青藏高原松多中三叠世洋壳的识别及其对松多古特提斯洋演化的制约  

Identification of the Middle Triassic Oceanic Crust of the Sumdo in the Tibet Plateau and Its Constraints on the Evolution of the Sumdo Paleo-Tethys Ocean

作　　者：段梦龙 解超明[1,2] 范建军 王斌[1] 郝宇杰 Duan Menglong;Xie Chaoming;Fan Jianjun;Wang Bin;Hao Yujie(College of Earth Sciences,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]东北亚矿产资源评价自然资源部重点实验室,吉林长春130061

出　　处：《地球科学》2019年第7期2249-2264,共16页Earth Science

基　　金：国家自然科学基金项目(No.41872231);中国地质调查局项目(No.DD20160026)

摘　　要：松多绿片岩分布于拉萨地块中部的松多地区,因对其时代及构造属性研究程度一直较低,严重制约了对松多古特提斯洋演化的认识.在详细野外地质调查基础上,对松多附近的绿片岩进行了LA-ICP-MS锆石U-Pb同位素测试,以及锆石Hf同位素分析,并开展了岩石学和全岩地球化学研究.在松多绿片岩中获得锆石U-Pb年龄约为232 Ma,为中三叠世,代表了绿片岩的原岩成岩时代.其锆石εHf(t)平均为3.6,显示弱亏损地幔的特征.岩石学和地球化学研究揭示,绿片岩原岩具有拉斑质基性岩特征,在球粒陨石标准化稀土元素配分曲线和原始地幔标准化多元素蛛网图中均为平坦型,与N-MORB相似.在各类判别图解上,也都落入N-MORB区域,表明松多绿片岩原岩可能为松多古特提斯洋壳残片.松多中三叠世绿片岩的识别,说明松多古特提斯洋可能在中三叠世时还存在洋盆.The Sumdo green schist is distributed in the Sumdo area in the segment of the Lhasa block. Because of the low level of research on its age and tectonic characteristics, it has seriously constrained our understanding of the evolution of the Sumdo PaleoTethys Ocean. Based on the detailed field geological survey, petrology, whole-rock geochemistry, LA-ICP-MS zircon U-Pb isotope and zircon Hf isotope analysis were carried out on the green schist. The zircon U-Pb age is approximately 232 Ma in the Sumdo green schist, which is the Middle Triassic, representing the protolith’s crystallization of the green schist. The εHf(t) of zircons is 3.6 on average, showing the characteristics of a weakly depleted mantle. Petrology and geochemistry studies reveal that the protolith of green schist has characteristics of tholeiite, which appears as a flat curve in the chondrite-normalized REE patterns and primitive mantle-normalized trace element spidergrams, similar to N-MORB attributes. In all kinds of discriminative diagrams, they all fall into the N-MORB field, indicating that the protolith of Sumdo green schist may be an oceanic crust fragment from the Sumdo Paleo-Tethys Ocean. The identification of the Middle Triassic green schist in Sumdo indicates the Sumdo Paleo-Tethys Ocean may hold oceanic basin during the Middle Triassic.

关 键 词：松多古特提斯洋 绿片岩 地球化学 锆石U-PB年代学 锆石HF同位素 

分 类 号：P583[天文地球—岩石学]