granulite facies A set of metamorphic mineral assemblages produced by metamorphism of a wide range of starting rock types under the same metamorphic conditions and typically characterized by the development, in rocks of basic igneous composition, of the mineral assemblage clinopyroxene—plagioclase— orthopyroxene—quartz. Other rocks of contrasting composition, for instance shales or limestones, would each develop their own specific mineral assemblage, even though they were all being metamorphosed under the same conditions. The variation of mineral assemblage with starting rock composition reflects a particular range of pressure, temperature, and P(H2O) conditions. Experimental studies of mineral P—T stability fields indicate that the facies represents high-pressure/high-temperature conditions which can be met near the base of the continental crust.
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