Petrogenesis and tectonic implications of late Mesozoic granitoids in southern Anhui Province, southeastern China

Abstract

ABSTRACTLate Mesozoic granitoids are widely distributed in southern Anhui Province, southeastern China, which also contains significant W–Mo–Cu mineralization. This study presents new geochronological and geochemical data that reveal the petrogenesis and tectonic affinity of the granitoids in this region. These granitoids can be divided into a high-K calc-alkaline and peraluminous I-type granodiorites, and an alkaline and metaluminous A-type granites, with zircon U–Pb dating indicating that they formed at 150–138 and 133–124 Ma, respectively. The early stage I-type granodiorites are adakitic, enriched in the light rare earth elements, and depleted in Nb, Ta, P, and Ti. They have negative zircon εHf(t) values (–19.8 to –2.5) that correspond to Hf crustal model ages of 2.4–1.4 Ga. These early stage granodiorites were derived from partial melting of thickened Palaeoproterozoic–Mesoproterozoic lower crust. The late-stage A-type granites with strong depletion in Sr, P, and Ti, contain higher Zr, Y, and Yb contents, higher zircon εHf(t) values (–1.5 to +2.1), and younger zircon Hf model ages (1.1–1.3 Ga) than the early stage granodiorites. The geochemistry of these A-type granites indicates they were likely generated by the reworking of Mesoproterozoic to Neoproterozoic juvenile crustal material that experienced the fractional crystallization of plagioclase and accessory minerals. Combining these data with other geological data from the study area indicates that the early stage granodiorites formed in a continental arc setting, whereas the late-stage granites formed in an extensional setting associated with roll-back of the subducted Palaeo-Pacific slab. The results indicate that zircon Ce4+/Ce3+ value can provide useful insight into oxygen fugacity conditions during magmatism.