Characteristics And Tectonic Attributes Of The Late Triassic Intrusive Rocks In The North Of Bayan Har Mountain Region Of Qinghai Province

In this paper,based on the study of Triassic rock stratigraphic division and tectonic deformation research in the north of Bayan Har Mountains area,Qinghai Province,Study on the distribution characteristics of intrusive rocks in the study area.Based on the zircon U-Pb isotope and Hf isotopic analysis of the intrusive rock formation age and material source,the magmatic process was deduced.According to the rock and mineral identification results and major,rare earth,and trace element analysis results,divide the rock composition of the study area,rock chemistry,and geochemistry of the intrusive rock,determine the rock type,the tectonic setting,the magmatic sequence,and the tectonic setting.From the cathodoluminescence map and the distribution curve of zircon rare earths,we can see that the intrusive zircons in the study area are mostly magmatic zircons.The dating results show that the ages of medium-acidic intrusive rocks are mainly distributed in the interval 209Ma-217 Ma.The age of intermediate-basic intrusive rocks is 208 Ma,and the age attributions correspond to the Late Triassic.The intrusive rocks in the study area are mainly composed of granodiorite-euply granite,granodiorite-pyroxene(quartz)diorite,and the dikes mainly include diabase,gabbro,and diorite,granite porphyry,granodiorite porphyry.The overall picture is a quasi-aluminum-peraluminous granite,and the normal chondrite distribution pattern diagram of rare earth element is a right-dip pattern in which rare-earth elements are relatively depleted of relatively heavy rare earth elements.There is basically no Eu anomaly in the sample,and only the rocks in the Jiangrigama area show the obvious negative Eu anomaly indicates that the formation of monzogranite and granite porphyry in the Jiangrigama area is related to the separation and crystallization of plagioclase.It can be seen in the original mantle standard map of trace elements that the sample is basically enriched with K,Rb,U,Th,Zr,Hf,loss of Ba,P,Ti,Nb,Ta and other elements,Rb increase and Sr,Ba decrease are caused by separation of crystals of K-feldspar and plagioclase,biotite,and are basically in line with the characteristics of I-S type granite.The intrusive rocks in the area and the surrounding volcanic rocks are products of different phases at the same period from the same time.Corresponding to the Late Triassic basalts of the rhyolite interbed of the Upper Triassic Wanghuling Formation on the southwest side of the Guoganjia Mountain and the south of Qiangtang Block.The observations show that in the Middle-Lower Triassic strata during the field observation,the plutonization occurred and the intrusive rocks did not show plutonization.Combined with the tectonic environment discrimination diagram,It is speculated that the rock droplets formed in the post-collision environment in the study area and the basic dykes formed in the relaxed environment after the collision.The relaxation environment may be related to the closure of the Xijinwulan-Ganzi-Litang Ocean.It is assumed that the Indosinian period plays a major role and that early Yanshan plays a certain role in the stage.