THE OTTAWAN OROGENY Himalayan style crustal channel?
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Transcript of THE OTTAWAN OROGENY Himalayan style crustal channel?
THE OTTAWAN OROGENY
Himalayan style crustal channel?
GOALS
• To present a Himalayan model for the development of the Grenville Orogenic Event.
• To apply this model to the a portion of the Canadian (Ontario) and adjacent Adirondack (New York) terrane assemblage.
• To examine this model with particular reference to the nature and timing of activity along the major terrane-bounding shear zones, periods of igneous intrusive activity, and timing of metamorphic events.
ADK. HIGHLANDSADK. LO
WLA
NDS
FRONTENAC
MSZR
LS
Z SHARBOT LAKE
MAZINAW ccsz
ELZ
EVIR
CMBBZ
BANCR
OFT
BSZ
CENTRALGNEISS BELT
Adapted from Davidson (1998)
40km
Terranes and shear zones
MSZRLSZ CCSZ
LL HL
Adirondack Highlands
Sharbot Lake-Frontenac/Adirondack lowlands
Mazinaw
ElzevirBancroft
Anorthosite (AMCG Suite)
1300-1200Ma
Igneous Events
1180-1120 Ma
MSZ
RLS
Z
AMCG etc.
1120-1095 Ma
HAWKEYE
1090-1050 Ma
CMBBTZ
LYON MOUNTAIN
Observations
• There is a shift in the locus of igneous activity through time (generally W to E) reflecting the assembly of Grenvillian Terranes along eastern Laurentia.
• The anorogenic/rift AMCG event magmas intrude the Adirondack (ADK) Highlands, Lowlands, Frontenac, Sharbot Lake and Mazinaw Terranes but are focused in the ADK Highlands
• Post AMCG pre Ottowan Orogney; Hawkeye granitoids are primarily found in the ADK Highlands.
• Lyon Mountain Granitoids rim the ADK Highlands are common along or adjacent to the CCSZ and scattered through the other terranes. (Pressure-release A-type magmas: )
OTTAWANTHERMAL EVENT
1090-1050 Ma
ADK H
ADK
LL
F
SL
MAZEL
B
CGB
1050-1020 Ma
1010-980 Ma
ObservationsMetamorphic events
• Adirondack Highlands and the Mazinaw terranes record the Ottawan Event.
• Adirondack Lowlands record a weak Ottawan Event focused along the CCSZ
• Frontenac and Sharbot Lake Terranes do not record the Ottawan Event.
• Terranes west of the CMBBZ record pluses of metamorphism at a slightly later time and cool quickly.
From Davidson (1998) An overview of the Grenville Province Geology, Canadian Shield.
ccsz
Dana Hillmetagabbro
Diana Syenite Body
ADK HL
ADK LL
Diana Syenite (ADK lowlands)
Dana Hill Metagabbro (ADK highlands)
1020 Ma
1041.3+/-1.7Ma
After (Streepey et al. 2001)
Sphene U/Pb
Sphene U/Pb
Hbl 39Ar/40Ar
989 +/- 1.7Ma
Hbl 39Ar/40Ar
979+/-8.6Ma
CC
SZ
• Early 30+m wide shear zones in the DHMG record recrystallization temperatures in excess of 700oC, sphene replacement of Fe-Ti Oxide minerals, and a complete lack of scapolite.
• Late (sub-meter wide) shear zones in the DHMG record recrystallization temperatures ranging from 670-700oC and widespread repalcement of plagioclase by scapolite.
• Shear zones (meter + and sub meter widths) in the Diana Syenite Body span a wide range of temperature conditions (sub 550oCa), and most show sphene replacement of Fe-Ti oxide minerals
• Shear zones contain widespread scapolite replacement of plagioclase.
aLamb (1993) (Streepey et al. 2001: Johnson et.al (2004)).
CC
SZ
• Large early-formed shear zones in Dana Hill Metagabbro (high temp) NO SCAPOLITE
• Scapolite replacement of plagioclase in (sub meter wide shear zones) Dana Hill Metagabbro Body
• Dana Hill Metagabbro (Highlands) Sphene cooling through 650oC at 1020 Ma.
• 39Ar/40Ar cooling through closure for hornblende (550oC) ~1000-978 Ma
• Scapolite replacement of plagioclase in shear zones (DSB)
• Diana Syenite Body (DSB) Sphene-growth in shear zones at ~ 1041 Ma.
• Thermal resetting/growth of sphene in DSB at 1035-1050 Ma age. Zircon records ~1150 Ma AMCG age (McLelland et al (2003).
• 39Ar/40Ar cooling through closure tor hornblende (550oC) ~990-978 Ma
CCSZ Thermal Profile
CC
SZ
100
300
500
700
-3 -2 -1 0 1 2 3 4 5
distance (km)
Tem
per
atu
re o
C
CCSZ~1040Ma~1020 Ma
~990Ma
Fluid Inclusion data (syn-post orogenic)_LYON MOUNTAIN GRANITE
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
0 100 200 300 400 500 600 700 800
Temperature (C)
P (b
ars)
3-phase
Carbonic
Late aqueous
Adapted from: Beaumont, R.A. Jamieson, M.H. and Lee B. (2001) Himalayan tectonics explained by extrusion of a low-viscosity crustal channel coupled to focused surface denudation: Nature, 414, pp. 738-742.
900oC
MOHO700oC
TEMPERATURE
CCSZ
800oC
Channel Flow Thermal Gradients
100 km
A’
TECTONIC CROSS-SECTIONS
MSZRLSZ CCSZ
LL
FLINTON GROUP
Crustal detachment
HL
Old Mt Holly Arc
Trench roll back
~ 1160-1110 Ma
AMCG main phase
Or delamination
1110-1100 Ma
MSZRLSZ CCSZ
LLCrustal detachment
HL
Old Mt Holly Arc
1155-1112 Ma arc
FLINTON GROUP
HAWKEYE GRANITOIDS
AMCG late phase-Hawkeye intrusive suite
FLINTON GROUP
HAWKEYE GRANITOIDS
LYON MOUNTAIN GRANITOIDS
1090-1040 Ma
OTTAWAN PHASE
MSZRLSZ CCSZ
LL HL
Amazonia?
Extrusion of the low viscositygranulite core of the orogen
1080-1030Ma
ADK HLF.T.SLTMAZ ADK LL
Granulite core
Zone of active footwall deformation
Lyon Mtn A-typeGranitoid
ADK HLF.T.SLTMAZ ADK LL
Granulite core
Zone of active footwall deformation
Lyon Mtn A-typeGranitoid
Conclusions• The Shawinigan- AMCG- pre-Ottawan development for this part of
the Grenville can be explained via tectonic switching and or collision along an Andean-type margin (first proposed by Hanmer et al. (2000)).
• AMCG magmas intrude into an evolving back-arc basin at a time when the ADK Highlands are structurally beneath the ADK LL/Frontenac/Sharbot Lake Terranes. All of these terranes receive AMGG magmas. (Flinton Group deposited)
• Continental-Continenal Collision occurs at or near to 1090Ma (Ottawan Orogeny)
Conclusions• During Ottawan compression, the ADK H.L. Terrane is mobilized
and extruded along a tectonic channel.
• This extrusion is oblique thrust in character and focused along the CCSZ. Thermal gradients established across the CCSZ with localized heating of the adjacent ADK lowlands (resets isotopic systems in the ADK lowlands near to the CCSZ: Dahl (2002)).
• Major un-named shear zones in the eastern Adirondack Highlands my represent the base of this channel.
• Extrusion is aided by the formation of pressure release melts (syn-post Ottawan Lyon Mountain Granitoids). Fluid inclusion data from Lyon Mountain Granitoids adjacent to the CCSZ record nearly isothermal uplift.
Conclusions
• Uplift results in gravity-driven collapse of cover rocks (ADK L.L. Frontenac over Sharbot Lake Terranes) to the W- NW. Extrusion of the granulite core with deflation of the mid-lower crust, rotates the Mazinaw Terrane triggering amphibolite facies metamorphism.
• Continued convergence reactivates shear zones to the west driving short tectonothermal events in terranes to the west (Central Gneiss Belt).