Earth and Environmental Science

3 April, 2017

GEOL 5903 Seminar: Gabriel Sombini dos Santos
Title: "Crustal Heating and Granite Magma Generation"
Location: Huggins Science Hall, Room 336, 12:30 p.m.

Abstract:
Granites are a fundamental component of the continental crust. Very early in the study of these rocks it was recognized they form by partial melting of previously existing crustal rocks, and much of the subsequent work on the petrogenesis of granite focused on the source rock and tectonic environment in which they were formed. The focus was largely on what melted, and not why it melted. The heat source for crustal melting is not a trivial problem, as the latent heat of melting of silicate minerals is extremely high. The production and overheating of 1 km³ of eutectic granite magma requires approximately 1.5x10¹⁸ J. Three geodynamic processes can provide such large amounts of heat: (1) advection by mantle magmas emplaced in the crust; (2) accumulation of radiogenic heat after crustal thickening; and (3) increased heat flow to the mantle. Each of the proposed mechanisms has its merits, and is most likely to operate in specific tectonic settings. Under- and intra-plating of mafic magmas in the crust are probably the heat source for granite generation in arc and continental rift environments, whereas a radiogenic heat generation model is more easily applied to continental plateaus. Although increased mantle heat flow can induce in the lower crust temperatures high enough to produce granite magmas, this mechanism almost invariably causes crustal extension. An extended and thin crust can more easily dissipate heat to the surface, making it unsuitable for the generation of batholith-scale granite intrusions