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1 Archaean Team, Géosciences-Rennes (UPR CNRS 4661), Campus de Beaulieu, 35042 Rennes Cedex, France
2 Centre de Recherche Pétrographiques et Géochimiques (CRPG-CNRS), 54501, Vandoeuvre-les-Nancy Cedex, France & Departement de Géologie, Université de Montréal, Montréal, CP 6128, Québec, Canada
3 École Polytechnique, CP 6079, Succ. Centre-Ville, Montréal, Québec, H3C 3A7, Canada
We present a comparison of the processes involved in the tectonic evolution of two Archaean cratons, the Superior Province of Canada and the Dharwar Craton of India. These two cratons exhibit distinct map patterns, the Superior Province being dominated by elongate belts, while the Dharwar Craton is characterized by dome and basin features.
We suggest that certain tectonic processes operating in the Phanerozoic, such as enhanced mantle plume activity, subduction of young (warm) oceanic crust, and faster than usual accretion of crust, may have been the norm during the Archaean. In the Superior Province rapid crustal growth occurred, largely due to horizontal tectonic forces. Models analagous to modern plate tectonics are applicable, but the rates of convergence and accretion exceeded those normal for the present day. Accreted crust was warm and subject to more ductile deformation than in modern accretionary zones. These accreted arc, ocean-floor and ocean-plateau fragments would have been underlain by a thick refractory, buoyant, warm lithospheric root that was rapidly underplated (or imbricated) below the recently accreted terranes. In the Dharwar craton a major thermal event appears to characterize its evolution at 2.5 Ga. Reheating of the lower and middle crust in response to magmatism and metamorphism, resulted in diapirism and growth of crust in a vertical sense.
The southern Superior Province’s evolution reflects accretion at the margins of a protocraton, while the Dharwar craton’s tectonic environment may reflect plume impact and incipient rifting in the centre of an Archaean craton.
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