东昆仑乌兰拜兴南中三叠世花岗岩成因探讨——LA-MC-ICP-MS锆石U-Pb年龄、元素地球化学及Sr—Nd—Pb同位素证据  

Genesis of the Middle Triassic granites in southern Wulanbaixing,Eastern Kunlun:Constraints from LA-MC-ICP-MS zircon U-Pb ages,element geochemical and Sr—Nd—Pb isotopic evidences

作　　者：徐博 刘建栋 王成勇[3] 岳涛 杨映春 魏有宁 史连昌 柴云 XU Bo;LIU Jiandong;WANG Chengyong;YUE Tao;YANG Yingchun;WEI Youning;SHI Lianchang;CHAI Yun(Key Laboratory of the Northern Qinghai—Xizang(Tibet)Plateau Geological Processes and Mineral Resources,Xining,810012;Qinghai Geological Survey Institute,Xining,810012;Qinghai Geological Survey Bureau,Xining,810000;No.5 Geological Survey Institute of Qinghai Province,Xining,810000)

机构地区：[1]青藏高原北部地质过程与矿产资源重点实验室,西宁810012 [2]青海省地质调查院,西宁810012 [3]青海省地质调查局,西宁810000 [4]青海省第五地质勘查院,西宁810000

出　　处：《地质论评》2020年第6期1515-1530,共16页Geological Review

基　　金：青海1∶25万布伦台(J46 C 004002)、大灶火(J46 C 004003)幅区调修测项目(编号:1212011121187);青海区域地质调查片区总结与服务产品开发(青海省新一轮地质志修编)项目(编号:12120114079701)的成果。

摘　　要：乌兰拜兴位于东昆仑西段,对该地区中三叠世花岗岩的研究不仅有助于认识东昆仑造山带印支期构造—岩浆演化历史,还可为古特提斯洋俯冲及洋盆闭合时限提供证据。本次在乌兰拜兴南石英闪长岩和英云闪长岩中分别获得了235.0±1.0 Ma和245.4±0.8 Ma的锆石U-Pb年龄,结合野外接触关系,可以确定该期花岗岩为中三叠世岩浆活动的产物。全岩地球化学分析结果显示,乌兰拜兴南中三叠世花岗岩为准铝到弱过铝质岩石,属中—高钾钙碱性系列,富集轻稀土和Rb、Th、K等大离子亲石元素,不同程度亏损Nb、Ta、P、Ti等高场强元素,具负铕异常,具有较高的[n(^(87)Sr)/n(^(86)Sr)]i值(0.709106~0.710136)和负的εNd(t)值(-4.18^-5.32),亏损地幔模式年龄TDM2为1356~1440 Ma,属I型花岗岩,显示板块俯冲阶段的特征。结合区域资料和本文研究,初步分析认为东昆仑地区该时期处于板块俯冲阶段的活动大陆边缘弧环境,古特提斯洋尚未闭合。Objectives:The Wulanbaixing is located in the western part of the Eastern Kunlun orogenic belt.The study of the Middle Triassic granites in this area not only helps to understand of the Indosinian tectonic—magmatic evolution history of the Eastern Kunlun orogenic belt,but also can provide evidences for the subduction and the closing time of the Paleo-Tethys Ocean.Methods:Detailed geological survey,LA-MC-ICP-MS zircon U-Pb dating of monzogranite,whole rock geochemical and Sr—Nd—Pb isotopes analysis of igneous rocks in Wulanbaixing,Eastern Kunlun orogenic belt.Results:The zircon U-Pb dating of the quartz-diorite and tonalite in southern Wulanbaixing are 235.0±1.0 Ma and 245.4±0.8 Ma,combining field contact relationship it can be ascertained that the granites are the products of Middle Triassic magmatic activities.The whole-rock geochemical analyses show that the Middle Triassic granites in southern Wulanbaixing lie in middle—high K calc-alkaline fields,the Aluminium saturation index show the metalumininous and weak peraluminous features,integrated with enrichments of LREE and LILE(Rb,Th,K et al.),depletions of Nb,Ta,P and Ti(HFSE)and Eu negative anomaly,high[n(87 Sr)/n(86 Sr)]i(0.709106~0.710136)and negativeεNd(t)(-4.18^-5.32),TDM 2=1383~1718 Ma,belongs to I-type granites,suggesting plate subduction-related geochemical affinities.Conclusions:Combining achievements of predecessors with this study,it’s believed that the Eastern Kunlun region was in the active continental margin arc environment during plate subduction,and the Paleo-Tethys Ocean was not completely closed in that period.

关 键 词：花岗岩 中三叠世 锆石U-Pb年龄 元素地球化学 Sr—Nd—Pb同位素 东昆仑山 乌兰拜兴 

分 类 号：P588.121[天文地球—岩石学] P597[天文地球—地质学]