西昆仑布孜完达坂岩体成因：LA-ICP-MS锆石U-Pb年代学与地球化学制约  

Petrogenesis of the Buziwandaban pluton in western Kunlun： Constraints from LA-ICP-MS zircon U-Pb geochronology and geochemical characteristics

作　　者：乔耿彪[1] 王萍 赵晓健[1] 

机构地区：[1]中国地质调查局西安地质调查中心,国土资源部岩浆作用成矿与找矿重点实验室,西安710054 [2]中国石油长庆油田分公司勘探开发研究院,西安710086

出　　处：《地质科学》2016年第4期1114-1136,共23页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家自然科学基金项目（编号： 41302051）、陕西省科学技术研究发展计划项目（编号：2014JM2-4037）、国家科技支撑计划项目 （编号：2011BAB06B05-02,2015BAB05B01-01）和中国地质调查局项目（编号：121201011000150003）资助 致谢 野外地质工作得到新疆地质矿产勘查开发局第六地质大队刘洋旭工程师的大力帮助;研究过程中得到西安地质调查中心叶芳研究员的有益指导;西安地质调查中心测试中心李艳广工程师和靳梦琪助理工程师在样品测试过程中保障了LA-ICP-MS仪器的正常运行;审稿过程中得到了匿名审稿专家提出的宝贵意见和建议;在此一并表示衷心的感谢!

摘　　要：布孜完达坂岩体位于新疆西昆仑地区的中酸性岩浆岩带中，其主要岩性为不等粒石英闪长岩和二长花岗岩。通过LA-ICP-MS锆石U-Pb定年，结合锆石阴极发光图像（CL）和U、Th元素特征，获得布孜完达坂岩体的年龄为225.5±2.3 Ma（n=18，MSWD=1.6），时代属晚三叠世（T3）。石英闪长岩和二长花岗岩均含有角闪石， 副矿物中出现少量榍石， SiO2含量为61.41％～73.01％，全碱变化于6.64％～8.25％；铝饱和指数A/CNK为0.98～1.04，属准铝质—弱过铝质；岩石轻重稀土元素分馏明显，（La/Yb）N为6.38～43.73，负Eu异常，δEu为0.53～0.85；富集Rb、Th、K和LREE等大离子亲石元素，而贫Ba、Sr、Ti、Nb、Zr等元素，属高钾钙碱性I型花岗岩系列。根据岩体的成因类型并结合区域构造环境演化，分析认为随着古特提斯洋在中三叠世晚期向北消减直至最终闭合过程中，岩体温度在707℃～718℃的条件下，地壳较深处且受一定程度幔源物质混染发生部分熔融作用，于晚三叠世后碰撞演化形成了布孜完达坂岩体。The Buziwandaban pluton is located in the intermediate acidic magmatic rocks belt of the western Kunlun area of Xinjiang. The pluton is composed mainly of the inequigranular quartz diorite and monzogranite. Combined with the cathodolumine scence（CL）images and element U and Th features of zircon, this study yielded an age of 225.5±2.3 Ma（n=18,MSWD=1.6）for the pluton using the LA-ICP-MS zircon U-Pb dating, indicating the Late Triassic（T3）. Both of quartz diorite and monzogranite have accessory minerals such as amphibole and sphene. The geochemical analysis show that the pluton is characterized by SiO2=61.41%～73.01%,total alkali（Na2O＋K2O）=6.64%～8.25%,and aluminum index A/CNK=0.98～1.04,indicating a transitional composition between metaluminous and peraluminous. The pluton is enriched in LREE,depleted in HREE（LREE/HREE=5.85～20.42,（La/Yb）N=6.38～43.73）,with negative Eu anomaly（δEu=0.53～0.85）. While the trace elements are characterized by Rb,Th,K,LREE enriched,and Ba,Sr,Ti,Nb,Zr depleted. All the features suggest a high K calcic-alkaline I type granite. According to the magma origin and formation research,the Buziwandaban pluton was derived from partial melting of the lower continental crust being intermingled with partial mantle source under the condition of temperature ca. 707～718℃. Based on comprehensive analysis of the genetic type of the pluton and evolution of regional tectonic environment,we suggested that when the paleo-Tethys ocean was gradually evolved from subduction toward north to the complete closure in the Late Middle Triassic,and the Buziwandaban pluton was formed just after this tectonic transfrom. That is to say,Buziwandaban pluton was formed in post-collisional tectonic setting in the Early Late Triassic.

关 键 词：布孜完达坂岩体 岩石成因 晚三叠世 I型花岗岩 后碰撞环境 

分 类 号：P588[天文地球—岩石学] P597[天文地球—地质学]