Zircon U-Pb geochronology, geochemical characteristics and geological significance of Chaohuolutaolegai granodiorite in Balong area, East Kunlun Mountains

In the East Kunlun orogenic belt (EKOB), a large number of Late Paleozoic-Early Mesozoic granitoids of island arc type are widely distributed due to the subduction of Buqingshan-A'nyemaqen Ocean. In this study, the authors carried out a comprehensive analysis of petrography, geochemistry and LA-ICP-MS zircon U-Pb chronology for host rocks and mafic microgranular enclaves of the Chaohuolutaolegai pluton in the Balong area on the southern margin of the eastern EKOB. The results show that the crystallization ages of host rocks and mafic microgranular enclaves are 242.3±1.3Ma and 241.2±0.8Ma, implying that the pluton was formed in Middle Triassic. The A/CNK ratios of host rocks and mafic microgranular enclaves are 0.86~1.06, suggesting metaluminous-weakly peraluminous type, the ΣREE are 119×10^-6~170×10^-6 and 189×10^-6, the REE patterns show right-oblique characteristics and moderate negative Eu anomalies. The trace element geochemistry is characterized evidently by positive Rb, Ba, Th anomalies and negative anomalies of high strength field elements Nb, Ta, Ti, and shows the characteristics of arc magmatic rocks. The field and petrographic characteristics of the mafic microgranular enclaves show that the rocks were formed by the rapid injection of the basic magma into the acid magma, being the product formed by the magma mingling, and that the underplating of basic magma was caused by the break-off of the subduction slab. The pluton is the magmatic record of the late subduction of Buqingshan-Anemaqen Ocean.