古特提斯洋闭合时限:来自南羌塘唐古拉岩浆带查吾拉岩体的证据  

Closure time of the Paleo-Tethys Ocean:Evidence from the southern Qiangtang Tanggula magmatic belt,Tibet,China

作　　者：张培烈 王根厚[1] 冯翼鹏 韩宁 ZHANG Peilie;WANG Genhou;FENG Yipeng;HAN Ning(School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China)

机构地区：[1]中国地质大学地球科学与资源学院,北京100083

出　　处：《成都理工大学学报（自然科学版）》2022年第3期311-323,共13页Journal of Chengdu University of Technology: Science & Technology Edition

基　　金：国家自然科学基金项目(49802019);中国地质调查局项目(200313000001)。

摘　　要：研究羌塘盆地查吾拉岩体的地球化学特征、侵位时代和大地构造意义等。在对查吾拉岩体进行详细的野外地质调查的基础上,进行岩石学、岩石地球化学及同位素地质年代学的研究。结果表明,该岩体为过铝质钙碱性S型花岗岩,SiO_(2)的质量分数为61.06%~74.94%,全碱(Na_(2)O+K_(2)O)的质量分数为4.65%~9.15%,铝饱和指数(A/CNK)为0.90~1.29,属于过铝质-强过铝质,CIPW标准矿物组合含刚玉分子。稀土元素特征显示,轻、重稀土分馏程度不高,均具δEu负异常,符合地壳重熔型花岗岩的特点;痕量元素具有富集Rb、Th、La、Hf等,亏损Nb、Sr、P、Ti等的特点,符合造山带花岗岩的特征。Nb亏损表明查吾拉岩体具有大陆壳特征,为增生在大陆边缘的花岗岩。花岗岩构造判别图解显示其集中在同碰撞花岗岩区附近。在查吾拉岩体中,获得了(219±21)Ma、(210±37)Ma的锆石U-Pb等时年龄。查吾拉岩体应属于龙木错-双湖缝合带在晚三叠世碰撞闭合之后,俯冲板片回撤,地壳熔融并伴随着幔源物质加入的产物。Field geological survey combined with the study of petrology,petrogeochemistry and isotope geochronology of the Chawula pluton in Qiangtang Basin are conducted in order to reveal the geochemical characteristics,emplacement age and tectonic significance of the Chawula pluton.The results show that the magmatic rocks are peraluminous calc-alkaline S-type granite,with SiO_(2) content ranging from 61.06%to 74.94%,Na_(2)O+K_(2)O content ranging from 4.65%to 9.15%,and aluminum saturation index(A/CNK)ranging from 0.90 to 1.29,belonging to peraluminous to strong peraluminous series.CIPW standard mineral assemblage contains corundum molecules.The REE characteristics of the rocks show that the fractionation degree of LREE and HREE is not high,and both have negativeδEu anomaly,which is consistent with the characteristics of crustal remelting granite.The trace elements are enriched in Rb,Th,La,Hf and depleted in Nb,Sr,P and Ti,which accords with the characteristics of granite in orogenic belt.The depletion of Nb indicates that the Chawula pluton is characteristic of continental crust,resulted from the accretion of the granite on the continental margin.The discrimination diagram of Chawula pluton granite shows that the plotting is concentrated near the syn-collision granite area.The zircon U-Pb dating for Chawula pluton yields(219±21)Ma and(210±37)Ma age,indicating that the emplacement of pluton was in Triassic period.It is considered that,after the late Triassic collision of Longmucuo-Shuanghu suture zone,subduction plate retraction,crustal melting and addition of mantle-derived material led to the formation of Chawula pluton.

关 键 词：羌塘盆地 印支期 同碰撞花岗岩 古特提斯洋 查吾拉岩体 

分 类 号：P588.121[天文地球—岩石学]