On oriented titanite and rutile inclusions in sagenitic biotite
Transcript of On oriented titanite and rutile inclusions in sagenitic biotite
-
8/20/2019 On oriented titanite and rutile inclusions in sagenitic biotite
1/13
American
Mineralogist, Volume
76,
pages
1205-1217, l99I
On oriented
titanite and rutile inclusions in
sagenitic biotite
YrN-HoNc
Snnu
Department
of Geological
Sciences,University
of
Michigan, Ann Arbor, Michigan 48109, U.S.A.
HouNc-Yr Y,tNc
Department
of
Earth
Sciences,National
Cheng Kung University , Tainan,
Taiwan 70101, Republic
of China
DoNar.o R. Pplcon
Department
of Geological
Sciences,
University of Michigan, Ann Arbor,
Michigan 48109,
U.S.A.
Arsrru.cr
Well-oriented,
needlelike
nclusions
occurring n sageniticbiotite
in
an orthogneiss
rom
the Tananao
complex, northeast
Taiwan, have
been studied by optical
microscopy, trans-
mission
and
analytical
electron microscopy,
and electron
microprobe
analysis.
Titanite
needles
n three
orientations
combine to form
equilateral triangles,
and
rutile needles n
three
other orientations
generally
ntersect
o form asterisk-shaped nits.
Titanite needles
are elongated arallel o (01 ). They are orientedwithin
{001}
ofbiotite, and one ofthe
three
sets,which intersect
at angles f60", is
parallel
o a ofbiotite.
The
{lll}
or
{433}
planes
of titanite
are approximately
parallel
to
{001}
of biotite.
Rutile needles
are
elon-
gated
parallel
o c, and rutile
{
100} s
parallel
o
{001}
of biotite. Of the three
setsof rutile
needles
ntersecting
at angles
of60", one s
parallel
o b ofbiotite.
The
preferred
orientation
of rutile inclusions
in
biotite is in
accord
with
their
mutually
parallel planes
of
closest-
packed
anions and chains
ofedge-sharing
octahedra.
Titanite inclusions contain approx-
imately
0.
0
(Al
f Fe)
per
formula
unit, have space
group
A2/a, and
give
electron dif-
fraction
patterns
that display
streaking
along b* and c*.
Rutile inclusions contain 0.2-0.3
wto/o
FerO.
(total
Fe
as FerOr),
exhibit
streaking and splitting
of reflections
n
electron
diffraction
patterns,
and display
a
planar
microstructure
parallel
to
{
100}, which
appears
to consist
of
precipitated
platelets
hat have
the
hematite
structure and a
probable
com-
position (Fe,Ti)rOr. The titanite and rutile inclusions are inferred to have topotaxially
precipitated
through
reactions
occurring
during
retrogressivemetamorphism
when
excess
Ti
and
Ca
were
derived from
biotite of igneousorigin.
INrnooucrroN
The
term
"sagenitic
texture" refers
to
the occurrence
of slender,
needlelike
nclusions
intersecting
at
anglesof
60'and
included
in
phlogopite, quartz,
or
other
minerals
(e.g.,
Gary etal.,1972).
Although
suchacicular nclusions
have long
been thought
to consist of rutile,
titanite, he-
matite, tourmaline, zircon, apatite, or allanite (Moor-
house,
1959;Winchell,
l96l;
Rim5aite,
1964:Rimsaite
and Lachance
1966;Niggli, 1965;
Gary
et al., 19721'Deer
et al.,
1982),
hey
have
not
been completely
character-
ized. The most
extensive
study of
sagenitic exture was
carried out
by NigSli
(1965),
who
used
electron micro-
probe
techniques
o analyzesagenitesn
biotite from
plu-
tonic rocks
and
gneisses
nd concluded
hat most
ofthem
consist
of titanite
but that some were
rutile. Some well-
oriented nclusions
n the cores
ofphlogopite
grains
from
a marble were
identified
optically
as rutile
(Rim5aite
and
Lachance, 1966).
Titanite
or rutile inclusions
have
been
observed n
biotite or
phlogopite
(Rimsaite,
1964;
Rim-
Saite
and
Lachance,
1966;
Niggli, 1965)
and in
chlorite
produced
by hydrothermal
alteration of biotite
(Rim-
saite, 1964;Ferry,19791, arry and Downey,
1982;
Veb-
len
and
Ferry, 1983;Eggleton nd Banfield,
1985).
Sageniticbiotite
occurs n the
grreisses
fthe
Tananao
metamorphic complex on the
island
of
Taiwan. This
complex consists
of
pre-Tertiary pelitic
schists,
marbles,
gneisses,
metabasites, mphibolites,and serpentinitesand
crops
out extensivelyalong he easternslopeofthe
north-
trending Central Mountain Range. Lo and Wang Lee
(1981) performed
X-ray analyses f the
inclusions
ex-
tracted from the sageniticbiotite
and reported that they
were
titanite and
sillimanite.
To
characterize hese
nclu-
sions better and to establish heir structural
and
crystal-
lographic relations with the host biotite, samplesof sage-
nitic
biotite
were collected
from
a
pre-Tertiary
orthogneiss
near the village of
Pihou, northeast Taiwan, and studied
by optical microscopy, transmission
and analytical elec-
tron
microscopy
(TEM
and AEM), and electron
micro-
probe
analysis
(EMPA).
OnsrnvlrroN
By
oprrcAr,
MrcRoscopy
The orthogneissofthe
present
nvestigation
s
generally
medium to coarse
grained
and
has a
granitoid
texture.
It
0003-o04x/9
/0708-l205$02.00
t205
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t206
SHAU
ET AL.:
ORIENTED
INCLUSIONS
IN BIOTITE
Fig.
l.
(a)
and
(b)
Photomicrographsof two sageniticbiotite
flakes.Titanite
(T)
needles orm equilateral
rianglesand
rutile
(R)
needles orm
asterisks
n
the biotite
host.
One of the equilateral
rianglesand one
of the asterisks
are ndicated
by white solid
lines.
The
a and b axes of biotite
were
chosenarbitrarily using one of
the three directions
of titanite and
one of the three
directions of
rutile
prisms,
respectively.Plane-polarized ight.
is composedof sodic
plagioclase Anro-or),
uartz,
biotite,
and
minor
amounts of
muscovite,
potash
feldspar, apa-
tite, titanite
(intergranular),
garnet,
chlorite,
ilmenite, and
trace
amounts of calcite,
which
generally
occurs as small
inclusions
(l-20 pm
in
diameter)
lying along the
parting
planes
or cleavages f
plagioclase.
The biotite commonly
exhibits
well-developed sagenitic texture.
Some biotite
grains
are overgrown by chlorite
or
have layers interca-
lated
with
chlorite.
No
sagenitic
nclusions
have
been
ob-
served
n
chlorite.
However, a
few isolated
anhedral
ti-
tanite
inclusions
up
to l0
pm
wide and 40
pm
long have
been observed in chlorite, with their long dimensions
subparallel
o
{001}
ofchlorite.
Subhedral itanite
grains
up to
I mm long also occur at
the interyranular sites
among other
major
phases.
The sagenitic exture can
best be examined
in
{001}
sections
of biotite.
Very
thin
{001}
sheets an
easilybe
peeled
from a biotite crystal,
and the
following charac-
teristic
features
of sagenitic
texture can be
readily ob-
served
n immenion oil
with
a
polarizing
microscope
Fig.
l). Needlelike
nclusions
0.1-2
p.m (most
are
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SHAU ET AL.:
ORIENTED INCLUSIONS
IN BIOTITE
Taele 1. AEM
analyses
of
rutile
and
titanite
inclusions
n
biotite and biotite
from the Tananao
orthogneiss,
northeast Taiwan
Rutile
Titanite
(ten
analyses)
Biotite
eight
nalyses)
t207
Oxides
(wt%)
1E-RU7
Range Range
sio,
Al,o3
Tio,
FerO.*
FeO'
Mn O
Mgo
CaO
KrO
Totalt'
Si
rrtAl
retAl
Ti
Fep-
F#*
Mn
Mg
Ca
K
Total
0.88
0.00
98.92
0-20
0.00
0.00
0.00
0.00
0.00
100.00
0.01
0.00
0-00
0.99
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I 208
SHAU
ET AL.:
ORIENTED
INCLUSIONS
IN BIOTITE
Trele 2.
Electronmicroprobe
nalyses f biotite,
muscovite, hlorite,
nd itanite
rom
Tananao rthogneiss,
ortheast
aiwan
Biotite
(27
analyses)
Muscovite
Titanite-
Oxides and elements
(wto/o)
Range
Ave.
Mu19
sio,
Alro3
Tio,
Cr,O3
FeO(Fe,O3)-'
MnO
Mg o
Ca O
BaO
Naro
Kr O
F
cl
Total
Si
r4tAl
relAl
Ti
FeF(Fe3*)*
Mn
Mg
16r>
Ca
Ba
Na
K
> cations
F
cl
35.03J5.56
1
.13-17.14
1.71J.83
0.00-o.04
20.80-22.57
0.20-0.36
7.65-8.64
0.00-0.1
0.06-0.32
0.05-0.1
9.33-9.65
0.03-0.30
0.00-0.05
5.479-5.545
2.521-2.455
0.431-0.694
0.208-0.446
0.000-0.005
2.712-2.936
0.026-0.047
1.771-2.016
0.000-0.017
0.004-0.020
0.015-0.036
't.851-1.927
0.01
-0.1 5
0.000-0.012
5.505
2.495
0.528
0.339
0.001
2.862
0.038
1.904
5.672
0.005
0 .010
0.023
1.888
15.598
0.067
0.005
14.007
0.000
0.005
0.007
0.016
20.025
0.061
0.006
30.69
2.26
36.39
0.00
0.54
o.21
0.00
28.77
0.14
0.03
o.o2
0.57
0.00
99.62
1.000
0.000
0.087
0.892
0.000
0.013
0.006
0.000
0.998
1.004
0.002
0.002
0.001
3.007
0.059
0.000
30.56
1.00
38.20
0.00
0.43
0.05
0.00
28.48
0.02
0.00
0.01
0.25
0.02
99.02
1.000
0.000
0.039
0.940
0.000
0.011
0.001
0.000
0.991
0.999
Al
:0 .042,Ti
:0 .014,Cr:0.0003,Fe:0.092,Mn:0.007,M9
:0 .0 3 8 ,
Ca :0 .0 0 0 8 ,
Ba :0 .0 0 1 , Na :0 .0 0 4 ,
K :0 .0 4 5 , F : O .O 2 7 ,l
0 .0 0 2 .
.
|
:
intergranular,R
:
replacing
lmenite nclusions n
biotite.
"
Total Fe
as
FeO tor
biotite,
muscovite,and chlorite, and as
FerO3 or titanite.
sumed to be 95.00/o or biotite, 99.00/o
or
titanite,
and
100.00/oor
rutile
(e.g.,
Shau
et al.,
l99l). Hole-count
spectraamount to only 0.50/o f the total counts
or
biotite
spectra
-60000
counts
for
each analysis)acquired
from
thin edges.
Nevertheless,
such
stray radiation contributes
up
to 300/o f intensities
for
elements
considered minor
in titanite and rutile
(e.g.,
K
and
Fe
of titanite).
Therefore,
analytical
data for titanite and rutile
were
corrected
by
subtracting
hole-count spectra.
For
biotite,
the
contri-
bution
of the
hole-count
spectrum
was negligible.
Rutile
Major
Ti
and O and
minor
Si
and Fe were detected
with
AEM
analysesof
needles orming the asterisks
Ta-
ble
1).
The
electron diffraction
patterns
from these hree
sets of
needleswere indexed
using the
cell
parameters
of
rutile
(a
:
4.59,
c
:2.96
A;. ttrese data,
n
combination
with the optical
properties
(very
high relief,
parallel
ex-
tinction, and
length
slow), show
that those
needles
onsist
of
rutile.
Figure 2 shows SAED
patterns
and a
TEM
bright
field
image obtained from a rutile
inclusion within
a biotite
flake that
was
oriented
with
(001) perpendicular
to the
electron beam.
The
electron beam
direction was thus ap-
proximately parallel
to c* of biotite.
It was
also
parallel
to a
(arbitrarily
defined
as
[010])
of
rutile.
The
SAED
pattern
in Figure 2a therefore
includes the
rutile
[010]
zone
pattern
and a slightly
misoriented
biotite
[001]
zone
pattern.
The
[001]
SAED
pattern
of biotite
is a
hexagonal
net that
includes
a*
and b*.
The
[010]
SAED
pattern
of
rutile exhibits h)l
reflections showing
elongation
or
streaking
along a*
(Fig.
2a). The
axes
c* and a* of rutile
are each
exactly
parallel
to
b* and a* of biotite,
respec-
tively,
when
projected
onto the
plane
ofthe
photograph.
The
[001]
axis of biotite
is
slightly
tilted toward
-a*,
as
is evident from the asymmetric intensity distribution of
biotite
reflections.
he
a axis
(instead
ofa*) ofbiotite
is
actually
nearly
parallel (+2)
to the
plane
of the
photo-
graph
when
the tilt
angle and
B
angle
ofbiotite are con-
sidered.
Therefore,
t is inferred that c*
of rutile is
parallel
to b* of
biotite
whereasa*
([00]*)
of
rutile
is
parallel
to
a of
biotite;
.e.,c*l lb"
and
(010)*l l(001)".
A
[010]
SAED
pattern
from another rutile
inclusion
shows
the following
features:an additional
set of
reflec-
tions occurring
as split
reflections along
a*, slight streak-
ing
ofreflections
along a*, and
superstructurelike
eflec-
tions that triple the
spacing
4,0,y
along
[01]*
or
[01]*
(Fig.
3a).
The additional set ofreflections
displays
a
per-
fect hexagonal-net
pattern
as
for biotite.
However, the
smallest
vectors
containing the
extra
reflectionsalong a*
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5/13
SHAU
ET
AL.: ORIENTED INCLUSIONS
IN BIOTITE
r209
Fig.2.
(a)
SAED
pattern
ofthe
[001]
zoneofbiotite
(B) (slight-
ly misoriented)
and of the
[010]
zone
of a
rutile
needle
R).
The
b* axis ofbiotite coincides
with
c* ofrutile,
whereas
he
projec-
tion ofa*
ofbiotite coincides
with
a* ofrutile.
Difuse reflections
of
rutile
are elongated
parallel
to a*. The reflections abeled D
arecaused y double diffraction
(cf.
Hirsch et al.,1977).
(b)
SAED
pattern
with
a
smaller camera
length showing
reflections only
from the rutile
needle.The
reflectionscaused
by double diffrac-
tion are
not
present
since
there are
no reflections
rom biotite.
(c)
TEM bright
field image ofthe
rutile
needleelongated
parallel
to its c axis and
to b of biotite.
The
maximum
width of the
needle
is 0.15&m.
of
rutile correspond
o a d-valueof
2.52
+
0.04 A
(cali-
brated from rutile
cell
parameters),
which
can be
indexed
as the
ll0
reflection
of
hematite
(a:
5.034 A
and d,,,o,
:
2.517 A for
the hexagonal
ell) or
ilmenite
(a
:
5.088
A
and
d,,,0,
2.544
A1 wittrin
measurement
rror. These
reflections
are thus identified
as he
[001]
zone
pattern
of
hematite-ilmenitewith
(001)parallel
o
(010)
of rutile. A
dark field image
that
was formed
by using
the adjacent
200*
and
I 10"
reflections howswavy
stripesextending
parallel
to c
(Fig.
3b).
The
tetragonal symmetry
of rutile
implies
that
the
platelets
are also orientedwith
(001) parallel
o
(100)
of
rutile.
The wavy
stripes shown
in Figure
3b thus corre-
spond to such edge-on
platelets
and cause
he streaking
of reflections
along a* of rutile. These
edge-on
platelets
also contribute
to a
I
l0] zone
pattern
of
hematite-il-
menite, which
includes
a 006
reflection
d,oou
2.29 L
for hematite)
superimposedon the 200 reflection
of rutile
and thereforecontributes
o the
white
contrast
ofthe
wavy
stripes in Figure
3b.
The
superstructurelike reflections
along ( l0 I )* can be derived from dynamic diffraction (or
double diffraction,
cf.
Hirsch
eL al.,
1977)
of the
[10]
zone reflections f
hematite-ilmeniteand
the
[010]
zone
reflections
of rutile.
Similar
platelet
microstructures
were
observed
in Fe-bearing
rutile in
metapelites
from Ver-
mont
(Banfield
and
Veblen,
l99l) and
in synthetic
non-
stoichiometric
utile
(e.9.,
Bursill et al.,
1984).
Figure 4 shows three
rutile
needles ntersecting at a
triple
junction,
with an angle of
120" betweeneach
pair.
As
the
prism
axes of rutile
needles
were
observed
with
an optical
microscope o
lie in the
(001) plane
of biotite,
the collective
TEM
and
optical data suggest
hat the
rutile
inclusions
and
biotite
matrix have the
following crystal-
lographic relationship:
for
one
of the three
sets of rutile
needles, of rutile
(the prism
direction)
is
parallel
to
b of
biotite,
whereas
ar
and a2 of rutile coincide
with
a
and c*
of biotite,
respectively.
n other
words,
(010)
of rutile
is
parallel
o
(001)
of biotite.
The
c axes
of the other
two
setsof rutile
needlesare oriented
120"
(or
60') clockwise
and counterclockwise
rom
the
b axis of
biotite
in
(001)
of biotite.
Their
(010)
planes
are also
parallel
o
(001)
of
biotite.
Although
almost
all rutile
needles
were oriented
as described above, one exceptionhas beenobserved n
which
(l
l0) of rutile
was
parallel
o
(001)
of biotite.
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t210 SHAU ET AL.: ORIENTED NCLUSIONS
N BIOTITE
Fig.
3.
(a)
SAED
pattern
of
the
[010]
zone of rutile. Reflections are difuse
and there are extra
reflections
(indicated
by black
arrows; see
ext) arranged
parallel
to a*.
The reflection
006n,superimposes n
the reflection
200". Superperiodic
eflections ripling
d,o, ie
along
[01]*
or
[0T]*.
R
:
rutile, H
:
plareletsll(010)R,
'
:
plateletsll(100)R.b)
A TEM dark
field image ormed
from
the reflections ncluding 200R,
006H,,and
I 10". The wavy
stripes
(indicated
by black arrows)
extending along c are
representative
ofthe edge-on
plateletsparallel
to
(100)*.
Fig. 4. TEM
bright
field image
of three
rutile
(R)
needles
intersecting at a triple
junction
and
partly
embedded n biotite
(B).
A fourth needle s located
at a
level
below the
three inter-
sectingneedles.
Titanite
The electron diffraction
patterns
of the
needlelike n-
clusions
orming equilateral riangles
can be
ndexed
with
the cell
parameters
of synthetic
titanite
(a
:
7
07, b
:
8 .72 , : 6 .57
A,
b :113 .86 ' ,
Speer
ndG ibbs ,
976 )
for space
gtoup
A2/a.
The AEM analyses
or these
nee-
dles
reveal the
presence
of
major Si, Ca,
Ti,
and
O with
minor
Al, Fe, and K
(Table
l).
These
data
collectively
show
that the
needlelike inclusions
that are elongated
parallel
to a ofbiotite
and oriented
as equilateral
riangles
are titanite.
Figure 5 showsa TEM image and a SAED
pattern
with
[01]
of titanite
and
(001)
of biotite
parallel
o the elec-
tron beam,
for which the specific
zone
of biotite
is
not
identified.
The
axis
I
lT]* of titanite
is
parallel
to
c* of
biotite,
indicating that
(l
I l)
oftitanite
is
parallel
or near-
ly
parallel
o
(001)
of biotite.
A
[213]
SAED
pattern not
shown
here) of the same
titanite
inclusion also
gave
a
diffraction
pattern
with
I
tT]x oftitanite
parallel
to c* of
biotite and therefore
onfirmed hat
(l1T)rll(001)"
or
that
titanite crystal.
Weak
and diffuse
streaks
parallel
to b* of
titanite
can be observed
n the
SAED
pattern (Fig.
5a).
Figure 6 is a SAED
pattern
of titanite
I
I l] and slightly
misoriented biotite
[001]
zones. Comparison
of the dif-
fraction pattern with the correspondingmageshows hat
the
prismatic
titanite
crystal
is elongated
parallel
to a* of
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8/20/2019 On oriented titanite and rutile inclusions in sagenitic biotite
7/13
SHAU ET
AL.: ORIENTED INCLUSIONS
IN BIOTITE
L2rr
Fig.
5.
(a)
SAED
pattern
of the
[l01]
zone
of titanite
(T)
and
of biotite
(B)
where c* of biot ite
is
parallel
to
[111]*
of titanite;
i.e.,
(l
11)
oftitanite is
parallel
to
(001)
ofbiotite. There
are weak and diffuse streaks
parallel
to b* oftitanite.
(b)
Brieht field image
showing
that the interface
(indicated
by arrows) between
he titanite needleand biotite
host is
parallel
to
(001)
ofbiotite.
biotite. However,
the
difference n intensity
between
bi-
otite r00
and h00
reflections
suggestshat
the
[001]
axis
was tilted toward -a*, and a is inferred to be the axis
that is
actually
parallel
to the
prism
axis oftitanite when
the
tilt angleand
B
angle
ofbiotite
are aken nto
account.
It is
thus consistentwith
the
optical observation
hat
prism
axes
of titanite
are
parallel
to
(001)
of biotite. The
prism
axis
oftitanite is
perpendicular
o
[2T ]*;
i.e., t is
parallel
to
(21l).
Other diffraction
patterns
not
shown),consist-
ing
of
the biotite
[001]
zone
and
(l)
titanite
[2lT]
zone
and
(2)
titanite
[4ll]
zone,
show that the
prism
axes
of
titanite
are
parallel
o
(1Tl)
and
(0Tl)
of titanire, espec-
tively,
and are also
parallel
to a ofbiotite. Therefore,
he
prism
axis
of titanite
was
parallel
to the zone
axis
of
(21
),
(l
I l), and
(01
), i .e., o [0] l] of t i tanire.
Orientations
of
planes
and axes
of titanite
and biotite
as
determined by
diffraction
relations
were
plotted
on a
stereographic
projection
to characterize
heir relations.
The results,
based on
the
reflections
in Figure
6,
show
that the
prism
axis and
[0
I I
]
of titanite,
and a of biotite
are
parallel
o each
other
(+0.5')
when
projected
on
(001)
ofbiotite. They
also show
that
(l
lT)
oftitanite is nearly
parallel
to
(001)
of
biotite,
with
an interfacial
angle
of
2.2. The
direction
of the slow
and
fast
rays
of titanite
can
be determined from
the orientation
of the
crystallo-
graphic
axesoftitanite,
and thus the
extinction
anglecan
be
predicted.
The
extinction
angle
as
predicted
for
the
above relationship (Fig. 6) in which (001) of biotite is
normal
to the optical
axis is 22
+
2.
It is measured
clockwise
rom
the
fast-ray direction to the
prism
axis of
titanite.
However, because he titanite
prisms
of
any one
parallel set can be elongatedparallel to either [0ll] or
[0Tl]
(symmetrically
equivalent),
both clockwise and
counterclockwise extinction angles
should be observed
for
any one set.
The observation of such symmetrically
re-
lated extinctions
(see
above)
verifies the
orientation
re-
lation and shows that
it is
the
general
relation for most
needlelike
itanite.
A SAED
pattern
corresponding
o
[0]
l] of titanite and
[00]
of biotite,
as obtained rom a titanite
needle
parallel
to the beam, shows hat
[0ll]
of
titanite is
parallel
o a
of biotite
(Fig.
7). However,
(001)
of biotite
is
parallel
to
(433)
rather than
(l
lT) of titanite, and c* of biotite and
I l l]* of titanite are inclined by approximately 10", in
contrast to the above
relation in Figures
5 and 6.
A
[313]
SAED
pattern
of titanite
(not
shown), or
which
the beam
was
parallel
to
(001)
of biotite, also
ndicates
hat
(433)rll
(001)".
In
other electron diffraction
patterns, (001)
ofbiotite
was
ound to be
parallel
o nearly
parallel
o
(001),
101),
(0lT),
or
(410)
of titanite.
Assuming
that the
prism
axes
of such titanite needlesare also
parallel
to a of biotite,
stereographic
projections
show that they
must have
ex-
tinction anglesdifferent from thoseusually observed
l
8-
25')
for the titanite needles orming equilateral triangles.
Titanite
inclusions
with
such orientations are rare
rela-
tive to thosecommonly occurringorientationswith (11l)r
or
(433),l l(001)"
nd
[0]
l]rl l l l00lB.
(b)
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8/20/2019 On oriented titanite and rutile inclusions in sagenitic biotite
8/13
t 2 1 2
SHAU ET AL.:
ORIENTED INCLUSIONS
IN BIOTITE
(c)
Fig.6.
(a)
SAED
pattern
of the
[1ll
zone
of
titanite. The
arrow is
parallel
o
[211]*.
(b)
SAED
pattern
ofthe
[001]
zone
of biotite
([001]
was
slightly tilted toward
-a*).
(c)
The
corre-
sponding bright field image shows hat the prism axis of titanite
(T)
is
perpendicular
o
[2
I
]*
of titanite
and
parallel
to the
pro-
iection
of a* of
biotite.
Fig.7 SAED
pattern
f the
0
I
]
zoneof titanite
T)
and he
u00l
zone
of biotite
B)
obtained
rom
a sample
with
the
prism
axisof titanite
parallel
o
the
electron eam.The axis I1]* of
this titanite
needle
s not
parallel
o c* ofbiotite.
Er,ncrnoN MrcRopRoBE ANALvsES
(EMPA)
Compositions of biotite, muscovite, chlorite, inter-
granular titanite, and titanite replacing ilmenite inclu-
sions
in
biotite
were
obtained
with
a Cameca Camebax
electron
microprobe
using
l2 kV
accelerating
oltage
and
l0 nA
beam current
(Table
2). The
standards
nclude
diopside
Si,Ca),
ndalusite
Al), geikielite Ti),
uvarovite
(Cr),
ferrosilite
(Fe),
rhodonite
(Mn),
olivine
(Mg),
san-
bornite
(Ba),
albite
(Na), potassium
feldspar
(K),
F-rich
topaz
(F),
and
barium chlorine apatite
(Cl).
The
beam
was astered veran area6
pm x
6
pm
forboth
standards
and specimens o
reduce oss
of alkali cations
resulting
from
diffusion.
The
composition
of biotite obtained
with EMPA is
consistentwith that obtained with AEM, except hat val-
ues
for minor elements are
better defined with EMPA.
The rangeand average
values
or 27 microprobe
analyses
of biotite and the
resulting compositions are
isted in Ta-
ble 2. Biotite that
has
been
overgrown or
partially
re-
placed
by chlorite
generally
contains
essTiOr. Muscovite
contains
essTiO, and
more NarO, whereaschlorite con-
tains much
lessTiO, but more MnO than biotite.
Structural
formulae of titanite
were normalized
to
I
Si,
as consistent
with occupancyofthe
tetrahedral site only
by
Si
and
assignmentof all
Ti, Fe3*,and
Al
to the octa-
hedral
site
(e.g.,
Higgins and
Ribbe, 1976).The coarser
grained
itanite,
which
either
replaces
lmenite inclusions
(in
biotite) or occurs
at intergranular
sites,
gives rise
to
titanite structural
formulae approaching
deal
values
(Ta-
[001]s
-
8/20/2019 On oriented titanite and rutile inclusions in sagenitic biotite
9/13
ble 2). The
titanite also contains
0.25-0.79
wto/o
f F.
However,
the titanite replacing ilmenite
contains much
less
AlrO. and F
but slightly more TiOr. When
compared
with
the acicular
itanite inclusions n biotite,
the coarser-
grained
titanite
exhibits
lower FerO,
and KrO
contents
and slightly higher
CaO content.
DrscussroN
Mineral
chernistry and microstructures
of
rutile
and titanite
Optical microscopy,
AEM microanalysis,
and electron
diffraction
have
shown that the needlelike
inclusions
forming
the asterisks
are rutile and those forming
the
equilateral
triangles n
projection
on
(001)
ofbiotite are
titanite. The
optical observations
and electron diffraction
data show
that the rutile
and titanite inclusions
generally,
but
not
always, have
a
preferred
orientation in
biotite.
The rutile
inclusions
contain minor
amounts of Si
and
Fe but no detectableTa5* or Nb5* that may be coupled
with
substitution
of
Fe3*
or
Fe2*,
as
observed by others
for rutile
(cf.
analysescompiled in Deer
et al., 1962b,
Rumble,
1976).As
described bove, he
SAED
patterns
ofrutile
exhibit features
ofstreaking,
reflections
rom
an
extra
phase,
and superstructurelike eflections.
The
streaking
of
reflections
along a*
of
rutile in
SAED
pat-
terns
(Figs.
2 and3) implies
the
presence
f
platelet
struc-
tures
parallel
to
(100)
of rutile, as directly seen n
dark
field images
Fig.
3b). The reflections rom
these
platelets,
though most
are superimposedon the reflections
of rutile,
can be indexed
as hematite-ilmenite
with
(001)rll(100)*.
The superstructurelike eflectionscan also be attributed
to dynamic
diffraction from
these
platelets
and rutile.
Furthermore,
the
additional set of
reflections
(Fig.
3a)
is
consistent
with
the
[001]
zone
pattern
of hematite-ilmen-
ite
that is
oriented
with
[T20]Hllc*
i.e.,
a..n
I
c.) and
(001)H
l(010)R.
Similar
streaking and splitting
of
reflections,
super-
structurelike reflections,
and
platelet
structureswere
ob-
servedby Banfield
and
Veblen
(
I
99
)
in
Fe-bearing utile
(FeO
:
0.5-3
wto/o)
rom chlorite-
to staurolite-grade
metapelites.They
have concluded that
coherently nter-
grown
hematite
(or
ilmenite)
platelets precipitated
par-
allel to
(100)
and
(010)
of rutile and that the streaking f
reflections
s due to
platelets
of irregular
spacing,whereas
the superstructurelike
eflections
are
causedby dynamic
difraction.
Putnis
and
Wilson
(1978)
and
Putnis
(1978)
noted
that experimental annealing of natural Fe-bearing
rutile
(FeO
:
0.55
wto/o)
t
temperaturesbetween47
5 and
595'C
resulted n
precipitation
of two
transitional
phases
(coherent
Fe-rich
precipitates)
and hematite. Bursill
et al.
(
I
984) observed
{
I
00}
platelet
defects,often occurring n
association with
crystallographic shear
planes,
in
syn-
thetic
nonstoichiometric
utile
(TiOr_",
0
=
x
<
0.0035).
They
srrggestedhat the
platelet
defects
precipitated
as
a
TirO,
phase
with
the corundum-type
structure and
that
the microstructuresare strongly determined by cooling
history. The
{
100}
platelet
defects hat
they observed
have
r213
0 .0
F
Fig.
8.
Plot
of
Al + Fe + Mn vs.F n ion numbers
er
ormula
unit for titanite rom the Tananao rthogneissopensymbols),
including ntergranularitanite
circles)
nd itanite eplacing
l-
menitenclusionsn biotite
triangles).
he
positive
rend s more
obvious
when
he analyses f titanite
compiled y
Higgins
and
Ribbe
1976)
realso
plotted
solid
squares).
zigzag changes
n
orientation
and are similar to the
wavy
stripesdescribedabove.
Putnis
(1978)
and
Bursill
et
al .
(1984) proposed
different
structural
models for the
pre-
cipitated
phases
o
interpret
the
superstructurelike
eflec-
tions tripling d,o,of rutile
(see
Banfieldand
Veblen, 99l
for review).Miser and Buseck 1988)observedpolysyn-
thetic
twinning
on
{100}
of rutile
and other defectstruc-
tures
in
O-deficient
rutile that occur
in mudstone xeno-
liths from
an
environment
with low
/o'
As evidencedby
the SAED
patterns
and
TEM images
(Figs.
2
and 3), the
rutile
inclusions n
the
sageniticbiotite
from
the
Tananao
orthogneisscontain
precipitated
{
100}
platelets
hat have
the
hematite structure.
However,
these
platelets
are ikely
to have Ti substituting
for Fe, as mplied by the
low
con-
tents of
FerOr(-0.2
wtolo)
n
rutile
and the abundanceof
platelets (Fig.
3b).
The titanite inclusions always contain minor
amounts
of Al, Fe,and K in addition to the major elementsSi, Ti,
and Ca, even after subtraction of
hole
counts
(Table
l).
The composition of titanite is
generally
afected by sub-
stitutions such
as
(Al,Fe)3*
+
(F,OH)-
:
Ti4+ +
6:-
lHig-
gins
and Ribbe, 1976; Deer et al.,
1982).Although
F and
OH could
not
be detectedby
AEM for the
titanite
inclu-
sions, microprobe
analysesof
the coarser
grained
titanite
indicated that F contents have a
positive
correlation
with
those of
Al + Fe
(Fig.
8).
The
substitution
of Al
and
Fe for Ti and of OH. Cl.
and
F for
O in natural titanite
favors
the
formation
of
domains between
which
the directions of
Ti
displacement
in TiOu-octahedra reverse from +a
or
-a
(Speer
and
Gibbs, 19761-Taylornd Brown, 1976).Synthetic itanite
undergoesa
reversible,
displacive
phase
ransition at
220
SHAU ET AL.: ORIENTED INCLUSIONS
IN BIOTITE
0.3
+
f r
+
e
0.1
0.3
.2. 1
-
8/20/2019 On oriented titanite and rutile inclusions in sagenitic biotite
10/13
tzt4
SHAU
ET
AL.:
ORIENTED
INCLUSIONS
IN BIOTITE
oo
+
.g)
(.)
f Y
0.60
0.55
0.50
0 . 1
0.2 0 .3
Ti
Fig.
9.
Plot
of
Fe/(Fe
+ Mg) vs. Ti
per
ormula
unit
(22
O)
for sageniticiotite rom theTananao rthogneiss.nalysesb-
tainedwith AEM
(solid
circles) nd
EMPA
(open
circles), e-
spectively.
+
20
"C
from
space
group
P2,/a
to A2/a
(Taylor
and
Brown, 1976).
Higgins
and Ribbe
(1976)
demonstrated
with X-ray
diffraction
and electron diffraction data
that
the space
group
of
natural
titanite varies from P2,/a for
relatively
pure
end-member compositions
to
A2/a wth
increasing
substitution
of
Al
and
Fe. The
SAED
patterns
oftitanite inclusions
n
the sageniticbiotite
generally
ex-
hibit no reflections
with k +
/ odd, as consistent with
spacegroup A2/a, but some of them have faint diffuse
streaks
parallel
to
b*
(Fig.
5a) or c*
(not
shown). The
results further
demonstrate that
titanite
with
significant
Al
and Fe has
disorder in Ti displacements
as consistent
with
space
group
A2/a.
Chemical relations for
titanian biotite
Biotite
commonly has up to a few weight
percent
of
TiO,
(l-5
wto/o)
nd less
han
I
wo/o of CaO
(e.g.,
Foster,
1960a, 1960b;
Deer er
al.,
1962a).The Ti in
biotite is
located in
octahedrally coordinated
sites, and
its
substi-
tution
is
coupled with substitution
of
Al for
Si
(i.e.,
Ti-
Tschermak's
substitution: Tio* + 2,\lt*
:
Mg2r +
2Si4+'
e.g.,Robert, 1976;
Guidotti,
1984;
Hewitt
and
Wones,
1984),
ubstitution
of O
for
OH
(e.g.,
Bohlen
et al., 1980),
or octahedral
vacancies
(e.g.,
Dymek, 1983
and refer-
ences herein). Therefore,
titanian biotite
may
consist of
one or more
of the componentsKr(Mg,Fe)5TiSi4Al4Oro
(OH)",Kr(Mg,Fe)rTiSiuAlrOrr(OH)r,
r
K,(Mg,Fe)oTiSi6Al,
Oro(OH)o.The
biotite
in
the
Tananao
orthogneiss
con-
tains I .5-3.8 wto/o iO,
(Tables
and 2). The
Ca contents
were near
limits
of detection by AEM and microprobe
analyses
CaO
:
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8/20/2019 On oriented titanite and rutile inclusions in sagenitic biotite
11/13
SHAUET AL.:ORIENTED NCLUSIONS
N BIOTITE
L2I5
conditionsofthe
greenschist
acies
T:350-475
"C
and
P
:
5
kbar)
(Chen
et al., 1983). The
orthogneisswas
derived from
the
granitic
intrusions
following
the second
amphibolite facies metamorphism.
The
entire sequence
of metamorphic rocks,
consistingof schists,
amphibolites,
serpentinites, marbles, metabasites,
and
gneisses,
was
known
as he
Tananao
schists
n
the
past
but as he
Tana-
nao complex in recentyears.
Yang
and
Wang
Lee
(
198
)
found
that titanite is
a com-
mon
accessory
mineral in
the
gneisses
nd
other
meta-
morphic
rocks
of the Tananao
complex and
that titanite
has wholly
or
partially
replaced
ilmenite
in the
ortho-
gneisses
and
amphibolites
derived from
basic igneous
rocks.
They
thus concluded
that titanite was
stable
and
should have
crystallized f Ti,
Ca, and Si were
available
under
the metamorphic
conditions for
the Tananao
com-
plex.
Rutile
was
also shown
to be stable n
the tempera-
ture
and
pressure
anges
of the metamorphism
(cf.
Jam-
ieson
and
Olinger, 1969).
Preferred orientation occurring in two intimately co-
existing
phases
s commonly
a
result
of exsolution
or to-
potaxial
(topotactic)
or epitaxial intergrowth.
However,
exsolution equires
hat the
reactant
componentsareequal
to those of the
sum of the
products;
simple exsolution of
titanite
and rutile is
therefore
precluded,
as the addition
of rutile and
titanite components
o the biotite leads
o a
nonsensible
ormula for
the hypothetical
precursor.
The
process
must
therefore nvolve
addition
or
loss
of one or
more
components.BecauseTi
and Ca are common
com-
ponents
of biotite
and because utile and
titanite are
ran-
domly
distributed throughout
biotite, the source
of the
Ti
and Ca of titanite and rutile was most likely as a solid
solution component
of the biotite. These elations
collec-
tively
require
dissolution
and
recrystallization
of at
least
a
portion
of the original biotite, with
gain
or loss
of com-
ponents.
As
discussedabove, the solubilities
of Ti and Ca in
biotite
generally
ncreasewith
increasing
emperature.
f
biotite of an igneous origin was metamorphosed
under
the amphibolite or
greenschist
acies
conditions deter-
mined for
the
Tananao
complex, high Ti
and Ca com-
ponents
inherited from higher
temperature
conditions
could
well
be
in
excessof the
limits
allowed at
lower
temperatures.Reactions nvolving
the breakdown
of the
Ti-
and Ca-rich biotite to Ti- and
Ca-depletedbiotite
plus
titanite, rutile,
and other
phases
might
thus take
place
during
metamorphism
when biotite with
high Ti and
Ca
contents
was no longer
stable. Studies
of
hydrothermal
experimentsalso
showed hat
Ti-rich
phlogopite
forming
at
higher
temperatures
=
1000
C)
breaksdown
to assem-
blagesof Ti-depleted
phlogopite,
rutile, and sanidine or
vapor
at
lower
temperatures
s800
"C)
(Forbes
and
Flow-
er,1974;Tronnes
et al., 1985).They
alsoshowed
hat the
Ti content
of
phlogopite
increases
with increasing
em-
perature
and
decreasing
pressure
or
a
given
bulk TiO,
content.
Alternatively, titanite andrutile could have ormed con-
comitantly with
the topotaxial
breakdown of biotite
to
chlorite
(cf.
Veblen
and Ferry, 1983; Eggleton
and Ban-
field, 1985)
during
an early
retrogressive
pisode
fpoly-
metamorphism.
Titanite
or
rutile formed in this manner
would likely be observed as
well-oriented acicular inclu-
sions
in
chlorite,
as
reported
by
Rim5aite
(1964),
al-
though
titanite usually occurs as
relatively large crystals
without
preferred
orientation
in chlorite
(Dodge,
1973;
Ferry,1979 Parry and Downey,
1982;
Veblen
and
Ferry,
1983). Baxter and Peacor (unpublished data) observed
both
titanite
and rutile
intergrown with interlayeredchlo-
rite and
biotite
in samplesof altered
ufaceous
rocks rom
New Z.ealand,
where
the chlorite
was
an alteration
prod-
uct of
Ti-rich
detrital
biotite.
Ferry
(1979)
suggested
reaction that accounts
or
the
formation of chlorite
and
titanite from
Ti-bearing
biotite
by
hydrothermal alter-
ation
in
granitic
rocks. The chlorite thus
formed
in
an
early stage of
retrograde metamorphism
might
have
transformed topotaxially
to biotite and
retained
well-ori-
ented titanite and
rutile
in
biotite
during a
final
progres-
sive episode of the
polymetamorphism,
which occurred
at the conditions well above the biotite isogradaccording
to several
prograde
eactions
e.g.,
Ernst,
1963; Brown,
r97 ).
However, since a sagenitic
biotite
with
well-oriented
inclusions of titanite
and rutile
may also be altered to
chlorite and
retain the
preexisting
nclusions
in
chlorite,
existenceof sagenitic
chlorite does
not necessarily mply
that the titanite
and rutile
inclusions
formed during al-
teration
of biotite to
chlorite.
In
addition,
titanite,
which
has been characterized
as one ofthe
products
during al-
teration ofbiotite to chlorite,
does
not
generally
occur as
well-oriented, needlelike
nclusions ike those
n
this study
(Dodge, 1973; Ferry, 1919; Parry and Downey, 1982;-
Veblen and
Ferry, 1983).Therefore,
t is more
likely
that
the sageniticbiotite
formed by a
precipitation
mechanism
where
titanite,
rutile, and
Ti-depleted biotite crystallized
topotaxially during
metamorphism through the
break-
down of a
Ti-
(and
Ca-)
rich biotite that
had formed under
conditions
of
higher temperatures
(e.g.,
gneous biotite)
than those of the
metamorphism.
Chlorite observed
n
the
present
nvestigation,
which is
presumed
o
replace
biotite
or overgrow biotite
during the
latest
greenschist
aciesmetamorphism, does
not contain
well-oriented acicular
nclusions.
t
apparently
has no re-
lationship
with
the
formation of acicular
inclusions
in
biotite.
In
addition,
the
rutile inclusions
n
biotite contain
precipitated
hematite-ilmenite
platelets
hat
should
post-
date he
formation of rutile
(cf.
Banfieldand
Veblen, 199
).
Precipitation
of
hematite
in rutile took
place
within
an
approximate
temperature
angeof
450-600
"C,
according
to observationsof experimentally
annealed
utile
(Putnis,
1978;Putnis
and
Wilson,
1978), hough he
precipitation
temperatures
are
probably
lower, based on
the observa-
tions by Banfield and
Veblen
(1991)
and
Bursill
et al.
(1984).
Therefore,
precipitation
of
rutile
and
titanite in
the sageniticbiotite
probably
took
place
during
the am-
phibolite
facies
metamorphism or
following
retrograde
metamorphism at temperatureshigher than those of the
latest
greenschist
acies metamorphism
for
the
Tananao
complex. Other examples
of
precipitated
nclusions, such
-
8/20/2019 On oriented titanite and rutile inclusions in sagenitic biotite
12/13
t 2 t 6
as well-oriented magnetite nclusions n
pyroxenes Fleet
et al., 1980)and hematite nclusions n sillimanite
(Fleet
and
Arima, 1985),
have been
reported
as occurring
n
metamorphic rocks with
a complex
retrogradehistory.
Structural control of the
well-oriented nclusions
in biotite
Optical and TEM
observationsshowed
hat one
of the
three sets
of
intersecting
rutile
needles orming
asterisks
is
parallel
to b
of biotite.
The
prism
axesof rutile
needle
are
parallel
o c, and
(100)
or
(010)
of rutile are
parallel
to
(001)
of biotite. The rutile structure s
composed
of
parallel
chains ofedge-sharingTiOu octahedra
hat
extend
parallel
o c
and are connected
aterally
by sharing
vertices.
The
O
layer, which
is
parallel
o
(
100)or
(0
10)
of
rutile,
is nearly
closest-packed, hough slightly
puckered.
The
biotite structure s
also basedon closest
packing
ofanions,
with
anion layers
being
parallel
to
(001)
of biotite.
(Draw-
ings
of the rutile
and biotite structures can be
found in
many standard textbooks
of
mineralogy
and
will not
be
given
here.)Preferred
orientation involving
(
I 00) or
(0
I 0)
of rutile and
(001)
of biotite
is
therefore understandable
in
terms of their similar closest-packed
eometries.
Fur-
thermore, he
(Mg,Fe,Al,Ti)(O,OH)u
ctahedra fthe bru-
cite-like octahedral sheet of biotite form chains of octa-
hedra
by sharing edges,as in rutile. Such chains extend
in three directions,
each oriented 60"
from
the others and
conforming o the
pseudohexagonal
ymmetryof
(001)
of
biotite. During
dissolution
(of
biotite) and crystallization
(of
rutile),
migration
of
Ti into
those octahedra
n
sub-
stitution of
Mg,
Al, and
Fe
and replacementof OH by O
could easily convert the edge-sharing (Mg,Fe,Al,Ti)-
(O,OH)6
octahedra nto
chains of edge-sharing
TiOu
oc-
tahedra
o
form
a
pattern
ofthree rutile needleswith ends
intersecting
at angles of
120"
(Fig.
a).
Superposition of
another
pattern
that
consists
of
three
needles
extending
in
the directions opposite to those of the first
pattern
createsan asterisk
pattern
with
adjacent
needles
at angles
of 60'
(Figs.
I and 4). Growth of
rutile
needles
hus
in-
volves minimum reconstruction
and cation diffusion.
Fleet and Arima
(1985)
studiedoriented
hematite n-
clusions
n
sillimanite and
indicated
that
(120)
of
he-
matite is
parallel
to c of sillimanite,
which is
the
direction
containing chains of edge-sharing octahedra for both
phases.
The
orientation
relationships
of
magnetite nclu-
s ions
in
pyroxenes,
nc luding
{
I I I
}Ml l
100}"
and
(
I I
2
),
ll
c", are also related o closest-packed
O
layersand
chains of edge-sharing ctahedra
(Fleet
et al., 1980).
Platelets
of
hematite
or
(Fe,Ti)rO,
nclusions n
rutile
with
{001}Hll{100}.
nd
(120)"l lc.
have
beenobserved
n the
present
nd other studies
Putnis
and
Wilson, 1978;Put-
nis, 1978;
Bursill
el al.,
1984;Banfield
and
Veblen, 1991).
Gilkes and Suddhiprakarn
(1979)
reported
a
preferred
orientation between
goethite
and
biotite
with
{100}cll 001}u
and collbu
n
deeply
weathered
ranitic
rocks, although
other orientations between
goethite
and
biotite
have
been
observed by
Banfield
and
Eggleton
(1988).
All these
preferred
crystallographic
elations
be-
SHAU ET AL.: ORIENTED
INCLUSIONS
IN BIOTITE
tween
rutile and biotite,
magnetite
and
pyroxenes,
utile
and
hematite, and
goethite
and
biotite
have a common
structural
similarity,
in
that
the two coexisting
phases
share
nearly closest-packed
anion
layers and chains
of
edge-sharing
octahedra
within the anion
layers
and
are
thus topotaxially
controlled
(cf.
Fleet,
1982; Fleet and
Arima. 1985).
Although
most titanite
inclusions
exhibit
prefened
ori-
entation
in biotite,
TEM data
have shown
that
many dif-
ferent
orientations
with
respect to
(001)
of biotite
also
occur.
It
is
estimated
that
more than
800/o f the
titanite
inclusions are elongated
parallel
to
(0
I I
)
and to
the three
directions
orming equilateral
riangles,
with
{
l l
}
or
{43
3
of
titaniteapproximately
arallel
o
{001
ofbiotite.
How-
ever,
n
contrast
o the
single
kind oforientation
occurring
almost
exclusively
for
rutile, other orientations
in which
{001}, {l0T},
{0lT},
or
{410}
of t i tanite
are
parallel
o
{001}
of biotite
were
also
observed.
An orientation
with
{
I
l0}
of titanite
parallel
o
{001}
of
mixed-layerbiotite-
chlorite in alteredgranitic biotite from southeasternAus-
tralia
was
observed
by
Eggletonand
Banfield
(1985).
The
variable orientations
of titanite
with respect o
{001}
of
biotite
indicate that titanite
does
not
have well-defined
structural
features n common
with biotite.
Nevertheless,
the
preferred
orientation
(0ll)'lla"
implies some struc-
tural control,
but
we have been unable
to define
one.
AcrNowr,nocMENTS
The
authors
are
grateful
o
Eric
J.
Essene,
amsin C. McCormick, and
J.
AlexanderSpeer
or critical
reviews
ofthe
manuscript.
We thank Pouyan
Shen
and Su-Cheng
Yu for many
helpful
discussions.
Transmission and
analltical electron microscopic work was carried out at the Institute of
Mining, Metallurgy
and Material Sciences
of the National Cheng
Kung
University
and the
Institute of Materials Science
nd Engineeringof the
National Sun
Yat-Sen University
in Taiwan,
Republic of China, and
in
the Electron
Microbeam Analysis
aboratory, the University of
Michigan,
Ann Arbor, Michigan.
A tit anite standard
B20360)
or AEM analyses
was
kindly
provided
by the
National Museum ofNatural
History, Smithsonian
Institution. The
present
study
was
supported
by the
grants
NSC-67M-
0202-
2(02\, NSC-75-M006-0202-03, and
NSC-76-M006-0202-02 to
H.-Y.Y. from the
National
Science
Council of the
government
of the
Republic of China, and by
NSF
grant
EAR-8817080 to D.R.P.
The
CM-
l2
STEM
was acquired under NSF
grant
EAR-8708276 and the electron
microprobe under
NSF
grant
EAR-8212764. Contribution
no. 476 from
the
Mineralogical l:boratory,
Department of Geological Sciences,Uni-
versity
of
Michigan, Ann Arbor, Michigan
48109,
U S.A.
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MeNuscrurr RECEI 'EDpnrr 23, 1990
Mnm-rscnrrr AccEmEDApntr 17, l99l
SHAU ET AL.:
ORIENTED INCLUSIONS
IN BIOTITE