LA-ICP-MS Zircon U-Pb Age of Late Triassic Intrusive Rocks in Bayinhudousen Area, East Kunlun and Its Tectonic Significance

The Bayinhudousen intrusive rocks are located at Qimantage Mountain in the western part of East Kunlun Mountains, and they are occurred in the North Kunlun magmatic arc.They are composed of gray white fine granite granodiorite, gray medium-fine grained monzonitic granite, flesh red fine-medium grained porphyritic monzogranite and light grey monzonitic granite porphyry.In this paper, the LA-ICP-MS Zircon U-Pb method has been used to date the samples of porphyritic monzogranite in Duodeng area and monzonitic granite porphyry in Jingren area.The obtained ages are (217.0±2.0)Ma and (212.0±1.0)Ma, respectively, suggesting that these plutons were formed in Late Triassic epoch.The geochemical results show that these rocks have high SiO₂ (67.01%~76.61%), K₂0 (3.47%~5.52%)and Na₂O (1.55%~4.52%)contents, but have low MgO (0.12%~1.37%), TiO₂ (0.06%~0.84%)and P₂O₅ (0.01%~0.36%)contents.Their rare earth elements have weak negative Eu anomaly (δEu values are 0.17~0.72), and their A/CNK ratios are less than 1.1, showing the features of peraluminous high-k calc-alkaline series.After analyzing the characteristics mentioned above, it's believed that these granites were formed in post orogenic extensional environment.Therefore, the existence of Bayinhudousen late triassic intrusive rocks has proved that the collision orogenesis was existed in Qimantage tectonic belt before Late Triassic epoch.