西藏中部中仓地区玄武岩锆石U-Pb年龄与岩石地球化学特征:对狮泉河-纳木错弧后洋盆演化的制约  

Zircon U-Pb ages and geochemical characteristics of basalts in Zhongcang area,central Tibet:constraints on the evolution of Shiquan River-Namu Co back-arc basin

作　　者：吴浩 林兆旭[1] 姜子崎 王崇浩 郑鑫 仰睿 WU Hao;LIN Zhaoxu;JIANG Ziqi;WANG Chonghao;ZHENG Xin;YANG Rui(Collaborative Innovation Center for Exploration of Nonferrous Metal Deposits and Efficient Utilization of Resources in Guangxi/Guilin University of Technology,Guilin 541004,Guangxi,China;College of Earth Sciences,Jilin University,Changchun 130061,Jilin,China)

机构地区：[1]有色金属矿产勘查与资源高效利用省部共建协同创新中心/桂林理工大学,广西桂林541004 [2]吉林大学地球科学学院,吉林长春130061

出　　处：《地质通报》2022年第10期1728-1739,共12页Geological Bulletin of China

基　　金：中国地质调查局项目《藏西北铜多金属资源基地综合调查评价》(编号:DD20190167);桂林理工大学人才引进科研启动项目(编号:RD2000002384);广西中青年教师基础能力提升项目《藏北多龙矿集区成矿期高硅流纹岩成因及其构造意义》(编号:2021KY0249)。

摘　　要：狮泉河-纳木错混杂带的构造属性和演化时限一直存在较大的争议,其研究对认识青藏高原早期形成与演化具有重要的意义。对西藏中仓蛇绿混杂岩中发育的玄武岩端元进行了系统的岩石学、地质年代学和地球化学研究,以揭示其形成时代、岩石成因及构造意义。中仓玄武岩LA-ICP-MS锆石U-Pb同位素年龄为115.7±2.0 Ma,与区域上辉长岩的形成时代一致。玄武岩整体具有相对平坦的球粒陨石标准化稀土元素配分曲线,与洋中脊玄武岩相似,且显示Th的富集和Nb、Ta的亏损。研究认为,中仓玄武岩起源于受俯冲沉积物改造的尖晶石橄榄岩地幔部分熔融,形成于弧后扩张脊环境。结合区域上同时期辉长岩的研究结果,认为狮泉河-纳木错混杂带是中生代弧后洋盆消亡的残迹,是班公湖-怒江洋南向俯冲,引发弧后拉张的产物。Tectonic attribute and evolution history of Shiquan River-Namu Co mélange zone have been controversial for a long time.This paper deals with the petrology,geochronology,and geochemistry of the basalts from the Zhongcang ophiolite mélange,in order to reveal its formation age,petrogenesis and tectonic significance.LA-ICP-MS zircon U-Pb age of Zhongcang basalt is 115.7±2.0 Ma,which is consistent with the formation age of gabbro in the region.The Zhongcang basalts have a relatively flat REE distribution curve,similar to the mid-ocean ridge basalt(MORB).Furthermore,these samples show Th enrichment and Nb,Ta depletion.It is proposed that the Zhongcang basalts were derived by partial melting of the spinel peridotite mantle,which was modified by subduction sediments,in the back-arc basin spreading center.Combined with the study of the regional gabbros,our research favors that the Shiquan River-Namu Co mélange zone represents the remnant of a Mesozoic back-arc basin,which was produced by the back-arc rifting in response to the southward oceanic subduction of Bangong-Nujiang Tethyan Ocean.

关 键 词：西藏中部 狮泉河-纳木错混杂带 玄武岩 早白垩世 弧后扩张 地质调查工程 

分 类 号：P588.145[天文地球—岩石学] P595[天文地球—地质学] P597.3