Ancient plate tectonics

Abstract

Taking multiple indicators into account together, there is good evidence for the operation of plate tectonics on the Earth as far back as 3.3 Ga, but it may have been a modified form until the late Proterozoic without deep subduction and the production of ultrahigh pressure metamorphic belts. In the early Archean, the production of early SiO2-rich crust may have been caused by melting at the base of a uniformly thick global crust or oceanic plateaux, with or without subduction as on the modern Earth. In the past few years, the number of lines of evidence for cool conditions at the end of the Hadean is increasing, such as the stable isotope signatures of zircons and the composition of TTG gneisses. The importance and abundance of komatiites and exceptional mantle temperatures in the Archean may have been overestimated in the past.