Quantitative REE Modeling for Genesis of Mesozoic Intermediate-Felsic Rocks at Tianzhushan in the Dabie Orogen

A large number of studies of geochronology and geochemistry indicate that Mesozoic intermediate-felsic rocks from the Dabie orogen have originated from recycling of the subducted Yangtze continental crust itself. A REE partition simulation suggests that the Tianzhushan intermediate rocks can be generated by partial melting, in coupling with fractional crystallization, of dioritic gneiss which is similar in chemical compositions to the mafic rocks in the lower crust in North Dabie; partial melting of intermediate grey gneiss which is similar in chemical compositions to the middle crust in North Dabie can generate the Tianzhushan felsic rocks. Quantitative calculation of trace element content for the residue after partial melting suggests that intermediate-mafic granulites outcropped in the Dabie orogen are not the residue of partial melting. The residue formed by partial melting of thickened crust due to anomalous heat supply by mantle superwelling at Early Cretaceous is possibly easy to detach from the crust because of its high density, leading to the remove of mountain root and large scale uplift of the orogen.