Petrogenesis of Late Jurassic granodiorites from Gutian, Fujian Province, South China: Implications for multiple magma sources and origin of porphyry Cu–Mo mineralization

Abstract

The Gutian porphyry Cu–Mo deposit is a newly proved porphyry copper deposit in the coastal South China associated with granodioritic porphyries. In this study, zircon U–Pb ages and Hf isotope data, as well as geochemical and Sr–Nd–Pb–Re–Os isotopic compositions, are reported for these intrusions and minerals. Both zircon U–Pb and molybdenite Re–Os dating suggest that the Gutian granodiorite porphyries and related mineralization formed at ~160Ma. The Gutian granodiorites show a low-Mg adakitic geochemical affinity, with relatively high K2O but low Cr and Ni contents. These rocks have initial (87Sr/86Sr)i ratios of 0.7085 to 0.7097, negative εNd(t) values (−12.5 to −7.8), (206Pb/204Pb)t ratios of 18.048 to 18.241, (207Pb/204Pb)t ratios of 15.609 to 15.628, and (208Pb/204Pb)t ratios of 38.494 to 38.667. Zircons from the granodiorites have negative εHf(t) values of −15.7 to −8.5, which are close to those of Cathaysia crust-derived melts. Geochemical and Sr–Nd–Pb–Hf isotopic compositions suggest that they may be derived from Late Jurassic thickened juvenile lower crust. These lower crustal magma sources may not only contain pre-Proterozoic basement rocks, but also involve Triassic and Middle–Late Jurassic arc magmas within the lower crust, which were likely derived from an enriched mantle source associated with paleo-Pacific Plate subduction from the Middle to Late Jurassic. The Gutian ore-related granodiorites represent a new example for significant contributions of ancient subduction melts and enriched mantle-derived sources for porphyry-type magmatism and Cu-Mo mineralization, which occurred in response to an arc regime during the Middle to Late Jurassic in South China.