西藏泽当蛇绿岩玄武岩SHRIMP锆石U-Pb年龄及其地质意义  

Zircon U-Pb dating of basalt from Zêtang ophiolite in Tibet and its geological implications

作　　者：刘维亮[1] 夏斌[1,2] 刘鸿飞 黄炜 周国庆[4] 韦栋梁[5] 钟云[1] 陈玉琴 

机构地区：[1]中山大学海洋学院/海洋石油勘探开发广东省普通高校重点实验室,广东广州510275 [2]中国科学院广州地球化学研究所,广东广州510640 [3]西藏自治区地质调查院,西藏拉萨850000 [4]南京大学地球科学系,江苏南京210093 [5]广西国土资源规划院,广西南宁530022 [6]广州市地质调查院,广东广州510100

出　　处：《地质通报》2013年第9期1356-1361,共6页Geological Bulletin of China

基　　金：中国地质调查局项目(编号:1212011120978;1212011121259;1212011221105);国家973计划项目(编号:2012CB214705)

摘　　要：雅鲁藏布江缝合带中各蛇绿岩体的准确定年对特提斯洋演化和青藏高原隆升的研究具有重要意义。泽当蛇绿岩是雅鲁藏布江缝合带东段最大的蛇绿岩块体,关于其形成年龄目前仍存在不同的认识。通过SHRIMP锆石U-Pb测年得到蛇绿岩中玄武岩的形成年龄为154.9Ma±2.0Ma(95%置信度,MSWD=0.98)。蛇绿岩中的玄武岩是洋脊扩张的产物,其形成年龄代表了扩张事件的时间,也代表了蛇绿岩的形成时代。结合已有的雅鲁藏布江缝合带蛇绿岩的形成年龄,该年龄进一步反映出雅鲁藏布江缝合带蛇绿岩形成时间具有东早西晚的特点。泽当蛇绿岩与含有埃达克质英云闪长岩的泽当岛弧火成岩基本为同期形成的。地球化学特征显示定年的玄武岩形成于俯冲带之上,且具有指示洋内俯冲环境的地球化学特征。因此,泽当SSZ型蛇绿岩可能形成于洋内俯冲机制。The precise dating of ophiolites from the Yarlung Zangbo suture zone can provide an important constraint on the geological evolution of the Neo-Tethys and the uplift of the Tibetan Plateau. Zeang ophiolite is the largest outcrop distributed in the eastern Yarlung Zangbo suture zone, but so far there has been no consensus concerning its formation time. This paper reports newly obtained SHRIMP U-Pb dating of zircons from the basalt of this ophiolite melange, i.e., 154.9Ma±2.0 Ma （95% conf., MSWD=0.98）. The age could represent the spreading time of the ancient oceanic crust. In comparison with ages of. other ophiolites in the Yalung Zangbo suturezone, this age indicates that the formation of ocean crust was earlier in the east than in the west. The Zetaug ophiolite has essentially the same formation age as the tonalities-bearing island arc rock assemblage, indicating the intra-Tethyan subduction. Based on the geochemistry of basalts as well as the characteristics of the setting and the boninite, the authors hold that Zetaug ophiolite was derived from an intra-oceanic subduction.

关 键 词：泽当蛇绿岩 SHRIMP锆石U-PB年龄 雅鲁藏布江缝合带 俯冲机制 

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