Characteristics of metamorphic processes in Early Precambrian

Relatively high geothermal gradient and greater depths of the erosion plane may account for certain distinctions of the Lower Archean metamorphic complexes. Their granulites and amphibolites could not have been formed at depths shallower than 15-16 and 10 km, respectively, as indicated by review of the available data. The granulite fades of metamorphism is not restricted to Precambrian rocks, but is found also in younger complexes, some of which outcrop on the surface of the ground, although they were subjected to intensive autodiaphthoresis, which usually accompanied crystallization of anatectic melts within the amphibolitic range of the temperature.