Transcript Crustal-scale Deformation and the Signature of Late Archean

Crustal-scale Deformation and
Late Archean Terrane Suturing
Southeastern Superior Province
Canada
Keith Benn
University of Ottawa
[email protected]
Conclusions
1. 2.7 Ga plate tectonics required to explain a
documented terrane boundary
2. Probable accretion of oceanic LIP to margin
of older crustal block
3. There is a very specific structural signature
in the suture and in the accreted plateau
4. The structural signature is best explained by
a crustal strength profile including a stiff
lower crust, probably mafic granulites
SE Superior Province
70°
Granulite-grade gneiss
Metasedimentary belts
Granitoid batholiths
Granitoids, Orthogneiss
Greenstone belts
Opatica
KS
Gr
Pr e n
ov vil
inc le
e
Abitibi
49°
Pontiac
300 km
80°
SE Superior Province: Geology
> 3000 Ma rocks below
Pontiac (Carignan et al.,
Chem Geol, 1993)
Tectonic delamination
Tectonic delamination: why ?
• Geothermal gradient calculated incorporating crustal heat production (Sandiford et al., 2004;
Afonso and Ranalli, 2004)
Magmatic modification
F4
S
N
A'
B'
Kenogamissi complex
Roblin batholith
bt Granite (2660 Ma)
White bt Granodiorite
hbl-bt Granodiorite (2682 Ma)
Grey bt Granodiorite
bt Granodiorite (2700 Ma)
hbl-bt Tonalite (2713 Ma)
10 km
Orthogneiss (2723 Ma)
hbl-bt Tonalite (2740 Ma)
Two of the Tonalite Suites
2713 Ma
2723 Ma
Granodiorite
2700 Ma to 2696 Ma
• Synmagmatic tectonic deformation of ca 2696 Ma Granodiorite
Differing granitoid chemistry
Provided by J.-F. Moyen
Remelting of diorites
Testing the model
• Positively identify surrounding terrane
boundaries
• Crustal rheological profile
– Strong lower crust (shear zones, faults) to be
verified in the Kapuskasing zone
• Modified oceanic LIP
– Detailed petrology / geochemistry of granitoids
• Define limits and nature of the old terrane
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