西藏冲尼中二叠世岛弧玄武岩的发现及意义  

Discovery of the Middle Permian Island-Arc Basalt in the Chongni Area,Tibet and its Tectonic Implication

作　　者：李楠 朱利东[1] 杨文光[1] 解龙[1] 张洪亮 钟摇 LI Nan;ZHU Lidong;YANG Wenguang;XIE Long;ZHANG Hongliang;ZHONG Yao(Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu,Sichuan 610059;College of Earth Sciences,Chengdu University of Technology,Chengdu,Sichuan 610059)

机构地区：[1]成都理工大学沉积地质研究院,四川成都610059 [2]成都理工大学地球科学学院,四川成都610059

出　　处：《地质与勘探》2020年第4期722-731,共10页Geology and Exploration

基　　金：国家自然科学基金项目(编号:41972118);冈底斯-喜马拉雅铜矿资源基地调查项目(编号:DD20160015)联合资助。

摘　　要：最近在西藏直孔地区冲尼村附近识别出一套二叠纪岛弧玄武岩。本文报道了其岩相学、全岩地球化学及锆石U-Pb年代学数据,探讨了其岩石成因和构造背景。锆石U-Pb年代学和全岩地球化学分析显示,玄武岩浆结晶年龄为270.8±2.1 Ma,时代属中二叠世;全岩地球化学分析表明:冲尼玄武岩为钙碱性系列,轻稀土元素(LREE)富集,重稀土元素(HREE)相对亏损,无Eu异常,微量元素蛛网图显示,冲尼玄武岩亏损高场强元素(HFSE),富集大离子亲石元素(LILE)。综合区域地质调查研究成果,中二叠世冲尼岛弧玄武岩形成于直孔-松多古特提斯洋向北俯冲消减的构造背景下,由俯冲板片之上经流体交代的地幔楔部分熔融形成。Recently,a set of Middle Permian island-arc basalt was identified near the Chongni village,Zhikong area,Tibet.This paper presents its petrology,geochemistry and dating data and studies its genesis and tectonic setting.The zircon U-Pb geochronology and whole-rock geochemical analysis suggest that the magma crystal age of this basalt is 270.8±2.1 Ma(Middle Permian).It is of a calc-alkaline series with enrichment of light REE and relative depletion of high REE,while without obvious Eu anomalies.The trace element spider diagrams show that the basalt has also depletion of high-field strength elements and enrichment of large ion lithophile elements.Based on comprehensive regional geological research,we infer that this basalt was formed in an island arc setting related to the northward subduction of the Zhikong-Songduo Paleo-Tethys ocean crust during the Middle Permian,a result of partial melt of a mantle wedge over the subdcution slab with metasomatic fluid.

关 键 词：直孔-松多古特提斯洋 岛弧玄武岩 锆石U-PB测年 冲尼 西藏 

分 类 号：P581[天文地球—岩石学] P597.3[天文地球—地质学]