Geochronology, geochemistry, and Sr–Nd–Pb isotopes of Cretaceous granitoids from western Tibet: petrogenesis and tectonic implications for the evolution of the Bangong Meso-Tethys

Abstract

New zircon U–Pb age data, whole-rock major and trace elemental data, and Sr–Nd–Pb isotopic data of granitoids from the Woruo and Bailong areas in the southern margin of the Qiangtang Block (western Tibet, China) provide important evidence for northward subduction of the Bangong Meso-Tethyan oceanic lithosphere. Five granitoid samples are dated at 120.7–112.7 Ma. These granitoids mostly belong to calc-alkaline and high-K calc-alkaline series, and show strong enrichments in large-ion lithophile elements (e.g. Rb, Ba, and Th), depletions in Nb and Ta, and negative correlations between P2O5, TiO2, MgO, and SiO2 contents, consistent with the evolution trend of I-type magmas. The samples are characterized by a wide range of Sr–Nd–Pb isotopic compositions (initial εNd values from −0.06 to 5.84, initial 87Sr/86Sr from 0.704458 to 0.705596, (206Pb/204Pb)0 from 18.5436 to 19.2465, (207Pb/204Pb)0 from 15.6115 to 15.6712, and (208Pb/204Pb)0 from 38.6427 to 39.6942). The trace elemental and Sr–Nd–Pb isotopic data suggest that these samples are derived from a mixture of lower crust and mantle materials. Together with the published data, these Early Cretaceous magmatic rocks represent a continental arc setting formed by the northward subduction of the Bangong Meso-Tethys during the Early Cretaceous (120–112 Ma).