The granulite-granite connexion

Abstract

Granulites may be produced in either fluid-present or fluid-absent metamorphism. Fluid-present granulites can be formed by relatively low-T dehydration reactions, in the presence of a fluid dominated by a species other than H2O (e.g., CO2). Much of the lowermost crust is composed of non-restitic metagabbros and cumulates. However, the middle and lower crust also contain a substantial component of granulitic restite. This is derived through fluid-absent partial melting of common crustal rock-types that had been through earlier hydration cycles. Non-restitic, mafic granulites represent basaltic magma that provided the heat source for metamorphism and melting of the overlying rocks. Restitic granulites are the refractory, residual complements of the granitoid magmas emplaced at higher levels. Silicic magmatism is most commonly a manifestation of crustal growth through under- and intra-plating of mantle-derived magma. -from Author