The consequences of crustal melting in continental subduction

Orogens grow in part by thrusting and burial of continental crust, in some cases, into the mantle by continental subduction. Deeply buried continental crust may partially melt during ascent, adding magma to the overlying continental crust, creating a continental plateau, and accounting for the large melt volumes observed in modern and ancient orogens. Thermal-mechanical models support a link among continental subduction, melting, and crustal flow in the overriding plate and show that partial melting may be a significant process in exhumation of ultrahigh-pressure (UHP) rocks and orogenic evolution in general. In Cordilleran orogens, the overriding plate is hot and thin and includes a back-arc region favorable for crustal-scale thrusting and high-temperature metamorphism. Collisional orogens have thicker lithosphere and experience lithosphere-scale thrusting and deeper burial of continental crust. In either case, the ultimate fate of continental crust is partial melting, the depth of which controls the processes and rates of crustal differentiation and exhumation. This paradigm relates continental subduction and crustal melting to lower-crustal flow and plateau development in the overriding plate and explains the presence of UHP rocks in migmatite and granite and their occurrence in the overriding plate of some orogens.