东昆仑沟里地区花岗岩年代学、岩石地球化学及其地球动力学意义

Geochronology,Geochemistry and Geodynamic Implications of the Gouli Area Granites in East Kunlun Mountains

东昆仑沟里地区位于青藏高原北缘东昆仑造山带东段,区内发育花岗闪长岩、黑云母二长花岗岩、似斑状二长花岗岩、钾长花岗岩、花岗岩。花岗闪长岩样品中锆石呈半自形-自形柱状,震荡环带较发育,为岩浆成因锆石,样品的U-Pb加权平均年龄为(225±1.7)Ma,代表其岩浆侵位时代为晚三叠世。岩石地球化学特征显示该地区花岗岩具有高硅、富碱和低钛特征,为准铝质-过铝质岩石,富集轻稀土元素(LREE)及Rb、Ba、U、K等大离子亲石元素,具有弱的Eu负异常,属于高钾钙碱性I型花岗岩。岩石地球化学、年代学研究以及区域构造演化表明,东昆仑沟里地区花岗岩形成在晚三叠世碰撞到后碰撞造山阶段,且该岩体的形成与布青山-阿尼玛卿洋俯冲作用有很大的关系。

Gouli area in East Kunlun Mountains,which is located in the North rim of the Qinghai-Tibet Plateau,develops granodiorite,biotite monzonitic granite,porphyroid monzonitic granite,moyite as well as medium grained granite.An in-depth study in this area unveils the geodynamic evolution characteristics of the whole East Kunlun orogenic belt.New information of the tectonic evolution of the eastern portion of East Kunlun will also be attained by this study.In this paper,zircon grains of granodiorite samples which emerge half since shape-the shape columnar and develop volatility band are proved to be magma genesis of zircon.The U-Pb weighted average ages of these zircon grains is（225±1.7）Ma,representing the magmatic emplacement age in Late Triassic.Based on geochemistry analysis,it is shown clearly that granite in this area which is attested to be aluminum-peraluminous rock is characterized by high silicon,titanium enrich alkali,low titanium,enriched-LREE and Rb,Ba,U,K,etc large ion lithophile elements,depletement of high field strength elements Nb,Sr,P,Ti,as well as flat HREE with weak Eu negative anomaly.In terms of its geochemistry characteristics,this granite may be aluminum-peraluminous rock and belongs to high-K calc-alkaline granite type I.According to the rock geochemistry,chronology study and regional tectonic evolution,the formation of granite in Gouli area and collision to post-collision orogenic stage in Late Triassic happened at the same time.The subduction of Buqingshan-A′nyemaqen ocean has a great influence on the formation of rock mass in this area.