东昆仑造山带波洛斯太地区晚三叠世中酸性火山岩锆石U-Pb年代学、地球化学及地质意义

东昆仑造山带东段波洛斯太地区出露一套晚三叠世中酸性火山岩,对研究古特提斯洋关闭及碰撞造山过程具有重要意义.通过对该火山岩进行详细的锆石U-Pb年代学、地球化学和Hf同位素研究来确定其形成时代、岩石成因和构造环境.研究结果表明,英安岩加权平均年龄为233.4±1.3 Ma和234.7±1.5 Ma,形成时代为晚三叠世.火...

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 ε_Hf(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.