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.
