西藏松多地区蛇纹岩成因及其对松多古特提斯洋俯冲的约束  

Origin of Serpentinite in Sumdo Area,Xizang and Its Constraint on Subduction of the Sumdo Paleo-Tethys Ocean

作　　者：王斌[1,2] 解超明[1,2,3] 董永胜[1] 段梦龙 宋宇航[1,2] 郝宇杰 Wang Bin;Xie Chaoming;Dong Yongsheng;Duan Menglong;Song Yuhang;Hao Yujie(College of Earth Sciences,Jilin University,Changchun 130061,China;Research Center for Tibetan Plateau,Jilin University,Changchun 130061,China;Key Laboratory of Mineral Resources Evaluation in Northeast Asia,Ministry of Natural Resources,Changchun 130061,China)

机构地区：[1]吉林大学地球科学学院,吉林长春130061 [2]吉林大学青藏高原地质研究中心,吉林长春130061 [3]自然资源部东北亚矿产资源评价重点实验室,吉林长春130061

出　　处：《地球科学》2024年第3期837-849,共13页Earth Science

基　　金：国家自然科学基金项目(No.42172226);自然资源部东北亚矿产资源评价重点实验室自主课题基金项目(No.DBY-ZZ-18-06)。

摘　　要：蛇纹岩中的锆石不仅可以提供年代学信息,还可以约束蛇纹岩的成因和区域构造演化过程.本文以唐加-松多古特提斯缝合带中的龙崖松多蛇纹岩为研究对象,对其进行了全岩地球化学、锆石U-Pb年代学和Lu-Hf同位素研究.结果显示,龙崖松多蛇纹岩具较高的MgO和TFeO含量、高Mg#值以及较低的Al_(2)O_(3)和TiO_(2)含量.样品稀土元素配分曲线呈较为宽缓的“U”型.微量元素蛛网图显示,样品富集U、Ta,亏损Th、Nb、Zr和Hf.龙崖松多蛇纹岩锆石U-Pb定年结果为(230.3±2.3)Ma,εHf(t)值在+13.4到+16.0之间.年代学和地球化学研究表明,龙崖松多蛇纹岩的原岩为地幔楔内尖晶石二辉橄榄岩部分熔融后的残留体.龙崖松多蛇纹岩受到松多古特提斯洋板片俯冲产生的超临界流体的交代形成了交代锆石,可能还受到富水流体的交代,导致流体活动性元素的富集.结合前人研究,本文认为松多古特提斯洋在晚三叠世可能尚处于北向俯冲阶段.Zircons in serpentinite can not only provide chronological information,but also constrain the genesis of serpentinite and regional tectonic evolution process.Longyasongduo serpentinite in Tangjia-Sumdo Paleo-Tethys suture zone was studied by means of zircon U-Pb dating,whole-rock geochemistry,and zircon Hf isotope in this paper.The results show that Longyasongduo serpentinites have high MgO,TFeO and Mg#values but low Al_(2)O_(3) and TiO_(2) contents.The chondrite-normalized REE patterns display a gentle U-type.The primitive mantle-normalized spider diagrams exhibit enrichment in U,Ta and depletion in Th,Nb,Zr and Hf.Zircon U-Pb dating of Longyasongduo serpentinite yielded ages of(230.3±2.3)Ma,with ε_(Hf)(t) values of+13.4 to+16.0.Through chronological and geochemical studies,we argue that the protolith of Longyasongduo serpentinite is the residual of partially melted spinel lherzolite in the mantle wedge.Longyasongduo serpentinite was metasomatized by supercritical fluid generated by subduction of Sumdo Paleo-Tethys oceanic crust to form metasomatic zircon,which may also be metasomatized by aqueous solutions,resulting in enrichment of fluid-mobile elements.Based on previous studies,we infer that the Sumdo Paleo-Tethys Ocean was still in a northward subduction setting in the Late Triassic.

关 键 词：青藏高原 松多古特提斯洋 蛇纹岩 交代锆石 岩石学 地球化学 

分 类 号：P581[天文地球—岩石学]