Granites, granulites, and crustal differentiation

Abstract

Partial melting and the ascent of granitoid magma are among the main processes leading to differentiation of the continental crust. Recent experimental studies and modelling indicate that fertile crustal rocks will typically produce 30 to 40 vol% melt at temperatures of 850°-900°C, even under fluid-absent conditions. Comparative studies of orogenic belts show a marked contrast between orogens with abundant granitoids and those with only scarce granitoids. This contrast in granitoid abundance does not appear to be the result of greatly different evolutionary stages, different levels of erosion, or contrasting orogenic processes. It might be simply interpreted in terms of the contrasting fertility of the major rock types involved in the different orogens. The abundances, types, and ages of crustally-derived granitoids reflect the compositions, ages and metamorphic states of their source regions, both prior to and following the magmatic events. -from Authors