SHRIMP zircon UPb dating, geochemistry and SrNdHf isotopes of the Tongcun ore-bearing porphyry in NW Zhejiang Province, South China

The Tongcun ore-bearing porphyry is located in the Tongcun porphyry MoCu deposit of NW Zhejiang Province, which is a key domain for providing deep insight into crust–mantle interaction and tectonic evolution of the South China block. SHRIMP zircon UPb geochronology indicates an emplacement age of 168.7±2.8Ma. Its inherited zircon age spectrum recorded the assembly and breakup of the Rodinia supercontinent, and the Triassic collision of the Yangtze and North China blocks. This porphyry does not contain peraluminous minerals (e.g. muscovite, cordierite and garnet), and has high SiO2 (73.52–64.68wt.%) and low FeOT/MgO and Zr+Nb+Ce+Y contents. It thus fits the I-type granite definition. Some major and trace elements show strong correlations with SiO2, indicating extensive fractional crystallization during magma evolution. Tectonic discrimination diagrams suggest a volcanic arc setting probably related to the subduction of the paleo-Pacific plate. Hf isotope of zircons with Jurassic age and bulk-rock SrNd isotopic data yield mostly negative εHf(t) values (2.5 to −4.5) and εNd(t) values (−3.55 to −5.83), together with high Mg# ratios (average 46.1), suggesting a mixed source of ancient crust and 30–50% juvenile components. Compared with the Dexing Cu-bearing porphyies, which have relatively higher Mg# ratios, more positive εHf(t) and εNd(t) values, the Jurassic porphyries in NW Zhejiang Province probably lack metallogenic potential to form a giant porphyry Cu deposit.