Evolution of the continental lithosphere

Stable cratons and stable continental platforms are salient features of the Earth. Mantle xenoliths provide detailed data on deep structure. Cratonal lithosphere is about 200 km thick. It formed in the Archean by processes analogous to modem tectonics and has been stable beneath the larger cratons since that time. Its high viscosity, high yield strength, and chemical buoyancy protected it from being entrained by underlying stagnant lid convection and by subduction. Chemically buoyant mantle does not underlie platforms. Platform lithosphere has gradually thickened with time as convection waned as the Earth's interior cooled. The thermal contraction associated with this thickening causes platforms to subside relative to cratons. At present, the thickness of platforrn lithosphere is comparable to that of cratonal lithosphere.