Permian-Triassic Magmatism in the Qin-Fang Tectonic Belt, SW China: New Insights into Tectonic Evolution of the Eastern Paleo-Tethys

The granites of ambiguous geodynamic mechanism in the Qin-Fang tectonic belt (SW China) were studied in detail based on petrological, element geochemical, zircon U-Pb geochronological, and Hf isotopic data. LA-ICPMS U-Pb analyses on zircon yield ages of 248-245 Ma for the granites from the Qin-Fang tectonic belt. The geochemical data show that they are high-K, calc-alkaline, and peraluminous series. Their epsilon Hf(t) values are from -14.01 to -7.75 with two-stage model ages of 1.74-1.43 Ga. These data, integrated with low Al2O3/TiO2, Rb/Sr, Rb/Ba, and (Na2O + K2O)/(FeOT + MgO + TiO2) ratios, and high CaO/Na2O ratios for the granite, suggest an origin from psammite source which was contaminated by mantle-derived components. These observations, in combination with the age data and stratigraphic records in the Jinshajiang, Ailaoshan, and Hainan Island areas suggest that the granites were formed in a post-collision tectonic setting. The Qin-Fang tectonic belt was likely a branched ocean basin of the eastern Paleo-Tethys.