今天是2018年10月18日

西藏班公湖-怒江缝合带西段洞错蛇绿岩中的辉长岩锆石U-Pb年代学及地质意义

DOI:10.3799/dqkx.2018.710

作者:武勇,陈松永,秦明宽,郭冬发,郭国林,张财,杨经绥

联系地址:核工业北京地质研究院,中核集团铀资源勘查实验室,北京 100029

摘要:洞错蛇绿岩位于班公湖-怒江缝合带西段阿里地区,前人对其空间展布、构造环境及成因有过一定的探讨,但研究程度薄弱.选择洞错蛇绿岩中的辉长岩为研究对象,对其开展详细的岩相学、地球化学、年代学等工作,解读洋盆的形成时间及构造环境.结果表明,辉长岩与N-MORB相比具有较高的Mg#,低K、Na、P和Ti的元素特征,亏损Hf、Zr、Nb等高场强元素(HFSE),具有轻稀土亏损型配分模式,表明可能源于N-MORB型亏损地幔源区. 地球化学元素研究表明辉长岩岩浆源自亏损的尖晶石二辉橄榄岩~30%部分熔融,可能形成于与洋内俯冲相关的岛弧或者弧前构造环境,属于SSZ型蛇绿岩.辉长岩锆石的U-Pb测年指示其结晶年龄为222±4.8 Ma(MSWD=0.5,n=28),代表了辉长岩的形成年龄,佐证了洞错蛇绿岩形成于晚三叠世,表明班公湖-怒江特提斯洋盆从晚三叠世开始存在洋内俯冲消减地质作用.

关键字:蛇绿岩;辉长岩;构造环境;锆石U-Pb年龄;班公湖-怒江缝合带;地质年代学

Zircon U-Pb Ages of Dongcuo Ophiolite in Western Bangonghu-Nujiang Suture Zone and Their Geological Significance

Author:Wu Yong, Chen Songyong, Qin Mingkuan, Guo Dongfa, Guo Guolin, Zhang Cai, Yang Jingsui

Author Address:CNNC Key Laboratory of Uranium Resources Exploration and Evaluation Technology, Beijing Research Institute of Uranium Geology,Beijing 100029, China

Abstract:The Dongcuo ophiolite is located at the western part of Bangong-Nujiang River suture zone, Gaize County. In spite of previous studies on its spacious distribution, tectonic environment and genesis, the key problem remains unresolved. Taking the gabbro of Dongcuo ophiolite as the research object, a detailed study of petrography, geochemistry, petrology and geochronology is carried out to understand the formation of Bangong-Nujiang ocean basin, the tectonic settings of the Dongcuo ophiolite. Compared with N-MORB, the major and trace elements of Dongcuo ophiolite are characterized by high content in Mg# and low content in K, Na, P, and Ti , the depletion of high field-strength elements (HFSE) of Hf, Zr, Nb and light rare earth element depletion. Geochemistry characteristics of the Dongcuo ophiolite indicate that it is originated from ~30% partial melting of depleted spinel lherzolite formed in the tectonic environment of subduction-related island arc or fore arc, belonging to super subduction zone (SSZ) ophiolite. The LA-ICP-MS of zircon U-Pb dating yields the age of 222±4.8 Ma (MSWD=0.5), providing the age constraint on the Dongcuo ophiolite (Late Jurassic), and showing that it belongs to the Tethyan system of the Bangong-Nujiang River suture zone, which indicates the intra-oceanic subduction process.

Keyword:ophiolite; gabbro; tectonic environment; zircon U-Pb dating; Bangong-Nujiang suture zone; geochronology

 

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作者简介:武勇(1986-),男,博士研究生,主要从事铀矿地质勘查与二次离子质谱同位素地质年代学研究.ORCID: 0000-0002-0978-2227. E-mail: cnncwuyong@outlook.com

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