藏东地区中奥陶世浪拉山糜棱岩化二长花岗岩LA-ICP-MS锆石U-Pb年代学及地质意义

对藏东地区浪拉山糜棱岩化二长花岗岩进行了LA-ICP-MS锆石U-Pb年龄测试,获得了该岩体的206Pb/238 U年龄加权平均值为470.5 Ma±3.7 Ma(MSWD=1.7,n=15),属于中奥陶世的产物。岩石地球化学特征表明,岩石具有高钾(Na2O/K2O=13.12~162.89)、铝(A/CNK值平均为1.30)、低钛的特征,岩石属于高钾钙碱性过铝质S型花岗岩。岩石具有明显Eu负异常,表现为Nb,Sr,P、Ti等高场强元素相对亏损,相对富集K,Rb,Th,U等大离子亲石元素,具有岛弧型花岗岩的特征。结合区域地质资料分析,该岩体与区内原特提斯洋的俯冲存在成因联系,藏东地区浪拉山糜棱岩化二长花岗岩的发现有助于进一步探索原特提斯洋演化过程。

GEOLOGICAL SIGNIFICANCE AND LA-ICP-MS ZIRCON U-Pb CHRONOLOGY OF THE MIDDLE ORDOVICIAN LANGLASHAN MYLONITIZED MONZONITIC GRANITE IN EASTERN TIBET

LA-ICP-MS zircon U-Pb dating on the Langlashan mylonitized monzonitic granite in eastern Tibet yields a weighted average age of 470.5Ma±3.7Ma(MSWD=1.7,n=15),aproduct of middle Ordovician.Geochemical analysis shows that the rock is characterized by high potassium (Na2O/K2O=13.12~162.89),aluminum(average A/CNK 1.30)and low titanium,belonging to high potassium calcium alkaline over-aluminum S-type granite.The rock has obvious Eu negative anormaly,with relative loss of high field strength elements,such as Nb,Sr,P and Ti,and relatively rich in large ionic pro-stone elements,such as K,Rb,Th and U,characteristic of island arc granite.Based on the geochemical and chronological studies,combined with the analysis of regional geological data,it is considered that the Langlashan mylonitized monzonitic granite is related to the subduction of Proto-Tethys Ocean.Therefore,the discovery of the Langlashan mylonitized monzonitic granite provides evidence for the discussion of Proto-Tethys Ocean evolution.