Geology of granite

Abstract

The genesis of granite is intimately related to the dynamic structure of the Earth. Granite is the main component of continents; it is one of the oldest known rocks; and the geological history of granite provides the main evidence about the growth and evolution of continents through time. Granite formed in a number of different situations. Some granite was generated in zones of rifted continental or oceanic crust, but most granite was generated in zones of collision between continents and oceanic crust, and where continents were amalgamated. Granite formed by two different processes: by fractional crystallization of basaltic magma; and by melting older continental crust. Between these end members, there is a spectrum of hybrid processes, including mixing of basaltic and granitic magmas, and contamination of basaltic magma by partial melts of different kinds of continental crust. Although superficially simple and similar, most granites reflect a complicated history of multistage, hybrid processes. This complexity has led to a diversity of interpretations, and the origin of granite has been one of the most hotly debated topics in geology. The following review outlines the nature and diversity of granite; where, how, and when granite was generated; how it was intruded through the crust; the structures that it formed; and the history of debates over its origin.