event, giving rise to the narrower
range of FWHM values. However, given sufficient development of α-decay prior to Paleogene
heating, differences among color populations were not completely lost to annealing. These
points are discussed below.
The distribution of the different color fractions also varies in bandwidth-FTGA space,
directly reflecting the decreased crystallinity of the pink/purple grains, and their fission-track age
(Figure 2-9). The relationship between bandwidth and FTGA has a positive slope, with the
pink/purple grains forming the high-damage end of the spectrum, and colorless and honey grains
overlap at the lower damage end of the spectrum. Several zircons are off this trend: three
pink/purple grains with the youngest FTGA, and the three pink/purple and colorless grains with
the oldest FTGA. The common factor among the three pink/purple zircons with young reset
FTGA, in addition to Early and Middle Proterozoic Pb-Pb ages, is very high eU, ranging from
694-1222 ppm (Table 2-2). At the older end of the range of FT ages, the common theme of the
colorless and pink/purple outliers is relatively low eU, ranging from 235-364 ppm. Interestingly,
these three grains also have old crystallization ages (1328-1981 Ma; Table 2-2), but at least in
part because of low eU, maintain older FTGA. Looking at the color populations separately, the
pink/purple distribution has a negative slope, as one might expect: where present crystallinities
are lowest (highest FWHM), FTGA are similarly low, and the youngest of these are the group
that form the young reset peak age.
Full-width at half maximum vs. Fission track grain age
10
100
1000
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
FWHM (cm -1
)
FT
GA
(M
a)
pink/purple (N = 14 grains)
colorless (N = 22 grains)
honey (N = 21 grains)
Figure 2-9. Full-width at half maximum (FWHM) versus fission-track grain age (FTGA) for color
fractions from Station 23, Huachuca Mountains. Cited uncertainties for
Raman FWHM quantified as described in Nasdala and others (2001); 95%
confidence intervals shown for FT ages. Note that the pink/purple fraction
has the youngest reset FT ages, in addition to retaining the greatest alpha-
damage.
95
96
Effective Dose/Effective Dose Factor
A “complete storage” value for accumulated α-damage based on eU and time since
cooling can be calculated (Nasdala and others, 2001). However, heating causes loss of α-
damage, and zircons from Station 23 store variable percentages of total α-damage possible,
given their crystallization ages and eU concentrations (compare with the “complete storage” line
calculated by Nasdala and others (2001; Figure 2-10a, Table 2-4 this work)). The “complete
storage” line was fitted to 33 Raman analyses from zircons considered to have remained at or
near surface temperatures following crystallization. When compared with these reference
zircons that define the complete storage line, the amount of damage stored in the pink/purple
series is much greater than that for either the honey or colorless zircons. There is also a wider
range of effective doses for these grains than for the colorless and honey populations. Honey
and colorless zircons store 7-80% of the maximum possible damage, with most grains having
10-40% of the total possible damage (Table 2-4). The honey and colorless populations also
demonstrate no correlation between increasing preservation of α-damage and crystallinity; i.e.
as preserved damage increases, there is no concomitant decrease in crystallinity. By contrast,
the pink/purple suite tends to store less of the total radiation damage possible, typically less than
25% of the total, and shows a narrower range of preserved damage. Pink/purple grains also
show a slight decrease in crystallinity with increasing damage stored. Given the older
crystallization ages of the pink/purple grains, it seems likely that the annealing of these grains
relates back to the observation that more radiation-damaged areas tend to anneal preferentially
relative to less damaged zones (Nasdala and others, 2001). These workers identified relatively
complete damage preservation only in zones with lower dosage (dominantly point defects), and
thus consider heavily damaged areas to be less stable and more easily annealed than point
defects.
Comparison of
color fraction data with 'complete storage' line
0.0
5.0
10.0
15.0
20.0
25.0
30.0
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50
calculated -dose (*1016
/mg),
given Pb-Pb age
FW
HM
(c
m-1
)
unannealed zirconscomplete storage linepink/purple UT-01 (N = 14 grains)colorless UT-01 (N = 22 grains)honey UT-01 (N = 20 grains)Linear (complete storage line)
Effective dose factor vs. eU
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
effective dose factor
(decimal % -damage stored)
eU
(p
pm
)
pink/purple (N = 14 grains)
colorless (N = 22 grains)
honey (N = 20 grains)
Effective dose factor vs. Fission track grain age
0
100
200
300
400
500
600
700
800
900
1000
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
effective dose factor
(decimal -damage stored)
FT
GA
(M
a)
pink/purple (N = 14 grains)
colorless (N = 22 grains)
honey (N = 20 grains)
Effective dose vs. eU
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
effective dose ( -decay events /mg *1016
)
(~ -damage stored)
eU
(p
pm
)
pink/purple UT-01 corr (N = 14 grains)
colorless UT-01 corr (N = 22 grains)
honey UT-01 corr (N = 20 grains)
Effective dose vs. Fission track grain age
0
100
200
300
400
500
600
700
0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
effective dose ( -decay events /mg *1016
)
(~ -damage stored)
FT
GA
(M
a)
pink/purple UT-01 corr (N = 14 grains)
colorless UT-01 corr (N = 22 grains)
honey UT-01 corr (N = 20 grains)
α
α
α
α
α
α
α
a.
b.
d.
c.
e.
full retention of
α-damage
97
Figure 2-10a. Comparison of color fractions from Station 23, Huachuca Mountains with 'complete storage' line and analyses of 33 zircons considered to have remained at sub-annealing temperatures since crystallization (Nasdala and others, 2001). Dose is complete storage given the crystallization age and eU concentration of a grain. Cited uncertainties for doses are one standard deviation, and dose and FWHM uncertainties are quantified as described in Nasdala and others (2001). Note that the effect of annealing is to decrease the FWHM (increasing crystallinity by annealing alpha-damage; shown schematically with heavy arrows).
Figure 2-10b. Comparison of effective dose factor with eU from color fraction zircons from Station 23. Effective dose factor is the alpha-damage stored given the present crystallinity of a grain, given here as decimal percent with one standard deviation uncertainty. eU concentrations from fission-track and laser ablation ICP-MS data, with 95% confidence intervals (refer to text for details).
Figure 2-10c. Effective dose factor compared to fission-track age of color fraction zircons from Station 23. Effective dose factor values given as decimal percent with one standard deviation; 95% confidence intervals shown for FT ages.
Figure 2-10d. Effective dose compared to eU concentration for color fraction zircons from Station 23. The effective dose is the amount of alpha-damage preserved in a zircon based on the current Raman bandwidth (FWHM) measurement. Cited uncertainties for both effective doses and eU concentrations are one standard deviation.
Figure 2-10e. Comparison of effective dose to FT age for color fraction zircons from Station 23. Cited uncertainties for effective doses are one standard deviation; 95% confidence intervals shown for FT ages.
Tab
le 2
-4.
Radia
tion d
am
age d
ose d
ata
for
colo
r fr
action z
ircons f
rom
Sta
tion 2
3,
Huachuca M
ounta
ins.
gra
in #
eff
ec
tive
do
se
fa
cto
r
(%)
err
or
(1 S
D;
%)
eff
ec
tive
do
se
(-d
ec
ay e
ve
nts
/mg
(*1
016))
err
or
(1 S
D;
* 1
016 /
mg
)
tota
l p
os
sib
le d
os
e
(-d
ec
ay e
ve
nts
/mg
(*1
016))
err
or
(1 S
D;
* 1
016 /
mg
)
pin
k/p
urp
le
L0
62
12
2.9
0.0
35
1.1
E-0
50
.30
0.0
74
d 1
95
12
2.3
0.0
34
1.5
E-0
50
.28
0.0
51
d 1
31
13
3.9
0.0
43
1.8
E-0
50
.34
0.1
0
d 1
65
13
2.1
0.0
52
9.0
E-0
60
.40
0.0
67
d 0
05
14
3.9
0.0
47
1.5
E-0
50
.33
0.0
90
d 1
61
16
4.1
0.0
75
2.1
E-0
50
.46
0.1
1
d 0
70
16
3.6
0.0
66
1.7
E-0
50
.40
0.0
89
d 1
27
18
3.9
0.0
51
1.4
E-0
50
.28
0.0
62
d 0
12
19
3.7
0.0
37
9.1
E-0
60
.20
0.0
38
d 1
44
19
4.2
0.0
36
1.1
E-0
50
.19
0.0
41
L0
49
20
5.6
0.0
47
2.0
E-0
50
.24
0.0
66
L3
04
22
2.9
0.0
40
1.1
E-0
50
.18
0.0
24
L3
30
27
9.2
0.0
40
1.2
E-0
50
.15
0.0
49
d 0
13
29
6.4
0.0
53
8.1
E-0
60
.18
0.0
41
co
lorl
ess
c2
22
21
24
.40
.01
92
.0E
-05
0.1
60
.06
1
c1
72
81
53
.30
.02
11
.8E
-05
0.1
40
.03
2
c2
25
01
52
.60
.02
21
.5E
-05
0.1
50
.02
6
c1
77
21
63
.30
.02
72
.3E
-05
0.1
70
.03
3
c2
28
51
83
.70
.03
02
.5E
-05
0.1
70
.03
6
c1
11
01
83
.40
.03
59
.0E
-06
0.2
00
.03
8
c2
06
51
85
.60
.01
81
.5E
-05
0.1
00
.03
0
c1
21
61
86
.90
.02
41
.9E
-05
0.1
30
.05
1
c2
52
82
14
.90
.02
31
.7E
-05
0.1
10
.02
5
c2
06
42
25
.10
.01
71
.6E
-05
0.0
74
0.0
17
c2
04
42
55
.70
.03
71
.0E
-05
0.1
50
.03
4
c1
30
02
56
.90
.01
71
.4E
-05
0.0
69
0.0
19
c2
54
42
75
.80
.02
82
.0E
-05
0.1
00
.02
2
c1
59
82
75
.50
.02
52
.7E
-05
0.0
90
.01
9
c1
29
12
96
.70
.02
56
.4E
-06
0.0
86
0.0
20
c1
43
73
04
.00
.02
49
.0E
-06
0.0
81
0.0
11
c2
29
73
16
.90
.02
21
.5E
-05
0.0
71
0.0
16
c1
22
33
21
70
.02
41
.6E
-05
0.0
77
0.0
42
c2
69
53
57
.50
.02
21
.6E
-05
0.0
64
0.0
14
c1
37
64
37
.10
.02
91
.6E
-05
0.0
69
0.0
11
c1
08
26
31
60
.02
52
.0E
-05
0.0
40
0.0
10
c2
03
11
86
74
0.2
22
1.8
E-0
50
.12
0.0
47
98
αα
Ta
ble
2-4
, co
ntin
ue
d
gra
in #
eff
ec
tive
do
se
fa
cto
r
(%)
err
or
(1 S
D;
%)
eff
ec
tive
do
se
(-d
ec
ay e
ve
nts
/mg
(*1
016))
err
or
(1 S
D;
* 1
016 /
mg
)
tota
l p
os
sib
le d
os
e
(-d
ec
ay e
ve
nts
/mg
(*1
016))
err
or
(1 S
D;
* 1
016 /
mg
)
ho
ne
y
h2
18
97
2.4
0.0
22
1.5
E-0
50
.33
0.1
2
h2
22
11
23
.60
.02
61
.3E
-05
0.2
30
.07
1
h2
24
91
44
.10
.02
21
.6E
-05
0.1
60
.04
6
h1
48
21
64
.70
.02
41
.7E
-05
0.1
50
.04
5
h2
51
11
76
.20
.04
01
.3E
-05
0.2
40
.09
2
h2
09
51
74
.40
.02
21
.3E
-05
0.1
30
.03
3
h2
11
91
83
.30
.02
21
.8E
-05
0.1
30
.02
4
h2
29
21
93
.80
.02
21
.1E
-05
0.1
10
.02
2
h2
37
42
26
.10
.01
62
.0E
-05
0.0
76
0.0
21
h1
30
02
44
.70
.02
51
.6E
-05
0.1
00
.02
0
h1
22
42
44
.20
.02
31
.5E
-05
0.1
00
.01
7
h1
10
92
59
.50
.02
21
.9E
-05
0.0
88
0.0
33
h2
35
82
54
.90
.03
21
.3E
-05
0.1
30
.02
4
h2
24
02
65
.30
.02
51
.8E
-05
0.1
00
.02
0
h2
27
63
35
.60
.01
81
.4E
-05
0.0
54
0.0
09
3
h2
39
03
35
.20
.02
51
.3E
-05
0.0
75
0.0
12
h2
03
13
98
.00
.03
01
.4E
-05
0.0
76
0.0
16
h2
24
84
58
.10
.02
31
.6E
-05
0.0
50
0.0
09
0
h1
10
17
42
10
.03
72
.1E
-05
0.0
51
0.0
14
h1
18
08
01
40
.03
21
.4E
-05
0.0
40
0.0
07
2
No
tes:
Eff
ective
do
se
fa
cto
r is
th
e r
atio
of
the
accu
mu
late
d d
ose
to
th
e t
ota
l d
ose
po
ssib
le (
giv
en
cry
sta
lliz
atio
n a
ge
an
d e
U),
mu
ltip
lie
d b
y 1
00
; i.e
. p
erc
en
t d
am
ag
e s
tore
d.
Eff
ective
do
se
is b
ase
d o
n R
am
an
FW
HM
da
ta a
nd
co
mp
ari
so
n w
ith
th
e c
om
ple
te s
tora
ge
lin
e o
f N
asd
ala
an
d o
the
rs (
20
01
).
99
αα
100
The current distribution of damage levels, wherein we see little change in
bandwidths/crystallinity within a population, may reflect homogenization and annealing of α-
damage during Paleogene heating. The current level of damage, reflected in the FWHM Raman
parameter, is probably not the result of bandwidths within a color population all being the same
prior to Paleogene heating: it is unlikely simply given the variation of both Pb-Pb and FT ages
that grains within a color population have very similar thermal histories. Given that more
damaged crystals anneal preferentially (Nasdala and others, 2001), a larger percent of the
damage in the high-damage grains would have been annealed by Paleogene heating. Thus the
older/high eU grains would have reduced FWHM values (i.e. better crystalline), and this event
would have had a lesser effect on grains with less prior α-damage, because these grains had
little damage to begin with (Figure 2-10a).
One can relate accumulated α-damage (given the current crystallinity) to the total
possible α-damage given crystallization age in terms of a percent α-damage stored; this is
termed the effective dose factor (refer to Appendix 3). Comparing the effective dose factor with
eU concentration (Figure 2-10b) shows that the pink/purple zircon fraction has relatively low eU
and relatively low effective dose factor when compared with the honey and colorless zircons,
which lie in a somewhat larger range in both fields. The general trend for zircons from this
sample is that as eU increases, effective dose factor increases, despite having been partially
annealed in the Paleogene.
The effective dose factor may also be compared to the FT ages (Figure 2-10c). This
plot reinforces the observation that the pink/purple grains store a somewhat smaller percentage
of their total possible α-damage than colorless and honey zircons. As well, colorless and honey
grains have a much higher degree of variability in how much damage is stored versus the
101
pink/purple fraction. This would lead to variability in preservation of pre-heating fission-track
ages within populations useful for provenance information. In other words, a honey or colorless
grain may not be suspected as having a reset FT age, but the age may indeed be reset because
significant damage was stored in the zircon prior to the annealing event. Other grain parameters
such as eU and crystallization age will help to identify these potentially reset zircon FT age as
well, but unless thermal history is constrained, this may still pose a problem in determining
partially reset grains.
The accumulated α-damage dose may also be compared with eU concentration (Figure
2-10d). In this case, all populations show a steep positive slope, where increased eU correlates
with slightly increased effective α-damage doses. The slope of the pink/purple fraction is
somewhat shallower than that of the other populations, indicating that with increasing eU for
pink/purple grains, a greater amount of α-damage is retained as compared with the other
populations.
A comparison of effective dose and FT age shows that effective doses are higher for the
pink/purple fraction than for the honey or colorless fractions (Figure 2-10e). The pink/purple
grains have a vague negative correlation between effective dose and FTGA: at increased
effective doses, fission-track ages are younger (to be expected). However, the same is not
obvious in the honey and colorless fractions; if anything there is a very low-slope positive
correlation, where higher doses are correlated with higher FTGA.
FT Ages versus Minimum Damage Storage Ages
Useful observations are also found in comparing effective doses to doses calculated
using the FT ages (Figure 11a). In Figure 11a, the effective dose given accumulation of α-
effective dose comparison
0.000
0.010
0.020
0.030
0.040
0.050
0.060
0.070
0.080
0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070 0.080
effective dose given FTGA ( -decay events /mg *1016
)
eff
ec
tiv
e d
os
e g
ive
n m
inim
um
da
ma
ge
sto
rag
e a
ge
(-d
ec
ay
ev
en
ts /
mg
*1
016)
pink/purple (N = 14 grains)colorless (N = 22 grains)honey (N = 20 grains)1:1 lineLinear (1:1 line)
FTGA compared to minimum damage storage age
0
100
200
300
400
500
600
700
800
900
0 100 200 300 400 500 600 700 800 900
FTGA (Ma)
min
imu
m d
am
ag
e s
tora
ge
ag
e (
Ma
)
pink/purple (N = 14 grains)colorless (N = 22 grains)honey (N = 20 grains)1:1 lineLinear (1:1 line)
Figure 2-11a. Comparison of effective doses using those calculated from the fission-track ages,
a.
b.
and those calculated based on present crystallinities (from Raman
microprobe data, FWHM). Uncertainties shown are one standard deviation.
Figure 2-11b. Comparison of minimum damage storage ages (based on Raman microprobe
data, FWHM) with fission-track ages. Uncertainties shown on FTGA are
95% confidence intervals.
102
α
α
103
damage since cooling through the FT closure temperature is compared to the actual measured
dose for each zircon. The actual effective dose (same parameter as that in Figures 10d, 10e)
utilizes the present crystallinity of the grain (in terms of measured FWHM), and provides a
minimum age for α-damage accumulation based on the present level of damage. Figure 2-11b
compares the FT age with the minimum damage storage age for each zircon.
Most grains have accumulated more α-damage than they should have if accumulation
only started since FT closure (Figure 2-11a). Therefore given the amount of α-damage the
grains currently store, more time is required than since FT closure. The fact that the minimum
damage storage ages are older than FT ages for most grains indicates that some α-damage is
more stable during thermal annealing than fission damage, as suggested by Nasdala and others
(2001). If this were not the case, both the FT age and the minimum damage storage age should
be nearly identical in all cases (Figure 2-11). Grains with minimum damage storage age similar
to FT age suggests that all types of α-damage was annealed at the same time as FT resetting.
Clearly, given the distributions shown in Figure 2-11, Paleogene annealing did not anneal all of
the α-damage, but did reset the FT ages of certain grains.
Some colorless and honey-colored grains have slightly less α-damage than would be
expected considering their FT age. There are several possibilities for such behavior. (1)
Minimum damage storage ages shown in Figure 2-11b are minimum storage ages, because they
are based on an assumed simple thermal history (i.e. one in which α-damage in the zircon is not
partially annealed multiple times). If these ages are actually older, which is likely because the
grains may not have had a simple thermal history, then these older damage storage ages would
pull the points up on the y-axis. However, this does not change the relationship of those grains
which plot below the 1:1 line on Figure 2-11a: doses given the FT age are still relatively higher
104
with respect to doses given the minimum damage storage ages, and points on the age
comparison plot will remain below the 1:1 line. (2) One conclusion from the finding that α-
damage ages are older than FT ages is that some types of α-damage might be resistant to
annealing compared with fission damage, and the closure temperatures for damage preservation
might overlap more directly with closure temperatures for fission damage (one possible situation
presented by Rahn and others, in press). In this case, the α-damage might be dominantly point
defects, which may remain stable to higher temperatures than more damaged areas created by
α-recoil (Nasdala and others, 2001). This latter scenario may be reflected in the behavior of
those grains which fall near the 1:1 line on either the effective dose or age comparisons (Figure
2-11).
It is likely that eU (in combination with sufficient retention time for α-damage) may be a
critical factor in determining the behavior of a zircon during heating to ~250°C or so: the higher
eU values indicate zircons with a propensity to have α-damage annealed under the same
conditions as FT damage. The higher eU values of zircons that have less α-damage than would
be expected given their FT ages (Figure 2-11) may help to set up a situation wherein either or
both of the following may have happened: (1) in the source area, at approximately 100 Ma
(based on both the FT ages and the minimum damage storage ages of those zircons that fall
below the 1:1 lines on Figure 2-11), rocks containing these zircons were heated to >400°C and
both fission damage and α-damage were completely annealed; (2) all of these grains
accumulated significant α-damage prior to heating at ~100 Ma, allowing resetting of both their
FT ages and minimum damage storage ages during the ~100 Ma thermal event without bringing
the rocks up to full annealing temperatures. The exception to this is a colorless zircon, that has
a lower eU value (235 ppm; Table 2-2), but older Pb-Pb, FT, and minimum damage storage
ages than those zircons which also plot below the 1:1 lines on Figure 2-11. The older Pb-Pb age
105
for this colorless zircon likely enables it to behave similarly to other honey and colorless zircons
that plot below the 1:1 relationships in Figure 2-11, but that have higher eU values.
It is also important to note that those grains that have minimum damage storage age ≈
FT age (1:1 line) are honey and colorless zircons (Figure 2-11), and that pink/purple grains
retain significant α-damage. For pink/purple zircons, the minimum damage storage ages are
greater than the FT ages, and doses are greater than those expected given only the FT age.
This observation indicates that the pink/purple grains probably had more damage going into the
~100 Ma annealing event, and thus exit the heating event with greater damage.
Consider the following scenario, by analogy with the present distribution of damage in
the different color populations (Figure 2-7). If, given a simple thermal history, the pink/purple
suite has more damage than honey and colorless zircons prior to a ~100 Ma annealing event in
the source area, then some damage could carry through this thermal annealing. On the other
hand, if the damage level of the pink/purple suite prior to the ~100 Ma event is equal to that of
the honey and colorless grains, then some other factor about the pink/purple grains would allow
some of that damage to carry through the thermal annealing. If the damage level of the honey
and colorless suites is much greater than that for the pink/purple zircons going into the ~100 Ma
event, then this is unexpected, and there is some other controlling factor.
Given the situation discussed above, and the following parameters, damage values for
pink/purple zircons are ~2.5 times that of the honey and colorless zircons going into a ~100 Ma
event, given simple thermal histories for both pink/purple and honey and colorless zircons, and
the following typical single-grain parameters:
106
pink/purple zircons honey and colorless zircons
Pb-Pb age = 1685 Ma Pb-Pb age = 480 Ma
eU = 600 ppm eU = 850 ppm
dose prior to 100 Ma = dose prior to 100 Ma =
0.27 *1016 α-decay events/mg 0.10 *1016 α-decay events/mg
The ages and eU values are averages for all grains from a color population, and honey
and colorless zircons were treated as one population. Th was taken to be 0.5U (Garver and
Kamp, 2002). According to these calculations, it is likely that at least some pink/purple zircons
entered the ~100 Ma thermal annealing with greater α-damage than most honey and colorless
zircons, thus allowing them to: (1) exit the thermal event with greater damage; and (2)
experience preferential annealing as a result of their increased α-damage level. Clearly, the
same analogy may be drawn for damage states prior to the ~60 Ma thermal event that all zircons
experienced.
Most of the honey and colorless grains have similar FT age and minimum damage
storage age (Figure 2-11b), and the remaining zircons have an excess of α-damage in relation to
the FT age. For the honey and colorless grains whose minimum damage storage ages and
FTGA are similar, thermal histories are likely relatively simple. There are two likely histories for
such zircons: (1) these grains were originally derived from rapidly-cooled volcanic rocks that
remained at sub-annealing temperatures until re-heating (annealing); (2) older grains (older Pb-
Pb ages; Table 2-2), might have been completely annealed at some point during their thermal
history, and following annealing remained at cool temperatures until the final thermal
perturbation. Either scenario would produce thermally concordant grains (similar ages for
accumulation of α-damage and fission damage). For those grains whose minimum α-damage
storage ages are much older than the FT ages (i.e. the pink-purple series), a more complicated
107
thermal history is likely. Pink/purple grains may have been heated and cooled during multiple
episodes since crystallization, and have older minimum storage ages than honey and colorless
grains.
The Raman microprobe data thus reveal certain critical details in the interpretation of the
FT and Pb-Pb age data for the color fractions. First, most zircons are not greatly damaged at
present, presumably due to Paleogene annealing, although most still retain sufficient differences
to distinguish color populations: (a) the pink/purple series retains more α-damage than the
honey and colorless series zircons; (b) several high eU and/or older honey-colored zircons also
have reset FT ages. All other assumptions being equal, these observations mean that damaged
pink/purple and honey-colored zircons had more α-damage going into the heating event, and
apparently were the most likely to have reset FT ages. This conclusion is borne out in the FT
data, wherein we see that the youngest FT ages, and the largest total percent of a population,
are from the pink/purple and honey fractions (Figure 2-3). Effective U appears to be an
important indicator of grains susceptible to thermal annealing: grains with high eU and
Proterozoic crystallization ages tend to be reset, whereas low eU grains with similarly older
crystallization ages retain older cooling ages for the source rocks. In general the reset grains,
particularly the pink/purple suite, retain the highest amounts, but the smallest percentage of the
total α-damage possible; nominal storage for pink/purple series grains is approximately 20%.
This resetting trend is likely indicative of preferential annealing of more damaged areas or more
damaged grains.
Thus far, it has been shown that in terms of FTGA, crystallization age, FWHM/Raman
band shift, and eU, the distributions of honey and colorless grains overlap. This finding suggests
that these populations behaved in a similar fashion, given the thermal and physical conditions
108
particular to this sample. Accordingly, for this particular distribution, honey and colorless grains
may be treated as essentially one thermal population. Further work remains to be done to
determine the applicability of this for other data sets. Additionally, as suggested by Gastil and
others (1967), there may be specific chemical distinctions, and it is unknown what influence
chemical variation may exert on thermal behavior, if any. The results of REE analysis for zircons
from Station 23 follow in an attempt to address this issue.
REE Data
Based on suggestions of color generation related to REE chemistry (Fielding, 1970;
Gaudette and others, 1983), these FT-dated grains were also analyzed for heavy and light REE
using LA-ICP-MS, with the same spot location as the Pb, U, and Th analyses. REE
concentration data for unknowns and standards appears in Table 2-5. Estimations of error for
light REE (LREE) and heavy REE (HREE) concentrations, based on sequential measurements
of the standard zircon (UT-01), are also noted. As expected for zircons, the HREE content is
higher than the LREE in all color populations (e.g. Fielding, 1970; Gromet and Silver, 1983;
Hinton and Upton, 1991; Hoskin and Ireland, 2000). Most of the LREE are at concentrations just
above the detection limit (~0.1 ppm) in most grains, with some notable exceptions in the
pink/purple fraction. Values for every REE for the pink/purple fraction are somewhat lower but
generally overlapping with the colorless and honey fractions. No correlation of color to REE
composition was detected.
REE concentrations from unknowns in this study were normalized and compared to the
well-studied Elie Ness zircons (ENZ) from Scotland (Hinton and Upton, 1991). The REE in the
majority of unknowns do not deviate greatly from ENZ (Figure 2-12). There is a greater spread
Tab
le 2
-5.
Rare
eart
h e
lem
ent
concentr
ation d
ata
(ppm
) fo
r colo
r fr
action z
ircons f
rom
Sta
tion 2
3,
Huachuca M
ounta
ins.
gra
in #
La
Ce
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
pin
k/p
urp
le
d0
05
33
11
07
75
78
36
77
85
36
14
63
32
33
45
d0
12
11
90
20
13
45
52
81
28
33
26
55
3
d0
13
12
80
21
14
44
92
21
03
25
17
74
0
d0
70
11
21
21
41
81
46
76
32
76
74
82
12
4
d1
27
11
00
20
13
13
31
23
35
10
d1
31
18
01
11
94
78
37
16
84
22
95
66
d1
44
11
90
10
94
44
21
10
42
72
24
50
d1
61
19
46
56
62
28
63
72
94
48
25
33
61
27
51
09
66
57
16
5
d1
65
11
40
10
11
45
22
41
13
26
19
24
8
d1
95
11
60
11
12
44
72
21
00
27
20
74
3
L0
49
15
02
01
95
65
29
12
42
81
96
46
L0
62
21
39
22
32
15
71
33
14
33
22
31
56
L3
04
04
02
01
85
73
32
13
93
63
00
46
L3
30
21
01
26
56
91
54
69
29
77
15
39
83
co
lorl
ess
c1
08
24
74
12
22
96
10
75
32
42
68
62
98
7
c1
11
00
90
22
32
71
14
54
23
85
75
04
74
c1
21
60
24
12
25
91
01
92
97
43
31
03
81
31
41
c1
22
30
28
02
22
66
95
46
21
45
65
00
77
c1
29
11
40
21
18
45
82
51
07
24
15
93
5
c1
30
01
70
22
11
44
31
88
52
42
00
51
c1
37
63
25
12
12
66
92
48
23
65
94
51
10
0
c1
43
71
22
12
13
36
95
48
22
55
33
65
81
c1
59
87
51
22
12
05
71
38
17
33
93
18
75
c1
72
80
18
01
11
24
54
27
14
03
73
28
93
c1
77
23
23
12
11
75
70
36
21
35
34
11
11
4
c2
03
11
19
01
11
65
70
30
15
83
93
60
89
c2
04
41
18
02
12
15
80
40
18
94
13
11
68
c2
06
41
32
01
11
55
71
36
18
14
23
45
86
c2
06
51
17
02
11
44
63
34
17
84
43
46
86
c2
22
21
19
01
11
34
58
29
15
04
03
36
84
c2
25
00
24
01
01
14
47
25
12
43
12
69
56
c2
28
57
46
23
10
58
91
87
96
43
81
11
94
11
61
c2
29
71
47
02
12
25
81
39
19
15
03
97
71
c2
52
81
24
02
22
86
98
51
25
96
85
54
12
4
c2
54
40
90
21
32
71
12
55
24
65
94
62
93
c2
69
51
14
02
12
46
90
47
21
74
73
34
91
109
Ta
ble
2-5
, co
ntin
ue
d
gra
in #
La
Ce
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
ho
ne
y
h1
10
11
58
13
69
61
42
25
11
55
80
13
61
03
01
92
h1
10
90
12
12
36
71
11
84
77
34
26
95
80
11
4
h1
18
00
40
12
55
61
01
53
73
36
08
06
49
17
0
h1
22
40
14
02
22
77
81
40
18
34
12
96
77
h1
30
00
67
12
24
89
14
97
73
57
81
65
51
35
h1
48
22
42
22
23
98
98
47
22
75
34
30
99
h2
03
10
90
21
31
79
74
52
24
54
39
68
9
h2
09
51
24
12
23
36
85
38
18
74
23
41
77
h2
11
90
27
02
12
36
77
37
18
95
04
41
97
h2
18
94
63
43
23
16
79
36
17
14
23
28
73
h2
22
10
19
02
32
97
77
31
13
83
63
17
56
h2
24
01
53
12
24
08
11
55
52
69
60
46
61
05
h2
24
80
18
02
11
86
67
34
17
84
23
40
81
h2
24
91
22
23
45
79
12
95
52
53
56
42
68
8
h2
27
60
14
02
01
05
47
21
11
92
92
43
65
h2
27
70
13
02
23
57
93
42
19
04
33
06
66
h2
29
20
11
12
12
97
83
36
16
94
33
68
67
h2
35
80
24
02
12
46
77
37
18
94
23
18
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or
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9
No
tes:
On
e s
tan
da
rd v
alu
e is g
ive
n f
or
ea
ch
da
y o
f a
na
lysis
, a
nd
cite
d u
nce
rta
intie
s f
or
UT
-01
zir
co
n a
re 1
sta
nd
ard
de
via
tio
n.
Be
ca
use
un
kn
ow
n z
irco
ns w
ere
to
o s
ma
ll f
or
rep
lica
te a
na
lysis
, u
nce
rta
intie
s f
or
ea
ch
da
y f
or
UT
-01
ap
pro
xim
ate
sin
gle
-gra
in u
nce
rta
intie
s f
or
ea
ch
ele
me
nt.
A
s d
escri
be
d in
th
e t
ext,
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-IC
P-M
S m
ea
su
rem
en
ts f
or
all R
EE
we
re m
ad
e o
n s
ing
le F
T-d
ate
d z
irco
n g
rain
s.
Fo
r fu
rth
er
info
rma
tio
n o
n d
ata
pro
ce
ssin
g a
nd
sta
nd
ard
iza
tio
n,
refe
r to
Ap
pe
nd
ix 1
.
110
REE variation
Station 23 color fraction zircon
0.01
0.10
1.00
10.00
100.00
1000.00
10000.00
100000.00
56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72
EN
Z-n
orm
ali
ze
d v
alu
e
Figure 2-12. Normalized rare-earth-element data for color fraction zircons from Station 23,
La Ce Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
pink/purple (N = 14 grains)
colorless (N = 22 grains)honey (N = 21 grains)
Huachuca Mountains. Elie Ness zircon (ENZ) average, to which unknowns
are normalized, is the result of the average of seven analyses reported for
the ENZ megacryst by Hinton and Upton (1991).
111
112
of normalized values in the pink/purple series than for the colorless or honey grains, and a few
pink/purple grains plot with abundances of 10-10,000 times that of the ENZ for the LREE. More
importantly, with the exception of some zircons from the pink/purple series, there is little
deviation in relative abundances among the different color fractions. As such, the difference
among these groups, in particular the colorless and honey grains, appears to be unrelated to
rare earth element chemistry, at least in these zircons. This finding is in contrast to the work of
Fielding (1970), and Gaudette and others (1981); both studies linked the development of color to
crystal chemistry, specifically that of U and certain REE.
Fielding (1970) investigated color zonation in serial sections of a Late Permian
pink/purple zircon from a pegmatite in the New England batholith. This work concluded that
bands of red color are correlated with areas with lower in Fe, Al, Mn, and Pr, and that the
reduction of Nb+5 to Nb+4 in combination with a structural defect capable of providing electrons
for this reduction aids in forming color centers. Fielding (1970) also noted an enrichment in
HREE over LREE (as expected for zircon, particularly that derived from a pegmatite), and higher
concentrations of Er in color bands. Gaudette and others (1981) presented evidence for the
relationship between Eu concentrations and brown color in detrital zircons from the Potsdam
Formation (New York State): ion microprobe data from 21 zircons indicates a positive Eu
anomaly in brown grains, whereas there is no Eu anomaly for colorless grains.
These studies unfortunately do not focus on zircons from a wide variety of sources, and
sampled grains are probably not numerous enough to make broad generalizations about the
control exerted by trace-element chemistry on color formation. Similar problems with not
capturing the full range of zircon types are no doubt encountered in the present study. It is likely
that there is a combination of chemical factors that contribute to color development in zircons.
113
For example, Krogh and Davis (1974) suggest that alteration of metamict zircon allows
enrichment in water, as well as Fe, Al, and Ca oxides. These impurities, in combination with
REE or other chemical variations and/or accumulation of radiation damage, may contribute to
color generation. As pointed out by Fielding (1970), there are also crystallographic
considerations; his work demonstrated that there is a tendency to isolate impurities and defects
along the (111) plane of zircon in the samples examined, and that colorless sections are typically
parallel to (110). Much work remains to be done on a full suite of genetically and temporally
distinct igneous zircons, including major- and minor-element chemistry and Raman microscopy,
to better determine the various contributing factors and their relative importance.
DISCUSSION
FT Age Data
In both the p and h fractions, zircons with FT ages between 60 and 70 Ma are present,
and the youngest peaks for these two fractions overlap at two sigma (63 Ma and 70 Ma; Table 2-
3). Significant variability of single-grain ages exists within the p fraction, as demonstrated by
peaks at 63 Ma and 175 Ma, the latter of which is a composite of ~150 Ma grains and several
older grain ages (Figure 2-3). This variability is probably related to the presence of grains with
different thermal histories in the same fraction. Differing thermal histories are likely, as zircons
have different Pb-Pb ages and variability in short-range lattice order within individual color
fractions (based on Raman microscopy data; Tables 2 and 4). Considering that there are young
reset grains from all the color populations, some key observations bear re-emphasis:
(1) All pink/purple zircons have Early and Middle Proterozoic crystallization ages,
whereas the majority of the colorless and honey young reset zircons have Ordovician-
Early Jurassic crystallization ages.
114
(2) All young FT-reset grains have elevated eU values, suggesting that only those
grains with α-damage prior to Paleogene annealing were reset.
(2) There is only one young reset colorless grain (c2_031; Table 2-2), which suggests
that this population will generally reflect provenance characteristics rather than being
reset, as in the case of high-damage colored zircons.
(3) All of the honey and colorless young reset zircons have relatively small FWHM (3.5-
4.6 cm-1), versus the pink/purple, which have FWHM two or more times greater (8.6-11.8
cm-1). This finding indicates that the pink/purple zircons retained greater amounts of α-
damage after Paleogene heating.
Cumulative probability density curves for each of the three color fractions (Figure 2-3)
show that peaks are similar to the bulk sample, indicating that color does not relate in a simple
fashion to either fission-track age or α-damage level. This observation suggests that there is a
complex interaction between radiation damage of the crystal lattice and thermal annealing of
zircons.
Both the colorless and honey fractions have peak ages between 75 and 120 Ma,
comprising the entire c fraction, and nearly half of the grains in the h fraction (Figure 2-3; Table
2-3). These are reasonable provenance ages for multi-cycle sediments that were shed into this
basin. This observation suggests that FT ages of colorless and honey zircons are most useful in
understanding provenance of the sediments.
Raman Crystallinity Data
Effective U, retention time (time since complete α-damage annealing), and thermal
history are the determining factors in how radiation-damaged a grain is at present, as measured
115
by Raman bandwidth. Crystallization age is also important in grains with rapid cooling to <200°C
and simple thermal histories, in which case the retention time may approximate the
crystallization age. Possible end members and intermediate scenarios are shown in Figure 2-
13; these scenarios are developed for zircons with simple thermal histories. In cases where
zircons have higher levels of α-damage (i.e. long retention times and/or high eU concentrations),
the potential for preferentially resetting fission-track ages at temperatures of 150°C-250°C
increases (as shown by increasingly darker shading of rectangles in Figure 2-13. However,
given younger retention ages and/or lower eU values, accumulated α-damage decreases,
thereby allowing higher retentivities in the fission-track system.
Relatively old crystallization ages, combined with lower eU values, allow certain
colorless and honey zircons to behave similarly to pink/purple grains in FWHM-eU space (i.e.
these old colorless/honey grains display a positive correlation between increasing eU and
decreasing crystallinity similar to the pink/purple grains; in contrast, other zircons from these two
populations show no decrease in crystallinity with increasing eU). Despite the fact that eU
concentrations are lower for pink/purple fraction zircons, these grains are more damaged. This
behavior may be attributable to an overall longer time since crystallization for the pink/purple
zircons, allowing for significant accumulation of α-damage prior to the onset of Laramide
magmatism. The fact that even very high eU grains in the honey and colorless suite do not have
wide Raman bandwidths may indicate that these grains were highly damaged in micro-areas
which were preferentially annealed during Paleogene heating.
The colorless and honey grains have a narrower distribution of bandwidths as compared
with the pink/purple zircons (Figure 2-7, Figure 2-8). Such behavior may indicate: (a) shorter,
less complicated thermal histories in grains with overall younger crystallization ages; or (b)
116
homogenization of the bandwidths of these populations during the Paleogene heating event.
The more crystalline nature of the honey and colorless populations may reflect both processes.
It is likely that prior to heating (60 Ma), the pink/purple grains had higher but variable
preserved α-damage levels, compared to the other populations. Heating anneals α-damage,
with the final product being a zero-damage zircon. Given enough time and sufficiently high
temperatures (temperatures greater than perhaps 400°C), all grains would be homogenized into
zero-damage zircons. This temperature estimate is based on the concept of the color-removal
zone and its thermal bounds, proposed by Garver and Kamp (2002). These authors suggested
that zircons derived from the reset FT color zone and from the reset FT colorless zone have
synorogenic cooling ages, experienced peak temperatures of 250-400°C, and approximately
80% of grains are colorless as a result of thermal annealing. Accordingly, above about 400°C,
color should be almost completely removed from most grains, at which point the majority of the
α-damage may also have been annealed.
Overlapping Behavior: Honey vs. Colorless Zircons
The differences in color between honey and colorless zircons in the Station 23 sample
cannot be attributed to differences in FT age, crystallization age, crystallinity, or REE
geochemistry. It is possible that there is variation in other major- or minor-element chemistry
that may affect color, and/or there may be inter-sample variation in the factors which contribute
to the development of honey color in zircons. This overlapping behavior presents the
opportunity for further study to understand the differences between the colorless and honey
series, and to define the factors which contribute to development of honey color. A well-selected
suite of igneous zircons from multiple genetic and temporal contexts would provide the best
means of understanding the generation of honey color. Zircons from an igneous series with
117
independently known and relatively simple thermal histories would provide the best starting point
for such a study. The basis of the data set would be FT ages for color-separated zircons. Other
desirable data include REE, Fe, Al, Ca, and Mn concentrations to thoroughly define the
geochemical variations among colorless and honey colored zircons. To define the α-damage
contribution to both color development and FT system behavior, Pb-Pb ages and Th and U
values, and short- and long-range lattice order measurements (via Raman microscopy and X-ray
diffraction, respectively) should be collected for color-separated grains.
Activation Energy for Damage Annealing
Clearly there is a decreased activation energy associated with annealing more damaged
zircon than annealing less damaged zircon: more α-damaged zircons have been preferentially
reset (Nasdala and others, 2001). The precise genesis of this phenomenon is unclear.
Activation energy for annealing damage probably varies as a complicated relationship between
eU and retention time. Decreased activation energy for annealing fission tracks in a highly α-
damaged grain probably relates to the relative ease of moving ions in a damaged lattice rather
than in a perfect crystalline lattice. In the case of a highly damaged crystal lattice, the material is
more glass-like (i.e. little structural order, and thus easier to rearrange weakly-bonded material).
In the case of a crystalline zircon, strongly bonded ions are ordered within the lattice structure.
The activation energy required to move ions back into place in the former situation is likely
decreased by the presence of weaker bonds in a more poorly ordered lattice. It is concluded
that each grain, depending on the eU, retention time, and thermal history, can have a different
activation energy for the annealing of either fission tracks or α-damage.
118
Criteria for Recognizing Reset Grains
From the age and crystallinity data presented above, it seems clear that the
relationships among thermal history, zircon color, and radiation damage are not straightforward.
For some time, it has been recognized that accumulation of α-damage is a function of eU,
retention time, and thermal history. Additionally, studies have linked the development of color to
accumulated α-damage since FT closure temperature (Garver and Kamp, 2002). At this point,
the occurrence of the FT-reset grains and their characteristics must be considered in this
context. Can one predict which grains will be reset by a low-temperature thermal event?
Given any eU concentration, a zircon at temperatures less than about 300°C-350°C
becomes increasingly α-damaged with time, and crystal lattices become increasingly disordered
(Figure 2-13). α-damage is complex, and it is clear that at low temperatures (150°C-250°C)
some fraction of the damage is repaired, but some remains and this latter fraction requires much
higher energies to anneal (i.e. color appears to anneal at 350°C-400°C; Garver and Kamp 2002).
α-damage causes disorder, which facilitates the annealing of fission tracks. All other things
being equal, a high-damage grain should have a lower closure temperature than a low-damage
grains (Kasuya and Naeser, 1988). Therefore, one would like to know, in a predictive sense,
which grains in a variably damaged population would be annealed if the strata were subjected to
low-temperature heating (150°C-250°C). Is it only total α-damage or is there some other basic
crystal property that determines track retention?
Because of uncertainties associated with variable thermal histories and levels of
accumulated radiation damage prior to the most recent heating for grains within a single color
population, total dose value alone cannot be used to distinguish grains that are potentially reset,
but it is probably of first-order importance. Provided with crystallinity measurements and U and
time
alp
ha
da
ma
ge
metamict
retention age;
Pb-Pb age
500 Ma 1000 Ma250 Ma 1500 Ma 2000 Ma
low eU <250 ppm
moderate eU 250-400
high eU 400-900 ppm
very high eU
>900 ppm
Figure 2-13. Qualitative relationship between time, alpha-damage, and effective uranium (eU)
best range to
preserve time since
cooling to <250°C
(provenance ages)
most likely to be
reset by post-
depositional low-T
events
concentration. Note that as eU increases, and/or retention time increases,
the propensity to develop damage to the point where fission tracks are
preferentially annealed in more damaged grains also rises (shown by
increasingly darker shaded rectangles). Note that these scenarios represent
the simplest cases, where zircons are not appreciably re-heated following
cooling to less than ~180°C at the retention age, which may or may not be
the same as the crystallization age.
119
120
Th concentrations, accumulated α-damage and the percent damage stored (effective dose
factor) may prove an effective means of establishing the potential for reset. Effective U content
alone is insufficient to determine potential for reset: if a zircon has a short retention time (i.e.
young crystallization age, and/or time since complete α-damage annealing), there remains
insufficient time to develop radiation damage even if the grain has high eU and is not annealed
subsequently. Zircon color alone is similarly problematic. Many of the young reset zircons are
pink/purple, but a number also come from the honey suite, and there is one reset colorless grain.
By the same logic, a number of the lower eU pink/purple, honey, and colorless zircons retain
provenance ages. As such one color population may comprise multiple thermal populations
because there is the possibility, if not likelihood, of sampling zircon with a diversity of low-
temperature thermal histories in a single sandstone.
In the data presented in this part of the study, several points are critical:
(1) Reset FT ages occur in specific grains with higher eU values and/or older
crystallization ages.
(2) Despite FT annealing and resetting of FT ages in certain zircons, some α-damage
remains in certain grains following an annealing event with widespread elevated
temperatures on the order of 200°C.
(3) Grains with older crystallization ages retain significant α-damage at the present,
despite the fact that they have been heated and cooled at least once.
(4) Honey color in zircons in this data set appears to be unrelated to α-damage, and
unrelated to REE content.
(5) Pink and purple color in zircons correlates to old crystallization age and elevated α-
damage levels, and is unrelated to REE content.
121
Conclusions that can be drawn from these points are: (1) grains in the pink/purple color series
have the greatest possibility of having old crystallization ages and/or high α-damage; and (2)
non-pink/purple grains which have high eU and long retention times should also be suspect.
Clearly, single-grain thermal history and the amount of accumulated radiation damage attained
prior to an annealing event are the controlling factors in grain response to heating. Because
thermal histories vary among grains within a detrital suite, eU concentrations and retention times
provide a means of quantifying the present level of α-damage, and in identifying potentially reset
grains.
Additionally, there might also be a threshold for grains in terms of their current damage
levels, wherein one might suspect that these grains were very highly damaged prior to partial
annealing. Grains coming out of the most recent heating event with higher damage levels likely
went in with higher levels, and all other things being equal, are the grains most likely to have
been reset. This point does not mean that a highly damaged zircon will come out of the heating
event completely undamaged; it simply means that the more damaged micro-areas will have
been preferentially annealed. Based on data presented herein, one might consider a possible
value of FWHM of 8 cm-1 as indicative of a grain that entered a heating event with significant α-
damage, but this is problematic for the following reasons:
(1) The threshold FWHM value selected depends on how much α-damage a grain
accumulated prior to the heating event. One might envision a case of two grains that
emerge from a heating event with equal FWHM, and thus equal crystallinities at present.
However, resulting from different thermal histories, one grain may have contained more
stable point defects, and thus entered the annealing event with similar crystallinity to the
present value. The other zircon might have been highly damaged to begin with, but
because it was much more damaged, it also preferentially annealed more than the other
122
(and because it was more damaged, would have been much more susceptible to the
annealing of fission tracks than the zircon in the first scenario).
(2) All color groups retain some grains with reset FT ages, and the colorless and honey
reset zircons have much lower FWHM than the pink/purple reset grains. Additionally, all
colorless and honey reset grains have FWHM < 8 cm-1.
It may also be helpful to consider maximum paleotemperature as a potential guide for
identifying reset fission-track ages. However, because the amount of resetting depends upon
other factors (eU, retention time), peak temperature should provide only a general guideline in
combination with other single-grain parameters. The simplest end member cases are
represented in Figure 2-14. Partial to full annealing of fission tracks might be expected to occur
in near-amorphous zircon at a temperature of perhaps as low as 180°C (Figure 2-14). Along the
same lines, almost no annealing of fission tracks may occur in fully crystalline zircon even at
temperatures as high as 260°C (Figure 2-14) (Brandon and others, 1998).
In the heated samples, it is clear that grains belonging to the 50-60 Ma peak have been
reset because these ages are younger than the depositional age. However, it is uncertain how
much, if any, damage was annealed in the other older grains. There are several options, but
one possibility is that resetting (FT and α-damage) only occurs above some threshold α-damage
value. This possibility is supported by the fact that older peak ages in samples that lack a young
reset peak are similar to older peak ages in samples that have a young reset peak (Chapter 1).
As such, in multi-component FT data sets, the first-order methods of differentiating
thermal populations, and determining which data yield provenance information and which yield
data on post-depositional thermal activity, are as follows:
123
(1) Separate zircons by color, and evaluate FTGA accordingly. This relatively simple
task can provide an efficient means of determining grains which might have been reset
by post-depositional thermal events.
(2) Evaluate etch behavior: grains in which fission tracks etch more rapidly do so
because of higher levels of radiation damage. This relative etching efficiency may be
used as a first-order proxy for damage levels (c.f. Gleadow, 1978).
(3) Evaluate FTGA with respect to model eU. There is a clear indication in data
presented herein that honey and colorless grains with higher eU values may be
preferentially reset, and thus provide constraints on post-depositional thermal activity.
(4) Obtain VR data: this is an efficient and inexpensive way to estimate maximum
paleotemperature.
If additional differentiation becomes necessary, crystallization ages and Th concentrations might
also assist in further defining thermal populations. Additionally, α-damage levels ascertained by
the use of Raman microscopy may provide supplementary data. However, one must recognize
that this is only a proxy for damage prior to the last reheating, and is highly dependent on
thermal history. Such data are most helpful when thermal histories are relatively simple.
CONCLUSIONS
This study provides the first correlation of FT ages, Pb-Pb crystallization ages, α-
damage levels, and trace-element geochemistry for the same detrital zircons with different
histories, but all subjected to a mild Tertiary heating event. Raman microscopy data and the
homogeneity of REE crystal chemistry for these grains provides a means of evaluating the major
contributing factors in the development and annealing of fission damage, α-damage, and the
development of color in zircons. These data provide the following observations and conclusions:
annealing temperature °C
pe
rce
nt
FT
an
ne
alin
g
0
150°
Figure 2-14. Inferred relationship between annealing of fission tracks, annealing temperature,
50
100
235° 260°210°
high
alpha-
damagelow
alpha-
damage
180°0°
moderate
alpha-
damage
and accumulated alpha-damage. As in Figure 2-13, these scenarios
represent the simplest cases, where zircons are not appreciably re-heated
following cooling at the retention age, except during the annealing event.
Note that the relationships between the amount of damage annealed, the
annealing temperature for a grain with a certain level of damage, and the
shape of the curve that describes these relationships, remain to be
constrained by further work on a suite of igneous zircons for which the
124
thermal history is known.
125
(1) Some grains that have young reset fission-track ages retain significant α-damage
despite having experienced the thermal input required for annealing fission tracks.
There is an overlapping range of stability for α-damage and fission damage.
Additionally, there is a higher thermal stability of α-damage relative to fission damage,
which is likely related to the amount and type of α-damage in a crystal (Nasdala and
others, 2001).
(2) Placing these observations in context, this study presents the criteria for determining
the presence of zircons with reset FT ages in multi-component populations. Critical
factors include FT age(s) in the context of known depositional age, color, eU content, as
well as supporting evidence in the form of the FTGA distributions of older rocks in the
section.
(3) Pb-Pb ages, total and effective α-doses, and spot crystallinity measurements
provide a means of more accurately identifying potentially reset grains which might not
otherwise be obvious.
(4) Pink/purple grains are currently more α-damaged than colorless or honey-colored
zircons, with most pink/purple zircons having FWHM > 6 cm-1.
(5) In general, fission-track ages of colorless detrital zircons provide a means of dating
the provenance of sandstones. In many cases, honey-colored grains will also yield
consistent provenance ages. Care must be taken in the selection of grains and in the
interpretation of grain age distributions to avoid high-eU zircons.
(6) More radiation-damaged zircons, such as those from the pink/purple series in the
present study, will be more likely to have been reset via post-depositional thermal
activity with temperatures perhaps as low as 180°C, up to 260°C, and as such provide a
means of dating local or regional cooling following magmatism. Again, care must be
taken to identify grains with relatively high eU contents. General context for the
126
interpretation of either provenance or post-depositional thermal activity is provided
simply and cost-effectively by the addition of vitrinite-reflectance data from interbedded
mudrocks.
(7) Honey and colorless zircons demonstrate overlapping behavior in terms of fission-
track age, Pb-Pb age, eU, crystallinity, and REE geochemistry.
A
pp
en
dix
1—
Ag
e d
ata
fo
r U
pp
er
Cre
tac
eo
us
an
d k
ey p
os
t-U
pp
er
Cre
tac
eo
us
ig
ne
ou
s r
oc
ks
in
s
ou
the
as
tern
Ari
zo
na
form
ati
on
locati
on
ag
eevid
en
ce
cit
ati
on
Tert
iary
qu
art
z v
ein
sS
anta
Rita M
ounta
ins
Oli
go
cen
e?
youngest
rock s
how
n a
s c
ross-c
ut
by t
hese
Dre
wes (
1971);
Marv
in
vein
s is r
hyolit
ic t
uff
/tu
ffaceous s
andsto
ne
and o
thers
(1973);
Marv
in
unit o
f G
ringo G
ulc
h v
olc
anic
s (
post-
60 M
a);
and o
thers
(1978)
Dre
wes (
1971)
links t
hese r
ocks t
o O
ligocene
Gro
svenor
Hill
s v
olc
anic
s;
dik
e s
warm
in B
ox
Canyon d
ate
d b
y M
arv
in a
nd o
thers
(1973)
at
26.5
Ma ±
1.3
m.y
. (K
-Ar,
sanid
ine),
als
o lik
ely
rela
ted
Tert
iary
rh
yo
lite
Santa
Rita M
ounta
ins
~28 M
a ±
2 m
.y.
K-A
rD
rew
es (
1971)
p
orp
hyry
Helv
eti
a s
tocks
Santa
Rita M
ounta
ins
54.9
Ma ±
1.3
m.y
.K
-Ar
on b
iotite
Dre
wes (
1976);
Marv
in a
nd
54.8
Ma ±
2.0
m.y
.K
-Ar
on b
iotite
oth
ers
(1973);
Marv
in a
nd
53.3
Ma ±
2.0
m.y
.K
-Ar
on b
iotite
oth
ers
(1978)
qu
art
z m
on
zo
nit
eS
anta
Rita M
ounta
ins
55.3
Ma ±
2.0
m.y
.K
-Ar
on b
iotite
Dre
wes (
1972)
s
tock,
Helv
eti
a a
rea
qu
art
z l
ati
te p
orp
hyry
Santa
Rita M
ounta
ins
55.2
Ma ±
2.0
m.y
.K
-Ar
on b
iotite
Marv
in a
nd o
thers
(1973);
p
lug
s E
of
Helv
eti
a57.1
Ma ±
2.1
m.y
.K
-Ar
on b
iotite
Marv
in a
nd o
thers
(1978)
57.6
Ma ±
2.1
m.y
.K
-Ar
on b
iotite
qu
art
z l
ati
te p
orp
yry
Santa
Rita M
ounta
ins
57.1
Ma ±
1.9
m.y
.K
-Ar
on b
iotite
Dre
wes (
1972)
p
lug
, G
reate
rvil
le
a
rea
Gre
ate
rvil
le p
lug
sS
anta
Rita M
ounta
ins
57.2
Ma ±
2.1
m.y
.K
-Ar
on b
iotite
Dre
wes (
1976)
57.8
Ma ±
2.1
m.y
.K
-Ar
on b
iotite
qu
art
z l
ati
te p
orp
hyry
Santa
Rita M
ounta
ins
57.0
Ma ±
2.3
m.y
.K
-Ar
on b
iotite
Marv
in a
nd o
thers
(1973);
n
ear
Gre
ate
rvil
leM
arv
in a
nd o
thers
(1978)
127
Appendix
1,
continued
form
ati
on
locati
on
ag
eevid
en
ce
cit
ati
on
gra
no
dio
rite
an
dP
ata
gonia
Mounta
ins
59 M
a ±
3 m
.y.
K-A
r on b
iotite
Marv
in a
nd o
thers
(1973)
a
sso
cia
ted
qu
art
z59 M
a ±
5 m
.y.
K-A
r on h
orn
ble
nde
m
on
zo
nit
e59 M
a ±
3 m
.y.
K-A
r on b
iotite
Red
Mo
un
tain
co
mp
lex
Pata
gonia
Mounta
ins
62-5
8 M
are
gio
nal re
lationship
sK
eith a
nd S
wan (
1995);
Keith a
nd W
ilt (
1986)
Gri
ng
o G
ulc
h v
olc
an
ics
Santa
Rita M
ounta
ins
61.3
Ma ±
4.3
m.y
.K
-Ar
on h
orn
ble
nde,
dacite p
orp
hyry
Marv
in a
nd o
thers
(1973);
62 M
a ±
3 m
.y.
K-A
r on b
iotite
, m
icro
gra
nodio
rite
Dre
wes (
1976);
Marv
in
and o
thers
(1978)
Gri
ng
o G
ulc
h p
luto
nS
anta
Rita M
ounta
ins
61.9
Ma ±
6.0
m.y
.K
-Ar
on b
iotite
, horn
ble
nde
Dre
wes (
1976);
Marv
in a
nd
c
onsid
ere
d ~
pene-
62.0
Ma ±
6.0
m.y
.K
-Ar
on b
iotite
, horn
ble
nde
oth
ers
(1973)
c
onte
mpora
neous w
ith
G
ringo G
ulc
h v
olc
anic
s,
o
ther
nearb
y r
ocks
(
Dre
wes,
1976)
qu
art
z l
ati
te p
lug
sS
anta
Rita M
ounta
ins
64-6
0 M
aA
r-A
r on b
iotite
, horn
ble
nde
Keith a
nd W
ilt (
1986)
(
Helv
eti
a s
tocks)
qu
art
z l
ati
te p
lug
sS
anta
Rita M
ounta
ins
64-6
0 M
aA
r-A
r on b
iotite
, horn
ble
nde
Keith a
nd W
ilt (
1986)
(
Gri
ng
o G
ulc
h
p
luto
n/v
olc
an
ics)
rocks a
sso
cia
ted
wit
hS
anta
Rita M
ounta
ins
67-6
5 M
ahorn
ble
nde
Keith a
nd W
ilt (
1986)
P
b-Z
n-A
g
d
ep
osit
s T
yn
dall
/
S
ale
ro/I
van
ho
e
m
ines
Jo
sep
hin
e C
an
yo
nS
anta
Rita M
ounta
ins
68.8
Ma ±
7.0
m.y
.K
-Ar
Dre
wes (
1976)
d
iori
te
128
Appendix
1,
continued
form
ati
on
locati
on
ag
eevid
en
ce
cit
ati
on
po
rph
yri
tic
da
cit
e d
ike
SS
anta
Rita M
ounta
ins
69 M
a ±
3 m
.y.
K-A
r on h
orn
ble
nde
Marv
in a
nd o
thers
(1973);
o
f S
ilver
Cave
Dre
wes (
1976);
Marv
in
and o
thers
(1978)
Mad
era
Can
yo
nS
anta
Rita M
ounta
ins
69.6
Ma ±
2.1
m.y
.K
-Ar
Dre
wes (
1976)
g
ran
od
iori
te
Ele
ph
an
t H
ea
d q
ua
rtz
Santa
Rita M
ounta
ins
69.9
Ma ±
3.0
m.y
.K
-Ar
on b
iotite
Dre
wes (
1976)
m
on
zo
nit
e70.8
Ma ±
2.9
m.y
.K
-Ar
on b
iotite
(
Qu
an
trell
sto
ck)
Ele
ph
an
t H
ea
d/Q
ua
ntr
ell
Santa
Rita M
ounta
ins
71-6
8 M
aK
eith a
nd W
ilt (
1986)
s
tocks
Jo
se
ph
ine
Can
yo
nS
anta
Rita M
ounta
ins
70-6
8 M
aA
r-A
r on b
iotite
Keith a
nd W
ilt (
1986)
d
iori
te
vo
lcan
ics o
f Jo
nes
Canelo
Hill
s72 M
aK
-Ar
on b
iotite
Hayes (
1970)
M
esa (
up
per
un
it
w
eld
ed
tu
ff);
u
nderlyin
g
c
onglo
mera
te lik
ely
F
ort
Critt
enden
F
orm
ation
Co
ron
a s
tock
Santa
Rita M
ounta
ins
72-7
1 M
aK
eith a
nd W
ilt (
1986)
Co
ron
a s
tock
Santa
Rita M
ounta
ins
75.5
Ma ±
2.7
m.y
.K
-Ar
on b
iotite
Marv
in a
nd o
thers
(1973);
Marv
in a
nd o
thers
(1978)
qu
art
z d
iori
te E
of
Mt.
Santa
Rita M
ounta
ins
75.3
Ma ±
2.9
m.y
.K
-Ar
on b
iotite
Marv
in a
nd o
thers
(1973);
F
ag
an
Ran
ch
Marv
in a
nd o
thers
(1978)
129
Appendix
1,
continued
form
ati
on
locati
on
ag
eevid
en
ce
cit
ati
on
Sale
ro F
orm
ati
on
Santa
Rita M
ounta
ins
74.0
Ma ±
2.2
m.y
.K
-Ar
on b
iotite
, w
eld
ed t
uff
mem
ber
Dre
wes (
1968);
Inm
an
c
onfo
rmable
ato
p F
ort
(1982)
C
ritt
enden F
orm
ation
in S
anta
Rita M
ounta
ins
(
Hayes a
nd D
rew
es,
1
978)
Sale
ro F
orm
ati
on
Santa
Rita M
ounta
ins
74.3
Ma ±
3.3
m.y
.K
-Ar
on b
iotite
, rh
yodacite w
eld
ed t
uff
Dre
wes (
1968);
Inm
an
(1982)
Sale
ro F
orm
ati
on
Santa
Rita M
ounta
ins
79-7
3 M
aA
r-A
r on b
iotite
, w
eld
ed t
uff
mem
ber
Keith a
nd W
ilt (
1986)
vo
lcan
ics o
f D
ove C
an
yo
nC
anelo
Hill
s73 M
a ±
4 m
.y.
K-A
r on b
iotite
Marv
in a
nd o
thers
(1973);
Marv
in a
nd o
thers
(1978)
trach
yan
desit
e o
fS
W o
f C
anelo
Hill
s73.9
Ma ±
3.0
m.y
.K
-Ar
on b
iotite
Marv
in a
nd o
thers
(1973);
M
ead
ow
Vall
ey
Marv
in a
nd o
thers
(1978)
an
desit
es o
f C
orr
al
Canelo
Hill
s,
W f
lank
75 M
aK
-Ar
on b
iotite
Hayes (
1987)
C
an
yo
n
(
confo
rmably
overlain
b
y F
ort
Critt
enden
F
orm
ation)
Note
s:
For
appro
xim
ate
ages (
desig
nate
d w
ith a
~ b
efo
re t
he c
ited a
ge):
ages a
re a
s c
ited in t
he t
ext
of
refe
renced g
eolo
gic
map;
uncert
ain
ties f
or
these
ages a
re a
ppro
xim
ate
. W
here
no info
rmation o
n t
he isoto
pic
syste
m o
r m
inera
l(s)
date
d w
as p
rovid
ed in t
he o
rigin
al re
fere
nce,
these f
ield
s a
re left
bla
nk.
130
131
Appendix 2—Sample suite field descriptions for fission-track work, Santa Rita and Huachuca Mountains, southeastern Arizona
The following are brief field descriptions for each sample included in this study. Note that compositions were estimated in the field using hand samples, and accordingly may not exactly match point-counted values. abbreviations F = % framework grains Q = % quartz M = % matrix (silt-sized and finer) F = % feldspar C = % cement R = % lithic fragments P = % porosity
132
station #/field sample # field description Station 9/990625-3 —Fort Crittenden Formation sandstone FT sample from Station 9
along Glance Ridge transect, Huachuca Mountains. —geologic map: Hayes and Raup (1968); topographic map: Pyeatt Ranch (3490000 m N, 549000 m E). —sample is a pink-gray (weathered and fresh) medium grained to granule subrounded to rounded sandstone; by hand sample, F75M10C10P5:Q40F20R30; contains significant pseudomatrix and somewhat squashed, but still coherent, mudclasts; some of feldspar may be altered, but difficult to tell in hand sample; at least partially calcite cemented; Fe-oxide common; this sandstone bed is approximately 20 cm thick, bounded by silty mudstones; evidence for low angle trough cross beds, and basal contact scours down into silty mudstone below (approximately 1-2 cm relief on basal scour surface); there are other beds of this type throughout the section exposed in Ferosa Canyon, interbedded with mudstones, siltstones, and very fine sandstones; all have sharp contacts, including upper contacts; sandstone beds generally ~20 cm thick, finer lithologies somewhat thicker, on the order of 30-70 cm thick; moderately indurated. —no strike/dip.
133
Station 11/990626-1 —Glance conglomerate FT sample from Station 11 along Wakefield transect, Huachuca Mountains —geologic map: Hayes and Raup (1968); topographic map: Miller Peak (3475000 m N, 562000 n E). —general lithology is red-maroon (fresh and weathered) sand rich granule, pebble, and cobble subrounded to well rounded conglomerate; significant mud/clay content (reddish-maroon), which has since become pseudomatrix; major clast lithologies include, but not limited to, volcanics, limestone, granite, andesite, sandstone; clast sizes range from sand sized to cobbles >6 cm in longest exposed dimension (grain size described excludes true matrix grain sizes); “matrix” supported conglomerate; crude structureless bedding, with intercalated sandy and more conglomeratic lenses; bedding generally on the order of 30-50 cm, but variable; moderately indurated; stratigraphic up uncertain. —strike/dip (with some question due to poor outcrop): N29W 88SW.
134
Station 13/990628-1 —Fort Crittenden Formation sandstone/conglomerate FT sample from Station 13 along Cemetery transect, Huachuca Mountains. —geologic map: Hayes and Raup (1968); topographic map: Montezuma Pass (3468000 m N, 560000 m E). —sample is a green-gray brown (weathered/fresh) medium to coarse grained rounded sandstone with sparse granule and pebble horizons and lenses, as well as intercalated granules within finer sandstone beds; by hand sample, F80M7C3P10:Q50F12R38; at least partially calcite cemented; beds are relatively structureless internally, and outcrop does not show evidence for beds having internal lamination, tabular, or trough cross bedding; beds have moderately sharp tops and sharp bases, and are uniform within outcrop; sandstones generally thick bedded (~30 cm thick), with some thinner beds (3-5 cm thick); sandstone moderately friable, poor to fair induration; beds fine upward within scope of outcrop. —strike/dip: N42W 39NE.
135
Station 14/990628-2 —Cintura Formation sandstone FT sample from Station 14 along Cemetery transect, Huachuca Mountains. —geologic map: Hayes and Raup (1968); topographic map: Montezuma Pass (3468000 m N, 560000 m E). —sample is a brownish gray (weathered) to light brown (fresh) fine to medium grained rounded sandstone (grain size and rounding difficult to discern in hand sample due to homogeneous grain type, quartz cement, well-indurated nature); by hand sample, F95M0C5P0:Q97F2R1 (again, difficult to tell for above reasons); at least partially quartz cemented, and potentially slightly recrystallized (though no local veining seen); no local evidence for internal stratification, though up section near contact with Fort Crittenden Formation, there are very large scale low angle trough cross beds well exposed in Bear Creek; beds here are essentially internally structureless, have sharp tops and bases, and are of a consistent thickness (>35 cm thick), color, and character; bounded above and below by similar sandstones; very well indurated. —strike/dip: N67W 58SW.
136
Station 23/990722-2 —Fort Crittenden Formation sandstone/conglomerate FT sample from Station 23 along Gate 7 transect, Huachuca Mountains. —geologic map: Hayes and Raup (1968); topographic map: Huachuca Peak (3478000 m N, 554000 m E). —sample is a brown (weathered) to gray (fresh) medium to coarse grained subangular to subrounded sandstone; this and other outcrops also have lenses and beds of coarse, granular, and pebbly sandstone and conglomerate, the finer of which were also included in the sample; the gross lithologies of these beds appear very similar to finer constituents; by hand sample on medium grained sandstone fraction, F87M1C8P5:Q50F10R40; partially cemented by calcite; no local evidence for fine scale laminae, tabular, or trough cross beds, but there are relatively fine scale individual beds 1-2 cm thick; overall thinly to thickly bedded (1-2 cm-40 cm); moderately to poorly indurated, (both levels of induration sampled equally); beds overall have gradational tops and bases, except where basal bed is conglomeratic, and bases of sandstone above are sharper; no evidence within outcrop for basal scour, but clear evidence for basal lags; sampled interval in this area is approximately 2 m thick, which seems to be average for Fort Crittenden Formation in this area; outcrop bounded above and below by finer lithologies (based on outcrop character). —strike/dip: N43W 87NE.
137
Station 33/990802-1 —Lower Temporal Formation arkosic fanglomerate unit FT sample from Station 33 along Last Chance transect, Santa Rita Mountains. —geologic map: Drewes (1971a); topographic map: Patagonia (3497000 m N, 520000 m E). —general lithology is a white-gray (weathered) to gray-white-green with obvious pink feldspar (fresh) granule to sandy pseudomatrix supported subangular granule conglomerate with sparse small subrounded cobbles; significant fine and mud/clay content which is likely the alteration product of tuffaceous materials, which has since become pseudomatrix (pseudomatrix:clast ratio ~60:40); major clast lithology includes, but not limited to, volcanics; some of the sandy detritus may also be granitic, but due to outcrop weathering it is difficult to discern more about the clast content; likely significant tuffaceous material included in this fanglomerate; clast sizes range from abundant sandy detritus to small cobbles 1-2 cm in longest exposed dimension; no evidence for basal scour, cross bedding, tabular cross strata, or basal lag; may have relatively thin (1-2 cm?) lamination, but very difficult to tell due to weathering profile; lumpy, amorphous, weathering-back texture; poorly indurated; many portions of outcrop have slight to significant Mn staining, and there are small hematite veins locally (rare); also some yellow streaks, some along joints; hematite and yellow streaks (jarosite? goethite?) likely associated with abundant Tertiary quartz veining within this area; gradational tops and bases; outcrop at least 10-15 m thick, but cannot here see the base of this unit. —strike/dip unavailable due to weathering profile, outcrop character of sample; will use Drewes (1971a) strike/dip in same area.
138
139
Station 38/990803-3 —Turney Ranch Formation sandstone FT sample from Station 38 along Cave Creek transect, Santa Rita Mountains. —geologic map: Drewes (1971a); topographic map: Mt. Wrightson (3510000 m N, 521000 m E). —sample is a light to dark pink (weathered) to pink lavender (fresh) medium to coarse (subordinate) grained subrounded sandstone; by hand sample, looks like F87M0C10?P3:Q80F5?R15; difficult to tell due to grain size what the potential RF fraction is; two main lithologies sampled in proportion to the proportions within the outcrop; lighter pink structureless, internally homogeneous medium to coarse sandstone is interbedded with thinly bedded, darker pink, finer grained sandstone, which itself has plane parallel laminations; generally will have one lighter pink sandstone bed approximately 5-10 cm thick, topped by 5-10 thinner (1-2 cm each), finer darker pink sandstone beds with intervening homogeneous lighter pink beds of similar thickness, and this sequence repeats throughout outcrop area; contacts between finer and coarser sandstone beds generally sharp; well indurated; no evidence for basal scour or lag, cross stratification; within area of outcrop there are also some fine beds of reddish siltstone, and some mudstone in the receding cutback of Sawmill Canyon; no obvious fining upward sequences, with the exception of the repetition as described above; sampled interval is bounded above and below by rocks of similar lithology and outcrop character; outcrop covers the full extent of the floor of Sawmill Canyon, and top and base of unit are not visible from sample site. —strike/dip: N36W 69SW.
140
Station 42/990805-3 —Fort Crittenden Formation upper red conglomerate member sandstone/conglomerate FT sample from Station 42 along Ditch Mountain transect, Santa Rita Mountains. —geologic map: Drewes (1971a); topographic map: Mt. Wrightson (3507000 m N, 523000 m E). —general lithologies are maroon-brown (weathered) to purple-brown (fresh) “matrix” supported, rounded pebble and small cobble conglomerate and coarse sandstone; sandstones and conglomerates are well-interleaved, and cobbles/pebbles are well mixed within “matrix” of finer particles; major clast lithologies in the conglomerate include, but are not limited to, abundant sandstone, abundant red mudstone, abundant red claystone, sparse green sandstone, sparse chert, sparse finely laminated limestone (which looks like clasts of Apache Canyon Formation or Mural Formation, Bisbee Group); there may also be significant granitic detritus, but it is difficult to tell if it’s granitic, or if it is recycled sandstone; it is also difficult to discern whether or not these were large clasts which have since been degraded, or if the detritus was sand-sized during deposition; clast sizes range from mud and probable clay grain sizes up to a maximum longest exposed dimension of 10-12 cm; sandstones are well-mixed vertically with conglomerates, and appear as lenses as well as discrete beds; granule and sand compositions are difficult to discern in sandstones, but they appear to be broadly similar to the clasts in the conglomerates; by hand sample on medium sand fraction, F80M5C5P10:Q55F15R30; there is some evidence for basal scour and lag at bases of conglomerate beds where they cut into sandstones beneath; this is the only clear evidence that these beds are stratigraphically upright; sandstones have limited calcite cement; vague plane laminae in some sandstones, on the order of 1-2 cm thick, but no evidence for other types of stratification or cross stratification; the conglomerate is crudely, thinly to thickly bedded, and beds are on the order of 2-10 cm thick; tops of both the sandstone and conglomerate are generally gradational, and bases of most conglomerates and sandstones are sharp (though there are sparse gradational bases in both within the interval sampled); all beds are moderately to well indurated, particularly in comparison with surrounding beds; beds above and below are very similar lithologically, and show similar outcrop character; outcrop continuous within this gulch. —strike/dip: N16W 64NE.
141
142
Station 44/990805-5 —Lower Bathtub Formation polymictic conglomerate FT sample from Station 44 along Ditch Mountain transect, Santa Rita Mountains. —geologic map: Drewes (1971a); topographic map: Mt. Wrightson (3506000 m N, 520000 m E). —general lithology is a brown (weathered/fresh), clast-supported subrounded to rounded large cobble conglomerate; dominant clast lithology is an almost porphyritic andesite; subordinate clast lithologies include rhyolite and chert; it is difficult due to exposure to tell percentages of clast types; grain sizes range from mud to the largest clasts which are approximately 15-20 cm in longest exposed dimension; grain sizes and lithologies are well mixed, the former perhaps suggesting a debris flow origin; no evidence for basal scour or lag, lamination, or cross stratification; internal contacts appear gradational; interval is crudely bedded, with beds on the order of 0.5-1 m in thickness; sampled interval is likely bounded above and below by finer lithologies, based on outcrop character (difficult to discern due to poor outcrop); sampled interval is approximately 2 m thick, with covered top and base. —strike/dip: N30W 24SW.
143
Station 45/000724-1 —Fort Crittenden Formation basal conglomerate subunit sandstone FT sample from Station 45 along N Brushy transect, Huachuca Mountains. —geologic map: Hayes and Raup (1968); topographic map: Pyeatt Ranch (3486000 m N, 551800 m E). —sample is an olive (weathered) to gray (fresh) coarse to medium grained angular to subangular sandstone; by hand sample, F80M5C5P10:Q30F2R78; RF fraction mostly VRF (dark purple-gray, angular); moderately well sorted mineralogically, well size sorted; at least partially cemented by calcite; finer intervals well-indurated; coarser intervals moderately indurated; common plane parallel laminations (individual bed sets 0.5-1 cm and thinner) to low angle trough cross-bedding (bed sets 5-10 cm); sharp upper and lower contacts between beds; interval sampled is a ~1.5 m thick group of interbeds of sandstone within cobble to small boulder conglomerate. —bedding-parallel slickensides ornamented by hematite common to sparse on several bedding planes beneath sampled interval (bedding parallel faults?—flexural slip?); very minor calcite veining in the area. —sample is located within Hayes’ (1986) basal conglomerate subunit, near upper portion. —strike/dip: N33W 26SW.
144
Station 46/000724-2 —Fort Crittenden Formation upper conglomerate subunit sandstone FT sample from Station 46 along N Brushy transect, Huachuca Mountains. —geologic map: Hayes and Raup (1968); topographic map: Pyeatt Ranch (3486000 m N, 551600 m E). —sample is a pink-beige (weathered) to pink-gray (fresh) coarse grained sub-rounded to rounded sandstone with rare rounded pebbles to granules (attempted not to sample pebbles and granular intervals); by hand sample, F85M0C5P10:Q70F3R27; RF fraction include VRF; moderately well sorted mineralogically; well size sorted; at least partially cemented by calcite; very well indurated; significant amount of Fe oxide; sparse to common very low angle trough cross-bedding in bed sets 10-20 cm thick; bases and tops of individual beds gradational; interval sampled is very thick (>50 m thick; refer to Hayes (1986) section), and approximately 75 cm above a pebble to small cobble conglomerate lag (possible channel lag) that overlies a significant thickness of conglomerate (>10 m thick; refer to Hayes (1986) section). —sample is from near the base of a thick sandstone interval near upper part of Hayes’ (1986) upper conglomerate subunit (approximately located stratigraphically on Hayes’ (1986) detailed measured section north of Brushy Canyon). —strike/dip: N34W 50SW.
145
Station 47/000724-3 —Fort Crittenden Formation shale subunit sandstone FT sample from Station 47 along N Brushy transect, Huachuca Mountains. —geologic map: Hayes and Raup (1968); topographic map: Pyeatt Ranch (3486000 m N, 550000 m E). —sample is a brown-gray (weathered) to gray (fresh) medium grained subrounded sandstone; by hand sample, looks like F90M0C10P0:Q80F0R20; R may be chert grains or VRF; moderately well sorted mineralogically; well size sorted; at least partially cemented by calcite; well indurated; common low angle trough cross-bedding in bed sets 5-10 cm thick; sharp bases and tops with interbedded mudstone and shale, with these fine intervals ranging from centimeters to 1 m thick; sample from a ~1 m thick interval of sandstone interbedded with other thicker and thinner sandstones, mudstones, and shales. —highly variable amounts of calcite veining in the area, from abundant to rare; unavoidable, but no portion of sample was veined or associated with veined areas. —sample within the upper part of Hayes’ (1986) shale subunit, Hayes’ (1986) geologic map where dips change from SW to NE. —strike/dip: N37W 35SW.
146
Station 49/000725-1 —Fort Crittenden Formation upper conglomerate? subunit sandstone FT sample from Station 49 along Ferosa transect, Huachuca Mountains. —geologic map: Hayes and Raup (1968); topographic map: Pyeatt Ranch (3489000 m N, 550000 m E). —sample is a red-orange-brown (weathered) to white (fresh) coarse grained sub-angular to sub-rounded sandstone with lags and thin intervals of granules (attempted to avoid the latter in sampling); by hand sample, F90M0C7P3:Q70F10?R20; RF are dark gray to black moderately well rounded grains; rare large (~4 cm in largest exposed dimension) rounded mud rip-up clasts; partially quartz cemented; moderately well indurated; structureless beds 15-20 cm thick (similar beds this thick nearby; difficult to tell here due to jointing); sample from an ~2 m thick interval of sandstone beds with interbedded conglomerate (laterally and vertically gradational with sandstone within 2 m). —sample near top? of upper conglomerate subunit; difficult to tell here due to faulting, folding in this area; particularly difficult to tell going further south along Ferosa Canyon, where there are fault slivers of upper conglomerate next to slivers of basal conglomerate in a repetitive fashion; does not appear to be interbedding of upper and basal (and there wasn’t interbedding or a gradational nature to this contact in Hayes’ (1986) section north of Brushy Canyon); however, it is difficult in this area find other evidence for faulting other than juxtaposition of these units, presence of faults and veining northward along Ferosa Canyon. —strike/dip: N34W 24NE (overturned?—no facing indicators here, map indicates overturning).
147
148
Station 52/000730-2 —Fort Crittenden Formation shale member sandstone FT sample from Station 52 along Ditch Mountain transect, Santa Rita Mountains. —geologic map: Drewes (1971a); topographic map: Mt. Wrightson (3511000 m N, 520000 m E). —sample is a pink-brown (weathered) to purple-gray (fresh) fine to medium grained, subrounded to subangular sandstone; by hand sample, F90M0C8P2:Q93F2R5; sample is well mineralogically sorted, well size sorted; large mud rip-up clasts (2-4 cm in longest exposed dimension) on some bedding planes; sample is very well indurated, at least partially calcite cemented; low angle trough crossbeds common within most layers, in bedsets 15-20 cm thick; beds range from 7-8 cm thick to 30-40 cm thick; sharp tops and bases; sample is from a 2 meter thick sandstone package bounded atop by red shale and below by similar sandstone; thin granule conglomeratic intervals present (2-5 cm and above and within each unit). —strike/dip: N20W 82SW.
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Appendix 3—Description of techniques used in this study
Fission-track Thermochronology
Fission track thermochronology is based on the formation of damage tracks in a crystal lattice
from the spontaneous fission of 238U in nature, and the retention and accumulation of these
damage tracks when samples remain below the closure temperature (235°C ± 25°C for zircon;
Brandon and Vance, 1992). Over time, trace amounts of uranium incorporated into a mineral
structure decay spontaneously by alpha emission or by fission. The fission process creates
spontaneous tracks, or trails of severe damage of the crystal lattice due to the high masses of the
daughter nuclei (atomic numbers 30 through 65; Faure, 1986) moving away from each other as a
large amount of energy is released (approximately 200 MeV; Faure 1986). The density of
spontaneous fission tracks depends upon 238U concentration and the length of time since cooling
through the temperature of track annealing (closure temperature).
The amount of 235U in the zircon, and therefore the amount of 238U in the zircon, is estimated by
measurement of the density of induced fission tracks in an external detector. This method
involves mounting mineral grains in Teflon, and grinding and polishing the mount to reveal a fresh
internal surface of the grain. A pre-annealed mica sheet is attached to this surface to serve as
the external detector; the mica print records the fission of 235U induced during slow neutron
irradiation (which causes only 235U to fission) within a reactor facility.
Both spontaneous fission tracks and induced fission tracks are counted on a polished, acid-
etched surface of the mineral or the detector. Enlargement of the damage zone by etching
reveals the tracks. Track densities are measured by counting etched fission track pits in reflected
light at high magnification (1250x). Spontaneous track densities are measured following
150
irradiation. Generally, densities of tracks must be on the order of 10/cm2 (Fleischer and others,
1975); below this lower limit, a statistically significant number of tracks are difficult to count.
Measured parameters include: the spontaneous track density within the mineral (ρs); the induced
track density within the external detector (ρi); the reactor neutron flux at the time of irradiation (Φ);
and the zeta (ζ) calibration factor for each counter. The latter is a pre-determined calibration
factor between the analyst and internationally accepted natural age standards.
The density of spontaneous fission tracks (ρs) is given by the equation ρs = (tλ)(Nvc238R238η238),
where t = time over which tracks have accumulated; λ = decay constant for fission of 238U
(1.551x10-10 y-1); Nv = number of atoms per unit volume in mineral; c238 = fraction of atoms in the
mineral that are 238U; R238 = length of etchable track of 238U fission fragment in the grain; η238 =
etching efficiency of the mineral (a ratio of the number of tracks revealed to the number that
intersect the etched surface for a given material and etch condition; Fleischer and others, 1975).
The density of induced fission tracks (ρi) is given by the equation ρi = (σΦ)(Nvc235R235η235), where
σ = cross-section for inducing fission of 235U; Φ = thermal neutron flux (neutrons/unit area); Nv =
number of atoms per unit volume in detector; c235 = fraction of atoms in the detector that are 235U;
R235 = length of etchable track of 235U fission fragment in the detector; η235 = etching efficiency
within the detector.
The neutron flux (Φ) is measured by including a dosimeter glass and attached mica at either end
of the tube of grain/mica mounts (Fleischer and others, 1975). The dosimeter glass contains a
known concentration of uranium. By counting the density of a statistically significant number of
track etch pits in the attached mica (which has recorded induced fission tracks in the dosimeter
during neutron bombardment), the neutron flux can be calculated using the following equation: ρd
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= BΦ, where B = σNvRdCdUηD (a constant); σ = cross section for inducing fission of 235U in the
dosimeter; Φ = thermal neutron flux (neutrons/unit area); Nv = number of atoms per unit volume in
dosimeter glass; CdU = fraction of atoms in dosimeter that are 235U in the dosimeter; R235 = length
of an etchable 235U track in the dosimeter; η235 = etching efficiency of the dosimeter. In the
equation above, B is a constant that does not require independent measurement provided that it
remains constant (Fleischer and others, 1975).
The above equations combine to give an equation for the age of the mineral since the last partial
or full resetting:
tgs
iw d= +
1 1λ
ρρ
ζ ρ λln , ( ) ( ) ( ) ( )σ σ ζt s i d z wN N N w= + + +1 1 1 2/ / / / ,
where t = age; λ = total decay constant for 238U (1.551x10-10 y-1); g = geometry factor for mica
external detector (= 2); ρs = spontaneous track density (tracks/cm2); ρi = induced track density in
external detector (tracks/cm2); ρd = spontaneous track density in dosimeter (tracks/cm2); Ns =
density of spontaneous tracks counted; Ni = density of induced tracks counted; Nd = density of
dosimeter tracks counted; ζw = weighted mean zeta calibration factor (see below); σζw = weighted
error of weighted mean zeta factor (see below).
The Zeta factor (ζ) varies among different counters; Zeta is a correction for the difference
between the calculated age of a known standard and the “true” age of that standard as
determined by independent means. The equations that describe this value and the associated
uncertainty are as follows:
ζσ ζ
σw
z j
j
n
z
j
n
j
j
=
−
−
−
−
∑
∑
2
2
1
1
, σ σζw jzj
n
= −
−∑ 2
1
,
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where ( )ζλ
ρρ ρ
λj
t i
s de gstd p
p
= −
1
( ) ( ) ( ) ( )σ σz s i d std stdj N N N t= + + + +1 1 1 2/ / /
tstd = known age of standard
σstd = known error of standard age
Several assumptions are inherent in using the above equations (Fleischer and others, 1975).
The Zeta value is assumed to be constant; ζ is a function of ρs, ρi, and ρd, which are (or should
be) constant. The counted tracks must have been derived only from the spontaneous fission of
uranium or of 235U in the case of induced fission. Methods of etching and track identification must
be the same for spontaneous and induced track counts. Based on counting a series of zircon
standards including zircons from the Fish Canyon tuff (Colorado; 27.90 Ma ± .50 m.y.) and the
Buluk tuff (Kenya; 16.40 Ma ± .20 m.y.), the author’s weighted mean ζ is 352.74 ± 8.09 (one
standard deviation).
Component statistical peak ages were fitted to the single-grain age data using the methodology
and programs presented in Brandon (1992, 1996). In general where less than 15 single-grain
ages were measured, the χ2 age is reported (Galbraith, 1981).
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Cathodoluminescence
Color FT mounts were carbon-coated and cathodoluminescence (CL) images of each FT-dated
grain were taken using an Oxford Instruments photomultiplier-based CL detector mounted on a
JEOL T330A scanning electron microscope; accelerating voltages range from 10-15 kV, as
described in Milliken (1994). CL images assist in differentiating zonation within a grain, degree of
heterogeneity within individual grains, and zonation present within the counted region. The
magnitude of CL response of geologic materials, particularly zircons, is the result of multiple
factors which are difficult to distinguish. These include the degree of metamictization (Chuanyi
and others, 1992) and varying, competing responses from trace element contributions (Hanchar
and Rudnick, 1995). As such, the use of CL remains a qualitative guide for other quantitative
portions of this work.
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Raman Microscopy
Short-range order of the crystal lattice, and therefore the degree of crystallinity of a zircon is
related to the amount of radiation damage, with α-damage being the overwhelming contributor
(Murakami and others, 1991; Nasdala and others, 1995; Nasdala and others, 2001). Raman
microprobe analyses were utilized to determine the short-range order of the crystal lattice within
the FT-counted area, and variations in lattice order among different CL-detected zones.
Representative Raman measurements (2-6 measurements per grain) were made based on the
FT-counted locations, and to characterize zonation detected in the CL images. Raman
measurements were made at the University of Mäinz using a Jobin Yvon LabRam-HR equipped
with an Olympus optical microscope (100x objective, numerical aperture 0.9). Spectra were
excited using the He-Ne 632.8 nm line (3 mW at the sample surface). Wave number accuracies
are ± 0.5 cm-1, with spectral resolution of approximately 0.5 cm-1. Methods, data reduction, and
errors are further discussed in Nasdala and others (2001).
The total possible α-damage dose, or the total amount of damage possible given the eU value
and the crystallization age, are calculated by the following formula:
Da = 8 * (cU*NA*0.9928/M238*106) * (eλ238t-1) + 7 * (cU*NA*0.0072/M235*106) * (eλ235 t-1) + 6 * (cTh*NA/M232*106) * (eλ232 t-1),
where Da = number of a-decay events per mg zircon; cU and cTh are the U and Th concentrations
in the zircon (ppm); NA is Avogadro’s number; M238, M235, and M232 are the molecular weights of
the parent isotopes; λ238, λ235, and λ232 are the decay constants for each of the parent isotopes;
and t is age (in this case, the crystallization age).
Accumulated α-damage dose, or the amount of damage stored based on the present crystallinity
of the grain, is calculated given the eU value and the amount of time required to achieve the
present level of damage. The equation cited above is utilized to calculate this value, with t in this
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case is the minimum damage storage age (the time required to achieve the present level of α-
damage).
156
U-Th-Pb and Rare-earth-element Analysis
To complement the crystallinity measurements and determine the total possible and accumulated
α-damage within each crystal, FT-dated zircons were analyzed for Pb, U, and Th within the FT-
counted area using laser ablation inductively-coupled mass spectrometry (LA-ICP-MS). FT-dated
grains were also analyzed for heavy and light REE using LA-ICP-MS, using the same spot
location as the Pb, U, and Th analyses.
The University of Texas LA-ICP-MS system (Platform quadrapole ICP-MS) utilizes an LUV 213
Nd:YAG laser which generates a 200 mJ beam at 1064 nm. The laser beam is polarized and
then passes through a series of harmonic resonators resulting in a final laser beam of up to 5 mJ
of 213 nm ultraviolet light. Based on grain behavior and machine response, the laser was used at
40-50% maximum power with 30-40 µm actual spot sizes. Material from the ablation pit is
injected into the plasma, extracted to the Hexapole cell, ionized, and passed through the
quadrapole mass analyzer to a single Daly-cup detector. For each grain a series of 78 scans of
all masses of interest was made (28Si, 91Zr, 96Zr, all REE, 176Hf, 179Hf, 206Pb, 207Pb, 208Pb, 232Th,
and 238U).
For calculation of Pb-Pb ages, the number of counts per second (CPS) of 206Pb and 207Pb were
ratioed against one another for multiple sequential analyses (up to 78) of each grain during the
sample run. The total number of scans for each grain was divided into three groups, and the
blank-subtracted averages of these groups were used to calculate the concentration ages for the
majority of grains for which FT, crystallinity measurements, and REE compositions were
determined. Precision estimates for the ages were determined by finding the standard deviation
of the three counts-per-second averages over the course of the 78 runs; the standard deviation of
these values is then used as the uncertainty (one standard deviation).
157
232Th, 238U, 235U, and REE concentrations were calculated based on CPS measurements from the
LA-ICP-MS. Reduction of these data for the unknown zircons involves comparison of counts per
second for a given element over the run time with solution concentration data for a standard
zircon (zircon UT-01, from the University of Texas at Austin Vargas Mineral Collection), and with
concentrations of Zr from electron microprobe analysis of the unknown zircons (analyzed at
Rensselaer Polytechnic Institute by K. Becker; Appendix 6). The UT-01 standard zircon was
dissolved and analyzed using the Platform quadrapole ICP-MS (analysis completed by J.
Lansdown, University of Texas). Data reduction procedure for calculation of the concentrations
follows.
A concentration/CPS (slope) for the element of interest is calculated by taking the concentration
of the element (determined by solution analysis of UT-01) and dividing this value by the
concentration of 96Zr (determined by solution analysis of UT-01), yielding a concentration ratio.
The CPS of the element of interest divided by CPS 96Zr yields a CPS ratio. The concentration
ratio is divided by the CPS ratio for each run of UT-01. An average of these values yields an
average concentration/CPS; this is the number (slope) by which the CPS and microprobe 96Zr
values are multiplied in the following procedure. The same procedure was completed for Hf, to
verify that similar values resulted. This analysis treats the solution concentration values for both
238U and 96Zr as ‘true’ values. This is not an issue for comparison of relative concentrations of
each element, since the same 96Zr concentration is used for each element as the standard.
The blank-subtracted CPS of the element of interest is divided by the blank-subtracted CPS of
96Zr (for a given grain). This value is multiplied by the concentration/CPS (slope) for the isotope
of interest, and by the microprobe value for 96Zr for that grain; this yields a parts-per-million (ppm)
concentration of the element of interest in a given grain. This analysis treats the microprobe-
158
determined concentration values for 96Zr for each grain as ‘true’ values, in addition to using the
slope (above), which treats the solution values as ‘true.’
Because of the size of the unknown zircons (most 50-75 µm in longest exposed dimension), and
the laser spot sizes (30-45 µm), multiple sequential scan series of each grain were not possible.
Estimates of errors for the concentrations were derived by comparing concentrations of the
element of interest for multiple laser ablation runs of UT-01, calculating an average concentration
for UT-01, and a standard deviation for those data. The blank-subtracted CPS of the element of
interest is divided by the blank-subtracted CPS of 96Zr. This value is multiplied by the
concentration/CPS value (slope) derived for UT-01, and by the ppm Zr (determined for UT-01 by
solution analysis) to derive a concentration of the element of interest in that analysis of UT-01.
These values are then averaged, and compared using the standard deviation as the uncertainty.
The same procedure was completed for Hf, with resulting similar concentrations and standard
deviations. Detection limits for laser ablation analyses were determined by a comparison of laser
analyses of NIST glasses with low concentrations to estimate lower detection limits (0.3 ppm).
COMPARISON OF SPOT SIZES FOR VARIOUS METHODS
Spot sizes varied among the different types of analyses. Spot sizes for Raman microprobe
analysis and LA-ICP-MS approximate the FT-counted area, and CL images were used to verify a
lack of zonation in the analyzed region. Raman measurements were made based on the FT-
counted location, as well as to represent different zones present in the CL images. LA-ICP-MS
data effectively encompass the entire FT-counted region.
159
Appendix 4—Complete fission track data for Jura-Cretaceous sandstone samples, Santa Rita and Huachuca Mountains, southeastern Arizona
abbreviations/symbols RhoS = density of spontaneous tracks (/cm2) Ns = number of spontaneous tracks counted RhoI = density of induced tracks (/cm2) Ni = number of induced tracks counted squares = number of squares counted (area of one counting square for University of Texas
Axioskop = 6.160x10-7 cm2) U+/-2s = ppm uranium, ± 2 standard deviations
160
Upper Cretaceous Fort Crittenden Formation, Station 9 990625-3 (Axioskop, 010412-19) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.968E+05 RELATIVE ERROR (%): 1.92 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 1 2.50E+07 ( 123) 1.79E+07 ( 88) 8 732 158 72.4 54.8 95.5 2 1.41E+07 ( 182) 9.12E+06 ( 118) 21 374 70 79.9 63.0 101.3 3 8.93E+06 ( 99) 6.49E+06 ( 72) 18 266 63 71.6 52.3 98.4 4 1.33E+07 ( 49) 8.93E+06 ( 33) 6 366 127 77.2 48.7 123.8 5 2.01E+07 ( 62) 1.56E+07 ( 48) 5 639 185 67.2 45.4 100.2 6 1.05E+07 ( 103) 6.70E+06 ( 66) 16 275 68 81.1 59.0 112.3 7 6.80E+06 ( 67) 5.99E+06 ( 59) 16 245 64 59.2 41.1 85.5 8 1.52E+07 ( 262) 1.25E+07 ( 216) 28 514 73 63.1 52.2 76.1 9 7.51E+06 ( 74) 9.23E+06 ( 91) 16 379 80 42.5 30.8 58.4 10 1.43E+07 ( 53) 1.00E+07 ( 37) 6 410 135 74.5 48.1 116.6 11 7.98E+06 ( 118) 6.43E+06 ( 95) 24 263 55 64.4 48.9 84.7 12 1.38E+07 ( 102) 1.08E+07 ( 80) 12 444 100 66.4 49.0 90.2 >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.957E+05 RELATIVE ERROR (%): 1.90 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 13 1.35E+07 ( 116) 1.12E+07 ( 97) 14 463 95 61.8 47.0 81.2 14 1.33E+07 ( 98) 6.22E+06 ( 46) 12 256 76 110.0 76.9 159.7 15 1.38E+07 ( 51) 1.27E+07 ( 47) 6 523 153 56.3 37.1 85.6 16 1.61E+07 ( 89) 1.42E+07 ( 79) 9 586 133 58.5 42.7 80.3 17 1.46E+07 ( 54) 1.38E+07 ( 51) 6 568 160 55.0 36.8 82.3 18 2.44E+07 ( 60) 1.38E+07 ( 34) 4 568 195 91.2 59.1 143.3 19 3.31E+07 ( 102) 1.30E+07 ( 40) 5 535 169 131.3 90.6 194.3 20 1.96E+07 ( 145) 8.93E+06 ( 66) 12 367 91 113.4 84.3 154.2 21 2.05E+07 ( 126) 1.07E+07 ( 66) 10 441 109 98.7 72.8 135.1 22 2.02E+07 ( 174) 6.26E+06 ( 54) 14 258 70 165.6 121.7 228.9 23 1.79E+07 ( 231) 9.89E+06 ( 128) 21 407 73 93.1 74.6 116.2 24 2.31E+07 ( 71) 1.62E+07 ( 50) 5 668 190 73.6 50.6 107.9 25 2.52E+07 ( 186) 1.42E+07 ( 105) 12 585 116 91.3 71.5 116.5 26 1.32E+07 ( 73) 1.75E+07 ( 97) 9 720 148 39.2 28.4 53.6 27 1.33E+07 ( 74) 1.17E+07 ( 65) 9 483 121 59.1 41.7 83.8 28 1.34E+07 ( 99) 8.12E+06 ( 60) 12 334 87 85.4 61.4 119.8 29 1.27E+07 ( 78) 9.90E+06 ( 61) 10 408 105 66.3 46.8 94.3 990625-3 (Axioskop, 010412-19) Number of grains = 29 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 26 1.32E+07 ( 73) 1.75E+07 ( 97) 39.2 28.4 53.6 100.0 39.3 28.5 53.9 9 7.51E+06 ( 74) 9.23E+06 ( 91) 42.5 30.8 58.4 71.2 40.6 32.5 50.8 17 1.46E+07 ( 54) 1.38E+07 ( 51) 55.0 36.8 82.3 37.7 43.7 35.9 53.1
161
15 1.38E+07 ( 51) 1.27E+07 ( 47) 56.3 37.1 85.6 35.7 45.8 38.3 54.7 16 1.61E+07 ( 89) 1.42E+07 ( 79) 58.5 42.7 80.3 27.3 48.5 41.4 56.8 27 1.33E+07 ( 74) 1.17E+07 ( 65) 59.1 41.7 83.8 28.2 50.1 43.3 58.0 7 6.80E+06 ( 67) 5.99E+06 ( 59) 59.2 41.1 85.5 32.0 51.2 44.6 58.8 13 1.35E+07 ( 116) 1.12E+07 ( 97) 61.8 47.0 81.2 28.1 53.0 46.7 60.2 8 1.52E+07 ( 262) 1.25E+07 ( 216) 63.1 52.2 76.1 18.9 55.7 49.8 62.4 11 7.98E+06 ( 118) 6.43E+06 ( 95) 64.4 48.9 84.7 19.8 56.7 50.9 63.1 29 1.27E+07 ( 78) 9.90E+06 ( 61) 66.3 46.8 94.3 21.9 57.3 51.6 63.6 12 1.38E+07 ( 102) 1.08E+07 ( 80) 66.4 49.0 90.2 23.4 58.0 52.4 64.2 5 2.01E+07 ( 62) 1.56E+07 ( 48) 67.2 45.4 100.2 26.6 58.4 52.8 64.6 3 8.93E+06 ( 99) 6.49E+06 ( 72) 71.6 52.3 98.4 23.9 59.2 53.7 65.3 1 2.50E+07 ( 123) 1.79E+07 ( 88) 72.4 54.8 95.5 19.7 60.2 54.7 66.2 24 2.31E+07 ( 71) 1.62E+07 ( 50) 73.6 50.6 107.9 19.6 60.7 55.3 66.7 10 1.43E+07 ( 53) 1.00E+07 ( 37) 74.5 48.1 116.6 20.7 61.1 55.7 67.1 4 1.33E+07 ( 49) 8.93E+06 ( 33) 77.2 48.7 123.8 20.9 61.5 56.1 67.4 2 1.41E+07 ( 182) 9.12E+06 ( 118) 79.9 63.0 101.3 9.7 63.0 57.6 68.9 6 1.05E+07 ( 103) 6.70E+06 ( 66) 81.1 59.0 112.3 7.2 63.7 58.3 69.7 28 1.34E+07 ( 99) 8.12E+06 ( 60) 85.4 61.4 119.8 4.5 64.6 59.1 70.5 18 2.44E+07 ( 60) 1.38E+07 ( 34) 91.2 59.1 143.3 3.2 65.1 59.7 71.0 25 2.52E+07 ( 186) 1.42E+07 ( 105) 91.3 71.5 116.5 0.6 66.7 61.3 72.7 23 1.79E+07 ( 231) 9.89E+06 ( 128) 93.1 74.6 116.2 0.1 68.5 63.1 74.5 21 2.05E+07 ( 126) 1.07E+07 ( 66) 98.7 72.8 135.1 0.0 69.6 64.1 75.6 14 1.33E+07 ( 98) 6.22E+06 ( 46) 110.0 76.9 159.7 0.0 70.5 65.0 76.5 20 1.96E+07 ( 145) 8.93E+06 ( 66) 113.4 84.3 154.2 0.0 71.9 66.3 78.0 19 3.31E+07 ( 102) 1.30E+07 ( 40) 131.3 90.6 194.3 0.0 73.1 67.4 79.2 22 2.02E+07 ( 174) 6.26E+06 ( 54) 165.6 121.7 228.9 0.0 75.4 69.6 81.7 POOL 1.46E+07( 3121) 1.01E+07( 2153) 0.0 75.4 69.6 81.7 MEAN URANIUM CONCENTRATION +/-2SE (ppm): 414.3, 23.9 POOLED AGE WITH 63% CONF. INTERVAL(Ma): 75.4, 72.4 -- 78.5 ( -3.0 +3.1) 95% CONF. INTERVAL(Ma): 69.6 -- 81.7 ( -5.8 +6.3) CHI^2 PROBABILITY: 0.0% CENTRAL AGE WITH 63% CONF. INTERVAL(Ma): 74.4, 69.8 -- 79.3 ( -4.6 +4.9) 95% CONF. INTERVAL(Ma): 65.7 -- 84.2 ( -8.7 +9.9) AGE DISPERSION (%): 26.0 CHI^2 AGE WITH 63% CONF. INTERVAL (Ma): 65.1, 62.3 -- 68.1 ( -2.8 +3.0) 95% CONF. INTERVAL (Ma): 59.7 -- 71.0 ( -5.4 +5.9) NUMBER AND PERCENTAGE OF GRAINS: 22, 76%
990625-3Upper Cretaceous Fort Crittenden Formation
Station 9, Huachuca Mountains
n = 29 grains (12 from 15 h etch, 17 from 11 h etch)
FT grain age (Ma)
30 50 70 300 50010 100
Pro
ba
bili
ty d
en
sity (
%/∆
z=
0.1
)
0
1
2
3
4
5
6
162
163
Lower Cretaceous Glance conglomerate, Station 11 990626-1 (Axioskop, 020628-020702) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.946E+05 RELATIVE ERROR (%): 1.88 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 1 2.33E+07 ( 172) 8.52E+06 ( 63) 12 352 89 139.3 104.1 186.1 2 2.11E+07 ( 156) 1.14E+07 ( 84) 12 469 104 95.2 72.8 124.6 3 1.99E+07 ( 98) 9.94E+06 ( 49) 8 411 118 102.9 72.5 148.2 4 2.60E+07 ( 192) 1.38E+07 ( 102) 12 570 115 96.6 75.6 123.4 5 1.92E+07 ( 248) 1.14E+07 ( 147) 21 469 79 86.8 70.3 107.1 6 2.14E+07 ( 158) 1.22E+07 ( 90) 12 503 107 90.1 69.3 117.2 7 2.39E+07 ( 265) 8.30E+06 ( 92) 18 343 72 147.2 115.6 187.2 8 2.44E+07 ( 150) 1.35E+07 ( 83) 10 557 124 92.7 70.6 121.6 9 2.11E+07 ( 117) 1.06E+07 ( 59) 9 440 115 102.1 74.1 142.1 10 1.96E+07 ( 121) 1.20E+07 ( 74) 10 496 116 84.3 62.6 114.3 11 2.68E+07 ( 165) 1.23E+07 ( 76) 10 510 118 111.1 84.4 146.2 12 2.04E+07 ( 151) 7.85E+06 ( 58) 12 324 86 133.6 98.3 184.2 13 3.06E+07 ( 151) 1.30E+07 ( 64) 8 536 135 121.3 90.1 165.2 14 2.65E+07 ( 147) 1.32E+07 ( 73) 9 544 129 103.1 77.6 136.9 15 3.33E+07 ( 164) 1.40E+07 ( 69) 8 578 140 121.5 91.5 161.3 16 2.09E+07 ( 206) 1.32E+07 ( 130) 16 545 98 81.5 65.1 102.1 17 2.48E+07 ( 153) 1.22E+07 ( 75) 10 503 117 104.5 79.0 138.1 18 2.39E+07 ( 147) 9.90E+06 ( 61) 10 409 105 123.8 91.4 169.8 19 1.54E+07 ( 114) 1.08E+07 ( 80) 12 447 101 73.2 54.8 97.7 20 1.66E+07 ( 184) 8.12E+06 ( 90) 18 335 72 104.8 81.1 135.4 21 1.43E+07 ( 88) 8.28E+06 ( 51) 10 342 96 88.9 62.4 128.2 22 2.15E+07 ( 199) 1.07E+07 ( 99) 15 443 90 103.1 80.6 131.8 23 1.76E+07 ( 260) 7.98E+06 ( 118) 24 330 62 113.0 90.4 141.2 24 2.00E+07 ( 332) 9.26E+06 ( 154) 27 383 63 110.7 90.8 134.9 25 1.64E+07 ( 363) 8.97E+06 ( 199) 36 371 54 93.9 78.3 112.5 26 1.89E+07 ( 210) 8.21E+06 ( 91) 18 339 72 118.2 92.0 151.7 27 2.61E+07 ( 257) 1.40E+07 ( 138) 16 578 101 95.7 77.3 118.4 28 2.44E+07 ( 240) 8.93E+06 ( 88) 16 369 80 139.4 108.8 178.6 29 2.49E+07 ( 245) 1.02E+07 ( 101) 16 423 86 124.2 98.1 157.3 30 1.62E+07 ( 120) 1.01E+07 ( 75) 12 419 98 82.1 61.3 109.9 >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.935E+05 RELATIVE ERROR (%): 1.85 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 31 3.54E+07 ( 218) 1.44E+07 ( 89) 10 599 129 124.9 97.2 160.4 32 2.97E+07 ( 183) 1.19E+07 ( 73) 10 491 116 127.6 97.0 167.8 33 2.65E+07 ( 163) 1.27E+07 ( 78) 10 525 120 106.6 81.1 140.1 34 5.25E+07 ( 291) 1.08E+07 ( 60) 9 449 117 244.3 185.0 322.2 35 3.21E+07 ( 237) 1.34E+07 ( 99) 12 555 113 122.2 96.2 155.1 990626-1 (Axioskop, 020628-020702) ------ GRAIN AGES IN ORIGINAL ORDER ------
164
Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 36 2.46E+07 ( 227) 1.36E+07 ( 126) 15 565 103 92.2 73.8 115.3 37 2.72E+07 ( 201) 1.83E+07 ( 135) 12 757 133 76.4 61.0 95.5 38 2.42E+07 ( 149) 1.49E+07 ( 92) 10 619 131 82.9 63.6 107.9 39 1.70E+07 ( 251) 1.01E+07 ( 149) 24 418 70 86.3 70.0 106.4 40 3.53E+07 ( 435) 4.55E+06 ( 56) 20 188 51 386.8 293.5 508.4 41 2.94E+07 ( 145) 1.70E+07 ( 84) 8 707 156 88.3 67.2 115.8 42 3.85E+07 ( 166) 1.37E+07 ( 59) 7 567 149 143.8 106.5 197.0 990626-1 (Axioskop, 020628-020702) Number of grains = 42 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 19 1.54E+07 ( 114) 1.08E+07 ( 80) 73.2 54.8 97.7 100.0 73.2 54.8 97.7 37 2.72E+07 ( 201) 1.83E+07 ( 135) 76.4 61.0 95.5 82.7 75.3 62.8 90.3 16 2.09E+07 ( 206) 1.32E+07 ( 130) 81.5 65.1 102.1 83.2 77.8 67.1 90.1 30 1.62E+07 ( 120) 1.01E+07 ( 75) 82.1 61.3 109.9 91.8 78.6 68.7 90.0 38 2.42E+07 ( 149) 1.49E+07 ( 92) 82.9 63.6 107.9 95.7 79.5 70.2 90.0 10 1.96E+07 ( 121) 1.20E+07 ( 74) 84.3 62.6 114.3 97.7 80.1 71.2 90.1 39 1.70E+07 ( 251) 1.01E+07 ( 149) 86.3 70.0 106.4 97.4 81.4 73.1 90.7 5 1.92E+07 ( 248) 1.14E+07 ( 147) 86.8 70.3 107.1 97.9 82.4 74.4 91.2 41 2.94E+07 ( 145) 1.70E+07 ( 84) 88.3 67.2 115.8 98.5 82.9 75.1 91.5 21 1.43E+07 ( 88) 8.28E+06 ( 51) 88.9 62.4 128.2 99.1 83.2 75.5 91.7 6 2.14E+07 ( 158) 1.22E+07 ( 90) 90.1 69.3 117.2 99.2 83.8 76.3 92.1 36 2.46E+07 ( 227) 1.36E+07 ( 126) 92.2 73.8 115.3 98.9 84.7 77.3 92.8 8 2.44E+07 ( 150) 1.35E+07 ( 83) 92.7 70.6 121.6 99.0 85.3 78.0 93.2 25 1.64E+07 ( 363) 8.97E+06 ( 199) 93.9 78.3 112.5 98.1 86.4 79.3 94.1 2 2.11E+07 ( 156) 1.14E+07 ( 84) 95.2 72.8 124.6 98.2 86.9 79.9 94.5 27 2.61E+07 ( 257) 1.40E+07 ( 138) 95.7 77.3 118.4 97.8 87.6 80.7 95.2 4 2.60E+07 ( 192) 1.38E+07 ( 102) 96.6 75.6 123.4 97.7 88.2 81.3 95.6 9 2.11E+07 ( 117) 1.06E+07 ( 59) 102.1 74.1 142.1 97.4 88.6 81.7 96.0 3 1.99E+07 ( 98) 9.94E+06 ( 49) 102.9 72.5 148.2 97.2 89.0 82.1 96.4 22 2.15E+07 ( 199) 1.07E+07 ( 99) 103.1 80.6 131.8 95.6 89.7 82.8 97.0 14 2.65E+07 ( 147) 1.32E+07 ( 73) 103.1 77.6 136.9 94.8 90.1 83.4 97.5 17 2.48E+07 ( 153) 1.22E+07 ( 75) 104.5 79.0 138.1 93.7 90.7 83.9 98.0 20 1.66E+07 ( 184) 8.12E+06 ( 90) 104.8 81.1 135.4 92.0 91.2 84.5 98.5 33 2.65E+07 ( 163) 1.27E+07 ( 78) 106.6 81.1 140.1 90.1 91.8 85.0 99.1 24 2.00E+07 ( 332) 9.26E+06 ( 154) 110.7 90.8 134.9 77.8 93.0 86.2 100.2 11 2.68E+07 ( 165) 1.23E+07 ( 76) 111.1 84.4 146.2 73.1 93.5 86.8 100.8 23 1.76E+07 ( 260) 7.98E+06 ( 118) 113.0 90.4 141.2 61.6 94.4 87.6 101.6 26 1.89E+07 ( 210) 8.21E+06 ( 91) 118.2 92.0 151.7 48.2 95.2 88.4 102.4 13 3.06E+07 ( 151) 1.30E+07 ( 64) 121.3 90.1 165.2 39.4 95.8 89.0 103.0 15 3.33E+07 ( 164) 1.40E+07 ( 69) 121.5 91.5 161.3 30.6 96.4 89.6 103.7 35 3.21E+07 ( 237) 1.34E+07 ( 99) 122.2 96.2 155.1 19.4 97.2 90.5 104.5 18 2.39E+07 ( 147) 9.90E+06 ( 61) 123.8 91.4 169.8 15.2 97.8 91.0 105.1 29 2.49E+07 ( 245) 1.02E+07 ( 101) 124.2 98.1 157.3 8.7 98.6 91.8 106.0 31 3.54E+07 ( 218) 1.44E+07 ( 89) 124.9 97.2 160.4 5.3 99.4 92.5 106.7 32 2.97E+07 ( 183) 1.19E+07 ( 73) 127.6 97.0 167.8 3.3 100.0 93.2 107.4 12 2.04E+07 ( 151) 7.85E+06 ( 58) 133.6 98.3 184.2 2.0 100.6 93.7 107.9 1 2.33E+07 ( 172) 8.52E+06 ( 63) 139.3 104.1 186.1 0.8 101.3 94.4 108.7 990626-1 (Axioskop, 020628-020702) Number of grains = 42 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 28 2.44E+07 ( 240) 8.93E+06 ( 88) 139.4 108.8 178.6 0.2 102.3 95.3 109.7 42 3.85E+07 ( 166) 1.37E+07 ( 59) 143.8 106.5 197.0 0.1 102.9 96.0 110.4
165
7 2.39E+07 ( 265) 8.30E+06 ( 92) 147.2 115.6 187.2 0.0 104.1 97.1 111.6 34 5.25E+07 ( 291) 1.08E+07 ( 60) 244.3 185.0 322.2 0.0 106.3 99.2 114.0 40 3.53E+07 ( 435) 4.55E+06 ( 56) 386.8 293.5 508.4 0.0 110.6 103.2 118.5 POOL 2.33E+07( 8239) 1.09E+07( 3837) 0.0 110.6 103.2 118.5 MEAN URANIUM CONCENTRATION +/-2SE (ppm): 448.3, 22.2 POOLED AGE WITH 63% CONF. INTERVAL(Ma): 110.6, 106.8 -- 114.6 ( -3.8 +4.0) 95% CONF. INTERVAL(Ma): 103.2 -- 118.5 ( -7.4 +7.9) CHI^2 PROBABILITY: 0.0% CENTRAL AGE WITH 63% CONF. INTERVAL(Ma): 108.8, 103.4 -- 114.5 ( -5.4 +5.7) 95% CONF. INTERVAL(Ma): 98.5 -- 120.2 ( -10.3 +11.4) AGE DISPERSION (%): 23.8 CHI^2 AGE WITH 63% CONF. INTERVAL (Ma): 100.6, 97.0 -- 104.3 ( -3.6 +3.7) 95% CONF. INTERVAL (Ma): 93.7 -- 107.9 ( -6.9 +7.4) NUMBER AND PERCENTAGE OF GRAINS: 36, 86%
166
990626-1Lower Cretaceous Glance conglomerate
Station 11, Huachuca Mountains
n = 42 grains (30 from 17 h etch, 12 from 12 h etch)
FT grain age (Ma)
30 50 70 300 50070010 1000
1
2
3
4
5
6
7
8
9
10
Pro
ba
bili
ty d
en
sity (
%/∆
z=
0.1
)
167
Upper Cretaceous Fort Crittenden Formation, Station 13 990628-1 (Axioskop, 010419-010502) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.925E+05 RELATIVE ERROR (%): 1.83 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 1 1.73E+07 ( 96) 1.05E+07 ( 58) 9 435 115 84.7 60.6 119.6 2 1.89E+07 ( 70) 1.68E+07 ( 62) 6 698 178 58.0 40.6 83.0 3 1.79E+07 ( 66) 1.62E+07 ( 60) 6 675 175 56.5 39.2 81.5 4 2.07E+07 ( 115) 5.95E+06 ( 33) 9 248 86 176.7 119.8 268.2 5 1.23E+07 ( 228) 1.42E+07 ( 262) 30 590 76 44.7 37.1 53.8 6 1.78E+07 ( 197) 9.29E+06 ( 103) 18 386 77 97.5 76.4 124.2 7 2.31E+07 ( 142) 9.42E+06 ( 58) 10 392 103 124.9 91.6 172.6 8 1.41E+07 ( 61) 7.65E+06 ( 33) 7 318 111 94.5 61.1 148.9 9 9.44E+06 ( 93) 9.84E+06 ( 97) 16 409 84 49.0 36.8 65.4 10 1.43E+07 ( 88) 1.19E+07 ( 73) 10 493 116 61.9 44.8 85.6 11 4.09E+07 ( 151) 1.19E+07 ( 44) 6 495 150 174.2 124.3 249.3 12 1.58E+07 ( 117) 1.08E+07 ( 80) 12 450 102 74.6 55.9 99.4 13 1.68E+07 ( 124) 1.15E+07 ( 85) 12 478 105 74.4 56.3 98.4 14 1.98E+07 ( 73) 9.20E+06 ( 34) 6 383 131 109.6 72.2 169.7 15 1.81E+07 ( 178) 1.22E+07 ( 120) 16 507 94 75.8 59.8 96.0 16 1.38E+07 ( 170) 5.28E+06 ( 65) 20 220 55 132.6 99.4 176.7 17 1.04E+07 ( 64) 1.54E+07 ( 95) 10 642 133 34.7 24.8 48.2 18 1.50E+07 ( 111) 1.43E+07 ( 106) 12 597 118 53.6 40.9 70.2 19 1.23E+07 ( 114) 1.14E+07 ( 105) 15 473 94 55.5 42.4 72.7 20 1.28E+07 ( 71) 1.52E+07 ( 84) 9 630 139 43.5 31.2 60.4 21 1.48E+07 ( 91) 8.77E+06 ( 54) 10 365 100 86.3 61.0 123.2 22 1.40E+07 ( 69) 7.51E+06 ( 37) 8 312 103 95.3 63.2 146.2 23 1.38E+07 ( 34) 1.34E+07 ( 33) 4 557 194 52.9 31.8 88.1 24 2.53E+07 ( 218) 1.17E+07 ( 101) 14 487 98 109.9 86.4 139.7 >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.914E+05 RELATIVE ERROR (%): 1.81 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 25 3.66E+07 ( 361) 3.65E+06 ( 36) 16 153 51 493.8 354.6 708.5 26 1.79E+07 ( 110) 1.69E+07 ( 104) 10 705 140 53.9 41.0 70.8 27 2.33E+07 ( 172) 1.45E+07 ( 107) 12 605 119 81.7 63.9 104.5 28 2.46E+07 ( 91) 1.24E+07 ( 46) 6 520 154 100.7 70.0 146.9 29 2.11E+07 ( 52) 8.93E+06 ( 22) 4 373 158 119.8 72.0 207.0 30 3.12E+07 ( 77) 1.30E+07 ( 32) 4 542 191 122.1 80.3 190.5 31 1.66E+07 ( 123) 8.79E+06 ( 65) 12 367 92 96.4 70.9 132.4 990628-1 (Axioskop, 010419-010502) Number of grains = 31 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 17 1.04E+07 ( 64) 1.54E+07 ( 95) 34.7 24.8 48.2 100.0 34.7 24.8 48.2
168
20 1.28E+07 ( 71) 1.52E+07 ( 84) 43.5 31.2 60.4 32.0 38.7 30.8 48.7 5 1.23E+07 ( 228) 1.42E+07 ( 262) 44.7 37.1 53.8 37.8 42.3 36.4 49.1 9 9.44E+06 ( 93) 9.84E+06 ( 97) 49.0 36.8 65.4 41.8 43.5 38.0 49.9 23 1.38E+07 ( 34) 1.34E+07 ( 33) 52.9 31.8 88.1 48.9 44.1 38.6 50.4 18 1.50E+07 ( 111) 1.43E+07 ( 106) 53.6 40.9 70.2 39.1 45.6 40.3 51.6 26 1.79E+07 ( 110) 1.69E+07 ( 104) 53.9 41.0 70.8 36.5 46.7 41.6 52.5 19 1.23E+07 ( 114) 1.14E+07 ( 105) 55.5 42.4 72.7 33.0 47.8 42.8 53.4 3 1.79E+07 ( 66) 1.62E+07 ( 60) 56.5 39.2 81.5 35.5 48.4 43.4 53.9 2 1.89E+07 ( 70) 1.68E+07 ( 62) 58.0 40.6 83.0 36.2 49.0 44.1 54.4 10 1.43E+07 ( 88) 1.19E+07 ( 73) 61.9 44.8 85.6 29.2 49.8 45.0 55.2 13 1.68E+07 ( 124) 1.15E+07 ( 85) 74.4 56.3 98.4 5.0 51.7 46.8 57.0 12 1.58E+07 ( 117) 1.08E+07 ( 80) 74.6 55.9 99.4 1.1 53.2 48.3 58.5 15 1.81E+07 ( 178) 1.22E+07 ( 120) 75.8 59.8 96.0 0.1 55.2 50.3 60.5 27 2.33E+07 ( 172) 1.45E+07 ( 107) 81.7 63.9 104.5 0.0 57.1 52.2 62.5 1 1.73E+07 ( 96) 1.05E+07 ( 58) 84.7 60.6 119.6 0.0 58.2 53.2 63.6 21 1.48E+07 ( 91) 8.77E+06 ( 54) 86.3 61.0 123.2 0.0 59.1 54.2 64.6 8 1.41E+07 ( 61) 7.65E+06 ( 33) 94.5 61.1 148.9 0.0 59.9 54.9 65.3 22 1.40E+07 ( 69) 7.51E+06 ( 37) 95.3 63.2 146.2 0.0 60.7 55.6 66.2 31 1.66E+07 ( 123) 8.79E+06 ( 65) 96.4 70.9 132.4 0.0 62.0 56.9 67.6 6 1.78E+07 ( 197) 9.29E+06 ( 103) 97.5 76.4 124.2 0.0 64.1 58.9 69.7 28 2.46E+07 ( 91) 1.24E+07 ( 46) 100.7 70.0 146.9 0.0 65.0 59.8 70.6 14 1.98E+07 ( 73) 9.20E+06 ( 34) 109.6 72.2 169.7 0.0 65.8 60.6 71.4 24 2.53E+07 ( 218) 1.17E+07 ( 101) 109.9 86.4 139.7 0.0 68.0 62.7 73.8 29 2.11E+07 ( 52) 8.93E+06 ( 22) 119.8 72.0 207.0 0.0 68.6 63.3 74.4 30 3.12E+07 ( 77) 1.30E+07 ( 32) 122.1 80.3 190.5 0.0 69.4 64.1 75.3 7 2.31E+07 ( 142) 9.42E+06 ( 58) 124.9 91.6 172.6 0.0 71.0 65.5 76.9 16 1.38E+07 ( 170) 5.28E+06 ( 65) 132.6 99.4 176.7 0.0 72.8 67.3 78.8 11 4.09E+07 ( 151) 1.19E+07 ( 44) 174.2 124.3 249.3 0.0 74.9 69.2 81.0 4 2.07E+07 ( 115) 5.95E+06 ( 33) 176.7 119.8 268.2 0.0 76.4 70.7 82.6 25 3.66E+07 ( 361) 3.65E+06 ( 36) 493.8 354.6 708.5 0.0 83.2 77.0 89.9 POOL 1.78E+07( 3727) 1.10E+07( 2296) 0.0 83.2 77.0 89.9 MEAN URANIUM CONCENTRATION +/-2SE (ppm): 457.4, 25.4 POOLED AGE WITH 63% CONF. INTERVAL(Ma): 83.2, 80.0 -- 86.5 ( -3.2 +3.3) 95% CONF. INTERVAL(Ma): 77.0 -- 89.9 ( -6.2 +6.7) CHI^2 PROBABILITY: 0.0% CENTRAL AGE WITH 63% CONF. INTERVAL(Ma): 81.9, 75.0 -- 89.4 ( -6.9 +7.5) 95% CONF. INTERVAL(Ma): 68.9 -- 97.3 ( -13.0 +15.4) AGE DISPERSION (%): 43.8 CHI^2 AGE WITH 63% CONF. INTERVAL (Ma): 53.2, 50.6 -- 55.8 ( -2.6 +2.7) 95% CONF. INTERVAL (Ma): 48.3 -- 58.5 ( -4.9 +5.4) NUMBER AND PERCENTAGE OF GRAINS: 13, 42%
169
Pro
ba
bili
ty d
en
sity (
%/∆
z=
0.1
)990628-1
Upper Cretaceous Fort Crittenden FormationStation 13, Huachuca Mountains
n = 31 grains (24 from 15 h etch, 7 from 11 h etch)
FT grain age (Ma)
30 50 70 300 50070010 1000
1
2
3
4
5
6
7
170
Lower Cretaceous Cintura Formation, Station 14 990628-2b/A (U16Z) & 990628-2b/a (U26Z) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.903E+05 RELATIVE ERROR (%): 1.79 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 1 2.54E+07 ( 188) 1.08E+06 ( 8) 12 45 31 1083.7 571.4 2346.4 2 2.80E+07 ( 138) 1.62E+06 ( 8) 8 68 47 813.1 421.3 1809.1 3 3.98E+07 ( 245) 1.79E+06 ( 11) 10 75 44 1036.4 596.9 1979.4 4 2.29E+07 ( 141) 5.52E+06 ( 34) 10 231 79 208.2 143.3 311.5 5 2.52E+07 ( 217) 5.10E+06 ( 44) 14 214 65 247.0 179.0 348.7 6 3.23E+07 ( 199) 4.87E+06 ( 30) 10 204 74 329.5 226.1 497.8 7 1.91E+07 ( 106) 7.03E+06 ( 39) 9 295 94 137.3 94.7 203.5 8 2.11E+07 ( 156) 3.92E+06 ( 29) 12 164 61 268.5 181.5 412.0 9 2.62E+07 ( 194) 1.89E+06 ( 14) 12 79 42 666.2 399.5 1203.9 10 3.26E+07 ( 321) 4.06E+06 ( 40) 16 170 54 396.9 288.0 561.9 11 1.89E+07 ( 93) 8.12E+06 ( 40) 8 340 108 117.7 80.7 175.0 >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.892E+05 RELATIVE ERROR (%): 1.77 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 12 2.77E+07 ( 256) 1.30E+06 ( 12) 15 55 31 993.5 584.1 1844.9 13 3.04E+07 ( 375) 5.93E+06 ( 73) 20 249 59 255.2 198.3 327.8 14 2.31E+07 ( 171) 6.22E+06 ( 46) 12 262 77 186.4 134.5 263.7 >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.975E+05 RELATIVE ERROR (%): 1.51 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 15 1.59E+07 ( 343) 4.45E+06 ( 96) 35 182 37 183.9 146.2 231.1 16 2.37E+07 ( 204) 4.75E+06 ( 41) 14 194 61 255.1 183.0 364.7 17 2.33E+07 ( 287) 6.25E+06 ( 77) 20 256 59 191.5 148.6 246.4 18 2.26E+07 ( 279) 5.76E+06 ( 71) 20 236 56 201.6 155.2 261.6 19 2.13E+07 ( 328) 4.22E+06 ( 65) 25 173 43 257.6 197.4 335.6 990628-2b/A (U16Z) & 990628-2b/a (U26Z) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.968E+05 RELATIVE ERROR (%): 1.49 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07
171
------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 20 1.65E+07 ( 122) 4.73E+06 ( 35) 12 194 65 179.3 123.1 268.5 21 2.88E+07 ( 266) 2.71E+06 ( 25) 15 111 44 531.1 358.5 822.4 22 2.50E+07 ( 246) 5.28E+06 ( 52) 16 216 60 242.4 180.1 332.5 23 2.16E+07 ( 200) 1.62E+07 ( 150) 15 666 110 69.2 55.7 86.0 24 2.35E+07 ( 116) 5.88E+06 ( 29) 8 241 89 205.2 136.8 318.7 25 2.24E+07 ( 331) 9.13E+06 ( 135) 24 374 65 126.6 103.2 155.4 26 1.97E+07 ( 327) 3.97E+06 ( 66) 27 163 40 252.4 193.8 328.4 27 1.60E+07 ( 158) 8.93E+06 ( 88) 16 366 79 92.8 71.3 120.8 28 1.52E+07 ( 225) 4.40E+06 ( 65) 24 180 45 177.4 134.5 233.8 29 2.31E+07 ( 171) 5.82E+06 ( 43) 12 239 73 204.3 146.4 291.7 30 2.58E+07 ( 143) 4.87E+06 ( 27) 9 200 76 270.1 180.0 421.6 31 1.47E+07 ( 127) 5.91E+06 ( 51) 14 242 68 128.8 92.7 181.8 32 2.22E+07 ( 137) 9.58E+06 ( 59) 10 393 102 120.2 88.2 166.0 33 2.53E+07 ( 374) 4.40E+06 ( 65) 24 180 45 292.2 224.7 379.4 990628-2b/A (U16Z) & 990628-2b/a (U26Z) Number of grains = 33 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 23 2.16E+07 ( 200) 1.62E+07 ( 150) 69.2 55.7 86.0 100.0 69.2 55.6 86.1 27 1.60E+07 ( 158) 8.93E+06 ( 88) 92.8 71.3 120.8 8.4 78.1 65.7 92.9 11 1.89E+07 ( 93) 8.12E+06 ( 40) 117.7 80.7 175.0 2.9 84.0 71.6 98.5 32 2.22E+07 ( 137) 9.58E+06 ( 59) 120.2 88.2 166.0 0.9 90.3 78.1 104.4 25 2.24E+07 ( 331) 9.13E+06 ( 135) 126.6 103.2 155.4 0.1 100.8 89.0 114.2 31 1.47E+07 ( 127) 5.91E+06 ( 51) 128.8 92.7 181.8 0.1 103.6 91.9 116.7 7 1.91E+07 ( 106) 7.03E+06 ( 39) 137.3 94.7 203.5 0.0 106.0 94.4 119.0 28 1.52E+07 ( 225) 4.40E+06 ( 65) 177.4 134.5 233.8 0.0 113.5 101.7 126.7 20 1.65E+07 ( 122) 4.73E+06 ( 35) 179.3 123.1 268.5 0.0 117.1 105.1 130.3 15 1.59E+07 ( 343) 4.45E+06 ( 96) 183.9 146.2 231.1 0.0 125.6 113.5 139.0 14 2.31E+07 ( 171) 6.22E+06 ( 46) 186.4 134.5 263.7 0.0 129.2 117.0 142.7 17 2.33E+07 ( 287) 6.25E+06 ( 77) 191.5 148.6 246.4 0.0 134.8 122.5 148.3 18 2.26E+07 ( 279) 5.76E+06 ( 71) 201.6 155.2 261.6 0.0 139.9 127.4 153.5 29 2.31E+07 ( 171) 5.82E+06 ( 43) 204.3 146.4 291.7 0.0 142.7 130.2 156.3 24 2.35E+07 ( 116) 5.88E+06 ( 29) 205.2 136.8 318.7 0.0 144.5 131.9 158.2 4 2.29E+07 ( 141) 5.52E+06 ( 34) 208.2 143.3 311.5 0.0 146.6 134.0 160.3 22 2.50E+07 ( 246) 5.28E+06 ( 52) 242.4 180.1 332.5 0.0 151.1 138.4 165.0 5 2.52E+07 ( 217) 5.10E+06 ( 44) 247.0 179.0 348.7 0.0 154.9 142.0 169.0 26 1.97E+07 ( 327) 3.97E+06 ( 66) 252.4 193.8 328.4 0.0 160.3 147.2 174.6 16 2.37E+07 ( 204) 4.75E+06 ( 41) 255.1 183.0 364.7 0.0 163.4 150.2 177.8 13 3.04E+07 ( 375) 5.93E+06 ( 73) 255.2 198.3 327.8 0.0 168.7 155.2 183.2 19 2.13E+07 ( 328) 4.22E+06 ( 65) 257.6 197.4 335.6 0.0 172.9 159.3 187.6 8 2.11E+07 ( 156) 3.92E+06 ( 29) 268.5 181.5 412.0 0.0 174.9 161.2 189.7 30 2.58E+07 ( 143) 4.87E+06 ( 27) 270.1 180.0 421.6 0.0 176.7 163.0 191.5 33 2.53E+07 ( 374) 4.40E+06 ( 65) 292.2 224.7 379.4 0.0 181.7 167.8 196.8 6 3.23E+07 ( 199) 4.87E+06 ( 30) 329.5 226.1 497.8 0.0 184.7 170.6 199.9 10 3.26E+07 ( 321) 4.06E+06 ( 40) 396.9 288.0 561.9 0.0 190.3 175.9 205.8 21 2.88E+07 ( 266) 2.71E+06 ( 25) 531.1 358.5 822.4 0.0 195.7 181.0 211.6 9 2.62E+07 ( 194) 1.89E+06 ( 14) 666.2 399.5 1203.9 0.0 200.0 185.0 216.2 2 2.80E+07 ( 138) 1.62E+06 ( 8) 813.1 421.3 1809.1 0.0 203.3 188.1 219.7 12 2.77E+07 ( 256) 1.30E+06 ( 12) 993.5 584.1 1844.9 0.0 209.7 194.0 226.5 3 3.98E+07 ( 245) 1.79E+06 ( 11)1036.4 596.9 1979.4 0.0 215.7 199.7 233.0 1 2.54E+07 ( 188) 1.08E+06 ( 8)1083.7 571.4 2346.4 0.0 220.3 204.0 237.9 POOL 2.30E+07( 7184) 5.24E+06( 1641) 0.0 220.3 204.0 237.9 MEAN URANIUM CONCENTRATION +/-2SE (ppm): 219.8, 13.4
172
POOLED AGE WITH 63% CONF. INTERVAL(Ma): 220.3, 211.8 -- 229.2 ( -8.5 +8.8) 95% CONF. INTERVAL(Ma): 204.0 -- 237.9 ( -16.3 +17.6) CHI^2 PROBABILITY: 0.0% CENTRAL AGE WITH 63% CONF. INTERVAL(Ma): 222.1, 200.1 -- 246.5 ( -22.0 +24.4) 95% CONF. INTERVAL(Ma): 180.9 -- 272.4 ( -41.1 +50.3) AGE DISPERSION (%): 56.3 CHI^2 AGE WITH 63% CONF. INTERVAL (Ma): 84.0, 77.4 -- 91.1 ( -6.6 +7.1) 95% CONF. INTERVAL (Ma): 71.6 -- 98.5 ( -12.4 +14.5) NUMBER AND PERCENTAGE OF GRAINS: 3, 9%
173
Pro
ba
bili
ty d
en
sity (
%/∆
z=
0.1
)
990628-2Lower Cretaceous Cintura Formation
Station 14, Huachuca Mountains
n = 33 grains (11 from 15 h etch, 3 from 11 h etch,
FT grain age (Ma)
30 50 70 300 500 70010 100 10000
1
2
3
4
5
6
5 from 13.5 h etch, 14 from 9.5 h etch)
174
Upper Cretaceous Fort Crittenden Formation, Station 23 (bulk sample) 990722-2 (Axioskop, 010401-10) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.881E+05 RELATIVE ERROR (%): 1.75 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 1 1.41E+07 ( 261) 4.60E+06 ( 85) 30 194 43 153.3 119.6 196.3 2 1.52E+07 ( 84) 3.79E+06 ( 21) 9 160 69 199.0 123.4 336.8 3 1.76E+07 ( 152) 1.36E+07 ( 117) 14 573 108 65.4 51.2 83.6 4 1.10E+07 ( 102) 4.55E+06 ( 42) 15 192 59 122.0 84.6 179.0 5 9.74E+06 ( 84) 1.01E+07 ( 87) 14 426 92 48.9 35.7 66.8 6 1.17E+07 ( 65) 8.30E+06 ( 46) 9 350 104 71.3 48.2 106.4 7 7.03E+06 ( 130) 3.68E+06 ( 68) 30 155 38 96.3 71.3 131.2 8 1.40E+07 ( 69) 7.10E+06 ( 35) 8 300 101 99.2 65.3 153.5 9 1.76E+07 ( 130) 1.01E+07 ( 75) 12 429 100 86.9 65.2 115.8 10 1.56E+07 ( 115) 9.47E+06 ( 70) 12 400 96 82.9 61.1 113.3 11 1.64E+07 ( 91) 5.59E+06 ( 31) 9 236 85 146.9 97.3 228.3 12 2.06E+07 ( 76) 1.03E+07 ( 38) 6 434 141 100.6 67.5 152.6 13 1.78E+07 ( 197) 1.11E+07 ( 123) 18 469 86 80.6 64.0 101.4 14 1.14E+07 ( 63) 8.12E+06 ( 45) 9 343 102 70.7 47.5 106.0 15 2.06E+07 ( 114) 7.22E+06 ( 40) 9 305 96 142.8 99.3 210.0 16 1.21E+07 ( 52) 1.41E+07 ( 61) 7 598 154 43.2 29.2 63.6 17 1.42E+07 ( 35) 1.26E+07 ( 31) 4 531 190 57.1 34.2 95.6 18 9.33E+06 ( 23) 5.68E+06 ( 14) 4 240 126 82.6 41.0 173.3 19 1.99E+07 ( 147) 9.74E+06 ( 72) 12 411 98 102.2 76.9 135.8 20 1.83E+07 ( 180) 7.71E+06 ( 76) 16 326 75 118.5 90.4 155.3 21 1.79E+07 ( 55) 1.01E+07 ( 31) 5 425 152 89.3 56.7 143.5 22 1.85E+07 ( 114) 9.42E+06 ( 58) 10 398 105 99.0 71.6 138.3 23 1.06E+07 ( 39) 8.39E+06 ( 31) 6 354 127 63.5 38.7 105.2 24 1.28E+07 ( 63) 4.67E+06 ( 23) 8 197 82 137.1 84.4 231.2 25 2.76E+07 ( 102) 1.33E+07 ( 49) 6 560 160 104.7 74.0 150.4 26 1.59E+07 ( 88) 1.05E+07 ( 58) 9 442 117 76.6 54.4 108.6 27 1.64E+07 ( 182) 1.23E+07 ( 136) 18 518 91 67.4 53.7 84.6 28 1.25E+07 ( 123) 3.65E+06 ( 36) 16 154 51 170.8 117.6 254.5 29 2.16E+07 ( 80) 1.06E+07 ( 39) 6 446 143 103.2 69.7 155.4 30 1.66E+07 ( 102) 1.06E+07 ( 65) 10 446 111 79.2 57.5 109.9 >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.871E+05 RELATIVE ERROR (%): 1.72 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 31 3.29E+07 ( 405) 4.38E+06 ( 54) 20 186 51 365.8 276.1 483.5 32 2.17E+07 ( 107) 1.56E+07 ( 77) 8 662 152 69.9 51.7 95.1 33 2.21E+07 ( 109) 2.35E+07 ( 116) 8 998 188 47.2 36.2 61.6 34 2.39E+07 ( 118) 1.54E+07 ( 76) 8 654 151 77.7 58.0 103.9 35 2.33E+07 ( 115) 1.42E+06 ( 7) 8 60 44 766.6 379.2 1830.5 990722-2 (Axioskop, 010401-10) ------ GRAIN AGES IN ORIGINAL ORDER ------
175
Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 36 1.62E+07 ( 199) 1.06E+07 ( 131) 20 451 80 76.2 60.8 95.5 37 2.39E+07 ( 177) 1.19E+07 ( 88) 12 505 109 100.5 77.5 130.2 38 2.60E+07 ( 401) 1.09E+07 ( 168) 25 462 73 119.4 99.1 143.9 39 1.98E+07 ( 122) 8.44E+06 ( 52) 10 358 100 117.5 84.5 165.8 40 2.01E+07 ( 198) 1.16E+07 ( 114) 16 490 93 87.0 68.8 110.0 41 1.70E+07 ( 262) 1.45E+07 ( 223) 25 614 85 59.1 49.1 71.2 42 2.65E+07 ( 98) 1.03E+07 ( 38) 6 436 141 128.9 88.2 192.7 43 2.15E+07 ( 106) 6.70E+06 ( 33) 8 284 99 160.1 108.0 244.0 44 1.84E+07 ( 170) 1.60E+07 ( 148) 15 679 114 57.7 46.0 72.4 45 1.93E+07 ( 143) 7.71E+06 ( 57) 12 327 87 125.6 92.0 173.8 46 2.11E+07 ( 156) 1.01E+07 ( 75) 12 430 100 103.8 78.6 137.1 47 2.30E+07 ( 298) 1.12E+07 ( 145) 21 475 80 102.9 83.9 126.2 48 2.00E+07 ( 148) 9.06E+06 ( 67) 12 384 94 110.1 82.3 147.2 49 2.94E+07 ( 217) 9.88E+06 ( 73) 12 419 99 147.8 113.1 193.0 50 2.52E+07 ( 186) 1.49E+07 ( 110) 12 631 122 84.7 66.6 107.7 51 2.71E+07 ( 100) 8.93E+06 ( 33) 6 378 131 151.1 101.6 231.0 52 2.44E+07 ( 135) 1.73E+07 ( 96) 9 734 152 70.5 54.0 91.9 53 1.16E+07 ( 43) 4.33E+06 ( 16) 6 184 91 133.8 74.6 254.0 54 3.23E+07 ( 179) 1.71E+07 ( 95) 9 726 151 94.2 73.2 121.3 55 3.50E+07 ( 194) 9.92E+06 ( 55) 9 421 114 175.8 130.2 241.5 56 2.44E+07 ( 240) 1.40E+07 ( 138) 16 594 103 87.2 70.3 108.1 57 2.95E+07 ( 109) 7.85E+06 ( 29) 6 333 123 186.8 124.0 291.2 58 2.64E+07 ( 195) 1.49E+06 ( 11) 12 63 37 829.4 472.4 1610.5 59 2.23E+07 ( 165) 1.04E+07 ( 77) 12 442 101 106.9 81.3 140.5 60 2.76E+07 ( 102) 1.70E+07 ( 63) 6 723 183 81.4 58.9 113.3 990722-2 (Axioskop, 010401-10) Number of grains = 60 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 16 1.21E+07 ( 52) 1.41E+07 ( 61) 43.2 29.2 63.6 100.0 43.2 29.2 63.6 33 2.21E+07 ( 109) 2.35E+07 ( 116) 47.2 36.2 61.6 68.4 45.8 36.8 57.1 5 9.74E+06 ( 84) 1.01E+07 ( 87) 48.9 35.7 66.8 87.2 46.8 39.0 56.2 17 1.42E+07 ( 35) 1.26E+07 ( 31) 57.1 34.2 95.6 83.9 47.9 40.3 56.9 44 1.84E+07 ( 170) 1.60E+07 ( 148) 57.7 46.0 72.4 61.6 51.3 44.5 59.1 41 1.70E+07 ( 262) 1.45E+07 ( 223) 59.1 49.1 71.2 50.8 53.9 47.9 60.7 23 1.06E+07 ( 39) 8.39E+06 ( 31) 63.5 38.7 105.2 57.7 54.4 48.3 61.1 3 1.76E+07 ( 152) 1.36E+07 ( 117) 65.4 51.2 83.6 45.4 56.0 50.2 62.5 27 1.64E+07 ( 182) 1.23E+07 ( 136) 67.4 53.7 84.6 33.0 57.6 52.0 63.9 32 2.17E+07 ( 107) 1.56E+07 ( 77) 69.9 51.7 95.1 29.5 58.6 53.0 64.7 52 2.44E+07 ( 135) 1.73E+07 ( 96) 70.5 54.0 91.9 24.8 59.6 54.1 65.7 14 1.14E+07 ( 63) 8.12E+06 ( 45) 70.7 47.5 106.0 27.2 60.0 54.6 66.1 6 1.17E+07 ( 65) 8.30E+06 ( 46) 71.3 48.2 106.4 29.3 60.5 55.0 66.5 36 1.62E+07 ( 199) 1.06E+07 ( 131) 76.2 60.8 95.5 15.4 62.0 56.6 67.9 26 1.59E+07 ( 88) 1.05E+07 ( 58) 76.6 54.4 108.6 14.3 62.6 57.3 68.5 34 2.39E+07 ( 118) 1.54E+07 ( 76) 77.7 58.0 103.9 11.3 63.4 58.1 69.3 30 1.66E+07 ( 102) 1.06E+07 ( 65) 79.2 57.5 109.9 9.5 64.1 58.8 69.9 13 1.78E+07 ( 197) 1.11E+07 ( 123) 80.6 64.0 101.4 5.0 65.3 60.0 71.1 60 2.76E+07 ( 102) 1.70E+07 ( 63) 81.4 58.9 113.3 4.3 65.9 60.6 71.7 18 9.33E+06 ( 23) 5.68E+06 ( 14) 82.6 41.0 173.3 5.2 66.1 60.8 71.8 10 1.56E+07 ( 115) 9.47E+06 ( 70) 82.9 61.1 113.3 4.2 66.7 61.4 72.5 50 2.52E+07 ( 186) 1.49E+07 ( 110) 84.7 66.6 107.7 2.1 67.8 62.5 73.5 9 1.76E+07 ( 130) 1.01E+07 ( 75) 86.9 65.2 115.8 1.3 68.5 63.2 74.2 40 2.01E+07 ( 198) 1.16E+07 ( 114) 87.0 68.8 110.0 0.6 69.5 64.2 75.2 56 2.44E+07 ( 240) 1.40E+07 ( 138) 87.2 70.3 108.1 0.3 70.6 65.3 76.3 21 1.79E+07 ( 55) 1.01E+07 ( 31) 89.3 56.7 143.5 0.3 70.9 65.6 76.6 54 3.23E+07 ( 179) 1.71E+07 ( 95) 94.2 73.2 121.3 0.1 71.8 66.5 77.6
176
7 7.03E+06 ( 130) 3.68E+06 ( 68) 96.3 71.3 131.2 0.0 72.5 67.2 78.3 22 1.85E+07 ( 114) 9.42E+06 ( 58) 99.0 71.6 138.3 0.0 73.1 67.8 78.9 8 1.40E+07 ( 69) 7.10E+06 ( 35) 99.2 65.3 153.5 0.0 73.5 68.2 79.3 37 2.39E+07 ( 177) 1.19E+07 ( 88) 100.5 77.5 130.2 0.0 74.4 69.1 80.2 12 2.06E+07 ( 76) 1.03E+07 ( 38) 100.6 67.5 152.6 0.0 74.8 69.4 80.6 19 1.99E+07 ( 147) 9.74E+06 ( 72) 102.2 76.9 135.8 0.0 75.5 70.2 81.3 47 2.30E+07 ( 298) 1.12E+07 ( 145) 102.9 83.9 126.2 0.0 76.9 71.5 82.8 29 2.16E+07 ( 80) 1.06E+07 ( 39) 103.2 69.7 155.4 0.0 77.3 71.9 83.1 46 2.11E+07 ( 156) 1.01E+07 ( 75) 103.8 78.6 137.1 0.0 78.0 72.5 83.8 25 2.76E+07 ( 102) 1.33E+07 ( 49) 104.7 74.0 150.4 0.0 78.4 73.0 84.3 990722-2 (Axioskop, 010401-10) Number of grains = 60 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 59 2.23E+07 ( 165) 1.04E+07 ( 77) 106.9 81.3 140.5 0.0 79.1 73.7 85.0 48 2.00E+07 ( 148) 9.06E+06 ( 67) 110.1 82.3 147.2 0.0 79.8 74.3 85.7 39 1.98E+07 ( 122) 8.44E+06 ( 52) 117.5 84.5 165.8 0.0 80.4 74.9 86.3 20 1.83E+07 ( 180) 7.71E+06 ( 76) 118.5 90.4 155.3 0.0 81.3 75.8 87.3 38 2.60E+07 ( 401) 1.09E+07 ( 168) 119.4 99.1 143.9 0.0 83.2 77.5 89.2 4 1.10E+07 ( 102) 4.55E+06 ( 42) 122.0 84.6 179.0 0.0 83.6 78.0 89.7 45 1.93E+07 ( 143) 7.71E+06 ( 57) 125.6 92.0 173.8 0.0 84.3 78.6 90.4 42 2.65E+07 ( 98) 1.03E+07 ( 38) 128.9 88.2 192.7 0.0 84.8 79.1 90.9 53 1.16E+07 ( 43) 4.33E+06 ( 16) 133.8 74.6 254.0 0.0 85.0 79.3 91.1 24 1.28E+07 ( 63) 4.67E+06 ( 23) 137.1 84.4 231.2 0.0 85.3 79.6 91.5 15 2.06E+07 ( 114) 7.22E+06 ( 40) 142.8 99.3 210.0 0.0 86.0 80.2 92.1 11 1.64E+07 ( 91) 5.59E+06 ( 31) 146.9 97.3 228.3 0.0 86.5 80.7 92.6 49 2.94E+07 ( 217) 9.88E+06 ( 73) 147.8 113.1 193.0 0.0 87.7 81.9 93.9 51 2.71E+07 ( 100) 8.93E+06 ( 33) 151.1 101.6 231.0 0.0 88.2 82.4 94.5 1 1.41E+07 ( 261) 4.60E+06 ( 85) 153.3 119.6 196.3 0.0 89.7 83.7 96.0 43 2.15E+07 ( 106) 6.70E+06 ( 33) 160.1 108.0 244.0 0.0 90.3 84.3 96.6 28 1.25E+07 ( 123) 3.65E+06 ( 36) 170.8 117.6 254.5 0.0 91.0 85.0 97.4 55 3.50E+07 ( 194) 9.92E+06 ( 55) 175.8 130.2 241.5 0.0 92.2 86.1 98.6 57 2.95E+07 ( 109) 7.85E+06 ( 29) 186.8 124.0 291.2 0.0 92.8 86.8 99.3 2 1.52E+07 ( 84) 3.79E+06 ( 21) 199.0 123.4 336.8 0.0 93.4 87.3 99.9 31 3.29E+07 ( 405) 4.38E+06 ( 54) 365.8 276.1 483.5 0.0 97.1 90.7 103.8 35 2.33E+07 ( 115) 1.42E+06 ( 7) 766.6 379.2 1830.5 0.0 98.3 91.9 105.1 58 2.64E+07 ( 195) 1.49E+06 ( 11) 829.4 472.4 1610.5 0.0 100.4 93.8 107.3 POOL 1.92E+07( 8315) 9.66E+06( 4177) 0.0 100.4 93.8 107.3 MEAN URANIUM CONCENTRATION +/-2SE (ppm): 408.0, 19.1 POOLED AGE WITH 63% CONF. INTERVAL(Ma): 100.4, 97.0 -- 103.9 ( -3.4 +3.5) 95% CONF. INTERVAL(Ma): 93.8 -- 107.3 ( -6.5 +7.0) CHI^2 PROBABILITY: 0.0% CENTRAL AGE WITH 63% CONF. INTERVAL(Ma): 100.6, 94.5 -- 107.2 ( -6.1 +6.5) 95% CONF. INTERVAL(Ma): 89.0 -- 113.9 ( -11.7 +13.2) AGE DISPERSION (%): 40.7 CHI^2 AGE WITH 63% CONF. INTERVAL (Ma): 68.5, 65.8 -- 71.4 ( -2.8 +2.9) 95% CONF. INTERVAL (Ma): 63.2 -- 74.2 ( -5.3 +5.7) NUMBER AND PERCENTAGE OF GRAINS: 23, 38%
177
Upper Cretaceous Fort Crittenden Formation, Station 23 (pink/purple fraction) 990722-2p (BX60/Axioskop, 011115-011116 & 011125, p = d+L) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 3.102E+05 RELATIVE ERROR (%): 2.11 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.700E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 1 1.71E+07 ( 103) 1.26E+07 ( 76) 9 494 115 73.7 54.2 100.6 2 2.91E+07 ( 117) 1.02E+07 ( 41) 6 400 125 153.9 107.4 225.2 3 2.45E+07 ( 148) 2.04E+07 ( 123) 9 800 148 65.3 51.1 83.4 4 1.41E+07 ( 330) 1.30E+07 ( 306) 35 512 62 58.6 49.7 69.2 5 2.57E+07 ( 138) 9.70E+06 ( 52) 8 381 106 143.3 103.7 201.2 6 2.70E+07 ( 163) 1.06E+07 ( 64) 9 416 105 137.7 102.6 186.9 7 2.59E+07 ( 278) 6.72E+06 ( 72) 16 264 63 206.5 158.9 268.0 8 2.90E+07 ( 291) 4.98E+06 ( 50) 15 195 56 310.0 230.3 425.8 9 2.60E+07 ( 174) 9.85E+06 ( 66) 10 386 96 141.6 106.4 188.4 10 2.97E+07 ( 239) 1.19E+07 ( 96) 12 468 97 134.1 105.3 170.7 11 1.95E+07 ( 157) 7.46E+06 ( 60) 12 293 76 141.4 104.5 193.8 >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 3.083E+05 RELATIVE ERROR (%): 2.03 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 12 3.03E+07 ( 112) 1.14E+07 ( 42) 6 449 139 143.1 99.9 209.1 13 2.52E+07 ( 248) 9.03E+06 ( 89) 16 356 77 149.0 116.4 190.5 14 3.52E+07 ( 390) 9.92E+06 ( 110) 18 392 76 189.1 152.3 234.7 15 4.25E+07 ( 157) 4.33E+06 ( 16) 6 171 84 508.2 310.3 893.3 990722-2p (BX60/Axioskop, 011115-011116 & 011125, p = d+L) Number of grains = 15 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 4 1.41E+07 ( 330) 1.30E+07 ( 306) 58.6 49.7 69.2 100.0 58.6 49.7 69.2 3 2.45E+07 ( 148) 2.04E+07 ( 123) 65.3 51.1 83.4 45.2 60.6 52.5 69.9 1 1.71E+07 ( 103) 1.26E+07 ( 76) 73.7 54.2 100.6 37.2 62.6 54.8 71.5 10 2.97E+07 ( 239) 1.19E+07 ( 96) 134.1 105.3 170.7 0.0 74.2 65.7 83.7 6 2.70E+07 ( 163) 1.06E+07 ( 64) 137.7 102.6 186.9 0.0 80.3 71.6 90.1 11 1.95E+07 ( 157) 7.46E+06 ( 60) 141.4 104.5 193.8 0.0 85.4 76.5 95.4 9 2.60E+07 ( 174) 9.85E+06 ( 66) 141.6 106.4 188.4 0.0 90.2 81.1 100.3 12 3.03E+07 ( 112) 1.14E+07 ( 42) 143.1 99.9 209.1 0.0 92.9 83.7 103.1 5 2.57E+07 ( 138) 9.70E+06 ( 52) 143.3 103.7 201.2 0.0 95.9 86.6 106.2 13 2.52E+07 ( 248) 9.03E+06 ( 89) 149.0 116.4 190.5 0.0 100.9 91.4 111.3 2 2.91E+07 ( 117) 1.02E+07 ( 41) 153.9 107.4 225.2 0.0 103.0 93.5 113.5 14 3.52E+07 ( 390) 9.92E+06 ( 110) 189.1 152.3 234.7 0.0 111.6 101.7 122.5 7 2.59E+07 ( 278) 6.72E+06 ( 72) 206.5 158.9 268.0 0.0 117.4 107.2 128.6 8 2.90E+07 ( 291) 4.98E+06 ( 50) 310.0 230.3 425.8 0.0 125.3 114.6 137.0 15 4.25E+07 ( 157) 4.33E+06 ( 16) 508.2 310.3 893.3 0.0 130.4 119.3 142.4 POOL 2.48E+07( 3045) 1.03E+07( 1265) 0.0 130.4 119.3 142.4
178
MEAN URANIUM CONCENTRATION +/-2SE (ppm): 404.0, 28.4 POOLED AGE WITH 63% CONF. INTERVAL(Ma): 130.4, 124.6 -- 136.4 ( -5.8 +6.0) 95% CONF. INTERVAL(Ma): 119.3 -- 142.4 ( -11.1 +12.1) CHI^2 PROBABILITY: 0.0% CENTRAL AGE WITH 63% CONF. INTERVAL(Ma): 138.0, 120.9 -- 157.6 ( -17.1 +19.6) 95% CONF. INTERVAL(Ma): 106.4 -- 178.9 ( -31.6 +40.9) AGE DISPERSION (%): 48.6 CHI^2 AGE WITH 63% CONF. INTERVAL (Ma): 62.6, 58.5 -- 67.0 ( -4.1 +4.4) 95% CONF. INTERVAL (Ma): 54.8 -- 71.5 ( -7.8 +8.9) NUMBER AND PERCENTAGE OF GRAINS: 3, 20%
179
Upper Cretaceous Fort Crittenden Formation, Station 23 (colorless fraction) 990722-2c (Axioskop, 011209-011214) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 3.047E+05 RELATIVE ERROR (%): 1.89 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 1 1.96E+07 ( 242) 1.28E+07 ( 158) 20 512 84 81.5 66.3 100.3 2 1.77E+07 ( 131) 1.77E+07 ( 131) 12 708 126 53.3 41.6 68.3 3 2.11E+07 ( 156) 5.95E+06 ( 44) 12 238 72 187.3 133.9 267.6 4 2.08E+07 ( 128) 1.20E+07 ( 74) 10 480 113 91.7 68.7 122.4 5 2.26E+07 ( 167) 1.12E+07 ( 83) 12 448 100 106.6 81.6 139.2 6 2.37E+07 ( 175) 1.18E+07 ( 87) 12 470 102 106.6 82.1 138.4 7 3.06E+07 ( 151) 2.11E+07 ( 104) 8 843 168 77.2 59.9 99.6 8 2.65E+07 ( 147) 1.57E+07 ( 87) 9 627 136 89.7 68.5 117.3 9 2.64E+07 ( 325) 1.82E+07 ( 224) 20 726 101 77.3 64.7 92.5 10 2.67E+07 ( 148) 1.23E+07 ( 68) 9 490 120 115.1 86.1 153.7 11 2.33E+07 ( 86) 1.65E+07 ( 61) 6 659 170 75.3 53.6 106.3 12 2.08E+07 ( 192) 1.42E+07 ( 131) 15 566 101 78.0 62.1 98.0 13 3.04E+07 ( 225) 1.52E+07 ( 112) 12 605 116 106.6 84.6 134.4 14 3.15E+07 ( 155) 1.44E+07 ( 71) 8 575 138 115.5 87.0 153.3 15 2.66E+07 ( 131) 1.10E+07 ( 54) 8 438 120 128.8 93.4 180.3 16 2.49E+07 ( 184) 1.96E+07 ( 145) 12 783 133 67.6 54.1 84.6 17 2.65E+07 ( 196) 1.34E+07 ( 99) 12 535 109 105.0 82.1 134.3 18 2.15E+07 ( 212) 1.50E+07 ( 148) 16 600 101 76.3 61.4 94.7 19 2.51E+07 ( 247) 1.63E+07 ( 161) 16 652 106 81.7 66.5 100.3 >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 3.065E+05 RELATIVE ERROR (%): 1.96 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 20 3.08E+07 ( 171) 1.57E+07 ( 87) 9 623 135 104.8 80.6 136.2 21 1.86E+07 ( 206) 6.67E+06 ( 74) 18 265 62 147.8 113.0 193.2 22 2.44E+07 ( 135) 1.48E+07 ( 82) 9 587 131 87.9 66.5 116.0 23 3.27E+07 ( 242) 1.37E+07 ( 101) 12 543 110 127.6 100.7 161.7 24 3.99E+07 ( 516) 3.94E+06 ( 51) 21 157 44 520.1 392.2 687.7 25 1.90E+07 ( 187) 1.36E+07 ( 134) 16 540 95 74.7 59.5 93.9 26 3.41E+07 ( 294) 1.61E+07 ( 139) 14 640 111 113.0 91.7 139.1 27 2.74E+07 ( 541) 1.11E+07 ( 218) 32 439 62 132.5 112.2 156.4 28 4.98E+07 ( 184) 2.00E+07 ( 74) 6 795 187 132.2 100.6 173.5 29 2.85E+07 ( 158) 1.37E+07 ( 76) 9 544 126 110.7 83.9 146.0 30 3.02E+07 ( 149) 1.93E+07 ( 95) 8 765 160 83.8 64.5 108.9 990722-2c (Axioskop, 011209-011214) Number of grains = 30 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 2 1.77E+07 ( 131) 1.77E+07 ( 131) 53.3 41.6 68.3 100.0 53.3 41.6 68.3 16 2.49E+07 ( 184) 1.96E+07 ( 145) 67.6 54.1 84.6 15.1 60.9 51.4 72.3
180
25 1.90E+07 ( 187) 1.36E+07 ( 134) 74.7 59.5 93.9 11.9 65.5 56.8 75.5 11 2.33E+07 ( 86) 1.65E+07 ( 61) 75.3 53.6 106.3 18.2 66.8 58.4 76.3 18 2.15E+07 ( 212) 1.50E+07 ( 148) 76.3 61.4 94.7 19.3 69.1 61.3 77.9 7 3.06E+07 ( 151) 2.11E+07 ( 104) 77.2 59.9 99.6 23.6 70.3 62.9 78.7 9 2.64E+07 ( 325) 1.82E+07 ( 224) 77.3 64.7 92.5 25.6 72.0 65.1 79.7 12 2.08E+07 ( 192) 1.42E+07 ( 131) 78.0 62.1 98.0 31.1 72.8 66.0 80.2 1 1.96E+07 ( 242) 1.28E+07 ( 158) 81.5 66.3 100.3 31.0 73.9 67.4 81.1 19 2.51E+07 ( 247) 1.63E+07 ( 161) 81.7 66.5 100.3 32.5 74.9 68.5 81.9 30 3.02E+07 ( 149) 1.93E+07 ( 95) 83.8 64.5 108.9 35.0 75.5 69.1 82.4 22 2.44E+07 ( 135) 1.48E+07 ( 82) 87.9 66.5 116.0 34.0 76.1 69.8 83.0 8 2.65E+07 ( 147) 1.57E+07 ( 87) 89.7 68.5 117.3 31.1 76.9 70.6 83.7 4 2.08E+07 ( 128) 1.20E+07 ( 74) 91.7 68.7 122.4 28.4 77.5 71.3 84.3 20 3.08E+07 ( 171) 1.57E+07 ( 87) 104.8 80.6 136.2 11.1 78.9 72.6 85.7 17 2.65E+07 ( 196) 1.34E+07 ( 99) 105.0 82.1 134.3 3.7 80.2 73.9 87.0 13 3.04E+07 ( 225) 1.52E+07 ( 112) 106.6 84.6 134.4 1.0 81.7 75.4 88.5 6 2.37E+07 ( 175) 1.18E+07 ( 87) 106.6 82.1 138.4 0.4 82.8 76.4 89.6 5 2.26E+07 ( 167) 1.12E+07 ( 83) 106.6 81.6 139.2 0.2 83.7 77.4 90.5 29 2.85E+07 ( 158) 1.37E+07 ( 76) 110.7 83.9 146.0 0.1 84.6 78.3 91.5 26 3.41E+07 ( 294) 1.61E+07 ( 139) 113.0 91.7 139.1 0.0 86.3 79.9 93.1 10 2.67E+07 ( 148) 1.23E+07 ( 68) 115.1 86.1 153.7 0.0 87.1 80.7 94.0 14 3.15E+07 ( 155) 1.44E+07 ( 71) 115.5 87.0 153.3 0.0 87.9 81.5 94.8 23 3.27E+07 ( 242) 1.37E+07 ( 101) 127.6 100.7 161.7 0.0 89.4 83.0 96.4 15 2.66E+07 ( 131) 1.10E+07 ( 54) 128.8 93.4 180.3 0.0 90.2 83.7 97.2 28 4.98E+07 ( 184) 2.00E+07 ( 74) 132.2 100.6 173.5 0.0 91.3 84.8 98.4 27 2.74E+07 ( 541) 1.11E+07 ( 218) 132.5 112.2 156.4 0.0 94.3 87.7 101.5 21 1.86E+07 ( 206) 6.67E+06 ( 74) 147.8 113.0 193.2 0.0 95.7 89.0 102.8 3 2.11E+07 ( 156) 5.95E+06 ( 44) 187.3 133.9 267.6 0.0 97.0 90.2 104.2 24 3.99E+07 ( 516) 3.94E+06 ( 51) 520.1 392.2 687.7 0.0 104.0 96.8 111.8 POOL 2.62E+07( 6181) 1.34E+07( 3166) 0.0 104.0 96.8 111.8 MEAN URANIUM CONCENTRATION +/-2SE (ppm): 536.0, 27.8 POOLED AGE WITH 63% CONF. INTERVAL(Ma): 104.0, 100.3 -- 107.9 ( -3.7 +3.9) 95% CONF. INTERVAL(Ma): 96.8 -- 111.8 ( -7.2 +7.7) CHI^2 PROBABILITY: 0.0% CENTRAL AGE WITH 63% CONF. INTERVAL(Ma): 101.2, 94.4 -- 108.4 ( -6.7 +7.2) 95% CONF. INTERVAL(Ma): 88.4 -- 115.8 ( -12.8 +14.6) AGE DISPERSION (%): 32.0 CHI^2 AGE WITH 63% CONF. INTERVAL (Ma): 80.2, 77.0 -- 83.6 ( -3.3 +3.4) 95% CONF. INTERVAL (Ma): 73.9 -- 87.0 ( -6.3 +6.8) NUMBER AND PERCENTAGE OF GRAINS: 16, 53%
181
Upper Cretaceous Fort Crittenden Formation, Station 23 (honey fraction) 990722-2h (Axioskop, 011214-011219) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 3.010E+05 RELATIVE ERROR (%): 1.76 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 1 2.29E+07 ( 254) 1.52E+07 ( 168) 18 613 97 79.5 65.0 97.3 2 3.04E+07 ( 281) 1.19E+07 ( 110) 15 481 93 133.6 106.7 167.3 3 2.04E+07 ( 151) 1.75E+07 ( 129) 12 706 126 61.6 48.5 78.3 4 2.52E+07 ( 186) 1.22E+07 ( 90) 12 492 105 108.2 83.8 139.7 5 2.27E+07 ( 140) 7.63E+06 ( 47) 10 308 90 155.9 111.7 221.6 6 2.08E+07 ( 462) 8.52E+06 ( 189) 36 345 52 128.2 107.4 152.9 7 1.92E+07 ( 142) 1.65E+07 ( 122) 12 667 123 61.3 47.9 78.4 8 2.23E+07 ( 206) 1.68E+07 ( 155) 15 678 111 70.0 56.4 86.7 9 1.66E+07 ( 123) 1.37E+07 ( 101) 12 552 111 64.0 49.0 83.6 10 2.08E+07 ( 231) 1.51E+07 ( 167) 18 609 97 72.8 59.3 89.4 11 1.67E+07 ( 278) 1.23E+07 ( 204) 27 496 72 71.8 59.5 86.6 12 1.73E+07 ( 256) 1.29E+07 ( 190) 24 520 77 71.0 58.4 86.2 13 2.41E+07 ( 238) 1.22E+07 ( 120) 16 492 91 104.0 83.1 130.2 14 2.30E+07 ( 170) 2.08E+07 ( 154) 12 842 139 58.2 46.5 72.8 15 1.90E+07 ( 176) 1.16E+07 ( 107) 15 468 92 86.4 67.6 110.3 16 2.48E+07 ( 244) 1.12E+07 ( 110) 16 451 87 116.2 92.3 146.2 >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 3.028E+05 RELATIVE ERROR (%): 1.83 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 17 2.52E+07 ( 93) 1.22E+07 ( 45) 6 489 146 109.2 75.9 159.6 18 2.00E+07 ( 197) 1.88E+07 ( 185) 16 754 114 56.5 45.9 69.5 19 2.96E+07 ( 219) 1.85E+07 ( 137) 12 745 130 84.5 67.9 105.2 20 2.74E+07 ( 270) 1.40E+07 ( 138) 16 563 98 103.3 83.6 127.5 21 2.69E+07 ( 199) 1.20E+07 ( 89) 12 484 104 117.7 91.3 151.6 22 2.40E+07 ( 237) 1.72E+07 ( 170) 16 693 109 73.8 60.2 90.5 990722-2h (Axioskop, 011214-011219) Number of grains = 22 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 18 2.00E+07 ( 197) 1.88E+07 ( 185) 56.5 45.9 69.5 100.0 56.5 45.9 69.5 14 2.30E+07 ( 170) 2.08E+07 ( 154) 58.2 46.5 72.8 84.3 57.3 49.0 67.1 7 1.92E+07 ( 142) 1.65E+07 ( 122) 61.3 47.9 78.4 87.4 58.4 50.9 67.0 3 2.04E+07 ( 151) 1.75E+07 ( 129) 61.6 48.5 78.3 93.2 59.2 52.3 67.0 9 1.66E+07 ( 123) 1.37E+07 ( 101) 64.0 49.0 83.6 94.3 59.9 53.3 67.3 8 2.23E+07 ( 206) 1.68E+07 ( 155) 70.0 56.4 86.7 77.0 61.8 55.5 68.8 12 1.73E+07 ( 256) 1.29E+07 ( 190) 71.0 58.4 86.2 63.7 63.5 57.5 70.2 11 1.67E+07 ( 278) 1.23E+07 ( 204) 71.8 59.5 86.6 56.1 64.9 59.1 71.3 10 2.08E+07 ( 231) 1.51E+07 ( 167) 72.8 59.3 89.4 53.6 65.9 60.2 72.1 22 2.40E+07 ( 237) 1.72E+07 ( 170) 73.8 60.2 90.5 51.2 66.7 61.2 72.8
182
1 2.29E+07 ( 254) 1.52E+07 ( 168) 79.5 65.0 97.3 34.6 68.0 62.5 74.0 19 2.96E+07 ( 219) 1.85E+07 ( 137) 84.5 67.9 105.2 18.3 69.2 63.8 75.1 15 1.90E+07 ( 176) 1.16E+07 ( 107) 86.4 67.6 110.3 10.8 70.2 64.7 76.1 20 2.74E+07 ( 270) 1.40E+07 ( 138) 103.3 83.6 127.5 0.3 72.3 66.8 78.3 13 2.41E+07 ( 238) 1.22E+07 ( 120) 104.0 83.1 130.2 0.0 74.1 68.5 80.1 4 2.52E+07 ( 186) 1.22E+07 ( 90) 108.2 83.8 139.7 0.0 75.4 69.8 81.4 17 2.52E+07 ( 93) 1.22E+07 ( 45) 109.2 75.9 159.6 0.0 76.0 70.4 82.1 16 2.48E+07 ( 244) 1.12E+07 ( 110) 116.2 92.3 146.2 0.0 77.8 72.2 84.0 21 2.69E+07 ( 199) 1.20E+07 ( 89) 117.7 91.3 151.6 0.0 79.2 73.5 85.4 6 2.08E+07 ( 462) 8.52E+06 ( 189) 128.2 107.4 152.9 0.0 82.6 76.8 88.9 2 3.04E+07 ( 281) 1.19E+07 ( 110) 133.6 106.7 167.3 0.0 84.6 78.6 91.0 5 2.27E+07 ( 140) 7.63E+06 ( 47) 155.9 111.7 221.6 0.0 85.8 79.8 92.2 POOL 2.22E+07( 4753) 1.36E+07( 2922) 0.0 85.8 79.8 92.2 MEAN URANIUM CONCENTRATION +/-2SE (ppm): 551.2, 28.1 POOLED AGE WITH 63% CONF. INTERVAL(Ma): 85.8, 82.6 -- 89.0 ( -3.1 +3.2) 95% CONF. INTERVAL(Ma): 79.8 -- 92.2 ( -6.0 +6.5) CHI^2 PROBABILITY: 0.0% CENTRAL AGE WITH 63% CONF. INTERVAL(Ma): 85.6, 80.1 -- 91.6 ( -5.5 +5.9) 95% CONF. INTERVAL(Ma): 75.1 -- 97.6 ( -10.5 +12.0) AGE DISPERSION (%): 26.1 CHI^2 AGE WITH 63% CONF. INTERVAL (Ma): 70.2, 67.3 -- 73.1 ( -2.8 +3.0) 95% CONF. INTERVAL (Ma): 64.7 -- 76.1 ( -5.4 +5.9) NUMBER AND PERCENTAGE OF GRAINS: 13, 59%
183
Pro
ba
bili
ty d
en
sity (
%/∆
z=
0.1
)990722-2 composite
Upper Cretaceous Fort Crittenden FormationStation 23, Huachuca Mountains
n = 127 grains
FT grain age (Ma)
30 50 70 300 50070010 100 1000
0
2
4
6
8
10
12
14
16
18
184
Middle Jurassic Temporal Formation, Station 33 990802-1 (Axioskop, 020121) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.838E+05 RELATIVE ERROR (%): 1.67 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 1 1.37E+07 ( 254) 1.47E+07 ( 271) 30 629 79 46.7 39.0 55.8 2 1.73E+07 ( 192) 8.30E+06 ( 92) 18 356 75 103.1 80.1 132.6 3 3.12E+07 ( 308) 1.20E+07 ( 118) 16 513 96 128.8 103.7 160.0 4 2.24E+07 ( 414) 1.43E+07 ( 265) 30 615 78 77.6 65.9 91.3 5 2.04E+07 ( 151) 1.56E+07 ( 115) 12 667 126 65.1 50.9 83.4 6 2.30E+07 ( 255) 1.05E+07 ( 116) 18 449 84 108.7 86.8 135.9 7 2.36E+07 ( 349) 1.46E+07 ( 216) 24 627 88 80.2 67.2 95.7 8 2.09E+07 ( 387) 1.19E+07 ( 220) 30 511 71 87.3 73.4 103.8 9 1.68E+07 ( 186) 9.11E+06 ( 101) 18 391 79 91.1 71.2 116.5 10 1.99E+07 ( 196) 9.74E+06 ( 96) 16 418 86 100.9 78.7 129.3 11 2.06E+07 ( 407) 7.66E+06 ( 151) 32 328 54 133.1 109.8 161.3 12 2.37E+07 ( 146) 1.72E+07 ( 106) 10 738 145 68.3 52.9 88.0 13 2.00E+07 ( 492) 6.90E+06 ( 170) 40 296 46 142.9 119.2 171.1 14 2.48E+07 ( 275) 1.60E+07 ( 177) 18 685 105 77.1 63.4 93.7 15 1.96E+07 ( 242) 7.22E+06 ( 89) 20 310 66 134.0 104.7 171.3 16 1.09E+07 ( 188) 8.58E+06 ( 148) 28 368 62 63.1 50.6 78.7 17 1.89E+07 ( 291) 7.86E+06 ( 121) 25 337 62 118.8 95.6 147.5 18 1.54E+07 ( 426) 1.42E+07 ( 394) 45 610 65 53.8 46.5 62.4 19 2.01E+07 ( 496) 1.19E+07 ( 292) 40 508 62 84.3 72.3 98.3 20 2.51E+07 ( 494) 1.18E+07 ( 233) 32 507 68 105.0 89.2 123.7 21 2.17E+07 ( 534) 8.73E+06 ( 215) 40 374 52 122.9 104.1 145.0 22 2.13E+07 ( 368) 1.26E+07 ( 217) 28 540 75 84.1 70.6 100.3 23 1.80E+07 ( 222) 1.62E+07 ( 199) 20 693 101 55.5 45.5 67.6 24 2.55E+07 ( 251) 1.57E+07 ( 155) 16 674 110 80.3 65.3 98.7 25 1.90E+07 ( 234) 1.66E+07 ( 205) 20 714 102 56.8 46.7 68.9 26 2.55E+07 ( 439) 9.91E+06 ( 171) 28 425 66 126.9 105.6 152.4 27 2.69E+07 ( 332) 1.06E+07 ( 130) 20 452 81 126.1 102.4 155.2 990802-1 (Axioskop, 020121) Number of grains = 27 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 1 1.37E+07 ( 254) 1.47E+07 ( 271) 46.7 39.0 55.8 100.0 46.7 39.0 55.8 18 1.54E+07 ( 426) 1.42E+07 ( 394) 53.8 46.5 62.4 20.1 50.9 45.2 57.4 23 1.80E+07 ( 222) 1.62E+07 ( 199) 55.5 45.5 67.6 32.6 52.0 46.7 58.0 25 1.90E+07 ( 234) 1.66E+07 ( 205) 56.8 46.7 68.9 40.1 53.0 47.9 58.5 16 1.09E+07 ( 188) 8.58E+06 ( 148) 63.1 50.6 78.7 26.4 54.2 49.3 59.6 5 2.04E+07 ( 151) 1.56E+07 ( 115) 65.1 50.9 83.4 19.7 55.2 50.3 60.5 12 2.37E+07 ( 146) 1.72E+07 ( 106) 68.3 52.9 88.0 12.3 56.2 51.3 61.4 14 2.48E+07 ( 275) 1.60E+07 ( 177) 77.1 63.4 93.7 0.6 58.5 53.7 63.7 4 2.24E+07 ( 414) 1.43E+07 ( 265) 77.6 65.9 91.3 0.0 61.2 56.4 66.4 7 2.36E+07 ( 349) 1.46E+07 ( 216) 80.2 67.2 95.7 0.0 63.2 58.4 68.4 24 2.55E+07 ( 251) 1.57E+07 ( 155) 80.3 65.3 98.7 0.0 64.4 59.6 69.6 22 2.13E+07 ( 368) 1.26E+07 ( 217) 84.1 70.6 100.3 0.0 66.1 61.3 71.3 19 2.01E+07 ( 496) 1.19E+07 ( 292) 84.3 72.3 98.3 0.0 68.1 63.2 73.3 8 2.09E+07 ( 387) 1.19E+07 ( 220) 87.3 73.4 103.8 0.0 69.5 64.6 74.7 9 1.68E+07 ( 186) 9.11E+06 ( 101) 91.1 71.2 116.5 0.0 70.2 65.4 75.5
185
10 1.99E+07 ( 196) 9.74E+06 ( 96) 100.9 78.7 129.3 0.0 71.2 66.3 76.4 2 1.73E+07 ( 192) 8.30E+06 ( 92) 103.1 80.1 132.6 0.0 72.1 67.2 77.4 20 2.51E+07 ( 494) 1.18E+07 ( 233) 105.0 89.2 123.7 0.0 74.3 69.3 79.7 6 2.30E+07 ( 255) 1.05E+07 ( 116) 108.7 86.8 135.9 0.0 75.4 70.4 80.8 17 1.89E+07 ( 291) 7.86E+06 ( 121) 118.8 95.6 147.5 0.0 76.8 71.7 82.3 21 2.17E+07 ( 534) 8.73E+06 ( 215) 122.9 104.1 145.0 0.0 79.4 74.2 84.9 27 2.69E+07 ( 332) 1.06E+07 ( 130) 126.1 102.4 155.2 0.0 80.9 75.6 86.5 26 2.55E+07 ( 439) 9.91E+06 ( 171) 126.9 105.6 152.4 0.0 82.7 77.4 88.5 3 3.12E+07 ( 308) 1.20E+07 ( 118) 128.8 103.7 160.0 0.0 84.0 78.6 89.8 11 2.06E+07 ( 407) 7.66E+06 ( 151) 133.1 109.8 161.3 0.0 85.7 80.2 91.5 15 1.96E+07 ( 242) 7.22E+06 ( 89) 134.0 104.7 171.3 0.0 86.6 81.1 92.5 13 2.00E+07 ( 492) 6.90E+06 ( 170) 142.9 119.2 171.1 0.0 88.6 83.0 94.6 POOL 2.05E+07( 8529) 1.15E+07( 4783) 0.0 88.6 83.0 94.6 MEAN URANIUM CONCENTRATION +/-2SE (ppm): 494.0, 21.8 POOLED AGE WITH 63% CONF. INTERVAL(Ma): 88.6, 85.7 -- 91.6 ( -2.9 +3.0) 95% CONF. INTERVAL(Ma): 83.0 -- 94.6 ( -5.6 +6.0) CHI^2 PROBABILITY: 0.0% CENTRAL AGE WITH 63% CONF. INTERVAL(Ma): 88.3, 82.5 -- 94.4 ( -5.7 +6.1) 95% CONF. INTERVAL(Ma): 77.4 -- 100.7 ( -10.9 +12.4) AGE DISPERSION (%): 30.3 CHI^2 AGE WITH 63% CONF. INTERVAL (Ma): 56.2, 53.6 -- 58.8 ( -2.5 +2.6) 95% CONF. INTERVAL (Ma): 51.3 -- 61.4 ( -4.8 +5.3) NUMBER AND PERCENTAGE OF GRAINS: 7, 26%
186
Pro
babili
ty d
ensity (
%/∆
z=
0.1
)990802-1
Upper Jurassic Temporal FormationStation 33, Santa Rita Mountains
n = 27 grains (27 from 15 h etch)
FT grain age (Ma)
30 50 70 300 50010 1000
1
2
3
4
5
6
187
Lower Cretaceous Turney Ranch Formation, Station 38 990803-3 (Axioskop, 011010-011121) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.817E+05 RELATIVE ERROR (%): 1.63 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 1 2.16E+07 ( 80) 3.79E+06 ( 14) 6 164 86 275.3 157.6 521.5 2 1.94E+07 ( 334) 1.91E+06 ( 33) 28 83 29 482.2 341.4 703.9 3 1.99E+07 ( 147) 1.10E+07 ( 81) 12 473 106 89.0 67.7 117.1 4 1.60E+07 ( 197) 4.55E+06 ( 56) 20 196 53 172.1 127.8 235.7 5 1.34E+07 ( 207) 6.04E+06 ( 93) 25 261 55 109.1 85.1 139.8 6 1.26E+07 ( 209) 3.85E+06 ( 64) 27 166 42 159.0 120.0 210.5 7 1.31E+07 ( 121) 1.08E+06 ( 10) 15 47 29 566.7 308.1 1173.1 8 1.13E+07 ( 439) 4.51E+06 ( 175) 63 195 30 123.1 102.6 147.6 9 8.17E+06 ( 141) 3.25E+06 ( 56) 28 140 38 123.7 90.4 171.7 10 1.35E+07 ( 50) 2.16E+06 ( 8) 6 94 64 298.3 144.3 717.6 11 1.28E+07 ( 142) 4.06E+06 ( 45) 18 175 52 154.5 110.3 221.0 12 1.86E+07 ( 80) 9.04E+06 ( 39) 7 391 125 100.9 68.2 152.0 13 1.16E+07 ( 57) 8.52E+06 ( 42) 8 368 114 67.0 44.3 102.3 14 1.86E+07 ( 103) 6.13E+06 ( 34) 9 265 91 148.3 100.3 225.2 >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.806E+05 RELATIVE ERROR (%): 1.61 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 15 3.43E+07 ( 148) 1.39E+06 ( 6) 7 60 47 1091.9 525.3 2719.0 16 1.26E+07 ( 116) 4.98E+06 ( 46) 15 216 64 123.4 87.3 177.5 17 1.76E+07 ( 152) 5.22E+06 ( 45) 14 226 67 164.6 117.9 234.7 18 2.26E+07 ( 390) 8.12E+06 ( 140) 28 352 60 135.9 111.5 165.7 19 2.56E+07 ( 189) 5.01E+06 ( 37) 12 217 71 247.1 174.3 360.3 20 2.94E+07 ( 163) 7.58E+06 ( 42) 9 329 101 188.7 134.5 271.1 21 2.16E+07 ( 93) 7.19E+06 ( 31) 7 312 112 146.3 97.1 227.0 22 2.76E+07 ( 153) 9.56E+06 ( 53) 9 415 114 141.0 102.9 196.5 23 2.35E+07 ( 145) 8.93E+06 ( 55) 10 387 105 128.9 94.2 179.2 24 9.97E+06 ( 43) 1.39E+06 ( 6) 7 60 47 337.7 148.5 947.2 25 3.33E+07 ( 205) 1.53E+07 ( 94) 10 662 138 106.5 83.1 136.4 26 2.24E+07 ( 124) 6.67E+06 ( 37) 9 289 95 163.3 112.9 242.1 27 1.50E+07 ( 139) 4.76E+06 ( 44) 15 207 62 154.1 109.6 221.3 28 2.68E+07 ( 99) 7.85E+06 ( 29) 6 340 126 166.1 109.6 260.2 29 2.52E+07 ( 186) 1.04E+07 ( 77) 12 452 104 117.7 90.0 153.9 30 2.07E+07 ( 153) 7.44E+06 ( 55) 12 323 87 136.0 99.6 188.5 31 1.79E+07 ( 199) 4.24E+06 ( 47) 18 184 54 205.7 149.8 288.4 32 1.73E+07 ( 149) 5.22E+06 ( 45) 14 226 67 161.4 115.5 230.3 33 2.16E+07 ( 160) 7.98E+06 ( 59) 12 346 90 132.6 98.1 181.9 34 1.93E+07 ( 107) 1.14E+07 ( 63) 9 493 125 83.4 60.6 115.8 35 1.97E+07 ( 109) 6.31E+06 ( 35) 9 274 92 151.8 103.5 228.7 990803-3 (Axioskop, 011010-011121) ------ GRAIN AGES IN ORIGINAL ORDER ------
188
Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 36 1.81E+07 ( 234) 3.87E+06 ( 50) 21 168 47 227.0 167.5 313.8 37 1.37E+07 ( 152) 5.95E+06 ( 66) 18 258 64 112.2 83.9 150.0 38 2.03E+07 ( 125) 5.19E+06 ( 32) 10 225 79 189.8 128.8 288.6 39 1.47E+07 ( 217) 7.44E+06 ( 110) 24 323 62 96.5 76.4 121.9 40 2.10E+07 ( 310) 1.10E+07 ( 162) 24 475 76 93.7 77.0 114.0 41 2.48E+07 ( 229) 1.18E+07 ( 109) 15 512 99 102.7 81.4 129.5 42 1.82E+07 ( 101) 6.49E+06 ( 36) 9 282 94 137.0 93.2 206.2 43 1.89E+07 ( 70) 1.00E+07 ( 37) 6 434 142 92.8 61.6 142.1 44 1.46E+07 ( 45) 9.42E+06 ( 29) 5 408 151 76.2 46.9 125.9 990803-3 (Axioskop, 011010-011121) Number of grains = 44 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 13 1.16E+07 ( 57) 8.52E+06 ( 42) 67.0 44.3 102.3 100.0 67.0 44.3 102.3 44 1.46E+07 ( 45) 9.42E+06 ( 29) 76.2 46.9 125.9 67.8 70.9 51.9 97.5 34 1.93E+07 ( 107) 1.14E+07 ( 63) 83.4 60.6 115.8 69.4 76.6 61.3 95.6 3 1.99E+07 ( 147) 1.10E+07 ( 81) 89.0 67.7 117.1 68.2 81.4 68.2 97.2 43 1.89E+07 ( 70) 1.00E+07 ( 37) 92.8 61.6 142.1 76.1 83.1 70.5 97.9 40 2.10E+07 ( 310) 1.10E+07 ( 162) 93.7 77.0 114.0 72.5 87.4 76.6 99.7 39 1.47E+07 ( 217) 7.44E+06 ( 110) 96.5 76.4 121.9 74.9 89.4 79.3 100.7 12 1.86E+07 ( 80) 9.04E+06 ( 39) 100.9 68.2 152.0 79.8 90.2 80.3 101.2 41 2.48E+07 ( 229) 1.18E+07 ( 109) 102.7 81.4 129.5 76.0 92.3 82.9 102.8 25 3.33E+07 ( 205) 1.53E+07 ( 94) 106.5 83.1 136.4 71.4 94.1 84.9 104.3 5 1.34E+07 ( 207) 6.04E+06 ( 93) 109.1 85.1 139.8 66.5 95.8 86.8 105.7 37 1.37E+07 ( 152) 5.95E+06 ( 66) 112.2 83.9 150.0 63.7 97.0 88.2 106.7 29 2.52E+07 ( 186) 1.04E+07 ( 77) 117.7 90.0 153.9 53.6 98.7 89.9 108.3 8 1.13E+07 ( 439) 4.51E+06 ( 175) 123.1 102.6 147.6 22.7 102.3 93.7 111.8 16 1.26E+07 ( 116) 4.98E+06 ( 46) 123.4 87.3 177.5 22.4 103.1 94.6 112.5 9 8.17E+06 ( 141) 3.25E+06 ( 56) 123.7 90.4 171.7 21.4 104.1 95.5 113.4 23 2.35E+07 ( 145) 8.93E+06 ( 55) 128.9 94.2 179.2 18.3 105.1 96.6 114.4 33 2.16E+07 ( 160) 7.98E+06 ( 59) 132.6 98.1 181.9 14.1 106.3 97.8 115.5 18 2.26E+07 ( 390) 8.12E+06 ( 140) 135.9 111.5 165.7 4.3 109.0 100.5 118.2 30 2.07E+07 ( 153) 7.44E+06 ( 55) 136.0 99.6 188.5 3.6 110.0 101.5 119.2 42 1.82E+07 ( 101) 6.49E+06 ( 36) 137.0 93.2 206.2 3.5 110.6 102.1 119.7 22 2.76E+07 ( 153) 9.56E+06 ( 53) 141.0 102.9 196.5 2.6 111.6 103.1 120.7 21 2.16E+07 ( 93) 7.19E+06 ( 31) 146.3 97.1 227.0 2.3 112.2 103.7 121.4 14 1.86E+07 ( 103) 6.13E+06 ( 34) 148.3 100.3 225.2 1.8 112.9 104.4 122.1 35 1.97E+07 ( 109) 6.31E+06 ( 35) 151.8 103.5 228.7 1.4 113.7 105.2 122.9 27 1.50E+07 ( 139) 4.76E+06 ( 44) 154.1 109.6 221.3 0.8 114.7 106.2 123.9 11 1.28E+07 ( 142) 4.06E+06 ( 45) 154.5 110.3 221.0 0.5 115.7 107.1 124.9 6 1.26E+07 ( 209) 3.85E+06 ( 64) 159.0 120.0 210.5 0.2 117.1 108.6 126.4 32 1.73E+07 ( 149) 5.22E+06 ( 45) 161.4 115.5 230.3 0.1 118.2 109.6 127.4 26 2.24E+07 ( 124) 6.67E+06 ( 37) 163.3 112.9 242.1 0.0 119.0 110.4 128.3 17 1.76E+07 ( 152) 5.22E+06 ( 45) 164.6 117.9 234.7 0.0 120.0 111.4 129.3 28 2.68E+07 ( 99) 7.85E+06 ( 29) 166.1 109.6 260.2 0.0 120.7 112.0 130.0 4 1.60E+07 ( 197) 4.55E+06 ( 56) 172.1 127.8 235.7 0.0 122.0 113.3 131.4 20 2.94E+07 ( 163) 7.58E+06 ( 42) 188.7 134.5 271.1 0.0 123.3 114.6 132.7 38 2.03E+07 ( 125) 5.19E+06 ( 32) 189.8 128.8 288.6 0.0 124.3 115.5 133.7 31 1.79E+07 ( 199) 4.24E+06 ( 47) 205.7 149.8 288.4 0.0 126.0 117.2 135.5 36 1.81E+07 ( 234) 3.87E+06 ( 50) 227.0 167.5 313.8 0.0 128.2 119.3 137.8 990803-3 (Axioskop, 011010-011121) Number of grains = 44 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI--
189
19 2.56E+07 ( 189) 5.01E+06 ( 37) 247.1 174.3 360.3 0.0 130.1 121.1 139.8 1 2.16E+07 ( 80) 3.79E+06 ( 14) 275.3 157.6 521.5 0.0 131.0 121.9 140.8 10 1.35E+07 ( 50) 2.16E+06 ( 8) 298.3 144.3 717.6 0.0 131.6 122.5 141.4 24 9.97E+06 ( 43) 1.39E+06 ( 6) 337.7 148.5 947.2 0.0 132.1 123.0 142.0 2 1.94E+07 ( 334) 1.91E+06 ( 33) 482.2 341.4 703.9 0.0 137.1 127.6 147.2 7 1.31E+07 ( 121) 1.08E+06 ( 10) 566.7 308.1 1173.1 0.0 138.9 129.4 149.2 15 3.43E+07 ( 148) 1.39E+06 ( 6)1091.9 525.3 2719.0 0.0 141.6 131.8 152.0 POOL 1.76E+07( 7012) 6.10E+06( 2434) 0.0 141.6 131.8 152.0 MEAN URANIUM CONCENTRATION +/-2SE (ppm): 263.4, 13.7 POOLED AGE WITH 63% CONF. INTERVAL(Ma): 141.6, 136.5 -- 146.8 ( -5.0 +5.2) 95% CONF. INTERVAL(Ma): 131.8 -- 152.0 ( -9.7 +10.4) CHI^2 PROBABILITY: 0.0% CENTRAL AGE WITH 63% CONF. INTERVAL(Ma): 145.4, 135.9 -- 155.7 ( -9.6 +10.2) 95% CONF. INTERVAL(Ma): 127.3 -- 166.1 ( -18.1 +20.7) AGE DISPERSION (%): 37.9 CHI^2 AGE WITH 63% CONF. INTERVAL (Ma): 113.7, 109.3 -- 118.3 ( -4.4 +4.6) 95% CONF. INTERVAL (Ma): 105.2 -- 122.9 ( -8.5 +9.2) NUMBER AND PERCENTAGE OF GRAINS: 25, 57%
190
Pro
babili
ty d
ensity (
%/∆
z=
0.1
)990803-3
Lower Cretaceous Turney Ranch FormationStation 38, Santa Rita Mountains
n = 44 grains (14 from 17 h etch, 30 from 12 h etch)
FT grain age (Ma)
30 50 70 300 50070010 100 10000
1
2
3
4
5
6
7
191
upper red conglomerate member, Upper Cretaceous Fort Crittenden Formation, Station 42 990805-3 (Axioskop, 010306-30) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.795E+05 RELATIVE ERROR (%): 1.59 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 1 1.62E+07 ( 140) 8.23E+06 ( 71) 14 358 86 95.8 71.9 127.8 2 1.22E+07 ( 45) 4.33E+06 ( 16) 6 188 93 136.3 76.4 257.8 3 1.46E+07 ( 81) 3.61E+06 ( 20) 9 157 70 195.5 120.0 335.5 4 1.40E+07 ( 138) 3.15E+06 ( 31) 16 137 49 215.0 145.9 327.4 5 1.15E+07 ( 106) 5.52E+06 ( 51) 15 240 67 101.5 72.2 144.7 6 8.66E+06 ( 48) 5.41E+06 ( 30) 9 236 86 78.3 48.7 127.8 7 1.62E+07 ( 100) 6.82E+06 ( 42) 10 297 92 116.1 80.5 170.6 8 1.66E+07 ( 205) 6.01E+06 ( 74) 20 262 61 134.3 102.7 175.4 9 9.42E+06 ( 116) 5.28E+06 ( 65) 20 230 57 87.3 64.0 120.2 10 1.51E+07 ( 149) 7.91E+06 ( 78) 16 345 79 92.9 70.5 122.5 11 1.98E+07 ( 220) 2.44E+06 ( 27) 18 106 41 387.7 262.9 595.8 12 1.63E+07 ( 201) 1.01E+07 ( 125) 20 442 80 78.5 62.5 98.6 13 1.33E+07 ( 115) 4.29E+06 ( 37) 14 187 61 151.0 104.0 224.7 14 1.69E+07 ( 125) 8.52E+06 ( 63) 12 371 94 97.0 71.2 133.5 15 2.60E+07 ( 128) 5.48E+06 ( 27) 8 239 91 228.5 151.4 358.6 16 1.10E+07 ( 68) 5.84E+06 ( 36) 10 254 85 92.3 60.9 142.2 17 2.23E+07 ( 329) 1.49E+06 ( 22) 24 65 27 693.5 461.2 1095.5 18 1.51E+07 ( 93) 5.19E+06 ( 32) 10 226 80 141.3 94.1 217.9 19 1.93E+07 ( 286) 7.44E+06 ( 110) 24 324 62 126.4 101.0 158.0 20 9.20E+06 ( 68) 5.14E+06 ( 38) 12 224 72 87.5 58.1 133.7 21 1.81E+07 ( 67) 2.16E+06 ( 8) 6 94 65 393.4 194.8 926.3 22 2.30E+07 ( 170) 2.57E+06 ( 19) 12 112 51 423.5 267.9 710.9 23 1.80E+07 ( 155) 3.71E+06 ( 32) 14 162 57 233.6 160.1 351.9 24 1.60E+07 ( 158) 5.58E+06 ( 55) 16 243 66 139.8 102.6 193.6 25 2.10E+07 ( 155) 1.15E+07 ( 85) 12 501 109 88.8 67.9 116.0 26 1.91E+07 ( 141) 3.92E+06 ( 29) 12 171 63 234.3 157.7 361.1 27 1.79E+07 ( 199) 3.16E+06 ( 35) 18 137 46 273.4 191.8 401.7 28 1.32E+07 ( 122) 5.52E+06 ( 51) 15 240 67 116.7 83.7 165.0 29 1.71E+07 ( 158) 1.84E+06 ( 17) 15 80 38 439.0 271.1 760.6 30 7.22E+06 ( 178) 2.80E+06 ( 69) 40 122 30 125.1 94.5 165.4 >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.784E+05 RELATIVE ERROR (%): 1.58 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 31 1.67E+07 ( 185) 3.52E+06 ( 39) 18 154 49 228.1 161.9 330.0 32 1.33E+07 ( 49) 8.66E+06 ( 32) 6 378 133 74.6 47.0 120.3 33 1.95E+07 ( 48) 1.01E+07 ( 25) 4 444 176 93.3 56.7 157.8 34 3.21E+07 ( 99) 1.49E+07 ( 46) 5 653 193 104.6 73.2 151.8 35 2.25E+07 ( 83) 7.58E+06 ( 28) 6 331 125 143.4 93.0 228.3 990805-3 (Axioskop, 010306-30)
192
------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 36 1.62E+07 ( 40) 1.10E+07 ( 27) 4 479 183 72.2 43.4 122.2 37 2.06E+07 ( 76) 3.52E+06 ( 13) 6 154 84 278.0 156.2 540.8 38 1.30E+07 ( 32) 2.44E+06 ( 6) 4 106 84 251.3 107.0 724.4 39 1.60E+07 ( 237) 6.09E+06 ( 90) 24 266 57 127.3 99.6 162.8 40 9.74E+06 ( 90) 4.44E+06 ( 41) 15 194 61 106.7 73.2 158.3 41 2.56E+07 ( 315) 4.22E+06 ( 52) 20 185 51 290.1 217.2 395.3 42 2.41E+07 ( 119) 4.67E+06 ( 23) 8 204 84 247.8 159.4 403.8 43 1.90E+07 ( 117) 7.31E+06 ( 45) 10 319 95 126.2 89.1 182.0 44 1.78E+07 ( 175) 8.02E+06 ( 79) 16 350 79 107.2 82.0 140.2 45 2.84E+07 ( 105) 1.30E+07 ( 48) 6 568 164 106.3 75.1 152.9 46 2.06E+07 ( 228) 8.57E+06 ( 95) 18 375 78 116.2 91.1 148.1 47 2.60E+07 ( 192) 1.30E+07 ( 96) 12 568 117 97.0 75.6 124.3 48 1.81E+07 ( 134) 6.63E+06 ( 49) 12 290 83 132.6 95.3 187.8 49 1.00E+07 ( 74) 9.74E+06 ( 72) 12 426 101 50.3 35.8 70.5 50 2.06E+07 ( 304) 5.61E+06 ( 83) 24 245 54 176.4 138.0 225.2 51 2.61E+07 ( 241) 5.84E+06 ( 54) 15 255 70 215.0 160.3 293.8 52 1.76E+07 ( 65) 1.08E+07 ( 40) 6 473 149 79.2 52.7 120.5 53 2.25E+07 ( 83) 4.06E+06 ( 15) 6 177 90 263.8 153.6 488.6 54 2.27E+07 ( 56) 1.01E+07 ( 25) 4 444 176 108.7 67.1 181.6 55 2.96E+07 ( 73) 1.62E+07 ( 40) 4 710 224 88.8 59.8 134.1 56 1.83E+07 ( 45) 5.28E+06 ( 13) 4 231 126 166.3 89.4 334.9 57 2.70E+07 ( 133) 6.09E+06 ( 30) 8 266 97 213.2 143.8 327.2 58 1.65E+07 ( 549) 6.25E+06 ( 208) 54 273 39 128.0 108.3 151.2 59 1.41E+07 ( 52) 5.41E+06 ( 20) 6 237 105 125.8 74.4 222.1 60 2.38E+07 ( 88) 1.35E+07 ( 50) 6 591 167 85.7 60.0 123.9 990805-3 (Axioskop, 010306-30) Number of grains = 60 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 49 1.00E+07 ( 74) 9.74E+06 ( 72) 50.3 35.8 70.5 100.0 50.5 36.0 70.8 36 1.62E+07 ( 40) 1.10E+07 ( 27) 72.2 43.4 122.2 22.0 56.0 42.7 73.6 32 1.33E+07 ( 49) 8.66E+06 ( 32) 74.6 47.0 120.3 26.3 60.6 47.9 76.6 6 8.66E+06 ( 48) 5.41E+06 ( 30) 78.3 48.7 127.8 30.2 63.9 51.7 78.9 12 1.63E+07 ( 201) 1.01E+07 ( 125) 78.5 62.5 98.6 23.8 70.4 60.0 82.5 52 1.76E+07 ( 65) 1.08E+07 ( 40) 79.2 52.7 120.5 32.3 71.5 61.5 83.0 60 2.38E+07 ( 88) 1.35E+07 ( 50) 85.7 60.0 123.9 34.1 73.4 63.8 84.5 9 9.42E+06 ( 116) 5.28E+06 ( 65) 87.3 64.0 120.2 34.2 75.4 66.2 86.0 20 9.20E+06 ( 68) 5.14E+06 ( 38) 87.5 58.1 133.7 39.4 76.4 67.3 86.7 25 2.10E+07 ( 155) 1.15E+07 ( 85) 88.8 67.9 116.0 38.6 78.3 69.6 88.1 55 2.96E+07 ( 73) 1.62E+07 ( 40) 88.8 59.8 134.1 44.1 79.1 70.5 88.6 16 1.10E+07 ( 68) 5.84E+06 ( 36) 92.3 60.9 142.2 48.1 79.8 71.4 89.2 10 1.51E+07 ( 149) 7.91E+06 ( 78) 92.9 70.5 122.5 46.6 81.3 73.1 90.4 33 1.95E+07 ( 48) 1.01E+07 ( 25) 93.3 56.7 157.8 52.1 81.7 73.5 90.8 1 1.62E+07 ( 140) 8.23E+06 ( 71) 95.8 71.9 127.8 50.1 83.0 75.0 91.9 14 1.69E+07 ( 125) 8.52E+06 ( 63) 97.0 71.2 133.5 50.1 84.0 76.1 92.7 47 2.60E+07 ( 192) 1.30E+07 ( 96) 97.0 75.6 124.3 47.7 85.3 77.6 93.9 5 1.15E+07 ( 106) 5.52E+06 ( 51) 101.5 72.2 144.7 47.4 86.1 78.5 94.6 34 3.21E+07 ( 99) 1.49E+07 ( 46) 104.6 73.2 151.8 46.0 87.0 79.3 95.3 45 2.84E+07 ( 105) 1.30E+07 ( 48) 106.3 75.1 152.9 43.8 87.8 80.2 96.1 40 9.74E+06 ( 90) 4.44E+06 ( 41) 106.7 73.2 158.3 43.3 88.5 80.9 96.8 44 1.78E+07 ( 175) 8.02E+06 ( 79) 107.2 82.0 140.2 37.1 89.7 82.2 97.9 54 2.27E+07 ( 56) 1.01E+07 ( 25) 108.7 67.1 181.6 39.1 90.1 82.6 98.3 7 1.62E+07 ( 100) 6.82E+06 ( 42) 116.1 80.5 170.6 34.2 90.9 83.4 99.1 46 2.06E+07 ( 228) 8.57E+06 ( 95) 116.2 91.1 148.1 21.0 92.7 85.2 100.8 28 1.32E+07 ( 122) 5.52E+06 ( 51) 116.7 83.7 165.0 18.1 93.5 86.1 101.7
193
30 7.22E+06 ( 178) 2.80E+06 ( 69) 125.1 94.5 165.4 9.8 95.0 87.5 103.1 59 1.41E+07 ( 52) 5.41E+06 ( 20) 125.8 74.4 222.1 9.7 95.4 87.9 103.5 43 1.90E+07 ( 117) 7.31E+06 ( 45) 126.2 89.1 182.0 7.2 96.3 88.8 104.4 19 1.93E+07 ( 286) 7.44E+06 ( 110) 126.4 101.0 158.0 2.6 98.3 90.8 106.4 39 1.60E+07 ( 237) 6.09E+06 ( 90) 127.3 99.6 162.8 1.2 99.8 92.3 107.9 58 1.65E+07 ( 549) 6.25E+06 ( 208) 128.0 108.3 151.2 0.2 102.8 95.3 110.9 48 1.81E+07 ( 134) 6.63E+06 ( 49) 132.6 95.3 187.8 0.1 103.5 96.0 111.6 8 1.66E+07 ( 205) 6.01E+06 ( 74) 134.3 102.7 175.4 0.1 104.6 97.1 112.7 2 1.22E+07 ( 45) 4.33E+06 ( 16) 136.3 76.4 257.8 0.1 104.9 97.3 113.0 24 1.60E+07 ( 158) 5.58E+06 ( 55) 139.8 102.6 193.6 0.0 105.8 98.2 113.9 18 1.51E+07 ( 93) 5.19E+06 ( 32) 141.3 94.1 217.9 0.0 106.3 98.7 114.4 990805-3 (Axioskop, 010306-30) Number of grains = 60 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 35 2.25E+07 ( 83) 7.58E+06 ( 28) 143.4 93.0 228.3 0.0 106.7 99.2 114.9 13 1.33E+07 ( 115) 4.29E+06 ( 37) 151.0 104.0 224.7 0.0 107.5 99.9 115.6 56 1.83E+07 ( 45) 5.28E+06 ( 13) 166.3 89.4 334.9 0.0 107.8 100.2 116.0 50 2.06E+07 ( 304) 5.61E+06 ( 83) 176.4 138.0 225.2 0.0 110.3 102.6 118.5 3 1.46E+07 ( 81) 3.61E+06 ( 20) 195.5 120.0 335.5 0.0 111.0 103.2 119.3 57 2.70E+07 ( 133) 6.09E+06 ( 30) 213.2 143.8 327.2 0.0 112.3 104.5 120.6 4 1.40E+07 ( 138) 3.15E+06 ( 31) 215.0 145.9 327.4 0.0 113.6 105.7 122.0 51 2.61E+07 ( 241) 5.84E+06 ( 54) 215.0 160.3 293.8 0.0 115.8 107.8 124.3 31 1.67E+07 ( 185) 3.52E+06 ( 39) 228.1 161.9 330.0 0.0 117.5 109.5 126.2 15 2.60E+07 ( 128) 5.48E+06 ( 27) 228.5 151.4 358.6 0.0 118.7 110.6 127.4 23 1.80E+07 ( 155) 3.71E+06 ( 32) 233.6 160.1 351.9 0.0 120.1 112.0 128.9 26 1.91E+07 ( 141) 3.92E+06 ( 29) 234.3 157.7 361.1 0.0 121.4 113.2 130.2 42 2.41E+07 ( 119) 4.67E+06 ( 23) 247.8 159.4 403.8 0.0 122.5 114.2 131.4 38 1.30E+07 ( 32) 2.44E+06 ( 6) 251.3 107.0 724.4 0.0 122.8 114.5 131.7 53 2.25E+07 ( 83) 4.06E+06 ( 15) 263.8 153.6 488.6 0.0 123.6 115.3 132.6 27 1.79E+07 ( 199) 3.16E+06 ( 35) 273.4 191.8 401.7 0.0 125.6 117.1 134.6 37 2.06E+07 ( 76) 3.52E+06 ( 13) 278.0 156.2 540.8 0.0 126.3 117.8 135.4 41 2.56E+07 ( 315) 4.22E+06 ( 52) 290.1 217.2 395.3 0.0 129.5 120.8 138.7 11 1.98E+07 ( 220) 2.44E+06 ( 27) 387.7 262.9 595.8 0.0 132.0 123.2 141.4 21 1.81E+07 ( 67) 2.16E+06 ( 8) 393.4 194.8 926.3 0.0 132.8 123.9 142.2 22 2.30E+07 ( 170) 2.57E+06 ( 19) 423.5 267.9 710.9 0.0 134.8 125.8 144.4 29 1.71E+07 ( 158) 1.84E+06 ( 17) 439.0 271.1 760.6 0.0 136.6 127.6 146.4 17 2.23E+07 ( 329) 1.49E+06 ( 22) 693.5 461.2 1095.5 0.0 141.1 131.8 151.1 POOL 1.72E+07( 8351) 5.93E+06( 2885) 0.0 141.1 131.8 151.1 MEAN URANIUM CONCENTRATION +/-2SE (ppm): 258.1, 12.6 POOLED AGE WITH 63% CONF. INTERVAL(Ma): 141.1, 136.3 -- 146.1 ( -4.8 +5.0) 95% CONF. INTERVAL(Ma): 131.8 -- 151.1 ( -9.3 +10.0) CHI^2 PROBABILITY: 0.0% CENTRAL AGE WITH 63% CONF. INTERVAL(Ma): 137.0, 128.2 -- 146.5 ( -8.9 +9.5) 95% CONF. INTERVAL(Ma): 120.2 -- 156.2 ( -16.8 +19.2) AGE DISPERSION (%): 43.9 CHI^2 AGE WITH 63% CONF. INTERVAL (Ma): 99.8, 95.9 -- 103.9 ( -3.9 +4.1) 95% CONF. INTERVAL (Ma): 92.3 -- 107.9 ( -7.5 +8.1) NUMBER AND PERCENTAGE OF GRAINS: 31, 52%
194
Pro
babili
ty d
ensity (
%/∆
z=
0.1
)990805-3
Upper Red Conglomerate, Upper Cretaceous Fort Crittenden FormationStation 42, Santa Rita Mountains
n = 60 grains (30 from 17 h etch, 30 from 12 h etch)
FT grain age (Ma)
30 50 70 300 50070010 100 1000
0
1
2
3
4
5
6
7
8
9
195
Middle Jurassic Bathtub Formation, Station 44 990805-5 (Axioskop, 020204-020207) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.774E+05 RELATIVE ERROR (%): 1.56 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 1 1.70E+07 ( 63) 6.22E+06 ( 23) 6 273 113 132.0 81.4 222.8 2 1.90E+07 ( 187) 6.80E+06 ( 67) 16 298 73 134.2 101.3 177.5 3 1.47E+07 ( 190) 1.41E+07 ( 182) 21 617 93 50.7 41.2 62.6 4 1.57E+07 ( 194) 8.93E+06 ( 110) 20 392 76 85.4 67.3 108.3 5 2.02E+07 ( 224) 2.01E+07 ( 223) 18 882 121 48.9 40.3 59.2 6 2.00E+07 ( 123) 1.44E+07 ( 89) 10 634 135 66.9 50.8 88.2 7 2.11E+07 ( 104) 1.24E+07 ( 61) 8 543 140 82.8 59.9 115.5 8 1.82E+07 ( 101) 5.77E+06 ( 32) 9 253 89 152.1 101.9 233.6 9 1.96E+07 ( 169) 1.02E+07 ( 88) 14 448 96 92.8 71.5 120.4 10 2.25E+07 ( 83) 9.47E+06 ( 35) 6 415 140 114.7 76.7 175.3 11 1.68E+07 ( 248) 1.43E+07 ( 212) 24 629 89 56.9 47.0 68.8 12 1.10E+07 ( 216) 4.52E+06 ( 89) 32 198 42 117.0 91.1 150.2 13 1.66E+07 ( 92) 1.46E+07 ( 81) 9 641 143 55.3 40.6 75.5 14 1.70E+07 ( 126) 6.36E+06 ( 47) 12 279 81 129.6 92.3 185.1 15 1.75E+07 ( 86) 8.52E+06 ( 42) 8 374 115 99.2 68.0 147.1 16 1.24E+07 ( 153) 1.69E+07 ( 208) 20 741 105 35.8 28.9 44.4 17 1.43E+07 ( 88) 1.51E+07 ( 93) 10 662 139 46.1 34.0 62.4 18 2.74E+07 ( 118) 2.34E+07 ( 101) 7 1028 207 56.7 43.3 74.2 19 2.19E+07 ( 162) 4.46E+06 ( 33) 12 196 68 234.9 162.1 351.4 20 2.53E+07 ( 187) 1.03E+07 ( 76) 12 451 104 118.5 90.6 155.0 21 2.13E+07 ( 118) 9.20E+06 ( 51) 9 404 113 112.0 80.2 158.7 22 2.06E+07 ( 152) 6.63E+06 ( 49) 12 291 83 149.7 108.2 210.8 23 2.00E+07 ( 185) 1.71E+07 ( 158) 15 750 121 56.9 45.7 70.7 24 1.88E+07 ( 139) 9.47E+06 ( 70) 12 415 100 95.8 71.7 127.9 25 1.95E+07 ( 120) 9.42E+06 ( 58) 10 413 109 100.3 72.9 139.7 26 1.61E+07 ( 89) 5.41E+06 ( 30) 9 237 86 143.0 94.2 223.8 27 1.76E+07 ( 65) 1.65E+07 ( 61) 6 724 186 51.9 36.0 74.9 28 1.89E+07 ( 105) 1.17E+07 ( 65) 9 514 128 78.5 57.1 108.7 29 2.44E+07 ( 120) 1.24E+07 ( 61) 8 543 140 95.4 69.7 132.1 30 1.26E+07 ( 140) 1.41E+07 ( 156) 18 617 101 43.6 34.5 55.1 >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.763E+05 RELATIVE ERROR (%): 1.55 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 31 3.06E+07 ( 113) 5.68E+06 ( 21) 6 250 108 255.4 161.3 426.1 32 2.53E+07 ( 156) 1.31E+07 ( 81) 10 579 130 92.6 70.6 121.5 33 3.14E+07 ( 116) 2.30E+07 ( 85) 6 1013 221 65.8 49.6 87.3 34 3.07E+07 ( 189) 5.19E+06 ( 32) 10 229 81 280.4 193.9 419.4 35 2.37E+07 ( 175) 9.20E+06 ( 68) 12 405 99 123.3 93.0 163.4 990805-5 (Axioskop, 020204-020207) ------ GRAIN AGES IN ORIGINAL ORDER ------
196
Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 36 3.41E+07 ( 126) 1.49E+07 ( 55) 6 655 177 110.5 80.1 154.5 37 2.64E+07 ( 325) 8.60E+06 ( 106) 20 379 74 147.0 117.6 183.7 38 2.48E+07 ( 153) 9.09E+06 ( 56) 10 400 107 131.5 96.5 181.9 39 2.13E+07 ( 197) 1.39E+07 ( 128) 15 610 109 74.3 59.2 93.2 40 2.47E+07 ( 152) 1.61E+07 ( 99) 10 708 144 74.0 57.3 95.7 41 2.46E+07 ( 182) 8.52E+06 ( 63) 12 375 95 138.2 103.6 184.2 42 2.15E+07 ( 238) 2.09E+07 ( 232) 18 922 124 49.7 41.2 60.0 43 2.93E+07 ( 271) 7.36E+06 ( 68) 15 324 79 190.0 145.5 247.9 44 1.81E+07 ( 167) 4.11E+06 ( 38) 15 181 59 210.0 147.9 306.2 45 2.08E+07 ( 192) 1.75E+07 ( 162) 15 772 124 57.3 46.3 71.1 46 2.76E+07 ( 102) 1.16E+07 ( 43) 6 512 156 114.3 79.6 167.2 47 2.37E+07 ( 175) 1.10E+07 ( 81) 12 483 108 103.8 79.5 135.4 48 2.33E+07 ( 115) 1.10E+07 ( 54) 8 483 132 102.8 73.9 144.8 49 3.06E+07 ( 151) 1.85E+07 ( 91) 8 813 172 79.9 61.4 104.0 50 2.62E+07 ( 129) 8.73E+06 ( 43) 8 384 117 144.2 101.8 208.4 51 2.62E+07 ( 258) 1.21E+07 ( 119) 16 532 99 104.4 83.6 130.3 990805-5 (Axioskop, 020204-020207) Number of grains = 51 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 16 1.24E+07 ( 153) 1.69E+07 ( 208) 35.8 28.9 44.4 100.0 35.8 28.9 44.4 30 1.26E+07 ( 140) 1.41E+07 ( 156) 43.6 34.5 55.1 20.7 39.2 33.3 46.1 17 1.43E+07 ( 88) 1.51E+07 ( 93) 46.1 34.0 62.4 28.5 40.6 35.1 47.0 5 2.02E+07 ( 224) 2.01E+07 ( 223) 48.9 40.3 59.2 17.0 43.4 38.4 49.0 42 2.15E+07 ( 238) 2.09E+07 ( 232) 49.7 41.2 60.0 15.5 45.0 40.4 50.1 3 1.47E+07 ( 190) 1.41E+07 ( 182) 50.7 41.2 62.6 16.7 46.0 41.6 50.8 27 1.76E+07 ( 65) 1.65E+07 ( 61) 51.9 36.0 74.9 22.0 46.3 41.9 51.1 13 1.66E+07 ( 92) 1.46E+07 ( 81) 55.3 40.6 75.5 21.7 46.9 42.6 51.6 18 2.74E+07 ( 118) 2.34E+07 ( 101) 56.7 43.3 74.2 17.9 47.6 43.4 52.3 11 1.68E+07 ( 248) 1.43E+07 ( 212) 56.9 47.0 68.8 10.4 48.9 44.8 53.4 23 2.00E+07 ( 185) 1.71E+07 ( 158) 56.9 45.7 70.7 8.9 49.7 45.6 54.1 45 2.08E+07 ( 192) 1.75E+07 ( 162) 57.3 46.3 71.1 7.9 50.3 46.3 54.7 33 3.14E+07 ( 116) 2.30E+07 ( 85) 65.8 49.6 87.3 4.2 51.0 47.0 55.4 6 2.00E+07 ( 123) 1.44E+07 ( 89) 66.9 50.8 88.2 2.0 51.7 47.7 56.1 40 2.47E+07 ( 152) 1.61E+07 ( 99) 74.0 57.3 95.7 0.3 52.8 48.8 57.2 39 2.13E+07 ( 197) 1.39E+07 ( 128) 74.3 59.2 93.2 0.0 54.0 50.0 58.4 28 1.89E+07 ( 105) 1.17E+07 ( 65) 78.5 57.1 108.7 0.0 54.7 50.6 59.1 49 3.06E+07 ( 151) 1.85E+07 ( 91) 79.9 61.4 104.0 0.0 55.7 51.6 60.1 7 2.11E+07 ( 104) 1.24E+07 ( 61) 82.8 59.9 115.5 0.0 56.3 52.2 60.8 4 1.57E+07 ( 194) 8.93E+06 ( 110) 85.4 67.3 108.3 0.0 57.6 53.4 62.1 32 2.53E+07 ( 156) 1.31E+07 ( 81) 92.6 70.6 121.5 0.0 58.7 54.5 63.2 9 1.96E+07 ( 169) 1.02E+07 ( 88) 92.8 71.5 120.4 0.0 59.8 55.5 64.3 29 2.44E+07 ( 120) 1.24E+07 ( 61) 95.4 69.7 132.1 0.0 60.5 56.3 65.1 24 1.88E+07 ( 139) 9.47E+06 ( 70) 95.8 71.7 127.9 0.0 61.4 57.1 66.0 15 1.75E+07 ( 86) 8.52E+06 ( 42) 99.2 68.0 147.1 0.0 62.0 57.6 66.6 25 1.95E+07 ( 120) 9.42E+06 ( 58) 100.3 72.9 139.7 0.0 62.7 58.4 67.4 48 2.33E+07 ( 115) 1.10E+07 ( 54) 102.8 73.9 144.8 0.0 63.4 59.0 68.1 47 2.37E+07 ( 175) 1.10E+07 ( 81) 103.8 79.5 135.4 0.0 64.5 60.1 69.2 51 2.62E+07 ( 258) 1.21E+07 ( 119) 104.4 83.6 130.3 0.0 66.0 61.5 70.8 36 3.41E+07 ( 126) 1.49E+07 ( 55) 110.5 80.1 154.5 0.0 66.7 62.2 71.6 21 2.13E+07 ( 118) 9.20E+06 ( 51) 112.0 80.2 158.7 0.0 67.4 62.9 72.3 46 2.76E+07 ( 102) 1.16E+07 ( 43) 114.3 79.6 167.2 0.0 68.0 63.4 72.9 10 2.25E+07 ( 83) 9.47E+06 ( 35) 114.7 76.7 175.3 0.0 68.5 63.9 73.4 12 1.10E+07 ( 216) 4.52E+06 ( 89) 117.0 91.1 150.2 0.0 69.7 65.1 74.7 20 2.53E+07 ( 187) 1.03E+07 ( 76) 118.5 90.6 155.0 0.0 70.8 66.1 75.8 35 2.37E+07 ( 175) 9.20E+06 ( 68) 123.3 93.0 163.4 0.0 71.8 67.0 76.9
197
14 1.70E+07 ( 126) 6.36E+06 ( 47) 129.6 92.3 185.1 0.0 72.5 67.7 77.6 990805-5 (Axioskop, 020204-020207) Number of grains = 51 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 38 2.48E+07 ( 153) 9.09E+06 ( 56) 131.5 96.5 181.9 0.0 73.4 68.6 78.6 1 1.70E+07 ( 63) 6.22E+06 ( 23) 132.0 81.4 222.8 0.0 73.8 68.9 78.9 2 1.90E+07 ( 187) 6.80E+06 ( 67) 134.2 101.3 177.5 0.0 74.8 70.0 80.0 41 2.46E+07 ( 182) 8.52E+06 ( 63) 138.2 103.6 184.2 0.0 75.9 70.9 81.1 26 1.61E+07 ( 89) 5.41E+06 ( 30) 143.0 94.2 223.8 0.0 76.4 71.4 81.7 50 2.62E+07 ( 129) 8.73E+06 ( 43) 144.2 101.8 208.4 0.0 77.1 72.1 82.5 37 2.64E+07 ( 325) 8.60E+06 ( 106) 147.0 117.6 183.7 0.0 79.0 73.9 84.4 22 2.06E+07 ( 152) 6.63E+06 ( 49) 149.7 108.2 210.8 0.0 79.8 74.7 85.3 8 1.82E+07 ( 101) 5.77E+06 ( 32) 152.1 101.9 233.6 0.0 80.4 75.2 85.9 43 2.93E+07 ( 271) 7.36E+06 ( 68) 190.0 145.5 247.9 0.0 82.2 76.9 87.8 44 1.81E+07 ( 167) 4.11E+06 ( 38) 210.0 147.9 306.2 0.0 83.3 78.0 89.0 19 2.19E+07 ( 162) 4.46E+06 ( 33) 234.9 162.1 351.4 0.0 84.5 79.1 90.2 31 3.06E+07 ( 113) 5.68E+06 ( 21) 255.4 161.3 426.1 0.0 85.3 79.9 91.1 34 3.07E+07 ( 189) 5.19E+06 ( 32) 280.4 193.9 419.4 0.0 86.8 81.3 92.7 POOL 2.05E+07( 7829) 1.15E+07( 4383) 0.0 86.8 81.3 92.7 MEAN URANIUM CONCENTRATION +/-2SE (ppm): 503.5, 21.9 POOLED AGE WITH 63% CONF. INTERVAL(Ma): 86.8, 84.0 -- 89.7 ( -2.8 +2.9) 95% CONF. INTERVAL(Ma): 81.3 -- 92.7 ( -5.5 +5.9) CHI^2 PROBABILITY: 0.0% CENTRAL AGE WITH 63% CONF. INTERVAL(Ma): 92.7, 86.5 -- 99.4 ( -6.2 +6.7) 95% CONF. INTERVAL(Ma): 80.9 -- 106.3 ( -11.8 +13.6) AGE DISPERSION (%): 43.8 CHI^2 AGE WITH 63% CONF. INTERVAL (Ma): 51.7, 49.7 -- 53.9 ( -2.1 +2.2) 95% CONF. INTERVAL (Ma): 47.7 -- 56.1 ( -4.0 +4.4) NUMBER AND PERCENTAGE OF GRAINS: 14, 27%
198
Pro
babili
ty d
ensity (
%/∆
z=
0.1
)990805-5
Upper Jurassic Bathtub FormationStation 44, Santa Rita Mountains
n = 51 grains (30 from 17 h etch, 21 from 12 h etch)
FT grain age (Ma)
30 50 70 300 500 70010 100 10000
1
2
3
4
5
6
7
199
basal conglomerate subunit, Upper Cretaceous Fort Crittenden Formation, Station 45 000724-1b/a (U20Y) & 000724-1d/c (U26Z) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.973E+05 RELATIVE ERROR (%): 1.66 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 1 2.26E+07 ( 668) 1.17E+07 ( 345) 48 478 54 100.6 87.4 115.7 2 1.79E+07 ( 275) 8.96E+06 ( 138) 25 367 64 103.3 83.7 127.4 3 2.56E+07 ( 189) 8.93E+06 ( 66) 12 365 90 147.4 111.2 195.2 4 3.44E+07 ( 297) 7.88E+06 ( 68) 14 323 79 223.5 171.5 290.8 5 2.26E+07 ( 292) 1.04E+07 ( 135) 21 427 75 112.0 90.9 138.1 6 1.75E+07 ( 517) 6.02E+06 ( 178) 48 246 38 150.1 125.8 179.1 7 1.86E+07 ( 240) 5.26E+06 ( 68) 21 215 52 181.2 138.2 237.3 8 2.86E+07 ( 247) 1.41E+07 ( 122) 14 579 106 104.9 84.0 130.9 9 2.84E+07 ( 175) 7.47E+06 ( 46) 10 306 90 196.0 141.6 276.8 10 1.53E+07 ( 170) 7.85E+06 ( 87) 18 321 69 101.1 77.8 131.3 11 3.09E+07 ( 343) 1.39E+07 ( 154) 18 569 93 115.4 94.8 140.4 12 3.16E+07 ( 175) 3.61E+06 ( 20) 9 148 65 440.1 281.5 727.9 13 1.68E+07 ( 249) 5.55E+06 ( 82) 24 227 51 156.4 121.5 201.1 >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.992E+05 RELATIVE ERROR (%): 1.71 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 14 1.69E+07 ( 416) 6.90E+06 ( 170) 40 281 44 127.5 106.0 153.4 15 1.14E+07 ( 105) 5.63E+06 ( 52) 15 229 64 105.5 75.2 150.1 16 2.39E+07 ( 147) 1.01E+07 ( 62) 10 409 105 123.7 91.5 169.3 17 2.04E+07 ( 151) 6.90E+06 ( 51) 12 281 79 154.1 111.9 215.8 >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.922E+05 RELATIVE ERROR (%): 1.58 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 18 2.31E+07 ( 456) 6.04E+06 ( 119) 32 251 47 193.7 157.7 237.9 19 1.80E+07 ( 133) 1.34E+07 ( 99) 12 558 113 68.5 52.6 89.2 20 2.21E+07 ( 204) 1.84E+07 ( 170) 15 766 120 61.4 49.8 75.7 21 2.06E+07 ( 190) 7.03E+06 ( 65) 15 293 73 147.8 111.4 196.0 22 2.02E+07 ( 373) 8.66E+06 ( 160) 30 361 58 118.7 98.0 143.7 23 1.83E+07 ( 339) 5.30E+06 ( 98) 30 221 45 175.0 139.3 219.7 000724-1b/a (U20Y) & 000724-1d/c (U26Z) >>NEW PARAMETERS--ZETA METHOD<<
200
EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.916E+05 RELATIVE ERROR (%): 1.63 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 24 2.51E+07 ( 278) 1.10E+07 ( 122) 18 459 84 115.7 93.1 143.8 25 3.06E+07 ( 226) 5.01E+06 ( 37) 12 209 69 305.6 217.1 442.8 26 2.49E+07 ( 276) 7.12E+06 ( 79) 18 297 67 176.2 136.9 226.5 000724-1b/a (U20Y) & 000724-1d/c (U26Z) Number of grains = 26 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 20 2.21E+07 ( 204) 1.84E+07 ( 170) 61.4 49.8 75.7 100.0 61.4 49.8 75.6 19 1.80E+07 ( 133) 1.34E+07 ( 99) 68.5 52.6 89.2 50.1 64.1 54.2 75.9 1 2.26E+07 ( 668) 1.17E+07 ( 345) 100.6 87.4 115.7 0.0 84.6 75.5 94.7 10 1.53E+07 ( 170) 7.85E+06 ( 87) 101.1 77.8 131.3 0.0 86.7 77.8 96.5 2 1.79E+07 ( 275) 8.96E+06 ( 138) 103.3 83.7 127.4 0.0 89.4 80.9 98.9 8 2.86E+07 ( 247) 1.41E+07 ( 122) 104.9 84.0 130.9 0.0 91.4 83.1 100.6 15 1.14E+07 ( 105) 5.63E+06 ( 52) 105.5 75.2 150.1 0.0 92.2 83.9 101.3 5 2.26E+07 ( 292) 1.04E+07 ( 135) 112.0 90.9 138.1 0.0 94.5 86.4 103.5 11 3.09E+07 ( 343) 1.39E+07 ( 154) 115.4 94.8 140.4 0.0 97.0 89.0 105.8 24 2.51E+07 ( 278) 1.10E+07 ( 122) 115.7 93.1 143.8 0.0 98.7 90.7 107.4 22 2.02E+07 ( 373) 8.66E+06 ( 160) 118.7 98.0 143.7 0.0 100.8 92.9 109.3 16 2.39E+07 ( 147) 1.01E+07 ( 62) 123.7 91.5 169.3 0.0 101.6 93.8 110.2 14 1.69E+07 ( 416) 6.90E+06 ( 170) 127.5 106.0 153.4 0.0 104.1 96.2 112.6 3 2.56E+07 ( 189) 8.93E+06 ( 66) 147.4 111.2 195.2 0.0 105.6 97.7 114.1 21 2.06E+07 ( 190) 7.03E+06 ( 65) 147.8 111.4 196.0 0.0 107.1 99.2 115.6 6 1.75E+07 ( 517) 6.02E+06 ( 178) 150.1 125.8 179.1 0.0 110.7 102.7 119.4 17 2.04E+07 ( 151) 6.90E+06 ( 51) 154.1 111.9 215.8 0.0 111.7 103.7 120.4 13 1.68E+07 ( 249) 5.55E+06 ( 82) 156.4 121.5 201.1 0.0 113.4 105.3 122.1 23 1.83E+07 ( 339) 5.30E+06 ( 98) 175.0 139.3 219.7 0.0 116.0 107.9 124.8 26 2.49E+07 ( 276) 7.12E+06 ( 79) 176.2 136.9 226.5 0.0 118.1 109.8 126.9 7 1.86E+07 ( 240) 5.26E+06 ( 68) 181.2 138.2 237.3 0.0 119.8 111.5 128.7 18 2.31E+07 ( 456) 6.04E+06 ( 119) 193.7 157.7 237.9 0.0 123.3 114.8 132.3 9 2.84E+07 ( 175) 7.47E+06 ( 46) 196.0 141.6 276.8 0.0 124.5 116.0 133.7 4 3.44E+07 ( 297) 7.88E+06 ( 68) 223.5 171.5 290.8 0.0 127.0 118.4 136.3 25 3.06E+07 ( 226) 5.01E+06 ( 37) 305.6 217.1 442.8 0.0 129.5 120.7 138.9 12 3.16E+07 ( 175) 3.61E+06 ( 20) 440.1 281.5 727.9 0.0 131.8 122.9 141.3 POOL 2.14E+07( 7131) 8.43E+06( 2808) 0.0 131.8 122.9 141.3 MEAN URANIUM CONCENTRATION +/-2SE (ppm): 344.9, 17.3 POOLED AGE WITH 63% CONF. INTERVAL(Ma): 131.8, 127.2 -- 136.6 ( -4.6 +4.8) 95% CONF. INTERVAL(Ma): 122.9 -- 141.3 ( -8.9 +9.5) CHI^2 PROBABILITY: 0.0% CENTRAL AGE WITH 63% CONF. INTERVAL(Ma): 135.6, 125.3 -- 146.7 ( -10.3 +11.1) 95% CONF. INTERVAL(Ma): 116.2 -- 158.2 ( -19.4 +22.6) AGE DISPERSION (%): 36.0 CHI^2 AGE WITH 63% CONF. INTERVAL (Ma): 64.1, 58.9 -- 69.9 ( -5.3 +5.7) 95% CONF. INTERVAL (Ma): 54.2 -- 75.9 ( -9.9 +11.7) NUMBER AND PERCENTAGE OF GRAINS: 2, 8%
201
Pro
ba
bili
ty d
en
sity (
%/∆
z=
0.1
)000724-1
Upper Cretaceous Fort Crittenden FormationStation 45, Huachuca Mountains
n = 26 grains (6 from 14 h etch; 3 from 13 h etch;
FT grain age (Ma)
30 50 70 300 500 70010 1000
1
2
3
4
5
6
13 from 10 h etch; 4 from 5 h etch)
202
upper conglomerate subunit, Upper Cretaceous Fort Crittenden Formation, Station 46 000724-2 b/A (U20Y) & d/c (U26Z) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.937E+05 RELATIVE ERROR (%): 1.57 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 1 2.16E+07 ( 319) 7.37E+06 ( 109) 24 306 59 149.2 119.6 186.1 2 2.11E+07 ( 208) 8.93E+06 ( 88) 16 370 80 120.6 93.7 155.2 3 2.34E+07 ( 144) 8.93E+06 ( 55) 10 370 100 134.0 97.8 186.2 4 1.95E+07 ( 108) 1.03E+07 ( 57) 9 426 113 97.3 70.1 136.5 5 3.46E+07 ( 256) 1.07E+07 ( 79) 12 443 100 164.7 127.7 212.3 6 1.61E+07 ( 149) 7.36E+06 ( 68) 15 305 74 111.7 83.7 149.1 7 2.64E+07 ( 130) 7.31E+06 ( 36) 8 303 101 183.8 127.0 273.2 8 3.75E+07 ( 231) 1.95E+07 ( 120) 10 807 149 98.6 78.7 123.4 9 2.53E+07 ( 437) 1.03E+07 ( 178) 28 428 65 125.6 104.8 150.4 10 2.34E+07 ( 360) 6.43E+06 ( 99) 25 266 54 184.8 147.4 231.4 >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.955E+05 RELATIVE ERROR (%): 1.61 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 11 2.12E+07 ( 209) 6.49E+06 ( 64) 16 267 67 166.7 125.9 220.7 >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.903E+05 RELATIVE ERROR (%): 1.74 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 12 3.08E+07 ( 190) 3.25E+06 ( 20) 10 136 60 465.6 298.7 767.9 13 3.33E+07 ( 246) 3.11E+06 ( 23) 12 130 54 522.4 346.6 826.1 14 1.59E+07 ( 196) 4.22E+06 ( 52) 20 177 49 189.7 139.7 262.4 15 1.87E+07 ( 138) 4.60E+06 ( 34) 12 193 66 203.8 140.1 305.2 000724-2 b/A (U20Y) & d/c (U26Z) ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 16 3.21E+07 ( 198) 1.01E+07 ( 62) 10 421 107 160.6 120.6 213.6 17 3.45E+07 ( 255) 1.27E+07 ( 94) 12 532 111 137.0 107.8 174.1 18 3.08E+07 ( 379) 2.52E+07 ( 311) 20 1056 125 62.1 53.0 72.8 000724-2 b/A (U20Y) & d/c (U26Z) Number of grains = 18 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------
203
Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 18 3.08E+07 ( 379) 2.52E+07 ( 311) 62.1 53.0 72.8 100.0 62.1 53.0 72.8 4 1.95E+07 ( 108) 1.03E+07 ( 57) 97.3 70.1 136.5 1.2 67.6 58.4 78.1 8 3.75E+07 ( 231) 1.95E+07 ( 120) 98.6 78.7 123.4 0.1 75.2 66.3 85.4 6 1.61E+07 ( 149) 7.36E+06 ( 68) 111.7 83.7 149.1 0.0 79.8 70.8 89.8 2 2.11E+07 ( 208) 8.93E+06 ( 88) 120.6 93.7 155.2 0.0 85.4 76.5 95.5 9 2.53E+07 ( 437) 1.03E+07 ( 178) 125.6 104.8 150.4 0.0 94.2 85.2 104.1 3 2.34E+07 ( 144) 8.93E+06 ( 55) 134.0 97.8 186.2 0.0 96.7 87.7 106.6 17 3.45E+07 ( 255) 1.27E+07 ( 94) 137.0 107.8 174.1 0.0 100.7 91.7 110.6 1 2.16E+07 ( 319) 7.37E+06 ( 109) 149.2 119.6 186.1 0.0 105.7 96.6 115.6 16 3.21E+07 ( 198) 1.01E+07 ( 62) 160.6 120.6 213.6 0.0 108.7 99.6 118.7 5 3.46E+07 ( 256) 1.07E+07 ( 79) 164.7 127.7 212.3 0.0 112.4 103.1 122.5 11 2.12E+07 ( 209) 6.49E+06 ( 64) 166.7 125.9 220.7 0.0 115.2 105.8 125.3 7 2.64E+07 ( 130) 7.31E+06 ( 36) 183.8 127.0 273.2 0.0 117.1 107.7 127.3 10 2.34E+07 ( 360) 6.43E+06 ( 99) 184.8 147.4 231.4 0.0 121.9 112.3 132.2 14 1.59E+07 ( 196) 4.22E+06 ( 52) 189.7 139.7 262.4 0.0 124.3 114.7 134.7 15 1.87E+07 ( 138) 4.60E+06 ( 34) 203.8 140.1 305.2 0.0 126.1 116.4 136.6 12 3.08E+07 ( 190) 3.25E+06 ( 20) 465.6 298.7 767.9 0.0 130.8 120.8 141.6 13 3.33E+07 ( 246) 3.11E+06 ( 23) 522.4 346.6 826.1 0.0 136.9 126.5 148.1 POOL 2.51E+07( 4153) 9.38E+06( 1555) 0.0 136.9 126.5 148.1 MEAN URANIUM CONCENTRATION +/-2SE (ppm): 388.8, 23.2 POOLED AGE WITH 63% CONF. INTERVAL(Ma): 136.9, 131.5 -- 142.5 ( -5.4 +5.6) 95% CONF. INTERVAL(Ma): 126.5 -- 148.1 ( -10.4 +11.2) CHI^2 PROBABILITY: 0.0% CENTRAL AGE WITH 63% CONF. INTERVAL(Ma): 149.3, 134.2 -- 166.1 ( -15.1 +16.8) 95% CONF. INTERVAL(Ma): 121.1 -- 184.0 ( -28.2 +34.6) AGE DISPERSION (%): 42.1 CHI^2 AGE WITH 63% CONF. INTERVAL (Ma): 67.6, 62.7 -- 72.7 ( -4.8 +5.2) 95% CONF. INTERVAL (Ma): 58.4 -- 78.1 ( -9.1 +10.5) NUMBER AND PERCENTAGE OF GRAINS: 2, 11%
204
Pro
ba
bili
ty d
en
sity (
%/∆
z=
0.1
)000724-2
Upper Cretaceous Fort Crittenden FormationStation 46, Huachuca Mountains
n = 18 grains (4 from 13 h etch; 13 from 10 h etch; 1 from 5 h etch)
FT grain age (Ma)
30 50 70 300 500 70010 1000
1
2
3
4
205
shale unit, Upper Cretaceous Fort Crittenden Formation, Station 47 000724-3 long etch (Axioskop, 030826) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.896E+05 RELATIVE ERROR (%): 1.81 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 1 3.71E+07 ( 183) 7.91E+06 ( 39) 8 333 107 234.5 166.3 339.5 2 1.99E+07 ( 184) 5.74E+06 ( 53) 15 241 66 174.5 128.4 241.4 3 1.90E+07 ( 234) 6.66E+06 ( 82) 20 280 62 143.3 111.1 184.8 4 2.79E+07 ( 258) 5.84E+06 ( 54) 15 246 67 238.9 178.5 325.9 5 2.57E+07 ( 380) 5.01E+06 ( 74) 24 210 49 255.4 198.8 327.7 000724-3 long etch (Axioskop, 030826) Number of grains = 5 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 3 1.90E+07 ( 234) 6.66E+06 ( 82) 143.3 111.1 184.8 100.0 143.3 111.1 184.8 2 1.99E+07 ( 184) 5.74E+06 ( 53) 174.5 128.4 241.4 33.1 155.7 127.5 190.0 1 3.71E+07 ( 183) 7.91E+06 ( 39) 234.5 166.3 339.5 7.2 173.6 145.6 206.8 4 2.79E+07 ( 258) 5.84E+06 ( 54) 238.9 178.5 325.9 2.8 189.2 162.1 220.8 5 2.57E+07 ( 380) 5.01E+06 ( 74) 255.4 198.8 327.7 0.7 205.9 179.7 235.8 POOL 2.45E+07( 1239) 5.98E+06( 302) 0.7 205.9 179.7 235.8 MEAN URANIUM CONCENTRATION +/-2SE (ppm): 251.2, 30.3 POOLED AGE WITH 63% CONF. INTERVAL(Ma): 205.9, 192.1 -- 220.7 ( -13.8 +14.8) 95% CONF. INTERVAL(Ma): 179.7 -- 235.8 ( -26.2 +29.9) CHI^2 PROBABILITY: 0.7% CENTRAL AGE WITH 63% CONF. INTERVAL(Ma): 203.4, 182.4 -- 226.7 ( -21.0 +23.3) 95% CONF. INTERVAL(Ma): 164.3 -- 251.6 ( -39.1 +48.2) AGE DISPERSION (%): 18.9 CHI^2 AGE WITH 63% CONF. INTERVAL (Ma): 189.2, 174.9 -- 204.7 ( -14.3 +15.5) 95% CONF. INTERVAL (Ma): 162.1 -- 220.8 ( -27.1 +31.6) NUMBER AND PERCENTAGE OF GRAINS: 4, 80%
206
upper? conglomerate subunit, Upper Cretaceous Fort Crittenden Formation, Station 49 000725-1 (Axioskop, 020708-020709) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.863E+05 RELATIVE ERROR (%): 1.52 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 1 2.17E+07 ( 187) 1.09E+07 ( 94) 14 463 96 99.2 77.1 127.5 >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.882E+05 RELATIVE ERROR (%): 1.52 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 2 3.21E+07 ( 237) 7.31E+06 ( 54) 12 308 84 218.8 163.0 299.1 3 2.25E+07 ( 166) 9.06E+06 ( 67) 12 383 94 123.8 93.1 164.6 4 3.11E+07 ( 134) 1.25E+07 ( 54) 7 529 144 124.7 90.5 174.2 5 2.20E+07 ( 217) 1.11E+07 ( 109) 16 467 90 100.0 79.1 126.3 000725-1 (Axioskop, 020708-020709) Number of grains = 5 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 1 2.17E+07 ( 187) 1.09E+07 ( 94) 99.2 77.1 127.5 100.0 99.2 77.1 127.5 5 2.20E+07 ( 217) 1.11E+07 ( 109) 100.0 79.1 126.3 96.6 99.8 83.7 119.0 3 2.25E+07 ( 166) 9.06E+06 ( 67) 123.8 93.1 164.6 41.9 106.0 90.9 123.5 4 3.11E+07 ( 134) 1.25E+07 ( 54) 124.7 90.5 174.2 45.6 109.1 94.8 125.7 2 3.21E+07 ( 237) 7.31E+06 ( 54) 218.8 163.0 299.1 0.0 124.9 109.7 142.3 POOL 2.50E+07( 941) 1.00E+07( 376) 0.0 124.9 109.7 142.3 MEAN URANIUM CONCENTRATION +/-2SE (ppm): 425.5, 45.7 POOLED AGE WITH 63% CONF. INTERVAL(Ma): 124.9, 116.9 -- 133.5 ( -8.0 +8.6) 95% CONF. INTERVAL(Ma): 109.7 -- 142.3 ( -15.2 +17.3) CHI^2 PROBABILITY: 0.0% CENTRAL AGE WITH 63% CONF. INTERVAL(Ma): 125.5, 110.7 -- 142.2 ( -14.8 +16.7) 95% CONF. INTERVAL(Ma): 98.2 -- 160.3 ( -27.3 +34.8) AGE DISPERSION (%): 23.9 CHI^2 AGE WITH 63% CONF. INTERVAL (Ma): 109.1, 101.6 -- 117.3 ( -7.6 +8.1) 95% CONF. INTERVAL (Ma): 94.8 -- 125.7 ( -14.4 +16.5) NUMBER AND PERCENTAGE OF GRAINS: 4, 80%
207
shale member, Upper Cretaceous Fort Crittenden Formation, Station 52 000730-2 (Axioskop, 020710) >>NEW PARAMETERS--ZETA METHOD<< EFFECTIVE TRACK DENSITY FOR FLUENCE MONITOR (tracks/cm^2): 2.790E+05 RELATIVE ERROR (%): 1.64 EFFECTIVE URANIUM CONTENT OF MONITOR (ppm): 12.17 ZETA FACTOR AND STANDARD ERROR (yr cm^2): 352.74 8.09 SIZE OF COUNTER SQUARE (cm^2): 6.160E-07 ------ GRAIN AGES IN ORIGINAL ORDER ------ Grain RhoS (Ns) RhoI (Ni) Squares U+/-2s Grain Age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- 1 3.13E+07 ( 231) 5.14E+06 ( 38) 12 224 73 291.4 207.8 420.2 2 3.52E+07 ( 195) 8.66E+06 ( 48) 9 378 109 196.4 143.3 274.7 3 2.78E+07 ( 137) 2.84E+06 ( 14) 8 124 65 459.7 271.3 846.8 4 4.42E+07 ( 218) 1.36E+07 ( 67) 8 593 146 157.0 119.2 206.7 5 3.04E+07 ( 375) 9.74E+06 ( 120) 20 425 79 151.4 122.7 186.7 6 2.15E+07 ( 185) 7.77E+06 ( 67) 14 339 83 133.5 100.8 176.8 7 3.69E+07 ( 182) 6.09E+06 ( 30) 8 266 97 290.5 198.7 440.4 8 3.08E+07 ( 456) 5.07E+06 ( 75) 24 221 51 290.6 227.5 370.7 9 3.28E+07 ( 182) 1.32E+07 ( 73) 9 574 135 120.7 91.8 158.7 10 3.04E+07 ( 225) 6.49E+06 ( 48) 12 283 82 226.0 165.8 314.7 11 2.81E+07 ( 415) 9.00E+06 ( 133) 24 392 69 151.2 123.7 184.7 12 2.95E+07 ( 291) 5.48E+06 ( 54) 16 239 65 259.2 194.4 352.3 13 3.34E+07 ( 288) 6.73E+06 ( 58) 14 293 77 237.9 179.4 314.8 000730-2 (Axioskop, 020710) Number of grains = 13 ------ GRAIN AGES ORDERED WITH INCREASING AGE ------ Grain RhoS (Ns) RhoI (Ni) Grain age (Ma) P(X2) Sum age (Ma) no. (cm^-2) (cm^-2) Age --95% CI-- (%) Age --95% CI-- 9 3.28E+07 ( 182) 1.32E+07 ( 73) 120.7 91.8 158.7 100.0 120.7 91.8 158.7 6 2.15E+07 ( 185) 7.77E+06 ( 67) 133.5 100.8 176.8 60.7 127.3 104.2 155.5 11 2.81E+07 ( 415) 9.00E+06 ( 133) 151.2 123.7 184.7 40.5 139.2 120.2 161.2 5 3.04E+07 ( 375) 9.74E+06 ( 120) 151.4 122.7 186.7 51.1 143.1 126.2 162.2 4 4.42E+07 ( 218) 1.36E+07 ( 67) 157.0 119.2 206.7 59.8 145.3 129.1 163.4 2 3.52E+07 ( 195) 8.66E+06 ( 48) 196.4 143.3 274.7 29.7 150.2 134.1 168.1 10 3.04E+07 ( 225) 6.49E+06 ( 48) 226.0 165.8 314.7 5.1 156.8 140.6 174.8 13 3.34E+07 ( 288) 6.73E+06 ( 58) 237.9 179.4 314.8 0.4 164.7 148.4 182.8 12 2.95E+07 ( 291) 5.48E+06 ( 54) 259.2 194.4 352.3 0.0 172.4 155.9 190.7 7 3.69E+07 ( 182) 6.09E+06 ( 30) 290.5 198.7 440.4 0.0 177.6 160.9 196.0 8 3.08E+07 ( 456) 5.07E+06 ( 75) 290.6 227.5 370.7 0.0 188.8 171.7 207.6 1 3.13E+07 ( 231) 5.14E+06 ( 38) 291.4 207.8 420.2 0.0 193.7 176.4 212.6 3 2.78E+07 ( 137) 2.84E+06 ( 14) 459.7 271.3 846.8 0.0 198.4 180.8 217.6 POOL 3.08E+07( 3380) 7.52E+06( 825) 0.0 198.4 180.8 217.6 MEAN URANIUM CONCENTRATION +/-2SE (ppm): 328.2, 25.3 POOLED AGE WITH 63% CONF. INTERVAL(Ma): 198.4, 189.2 -- 208.0 ( -9.2 +9.6) 95% CONF. INTERVAL(Ma): 180.8 -- 217.6 ( -17.6 +19.2) CHI^2 PROBABILITY: 0.0% CENTRAL AGE WITH 63% CONF. INTERVAL(Ma): 203.2, 183.9 -- 224.5 ( -19.3 +21.3) 95% CONF. INTERVAL(Ma): 167.0 -- 247.0 ( -36.1 +43.8) AGE DISPERSION (%): 31.9 CHI^2 AGE WITH 63% CONF. INTERVAL (Ma): 156.8, 148.3 -- 165.7 ( -8.5 +8.9) 95% CONF. INTERVAL (Ma): 140.6 -- 174.8 ( -16.2 +18.0) NUMBER AND PERCENTAGE OF GRAINS: 7, 54%
208
Appendix 5—Compositional data for Upper Cretaceous Fort Crittenden Formation sandstones, Santa Rita and Huachuca Mountains, southeastern
Arizona
station # Qm Qp Ls Lv Lm K P U % Qm % Qp % Qt % Ls % Lv % Lm % Lt % K % P % F % U Station 13 60 67 26 51 10 72 7 7 20 22 42 9 17 3 29 24 2 26 2 Station 23 67 34 33 18 5 110 29 4 22 11 34 11 6 2 19 37 10 46 1 Station 42 113 33 72 19 10 37 8 8 38 11 49 24 6 3 34 12 3 15 3 Station 45 81 25 21 3 73 76 10 11 27 8 35 7 1 24 32 25 3 29 4 Station 46 77 67 16 0 78 48 7 7 26 22 48 5 0 26 31 16 2 18 2 Station 47 65 85 31 8 75 7 14 15 22 28 50 10 3 25 38 2 5 7 5 Station 49 96 65 11 49 52 3 12 12 32 22 54 4 16 17 37 1 4 5 4 Station 51 105 53 3 129 2 1 4 3 35 18 53 1 43 1 45 0 1 2 1 Station 52 139 116 6 1 13 9 4 12 46 39 85 2 0 4 7 3 1 4 4 Station 61 74 23 21 24 43 71 33 11 25 8 32 7 8 14 29 24 11 35 4 Notes: Point counts for composition of sandstones made at 10x magnification, 300 points total. Qm = monocrystalline quartz; Qp = polycrystalline quartz (excluding microcrystalline quartz); Ls = sedimentary lithic fragments; Lm = metamorphic lithic fragments; Lv = volcanic lithic fragments; K = potassium feldspar (both relict and fresh); P = plagioclase feldspar; U = unidentified grain; Qt = total quartz (excluding microcrystalline quartz); Lt = total lithic fragments; F = total feldspar.
Ap
pe
nd
ix 6
—E
lec
tro
n m
icro
pro
be
an
aly
se
s o
f 5
7 z
irco
ns
fro
m S
tati
on
23
, H
ua
ch
uc
a M
ou
nta
ins
po
int
#g
rain
#Z
rO2 (
%)
SiO
2 (
%)
HfO
2 (
%)
Y2O
3 (
%)
Ce
2O
3 (
%)
tota
l
pin
k/p
urp
le f
rac
tio
n
1d
127
65.8
5
32.3
5
1.4
0
0.0
0
-
99.6
1
1d
144
65.5
6
32.7
5
1.4
6
0.0
9
0.0
2
99.8
8
1d
161
66.4
2
32.4
1
1.1
9
0.1
1
0.0
3
100.1
6
2d
161
53.0
7
25.6
2
1.0
4
0.2
4
0.0
4
80.0
2
1d
165
66.3
3
32.6
6
1.4
4
0.1
0
0.0
1
100.5
4
2d
165
66.0
6
32.6
7
1.3
9
0.1
1
0.0
2
100.2
4
1d
070
65.6
5
32.5
6
1.4
9
0.2
2
0.0
2
99.9
3
1d
195
67.0
9
32.1
9
1.3
2
0.1
0
0.0
2
100.7
1
1d
005
61.0
1
29.3
5
1.4
4
0.0
2
0.0
6
91.8
8
2d
005
67.5
7
29.8
8
1.6
3
0.0
1
0.0
4
99.1
3
1d
131
65.1
4
32.9
9
1.2
9
0.1
5
0.0
2
99.5
9
2d
131
65.3
8
32.7
2
1.3
6
0.2
4
0.0
1
99.7
1
1d
012
65.6
5
33.0
7
1.3
7
0.1
0
0.0
4
100.2
2
2d
012
66.0
1
32.5
9
1.3
5
0.1
0
0.0
0
100.0
6
1d
013
66.8
1
33.1
3
1.2
9
0.1
0
0.0
4
101.3
7
2d
013
66.4
1
33.0
3
1.3
1
0.0
9
0.0
1
100.8
4
1L
330
65.3
4
32.7
6
1.1
3
0.3
3
0.0
5
99.6
1
2L
330
65.6
3
33.1
2
1.1
3
0.2
7
0.0
0
100.1
6
1L
304
66.2
2
33.0
0
1.4
8
0.1
3
0.0
3
100.8
6
2L
304
65.8
8
32.9
7
1.4
8
0.1
2
-
100.4
6
1L
062
65.8
2
32.8
3
1.2
6
0.2
4
0.0
3
100.1
9
2L
062
66.2
8
32.9
1
1.3
2
0.2
2
0.0
2
100.7
6
1L
049
65.8
2
32.8
9
1.3
4
-
0.0
2
100.0
7
2L
049
66.3
5
33.1
3
1.3
3
0.0
9
0.0
3
100.9
2
209
Appendix
6,
continued
po
int
#g
rain
#Z
rO2 (
%)
SiO
2 (
%)
HfO
2 (
%)
Y2O
3 (
%)
Ce
2O
3 (
%)
tota
l
co
lorl
ess f
racti
on
1c1_110
65.3
3
32.8
1
1.4
9
0.1
0
0.0
2
99.7
5
2c1_110
66.0
0
32.5
4
1.4
0
0.2
0
0.0
1
100.1
5
1c1_223
65.3
1
32.8
1
1.5
1
0.1
9
-
99.8
2
2c1_223
65.9
1
32.5
2
1.4
5
0.2
0
0.0
2
100.1
0
1c1_376
65.7
9
32.8
7
1.2
6
0.2
9
-
100.2
1
2c1_376
65.2
7
32.8
1
1.2
3
0.3
2
0.0
0
99.6
3
1c1_437
65.8
0
32.6
8
1.5
7
0.2
2
0.0
2
100.3
0
2c1_437
66.1
5
32.7
0
1.5
5
0.2
4
0.0
4
100.6
9
1c1_216
64.3
6
31.5
8
1.2
4
0.2
4
0.0
2
97.4
4
2c1_216
66.6
1
32.9
2
1.3
8
0.2
3
0.0
3
101.1
7
1c1_082
65.1
6
32.4
7
1.3
8
0.2
6
0.0
1
99.2
9
2c1_082
66.1
5
32.3
3
1.3
8
0.2
5
0.0
2
100.1
2
1c1_291
66.1
0
32.8
5
1.1
6
0.2
2
0.0
4
100.3
7
2c1_291
65.4
7
32.3
1
1.1
9
0.2
3
0.0
1
99.2
2
1c1_300
65.4
9
33.2
3
1.6
7
0.0
6
-
100.4
4
2c1_300
65.5
9
33.2
2
1.6
6
0.0
9
-
100.5
6
1c1_598
64.6
0
32.6
3
1.4
4
0.2
5
0.0
5
98.9
7
1c1_728
65.0
6
33.0
4
1.5
6
0.2
2
0.0
3
99.9
1
2c1_728
66.1
5
33.2
5
1.3
8
0.1
9
0.0
1
100.9
9
1c1_772
65.1
4
32.6
1
1.3
5
0.1
9
0.0
7
99.3
6
2c1_772
65.9
6
33.1
8
1.4
0
0.1
3
0.0
4
100.7
0
1c2_695
65.2
7
32.5
5
1.2
5
0.2
8
0.0
2
99.3
8
2c2_695
66.4
2
33.1
9
1.2
9
0.0
9
0.0
6
101.0
5
1c2_031
65.8
8
32.1
8
1.3
4
0.1
1
0.0
8
99.6
0
2c2_031
66.5
8
32.3
6
1.2
8
0.1
4
0.0
1
100.3
7
1c2_222
66.0
3
32.3
2
1.4
6
0.1
0
0.0
4
99.9
5
2c2_222
66.0
3
32.3
3
1.3
8
0.0
9
0.0
5
99.8
9
1c2_250
65.2
8
32.1
2
1.7
3
0.1
2
0.0
6
99.3
1
2c2_250
65.5
2
32.1
2
1.6
8
0.1
3
0.0
5
99.5
0
1c2_044
63.7
5
30.4
2
1.3
9
0.1
6
0.0
3
95.7
4
2c2_044
65.5
5
31.6
9
1.3
3
0.1
5
-
98.7
1
1c2_064
66.9
9
32.3
4
1.2
5
0.2
3
0.0
0
100.8
1
2c2_064
66.8
5
32.3
8
1.2
9
0.2
0
0.0
2
100.7
4
210
Appendix
6,
continued
po
int
#g
rain
#Z
rO2 (
%)
SiO
2 (
%)
HfO
2 (
%)
Y2O
3 (
%)
Ce
2O
3 (
%)
tota
l
co
lorl
ess f
racti
on
, co
nti
nu
ed
1c2_065
66.8
4
32.3
6
1.1
7
0.2
2
0.0
0
100.5
9
2c2_065
67.3
6
32.3
9
1.2
0
0.1
1
0.0
2
101.0
8
1c2_297
65.4
7
31.7
4
1.4
9
0.1
7
0.0
3
98.9
0
2c2_297
65.0
3
31.8
7
1.4
9
0.2
0
0.0
4
98.6
3
1c2_528
65.0
2
32.2
4
1.1
8
0.3
5
0.0
3
98.8
3
2c2_528
65.8
5
32.4
7
1.4
2
0.0
5
0.0
1
99.8
0
1c2_285
66.1
7
32.2
8
1.2
4
0.2
6
0.0
4
99.9
9
2c2_285
65.3
7
31.7
3
1.2
2
0.3
1
0.0
3
98.6
8
1c2_544
66.1
4
32.6
4
1.1
6
0.2
3
0.0
1
100.1
9
2c2_544
65.4
6
32.0
3
1.1
6
0.2
2
0.0
1
98.8
7
ho
ney f
racti
on
1h
1_300
66.2
8
32.5
4
1.6
5
0.2
2
0.0
6
100.7
5
2h
1_300
65.4
7
31.9
9
1.6
2
0.2
5
0.0
3
99.3
7
1h
1_180
66.3
1
32.4
7
1.3
4
0.3
1
0.0
1
100.4
4
2h
1_180
66.5
8
32.5
1
1.3
6
0.3
0
0.0
1
100.7
6
1h
1_101
67.0
2
32.0
2
1.1
0
0.2
4
0.0
2
100.4
1
2h
1_101
67.1
7
32.0
5
1.1
8
0.2
4
0.0
1
100.6
5
1h
1_109
66.4
5
32.1
0
1.3
3
0.2
7
0.0
5
100.2
0
2h
1_109
66.8
3
32.1
9
1.3
3
0.2
8
0.0
4
100.6
6
1h
1_224
66.7
4
32.1
6
1.2
2
0.2
3
0.0
3
100.3
8
2h
1_224
67.3
4
32.3
6
1.2
1
0.2
0
0.0
3
101.1
4
1h
1_482
66.3
9
32.6
6
1.5
3
0.2
5
0.0
4
100.8
7
2h
1_482
66.9
5
32.5
9
1.5
5
0.2
1
0.0
3
101.3
2
1h
2_031
66.0
0
32.2
1
1.4
8
0.2
4
0.0
2
99.9
5
1h
2_095
63.0
3
31.0
8
1.3
1
0.2
2
0.0
3
95.6
7
1h
2_221
65.0
4
32.1
0
1.3
5
0.1
8
0.0
4
98.7
1
1h
2_119
66.6
3
32.8
8
1.2
2
0.1
3
0.0
3
100.8
8
1h
2_189
64.8
0
32.0
1
1.4
4
0.2
4
-
98.5
0
1h
2_240
65.6
4
32.3
6
1.3
1
0.2
6
0.0
1
99.5
8
1h
2_248
61.9
6
29.9
4
1.5
0
0.1
3
0.0
3
93.5
4
1h
2_249
66.3
6
32.9
3
1.3
1
0.1
9
0.0
2
100.8
1
2h
2_249
66.3
0
32.9
5
1.3
3
0.1
9
0.0
2
100.7
8
211
Appendix
6,
continued
po
int
#g
rain
#Z
rO2 (
%)
SiO
2 (
%)
HfO
2 (
%)
Y2O
3 (
%)
Ce
2O
3 (
%)
tota
l
ho
ne
y f
rac
tio
n,
co
nti
nu
ed
1h
2_374
65.8
7
32.0
8
1.5
2
0.1
4
0.0
0
99.6
1
2h
2_374
63.6
9
30.8
4
1.5
2
0.0
9
0.0
3
96.1
7
1h
2_276
66.4
3
32.7
4
1.4
0
0.0
9
-
100.6
6
2h
2_276
66.5
1
32.5
1
1.3
7
0.1
3
0.0
8
100.6
1
1h
2_277
60.2
9
29.5
0
1.3
7
0.1
5
0.0
3
91.3
4
2h
2_277
66.6
2
32.8
9
1.4
7
0.1
5
0.0
3
101.1
6
1h
2_358
64.9
0
31.6
3
1.4
2
0.2
2
0.0
6
98.2
3
2h
2_358
64.4
9
31.1
9
1.4
3
0.2
3
0.0
3
97.3
7
1h
2_292
66.4
0
32.0
4
1.3
8
0.2
4
0.0
2
100.0
8
2h
2_292
66.5
4
31.9
1
1.4
3
0.2
0
-
100.0
9
1h
2_390
67.0
7
32.7
1
1.1
5
0.2
2
0.0
1
101.1
5
2h
2_390
65.7
1
33.0
2
1.2
1
0.2
4
0.0
5
100.2
3
1h
2_511
65.9
5
32.9
6
1.0
1
0.5
0
0.0
1
100.4
3
2h
2_511
66.1
8
33.0
7
1.0
6
0.4
2
0.0
9
100.8
3
Note
s:
Ele
ctr
on m
icro
pro
be a
naly
ses m
ade b
y K
. B
ecker
at
Renssela
er
Poly
technic
Institu
te,
Tro
y,
NY
. B
eam
/counting p
ara
mete
rs:
15kv;
50nA
;120 s
econds m
axim
um
counting t
ime;
25-3
0 m
m b
eam
dia
mete
r.
Mean d
ete
ction lim
its:
HfO
2 =
0.0
68%
; Y
2O
3 =
0.0
22%
; C
e2O
3 =
0.0
68%
.
212
213
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Vita
Brook Colleen Daun Riley was born on the 28th of April, 1973 in Tucson, Arizona, to
parents Bill and Dianne Riley. She grew up in the mountains of southeastern Arizona, and
attended the University of Arizona from 1991-1996. Following receipt of a B.S. in Geosciences
from the University of Arizona, the author attended the University of New Mexico Department of
Earth and Planetary Sciences. During May of 1997, the author began an extended internship
with Exxon Production Company in Houston, Texas, and subsequently transferred to the Ph.D.
program at the University of Texas in 1998. During the author’s time at the University of Texas,
she has been fortunate to have taught undergraduate field camp, field methods, structural
geology, and sedimentology, as well as graduate-level carbonate geology. During the summer of
1998, Brook completed an internship with BHP Petroleum in Houston, Texas. The author’s
publications include work from her senior thesis on detrital zircon geochronology of the Roberts
Mountains and Golconda allochthons in north-central Nevada, the results of independent field
studies in the Huachuca Mountains, and abstracts related to her Ph.D. work.
Permanent address: 1012 English Street Houston, Texas 77009
This dissertation was typed by the author.
