The Correlation Between the Palaeoproterozoic Orogens and Granulite Belts in the Baltic Shield and North America Craton: A Suggested Model of Palaeoproterozoic Plate Tectonics

Abstract

The Earth's Archaean history was completed with the formation of the first Supercontinent (Pangaea-0) at ca.2.5 Ga ago. The main tectonic units of the younger Palaeoproterozoic crust in the North Atlantic realm include the collision and accretional orogens and in some cases the granulite thrust-nappe belts. Three cycles of geodynamic activities are known in Palaeoproterozoic, at 2.5-2.33 Ga, 2.25-1.9 Ga and 1.9-1.82 Ga. Not only the starting and final events of the Palaeoproterozoic megacycle (with the corresponding extension and compression stages) but also each cycle of evolution of the collision orogens (including both Pechenga-Imandra-Varzuga, Trans-Hudson, Cape-Smith, New-Quebec and other suture belts and Lapland, Snowbird, Queen-Maud granulite thrust-nappe belts) and of accretional orogens (Svecofennian, Penokean, Wopmay) are strongly correlatable. The Palaeoproterozoic “plate tectonic” evolution appears unique in the absence of (1) general dispersal of the Archaean Supercontinent and (2) manifestation of subduction related magmatism in the accretional orogens along the craton margins of the North Atlantic realm during 2.45 to 1.93 Ga (i.e. for about 600 Ma). An exception from the above generalization is the reported intrusion of calc-alkaline granitoid complex cutting the lower part of the Huron Supergroup along the passive margin of the Superior Craton during 2.39-2.33 Ga. It is presumed that during Palaeoproterozoic the oceanic crust in the Oceanic Hemisphere underwent rapid recycling that was accompanied by unusually slow Wilson-type evolution within the Supercontinent that was probably nowhere disrupted in full. Rapid recycling of oceanic crust appears possible if the mid ocean ridges (MORs) are presumed to lie above the sea level. This might have prevented hydration of oceanic lithosphere which inhibited evolution of calc-alkaline magmas. This particular model of global tectonics during the Palaeoproterozoic may be styled as “microocean tectonics” to distinguish it from the Archaean “microplate tectonics” and the Phanerozoic “plate tectonics”.