藏北羌塘中部日湾茶卡地区晚三叠世安山岩与闪长质包体岩石成因及地质意义  

The petrogenesis and geological significance of the Late Triassic andesite and dioritic xenolith in the Riwanchaka area, central Qiangtang, northern Tibet

作　　者：吴浩 李才[2] 解超明[2] 范建军[2] 陈景文[3] WU Hao;LI Cai;XIE Chaoming;FAN Jianjun;CHEN Jingwen(School of Earth Sciences and Engineering,Hohai University,Nanjing 210098,Jiangsu,China;College of Earth Sciences,Jilin University,Changchun 130061,Jilin,China;Gold Geological Party of Chinese Armed Police Force,Mudanjiang 157000,Heilongjiang,China)

机构地区：[1]河海大学地球科学与工程学院,江苏南京210098 [2]吉林大学地球科学学院,吉林长春130061 [3]中国武警黄金部队,黑龙江牡丹江157000

出　　处：《地质通报》2018年第8期1428-1438,共11页Geological Bulletin of China

基　　金：中国博士后科学基金<西藏多不扎地区下白垩统去申拉组的发现与地质意义探讨>(编号:2016M600353);江苏省青年基金项目<西藏中部拉布错蛇绿岩中斜长石的形成时代;岩石成因与大地构造意义>(编号:BK20170877)

摘　　要：龙木错-双湖-澜沧江缝合带将羌塘板块划分为南、北2个次级板块,在缝合带两侧大规模发育晚三叠世岩浆作用,并伴随大量的高压超高压变质岩。在缝合带以南的日湾茶卡地区识别出一套安山岩,其中发育大量的暗色闪长质捕虏体,锆石U-Pb测年结果在安山岩中获得了364.7±1.9Ma和223.9±1.3Ma两组年龄信息,锆石原位Hf同位素测试结果εHf(t)分别为+7.22^+8.69和-5.94^-4.14。结合羌塘中部已有的研究成果,认为闪长质捕虏体形成于晚泥盆世洋壳俯冲背景,是地幔楔部分熔融底侵至地壳的产物;而安山岩形成于晚三叠世碰撞后伸展背景,是深部板片断离机制下深俯冲陆壳边缘一侧熔体混染晚泥盆世新生地壳的产物。安山岩中闪长质捕虏体的发现支持了俯冲带作为大陆生长的重要场所的观点。The Qiangtang terrane can be divided into northern and southern terranes by the Longmu-Shuanghu-Lancangjiang Suture Zone(LSLSZ).Late Triassic magmatic rocks are widely exposed on both sides of LSLSZ,coeval with exhumation of the metamorphic rocks.Recently,Late Triassic andesite and dioritic xenolith were identified in the Riwanchaka area of central Qiangtang.New U-Pb zircon ages and geochemical and Hf isotopic data for andesite and dioritic xenolith are reported in this paper.Crystallized and inherited zircons from the andesites yielded ages of 223.9±1.3Ma and 364.7±1.9Ma,with initialεHf(t)values being-5.94 to-4.14 and+7.22 to+8.69,respectively.Together with recently published data,the authors hold that the dioritic xenoliths were derived from the mantle wedge in an oceanic subduction setting of Late Devonian while the andesites were derived from mixing between Southern Qiangtang crust-derived melt and Late Devonian dioritic juvenile crust under a post-collisional extension setting by slab breakoff.The presence of dioritic xenoliths in the andesites further supports the viewpoint of the existence of a subduction zone as an important site for the growth of continental crust.

关 键 词：羌塘中部 晚三叠世 安山岩 板片断离 地壳生长 

分 类 号：P534.51[天文地球—古生物学与地层学] P588.1[天文地球—地质学]