The Geochemical Characteristics And Tectonic Significance Of Early Permian Granites In The Western Region Of Sonid Left Banner

A mass of granite(or granitic rocks)is developed in the collision orogenic belt.The nature of granite source zone,genetic type and formation and tectonic environment etc.,have important significance on the evolution of orogenic belt and the interaction between crust and mantle material in orogenic process.The study area is located in the central and northern portion of Inner Mongolia,which is the borders of China and Mongolia.In geotectonic position it is part of the orogenic belt between North China plate and Siberia plate subduction and collision,belonging to the central Asian orogenic belt(CAOB)eastern(Xing Mongolia orogenic belt).And it is an important part of researching Paleo-Asian Ocean tectonic evolution.In this paper,the research object is the Early Permian granite.Based on previous research,we make the detailed field geological survey and research the petrology and rock geochemical research of representative rock samples collected in target area.So we can infer the cause of the research object,the nature of the source area and tectonic environment.Even we can explore the dying process of Paleo-Asian ocean,the Siberian plate and north China plate collision suture and regional tectonic evolution history.The results show that the Early Permian rocks in Sonid Left Banner west are mainly granodiorite,porphyric adamellite,adamellite,porphyritic syenogranite.The characteristics of the main elements in granite are shown high potassium calc-alkaline,aluminum-weakly peraluminous type I granite.Large ion lithophile elements(such as LILEs,such as the Rb,Th,U,K,etc.)are relative concentration.High field strength elements(such as HFSEs,Nb,Ta,P,Ti,etc.)are relative defect.Ba and Sr elements are characterized by negative anomaly in the granite microelements,and they have the geochemical characteristics of arc magmatic rocks related to the subduction zone.Total rare earth and light rare earth content are lower than the average rare earth content of Chinese granite type,and they are characterized by light enrichment of light rare earth light enrichment.Light rare earth happened more obvious fractionation effect,and heavy rare earth fractionation effect is not obvious with obvious Eu negative anomaly.This phenomena shows that source area may had residual plagioclase.Geochemical analysis result shows that the property of magma in the study area is complex,and it was formed partly by the basic rock melted and by the metamorphic sandstone melted in the earth's crust.It is charactered by crust-mantle mixing.Early Permian granites in Sonid Left Banner west was formed before the collision-collision early granite environment in active continental margin,which shows the characteristics of the continental arc granite.So it indicates that in the study area the Siberian plate were impending to collide with the north China plate in the Early Permian,and residual island arcs may still can be seen in local area.