Zircon U-Pb Chronology, Geochemistry and Geological Significance of Late Triassic Intermediate-Acid Volcanic Rocks in Boluositai Area, East Kunlun Orogenic Belt

Late Triassic intermediate-acid volcanic rocks exposed in the Boluositai area, East Kunlun orogenic belt are of great significance for studying the closure of the Paleo-Tethys ocean and subsequent collision orogenic processes. It conducted detailed zircon U-Pb chronology, geochemistry and Hf isotopic studies of the volcanic rock to determine its formation age, petrogenesis and tectonic environment. The results show that the zircon weighted average ages of dacites are 233.4±1.3 Ma and 234.7±1.5 Ma respectively, suggesting the Late Triassic. The whole-rock geochemical results show that the SiO2 contents range from 64.57% to 71.27%, with the total alkali contents (ALK) from 7.53% to 8.07%, the Na2O/K2O ratios from 0.84 to 1.01, the Mg# values from 35.66 to 45.39, and the A/CNK from 1.0 to 1.1. These features show weak peraluminous, high-potassium calcium alkaline series. The light and heavy rare earth elements of the rocks are obviously fractionated, which is characterized by the enrichment of light rare earth elements and the depletion of heavy rare earth elements, with a weak negative Eu anomaly. The zircon εHf(t=235) of dacites ranges from -4.81 to +0.09, and the two-stage model age is 1 059-1 309 Ma. The petrogenesis research indicates that the dacites were derived from feldspar-rich sandstone and basalts in the continental crust. Based on regional geological data, it is suggested that the dacites were formed in a post-collision setting and that the Paleo-Tethys Ocean had been closed in the early Late Triassic and the East Kunlun orogen transformed into a post-collision stage. © 2022, Editorial Department of Earth Science. All right reserved.