The Genesis And Tectonic Significance Of The Quasi-Adeger Triassic Granite In The Area Of Sonid Right Banner In Inner Mongolia

The study area is located in 50 km southwest of Erenhot city in the north-central part of Inner Mongolia.The northeast part belongs to Sunite Right Banner of Ximeng,which is in the middle part of Xingmeng orogenic belt.The study area has undergone long-term,multi-stage,different deformation mechanisms and tectonic levels of tectonic deformation.Structures of different periods and properties interweave and overlap with each other,forming extremely complex tectonic framework in the area.In this paper,the Quasi-Adeger Triassic granite in the area of SuniteRight Bannerwas selected as the research object.On the basis of field geological survey and previous research results,the Quasi-Adeger granite of the geochemical characteristics of petrology,petrography,major elements,trace elements and rare earth elements are analyzed and studied.Through the studies,the rock types and series,tectonic environment and tectonic significance of magma formation are discussed.The Quasi-Adeger granite in the area of SuniteRight Banner is mainly composed of coarse-grained pseudoporphyritic monzograniteand and fine-grained pseudopophyritic monzogranite.The lithology and mineral composition are similar,but the grain size is different,and the structure is also different.Based on LA-ICP-MS zircon U-Pb isotope data,two types of granites were started developing in 232Ma-243 Ma of the Middle Triassic period,and their ages were defined as indo-chinese epoch.Secondly,geochemical analysis shows that the main body of Triassic granite is characterized by weak peraluminous and high potassium-calcium series granites.Trace element analysis shows that large ion lithophile elements Rb and Th are relatively enriched,high field strength elements Nb and Ti are relatively deficient;Zr and Hf are relatively enriched,and rare earth elements La and Ce are relatively enriched,while P is relatively deficient.Rare earth elements show obvious internal fractionation.There is pronounced Eu weak negativeanomaly and there is no Ce pronounced anomaly.The total REE content is low,which indicates the characteristics of crust-mantle mixed magma.According to the comprehensive geochemical characteristics,the porphyritic biotite monzonitic granite of the Quasi-Adegar Triassic rock body is type A-2 granite in the post-orogenic extensional environment.Based on the geochemical characteristics and tectonic background,the author believes that the Middle-Late Triassic intrusive rocks in this area were formed in post-collision extension,and their petrogenesis is a plutonic intrusive body formed by the decompression and melting of rocks in the late subduction stage and the melting of upper rocks due to the underplating of magma caused by the thinning of lower crust.It further proves the previous view that the Triassic was still in the Subduction-Collision orogenic environment.