Petrogenesis of the granites in Sandun area-Constraints from petrochemistry, zircon U-Pb chronology and Hf Isotope

In this paper, the authors studied the petrogenesis and tectonic-significance of the granite from the Sandun Cu-Pb-Zn polymetallic deposit in northeastern Hu'nan Province by means of zircon U-Pb isotope chronology, whole rock geochemistry and Hf isotope. LA-ICP-MS zircon U-Pb dating yielded crystallization age of 131.9±1.1Ma for the Sandun granite. The Sandun granite is a peraluminous high-Al calc-alkaline intrusive granite. The rocks are characterized by high U, Ta, Pb and low Ba, Nb, Sr, Zr, Ti val-ues. The REE distribution patterns are strongly LREE enriched and HREE depleted, with weakly negative Eu anomalies. The Hf iso-tope analyses show that the ε_Hf(t) values of the late Yanshanian granite zircons are between -5.9 and -2.4, and the two stage Hf model ages ranging from 1558Ma to 1338Ma, which indicates that its parental magma was derived from partial melting of rocks of Middle Proterozoic paleo-crust. Inherited zircon with an age of 749.5Ma has the ε_Hf(t) of +4.8 and two stage Hf model age of 1355Ma, re-spectively, which indicates that its parental magma was mainly derived from the mantle. The Sandun granite probably resulted from the formation of the molten magma in the middle and lower crust and the formation of a small amount of mantle derived material.