Experimental studies on biotite- and muscovite-granites and some crustal magmatic sources

High-grade metamorphism is certainly associated with melting and the formation of migmatites, and migmatization may culminate in the production of discrete bodies of granite. I am impressed, however, by the evidence that most granitic intrusions represent a single, frozen stage in a complex sequence of events with origin in the mantle, rather than in the crust. Recent trace element and isotope studies of many granites confirm that these were derived from source materials in both mantle and crust (Atherton and Tarney, 1979). Heat and magmas from the mantle generate more magma by partial fusion of crustal rocks. The magmas rise through the crust, in ways controlled by the regional tectonics. They may become stalled to form batholiths, they may blister upwards into plutonic stocks, and they may burst through to the surface in volcanic eruptions. They exsolve hot, enriched, aqueous solutions during the late stages of solidification, and they impel meteoric water into enormous subterranean circulation s. The solutions cause chemical changes in both intrusive and country rocks