Chronological,Geochemical Characteristics And Tectonic Significance Of Misimiao Granodiorite In Inner Mongolia

Misimiao granodiorite is located in the eastern part of Xingmeng-Mongolia orogenic belt,southwest of Xiwuqi,Inner Mongolia,and tectonically located in the Hegenshan suture zone in the eastern part of Xingmeng-Mongolia orogenic belt.The study area has strong magmatic activity and intermittent ophiolite exposure,which is an important area for solving the tectonic evolution of Xing Meng-Mongolia orogenic belt.This paper intends to take Misimiao granodiorite as the main object,based on detailed field work and petrology,zircon U-Pb chronology and petrogeochemistry,to carry out detailed petrology and petrogeochemistry work.And the formation reason and tectonic setting of the granodiorite are discussed,which provide evidences for the expansion time,subduction and subduction process of Erenhot-Hegenshan ocean basin in the eastern section of Paleo-asiatic ocean.The Misimiao granodiorite is medium-fine-grained granodiorite and intrudes into the volcanic rock of Permian Shoushangou Formation.The granodiorite is produced in an east-west direction in the southwest of the early Carboniferous Diyanmiao SSZ ophiolite.It is mainly composed of plagioclase（about 50～55%）,quartz（about 20～25%）,potassium feldspar（about 15%）,dark minerals such as hornblende and biotite.The geochemical data of the five samples show that the content of SiO₂ is 61.37%～62.47%,the content of A1₂O₃ is 15.21%～15.77%,the content of MgO is 2.65%～2.99%,the content of sodium rich and potassium poor（Na2O:3.11%～3.62%,K₂O:1.83%～2.91%,Na₂O/K₂O:1.07～1.98）,belonging to calc-alkaline series;The content of rare earth elements is low(53.95×10^-6～65.70×10^-6),and the fractionation of light and heavy rare earth elements is obvious,(La/YbN) is 2.90～3.15,and the negative europium anomaly is weak（δEu=0.65-0.78）.These rocks are rich in large ion lithophile（LILE）,but lack of high magnetic field（HFSE）.In conclusion,the geochemical characteristics of the granodiorite in this survey area reflect the characteristics of island arc igneous rocks.LA-ICP-MS zircon U-Pb dating test shows that the crystallization age of the Misimiao granodiorite is 305.6±3.3Ma,indicating that it was formed in the Late Carboniferous.According to the analysis of tectonic environment discriminant map,the rock mass samples are located in the volcanic arc granite area.Combined with the regional tectonic location and evolution,it can be concluded that the Misimiao granodiorite was formed in the island arc tectonic environment of the subduction zone in the late Carboniferous.