Fluid regime during the formation of continental crust

Abstract

Many studies have been devoted to the study of oceanic crust, much less on its continental equivalent. It has been known for a long time that the average composition of the continents is approximately granitic, with however a marked difference between a granitic Upper/Middle crust, also including metamorphic rocks of low-to medium grade (up to amphibolite facies), and a granulite Lower crust, which tends to be more basic (metagabbros) at the crust-mantle interface. Both units are separated by a weak geophysical discontinuity (Conrad), less continuous and obvious than the Moho at the lower limit of the crust. Granite formation in the Upper/Middle crust is believed to occur mainly by dehydration melting, breakdown of H2O-bearing minerals (mainly muscovite and other micas) and melting under the influence of liberated H2O.