东昆仑东段古特提斯洋俯冲作用——乌妥花岗岩体锆石U-Pb年代学和地球化学证据  

Paleo-Tethys Ocean subduction in eastern section of East Kunlun Orogen: Evidence from the geochronology and geochemistry of the Wutuo pluton

作　　者：李瑞保[1,2,3] 裴先治[1,2,3] 李佐臣[1,2] 裴磊 陈国超[1] 陈有炘[1] 刘成军[1] 王生明 LI RuiBao;PEI XianZhi;LI ZuoChen;PEI Lei;CHEN GuoChao;CHEN YouXin;LIU ChengJun;WANG ShengMing(MOE Key Laboratory of Western China＇s Mineral Resources and Geological Engineering,Chang＇an University,Xi＇an 710054,China;School of Earth Science and Resources,Chang＇an University,Xi＇an 710054,China;MLR Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits,Xi＇an 710054,China;No.3 Exploration Institute of Geology and Mineral Resources of Qinghai Province,Xining 810029,China)

机构地区：[1]长安大学西部矿产矿产资源与地质工程教育部重点实验室,西安710054 [2]长安大学地球科学与资源学院,西安710054 [3]国土资源部岩浆作用成矿与找矿重点实验室,西安710054 [4]青海省第三地质矿产勘察院,西宁810029

出　　处：《岩石学报》2018年第11期3399-3421,共23页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41502191;41472191;41172186);中央高校基本科研业务费专项资金项目(CHD2011TD020;CHD2009JC070;CHD2009JC046;310827161002;310827161006);青海省国土资源厅-中国铝业公司公益性区域地质矿产调查基金项目(中铝基金200801)联合资助

摘　　要：东昆仑东段发育了一条晚二叠世-中三叠世以花岗质岩石为主的巨型弧岩浆岩。本文对东昆仑东段的中三叠世乌妥花岗岩体开展了岩石学、LA-ICP-MS锆石U-Pb年代学及地球化学研究。结果表明,乌妥花岗岩体主要包括花岗闪长岩、斑状二长花岗岩和正长花岗岩三种岩石类型,对应的锆石U-Pb年龄分别为248Ma、247Ma和245Ma,形成时代为中三叠世。主量元素特征显示其具有高钾钙碱性、准铝质-弱过铝质的I型花岗岩的属性。球粒陨石标准化稀土元素配分图解具轻稀土明显富集、重稀土亏损和Eu弱负异常-强负异常特征。原始地幔标准化微量元素蛛网图显示富集大离子亲石元素(Cs、Rb、Th、Ba、U等)、亏损高场强元素(Nb、Ti、Ta等)、而Zr和Hf无明显异常的特点。乌妥岩体总体具有负的Hf同位素组成特征,花岗闪长岩εHf(t)为-1. 5～+3. 4、斑状二长花岗岩εHf(t)为-4. 1～-0. 6、正长花岗岩εHf(t)为-6. 9～-0. 9。多种微量元素构造环境判别图解表明其形成于类似安第斯型陆缘弧的构造环境。岩石成因研究表明洋壳俯冲带上部壳幔接触过渡部位多次岩浆MASH过程及分离结晶作用是形成乌妥花岗岩体的重要方式。综合前人东昆仑地区有关三叠纪沉积地层及岩浆岩资料,认为布青山-阿尼玛卿古特提斯洋于晚二叠世向北俯冲于东昆仑地块之下,弧岩浆岩记录的布青山古特提斯洋盆向北俯冲过程一直持续到中三叠世晚期。晚三叠世,东昆仑南缘古特提斯洋盆关闭,东昆仑造山带转换为碰撞及后碰撞造山阶段,并形成了区域上具碰撞构造属性的侵入岩。Voluminous arc granitoids with age of Late Permian-Middle Triassic is located in the East Kunlun orogen belt. This paper mainly presents new petrological,whole-rock geochemistry and zircon U-Pb geochronology for the Wutuo pluton. The Wutuo pluton comprises medium-to fine-grained granodiorites,porphyritic monzogranites,and syenogranites with minor dark mafic microgranular enclaves. The LA-ICP-MS zircons U-Pb dating of the Wutuo pluton yield a weighted mean206 Pb/238 U age of 248 ～ 245 Ma,which represents the crystallization age of Wutuo pluton. The whole-rock geochemical data indicates that the each unit of Wutuo pluton have similar geochemical feature,such as the high-K calc-alkaline,metaluminous to weak peraluminous I-type granitoids. Trace elements analysis shows that the granites are enriched extremely in Cs,Rb,Ba,Sr and Eu,and depleted in some HFSEs（ Nb,Ta,Ti,etc.）.They have enriched Hf isotopic compositions with εHf（ t） values of-1. 5 ～ ＋ 3. 4 from granodiorites,-4. 1 ～-0. 6 from porphyritic monzogranites and-6. 9 ～-0. 9 from syenogranites. Several tectonic discrimination diagrams suggest a continental magmatic arc setting. Combined with the previous data,it is concluded that the Buqingshan-Anyêmaqên Ocean began to subduct northward beneath the East Kunlun terrane in Late Permian,with its subduction terminated almost during late Middle Triassic. During Late Triassic,these discrete terranes,such as the East Kunlun terrane and Bayan Har terrane,collided together and generated some collision-type granites regionally.

关 键 词：东昆仑 安第斯型陆缘弧 乌妥花岗岩 构造环境 中三叠世 古特提斯洋 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]