Heat source for crustal magma layers: tectonic models
In Chapter 2, a number of ways of generating sufficient heat to cause crustal melting and the formation of partial melt layers were described, i.e. thickening of radiogenic heat-producing rocks, lithospheric extension, injection of magma into the continental crust, shear heating and isothermal decompression. Yet, as outlined in Chapter 3, partial melting of rocks cannot produce granite magma that forms batholiths if there is no convection within the region of partial melting. For this to occur, constant energy input into the system is essential for the formation and evolution of a crustal granite magma layer. Such a requirement requires the large dynamic system of plate convergence with which granite belts of ‘hot orogens’ formed in different geological times are mostly related to coeval plate convergences, e.g. the circum-Pacific and Tethys Meso–Cenozoic granite belts, the Paleozoic granite belts of the North American Appalachians, Europe, the north and south Tianshan Mountains, NW China. Surface heat flow measurements indicate that crustal temperatures of continental margins are strongly perturbed by plate convergence. In this Chapter, two examples, i.e. SE China and Tibet–Himalayas from the western continental margin of the Pacific and the Tibet–Tethys, respectively, representing different convergent types, i.e. oceanic plate subduction and continent collision, are used to model the relationship between plate convergence and formation/evolution of crustal convection layers of granite magma.
KeywordsConvection Dehydration Cretaceous Jurassic Subduction
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