Crustal-scale Deformation and Late Archean Terrane Suturing

Keith Benn

University of Ottawa

kbenn@uottawa.ca

Southeastern Superior Province

Canada

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 Province70°

80°

49°

300 kmPontiac

Granulite-grade gneissMetasedimentary beltsGranitoid batholithsGranitoids, OrthogneissGreenstone belts

Opatica

Abitibi

Gre

nville

Provi

nce

KS

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 modificationF4

10 km

B 'A '

hbl-bt G ranodiorite (2682 M a)

bt G ranite (2660 M a)

bt G ranodiorite (2700 M a) hbl-bt Tonalite (2740 M a)

O rthogneiss (2723 M a)

Kenogamissi complex R oblin batholith

hbl-bt Tonalite (2713 M a)

W hite bt G ranodiorite

G rey bt G ranodiorite

NS

Two of the Tonalite Suites

2723 Ma

2713 Ma

• Synmagmatic tectonic deformation of ca 2696 Ma Granodiorite

Granodiorite

2700 Ma to 2696 Ma

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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Geophysical Monograph Series, Volume 164, 370 pages, 2005, AGU Member Price - $ 62.30