Zircon U-Pb Geochronology,Geochemistry,Lu-Hf Isotope And Genesis Of Granitic Rocks,Lang Jing,Eastern Tianshan,China

In recent years,isotope geochronology studies have proved that Permian-Triassic granitoids are widespreaded in the East Tianshan area,which is related to metal mineralization,and the most widely distributed granite.Lang Jing is located in the eastern section of the Kanggur-Huangshan ductile shear zone in the eastern Tianshan Mountains.A large number of granitic rocks are exposed in this area,which provides new information for the study of Mesozoic magmatism and mineralization in the East Tianshan Mountains.In this paper,the geochemical geochemistry,zircon U-Pb geochronology and Lu-Hf isotopic composition of the Wolfong and Hongliugou rocks in the Lang Jing area are studied.(1)The LA-ICP-MS zircon U-Pb dating results show that the magmatism of the Langjing and Hongliugou rocks occurred at 226±1 Ma and268±2 Ma,respectively,belonging to the Late Triassic and Late Permian.(2)The geochemical data of the rock indicate that the granitic rocks in the area have higher Si O₂(67.39%?72.74%)and total alkali content(6.24%?7.43%),and the A/CNK values<1.1,it is a quasi-aluminum to over-aluminum type I granite.The rock has obvious light and heavy rare earth differentiation and weak Eu negative anomaly,enrichment of large ion lithophile elements(e.g.K,Rb and Sr),relative loss of high field strength elements(e.g.Nb,Ta and Ti),with high Sr The/Y and La ratios of Yb show similar geochemical characteristics to the Adakite.(3)The zircon Lu-Hf isotope data of the granitic rocks in the Lang Jing area show that zircons from the Langjing monzogranite have uniform positive?_Hf(t)values(+5.6?+18.2)and relatively young crust model ages.Zircons from the Hongliugou grandiorite are ranging from+11.3 to+14.9.(4)Combined with geochemical and isotopic geochemical characteristics of rock,this paper believes that the granitic rocks in the Lang Jing area may be derived from the partial melting of the thickened lower crust,and may be mixed with mantle sources.The Langjing monzogranites were formed in the post-collision or intra-plate environment.While the Hongliugou grandiorite wree fromed in an active continental margin environment.