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 εHf(t) values are from-14.01 to-7.75 with two-stage model ages of 1.74-1.43Ga.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.