Thermal model for origin of granitic batholiths

THE origin of granitic batholiths has been reviewed in the light of our understanding of the processes operative at destructive plate margins¹. The thermal patterns at island arcs suggest that significant amounts of thermal energy must be released within downgoing oceanic plates, and that this energy may be transferred to the surface behind island arcs. In these regions heat flow values are abnormally high and andesitic volcanism is present. The high heat flow may be produced because the normal geothermal gradient is enhanced by penetrative convection of magmatic material which is derived from the downgoing plate. Many large granitic batholiths, such as those in Chile, are localised at plate margins, and some authors have proposed that the Sierra Nevada batholith originated in a similar setting along the continental margin in the down-warped portion of the lower crust. Dickenson² suggested that the magma for the batholiths was produced by partial melting within the downgoing plate, and was subsequently emplaced into the overlying continental crust. Bateman and Dodge³, and Brown¹ suggested that emplacement into the lower crust, of andesitic material derived from the mantle, causes partial melting of crustal material, with the mixed product forming the magma for the granitic batholiths.