西藏雅鲁藏布江缝合带中段沉积混杂岩的变质特征及构造意义  

Metamorphism and tectonic evolution of the sedimentary-matrix mélange in the central Yarlung Zangbo Suture Zone, southern Tibet

作　　者：王晓曼 李旭平 孔凡梅 张艳成 孙光明 王笑 刘浩 WILLNER Arne WANG Xiaoman;LI Xuping;KONG Fanmei;ZHANG Yancheng;SUN Guangming;WANG Xiao;LIU Hao;WILLNER Arne(College of Earth Science and Engineering,Shandong University of Science and Technology,Qingdao,Shandong 266590,China;Institute of Geology,Mineralogy and Geophysics,Faculty of Geosciences,Ruhr-University Bochum,Bochum 44780,Germany)

机构地区：[1]山东科技大学地球科学与工程学院,山东青岛266590 [2]波鸿鲁尔大学地球科学学院地质矿产地球物理研究所,德国波鸿44780

出　　处：《山东科技大学学报（自然科学版）》2020年第2期12-23,共12页Journal of Shandong University of Science and Technology(Natural Science)

基　　金：国家自然科学基金项目(41572044);山东科技大学科研创新团队项目(2015TDJH101);山东科技大学大学生创新训练项目(201810424017)

摘　　要：通过岩相学与矿物化学分析和视剖面图模拟计算对雅鲁藏布江缝合带中段地区沉积混杂岩带中多硅白云母石英片岩和黑硬绿泥石片岩的变质特征进行研究。多硅白云母石英片岩峰期矿物组合为多硅白云母+绿泥石+钠长石+石英+榍石,峰期条件为366℃/6.4 kbar;黑硬绿泥石片岩峰期矿物组合为阳起石+绿泥石+绿帘石+钠长石+石英+榍石+钛铁矿,峰期条件为363℃/6.1 kbar,黑硬绿泥石为峰后降温减压阶段的产物。雅鲁藏布江缝合带中段地区的沉积混杂岩变质温压条件达到了高压绿片岩相,指示俯冲深度21~23 km,地温梯度15~18℃/km,其变质特征与俯冲洋壳被上部地幔楔刮削进入增生楔系统经历变质作用形成的低级变质岩十分相似。结合前人年代学数据,研究认为雅鲁藏布江缝合带中段地区的沉积混杂岩在增生楔深部经历高压绿片岩相变质作用,形成于单一的特提斯洋洋壳向欧亚大陆南缘俯冲的构造体制之下印度-亚洲大陆初始碰撞时期。In this paper,petrographic and mineral chemical analysis and pseudosection computation were adopted to investigate the metamorphic characteristics of the phengite schist and stilpnomelane schist from the central Yarlung Zangbo Suture Zone(YZSZ).The study reveals that the phengite schist has a mineral assemblage of phengite,chlorite,albite,quartz and sphene,and a peak condition of 366℃/6.4 kbar,while the stilpnomelane schist,as a product of post-peak temperature and pressure reduction,has a mineral assemblage of actinolite,chlorite,epidote,albite,quartz,sphene and ilmenite,and a peak condition of 363℃/6.1 kbar.The peak metamorphic temperature and pressure conditions of these sedimentary-matrixmélange have reached the high-pressure greenschist facies with a subduction depth of 21~23 km and a geothermal gradient of 15~18℃/km.The metamorphic characteristics are very similar to those of low-grade metamorphic rocks formed when the subducted ocean crust scraped into the accretion wedge system by the upper mantle wedge.Combined with previous geochronology studies,this study further proposes that the sedimentary-matrix mélange in the central part of YZSZ experienced high-pressure greenschist facies metamorphism as a response to a northward subduction of the Neo-Tethyan oceanic lithosphere during the initial India-Asia collision stage.

关 键 词：沉积混杂岩 变质作用 P-T条件 印度-亚洲大陆碰撞 

分 类 号：P581[天文地球—岩石学]