Article Abstract:
Seismic data from a collision zone in the Superior Province of Canada, involving the Abitibi granite-greenstone Subprovince and the plutonic, arc-related Opatica belt provides evidence that plate tectonics were active in late Archaean times, 800 million years earlier than the previous seismic reflection surveys. Dipping seismic reflections that extend 30 km into the mantle were considered evidence of a 2.69 Gyr-old subduction suture. The data implies plate tectonic activity despite the differences in crustal structure, lithospheric thicknesses and convergence rates compared with modern day.
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Article Abstract:
The survival of electrical anisotropy in the upper mantle of the Canadian shields gives strong indication about the formation of upper mantle root relatively early in their accretion history. The upper mantle root of Superior Province has survived relatively intact to modern times. Seismic tomography of the Superior Province of the Canadian shield suggest the existence of cold, deep (up to 250 km) roots. The rheological profiles confirm the mantle brittleness down to a depth of 150 km.
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Article Abstract:
It is argued that the gravitational spread of Archaean continents would have causes continuous overflowing onto adjacent ocean basins, ceasing at the end of the Archaean era. The cessation corresponds to the cratonization at the end of the Archaean era, depending on the geothermal gradient evolution and the depth of the ocean basins. It is likely that a ductile zone was present within the hotter Archaean continental crust.
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