Archean Plate Tectonics: Constraints and Inferences

The earth has been cooling since Archean time. The higher temperatures beneath Archean ridges resulted in more partial melting which extended down to greater depths than at present. The Archean oceanic crust was much thicker (>20 km) than modern crust (~5 km). This inference is compatible with previous ideas of suspected oceanic crust. The thicker oceanic crust in the Archean tended to resist subduction similar to modern aseismic ridges, but could not prevent it. Short-lived episodes of intra-arc spreading followed by Cordilleran-type compression may have produced Archean greenstone belts. Archean meta-tonalites represent a significant part of the continental crust and were probably produced by melting of the subducted slab which was favored by the higher mantle temperatures.