A model is presented in which the Earth is characterized by the mantle deep convection, and the thickness of the continental and oceanic lithospheres change with time as the pressure-temperature-geochemical conditions alter in the upper mantle. This model predicts that no island arc differentiation took place before 4000 Ma. During the Archaean, the shallow lithosphere allowed local, tectonic coherence and a gradual increase in the depth of subduction differentiation processes. The change to large cratonic-scale tectonic stability during the Proterozoic occurred as a result of lower lithosphere conditions allowing granulites to be stable—the consequential dehydration of the continental lithosphere creating extensive lateral and vertical stability. The change to ‘modern’ plate tectonics finally took place when the strengths of the oceanic and continental lithospheres became sufficiently close that mantle convection could produce continental splitting. It is suggested that this model accounts for the overall changing tectonic and geochemical features of the continental crust, although such generalities must be applied cautiously to specific localities.

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