西藏中部聂尔错地区辉绿岩锆石U-Pb年龄与地球化学特征:对新特提斯洋板片断离的指示  

Zircon U-Pb ages and geochemical characteristics of diabase in Nie'erco area,central Tibet:Implication for Neo-Tethyan slab breakoff

作　　者：吴浩 徐祖阳 严维兵 郝宇杰 刘海永 WU Hao;XU Zuyang;YANWeibing;HAO Yujie;LIU Haiyong(College of Earth Sciences,Guilin University of Technology,Guilin 541004,Guangxi,China;School of Earth Sciences and Engineering,Hohai University,Nanjing 211100,Jiangsu,China;Geological Exploration Technology Institute of Jiangsu Province,Nanjing 210000,Jiangsu,China;Key Laboratory of Mineral Resources Evaluation in Northeast Asia,Ministry of Natural Resources of China,Changchun 130061,Jilin,China;Tibet Institute of Geological Survey,Lhasa 850000,Tibet,China)

机构地区：[1]桂林理工大学地球科学学院,广西桂林541004 [2]河海大学地球科学与工程学院,江苏南京211100 [3]江苏省地质勘查技术院,江苏南京210000 [4]自然资源部东北亚矿产资源评价重点实验室,吉林长春130061 [5]西藏自治区地质调查院,西藏拉萨850000

出　　处：《中国地质》2023年第6期1804-1816,共13页Geology in China

基　　金：江苏省基础研究计划(自然科学基金)资助项目(BK20170877)资助。

摘　　要：【研究目的】幔源岩浆活动是探讨深部动力学演化的理想研究对象,西藏中部聂尔错地区广泛发育的基性岩脉无疑是探讨区域构造-岩浆演化的关键所在。【研究方法】本文对聂尔错辉绿岩脉进行了系统的岩石学、地质年代学和地球化学综合研究。【研究结果】分析结果表明,聂尔错辉绿岩锆石U-Pb定年结果为(50.8±0.6)Ma,为始新世早期岩浆活动的产物。全岩地球化学组成显示辉绿岩具有低Si O_(2)、高Mg O、Al_(2)O_(3)、Ti O_(2)和全碱含量(Na_(2)O+K_(2)O),富集轻稀土元素、亏损重稀土元素等特征,显示碱性洋岛型玄武岩(OIB)的地球化学特征。地球化学特征指示辉绿岩可能起源于软流圈地幔,同时岩浆在上升过程中受到一定程度的地壳物质混染。【结论】结合西藏南部地区广泛发育的同时期碰撞后林子宗火山岩与OIB型基性岩,研究认为西藏地区新生代岩浆活动主要受控于新特提斯洋的北向俯冲以及印度-欧亚板块的碰撞过程,板片断离所导致的上涌软流圈地幔减压熔融是聂尔错辉绿岩最为合理的成因解释。This paper is the result of geological survey engineering.[Objective]Mantle-derived magmatism generally provided an ideal research object to reveal the geodynamic evolution in the depth.The mafic dikes,which shown intensive distribution in Nie'erco area of central Tibet,are regarded as a key aspect to understanding the regional tectono-magmatic evolution.[Methods]In this paper,we report geochronological and geochemical data of the diabases in the Nie'erco area.[Results]The zircon U-Pb dating yielded magmatic crystallization ages of(50.8±0.6)Ma,indicating the Nie'erco diabases emplacement in the early Eocene.The diabase samples have low SiO_(2),high MgO,Al_(2)O_(3),TiO_(2) and total alkali(Na_(2)O+K_(2)O)contents,similar to alkaline ocean island basalt(OIB).These geochemical features suggest that the studied diabases were generated by partial melting of asthenosphere,with the involvement of continental crustal components.[Conclusions]Combined with the post-collisional Linzizong volcanic rocks and OIB-like mafic rocks in southern Tibet,we prefer that the Cenozoic magmatism in Tibet is mainly controlled by the northward subduction of the Neo-Tethyan ocean and the following continent collision between India and Eurasia plates.Our research favor that the Nie'erco diabases were generated in response to the slab breakoff and related upwelling and decompressional melting of sub-slab asthenosphere.

关 键 词：锆石U-PB年龄 辉绿岩 始新世 新特提斯洋 板片断离 地质调查工程 聂尔错 西藏 

分 类 号：P581[天文地球—岩石学] P597[天文地球—地质学] P541