Geochemistry And Tectonic Implications Of Qianjinchang Rock Mass In Xiwuqi,Inner Mongolia

The research area of this article is located in south of Xi Ujimqin Qi in InnerMongolia.The collision between north China plate and Siberian plate is in thegeotectonic position of this area.This article mainly aims at analyzing the geologicalfeatures，the petrological feature,geochemistry and chronology of the Qianjinchangrock mass.The analysis result is helped to explain the tectonic structure of the researchare.The morphological characteristics of Qianjinchang rock mass shows thenortheastward direction of distribution.It is probably subject to the structurallineament. The magmatic rock of Qianjinchang rock mass includes：granodiorite,monzonitic granite,moyite.The field geological features show two faciesbelt in Qianjincang rock mass. The parlicle size of mineral in the border facies issmaller than the one in the center facies belt. The quartz geodes and feldspar geodeswidely distributed in the border faies while in the center facies derived enclaves aremore easy to find.5samples of U-Pb isotope age which obtained by the method of LA-ICP-MSshow two stages magma activity:300-290Ma,290Ma-280Ma.The geochemical data shows that the major elements of early granite are rich insilicon，potassium，alkali.The value of A/CNK>1.1.It is probobaly “S”type granitethrough the above all the analysis.The Al content the late granite is less than the ealyone,and the value of A/CNK<1.1.It has characteristics of “A”type granite.It is founda negative linear correlation between oxide and SiO2inHacker diagram. It is came toconclusions that the two-stage granite came from comagma.The light REE of thesetwo kinds of sample is rich while REE content is on the high level.Th,Rb,Zr is richand Nb,Ta,Sr,Ti,P is lower.Above the characteristics with negative anomaly Euindicates that magma has followed by crystal fractionation.It maybe safely draw a conclusion that in the early Permian,the collision betweenthe north China plate and Siberia has finished in the research area.In the next10Ma,geotectonics has changed to extension setting.The inference on facts provide the basis for Paleo-Asian Ocean closing time.