Figure 9.

Schematic temporal evolution of the lithosphere associated with decreasing mantle temperature. Early Earth, prior to 3.2 Ga involves a non-plate tectonic regime, with magmatism characterized by a bimodal association of TTG (tonalites, trondhjemites and granodiorites) and greenstone belts. Mantle plumes are a major source of mafic magmatism. Recycling occurs through delamination and mantle convection is of relatively small wavelength. Subduction where present is transitory. Plate tectonics is envisaged to have commenced after 2.5 Ga and is associated with large aspect ratio mantle convection. Between these two tectonic regimes is a transition phase in which the lithosphere is stabilized, differentiates into oceanic and continental types, with the latter undergoing thickening enabling its emergence and erosion.