塔里木北缘库鲁克塔格地区新元古代花岗岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及其构造意义

LA-ICP-MS Zircon U-Pb Dating,Geochemical Characteristics and Tectonic Significance of Neoproterozoic Granite in the Quruqtagh Area,Northern Margin of Tarim Craton,NW China

采用LA-ICP-MS法分析了塔里木北缘库鲁克塔格一带二长花岗岩锆石U-Pb年龄,获得该二长花岗岩岩体的年龄为(832.3±3.3)Ma(MSWD=2.8,n=24)。岩石地球化学特征显示,二长花岗岩属于准铝质高钾钙碱性系列,为I型花岗岩。微量元素富集大离子亲石元素(LILE)Ba、K、Sr、U等,亏损高场强元素(HFSE)Nb、Ta、Ti、P等;稀土元素总体含量较低(29.88×10^(-6)~63.57×10^(-6)),具有弱Eu正异常(δEu=0.87~1.39),整体配分模式与下地壳一致。结合区域地质背景对岩浆岩地球化学特征进行综合分析,认为二长花岗岩形成于岛弧环境。区域构造演化特征指示832 Ma该区洋壳已经开始俯冲,使得这一地区的地壳加厚,同时地幔柱的上涌加热作用导致古老地壳物质发生部分熔融而形成该期花岗岩。

In this study,we conducted LA-ICP-MS zircon U-Pb dating on the monzogranite from the Quruqtagh area,which yielded a concordant age of(832.3±3.3)Ma(MSWD=2.8,n=24).The monzogranite is metaluminous,high-K calc-alkaline,and I-type.As for trace elements,the samples are enriched in large-ion lithophile elements(LILEs,e.g.,Ba,K,Sr and U)and depleted in high field strength elements(HFSEs,e.g.,Nb,Ta,Ti and P).The total rare earth element(REE)contents are relatively low(29.88×10^(-6) to 63.57×10^(-6)),and the samples exhibit weakly positive Eu anomaly(δEu=0.87-1.39).The overall trace element distribution pattern resembles that of the lower crust.Comprehensive analysis of magmatic lithogeochemistry and regional geological background shows that the monzonitic granite was likely formed in an island arc environment.Combined with the regional tectonic evolution,we considered that the oceanic crust in the region began to subduct at around 832 Ma.This may have made the crust thicker,and the heating from the upwelling mantle plume may have partially melted the ancient crust materials,forming the Neoproterozoic granites.