Crustalscale Deformation and Late Archean Terrane Suturing Southeastern

Crustal-scale Deformation and Late Archean Terrane Suturing Southeastern Superior Province Canada Keith Benn University of Ottawa kbenn@uottawa. ca

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

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 S N

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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