Abstract

The feasibility of a tectonic model that would explain some of the major features of the Archean Superior Province is examined. This model assumes that about 3.5 Ga (1 Ga = 109 years) ago, a thin granitoid crust covered most of the Earth and there was no clear separation into oceans and continents. Basalts would partially melt in the upper mantle and rise to the surface forming thick volcanic plateaus. After cooling, the dense volcanics (2.9 g/cm3) overlying the granitic crust (2.65 g/cm3) would sink if both materials' viscosity were reduced. A succession of cycles of volcanism and vertical tectonism may have lasted until the Kenoran orogeny. One-dimensional thermal modelling shows that under reasonable assumptions, the temperature jump which follows the deposition of a volcanic layer at −3.2 Ga is sufficient to reduce the viscosity by five orders of magnitude. This was no longer the case under post Kenoran conditions when radioactive heat production was lower, and deep erosion had reduced even further the amount of radioactivity in the crust.

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