冈底斯中段卡热辉长岩锆石U-Pb年代学、地球化学及构造意义  

Zircon U-Pb dating and geochemistry of the Kare gabbro in the middle segment of the Gangdese belt and its tectonic implications

作　　者：徐向珍[1] 熊发挥[1] 杨经绥[1] 巴登珠[1] 张然 段建兵 赵娇 XU Xiangzhen;XIONG Fahui;YANG Jingsui;BA Dengzhu;ZHANG Ran;DUAN Jianbing;ZHAO Jiao(CARMA(Center for Advanced Research on Mantle,Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing,100037;State Key Laboratory Breeding Base of Nuclear Resources and Environment,East China Institute of Technology,Nanchang,330013)

机构地区：[1]地幔研究中心,自然资源部深地动力学重点实验室,中国地质科学院地质研究所,北京100037 [2]核资源与环境省部共建国家重点实验室培育基地,东华理工大学,南昌330013

出　　处：《地质学报》2019年第10期2542-2555,共14页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号41672046、41502062、41720104009);中国地质调查局工作项目(编号DD20160023-01、DD20190060)联合资助成果

摘　　要：以冈底斯中段曲水县西南方向卡热乡一带出露的辉长岩为研究对象,进行了LA-ICP-MS锆石UPb测年以及全岩地球化学的系统测定,据此讨论岩石的成因及其构造意义。该辉长岩主要由单斜辉石和斜长石组成,辉长岩具有低硅、贫碱、富铝,中等富集轻稀土,富集大离子亲石元素,亏损高场强元素的地球化学特征,与岛弧和大陆边缘地区产出的高铝玄武岩化学组成十分相似,表明辉长岩原生岩浆为被俯冲改造的岩石圈幔源岩浆,在演化过程中受到了上地壳物质的混染。锆石LA-ICP-MS U-Pb年龄为49.01±0.51Ma(MSWD=0.41),指示岩体形成时代为始新世。卡热辉长岩具有显著亏损的锆石Hf同位素组成,εHf(t)值均为正值,分布在+10.88^+13.71之间,综合分析表明卡热辉长质侵入体可能为近期遭受俯冲板片析出流体交代作用的亏损地幔部分熔融的产物。结合区域构造演化史认为该岩体在冈底斯南缘的始新世期间存在着强烈的岩浆底侵和壳幔岩浆混合作用。In this paper,we collected the gabbro samples from Kare near Qushui county in the middle segment of the Gangdese belt,and conducted an integrated study including petrological,elemental geochemical analyses and LA-ICP-MS zircon dating,aiming at understanding their petrogenesis and the implications for tectonic evolution.speaking,Gabbro is lithologically composed of clinopyroxene and plagioclases.Chemically,the gabbro has low SiO2and K2O+Na2O,but high Al2O3contents,and is enriched in LREEs and LILEs,depleted in HFSEs,showing the chemical features similar to the high-alumina basalts of island arcs and continental margins.The geochemical characteristics indicate the gabbro has subduction-reformed lithospheric mantle-derived primary magma that was contaminated by upper crustal materials during its evolution.The LA-ICP-MS U-Pb age of zircon is 49.01+0.51Ma(MSWD=0.41),indicating the Eocene formation age.The Kare gabbro has highly depleted zircon Hf isotopic compositions,withεHf(t)values of+10.88^+13.71.The integrated lithologic and chemical compositions suggest that the gabbros were generated by the hydrous partial melting of depleted mantle metasomatized by fluids released from subducted oceanic slab.Combining with the regional tectonic evolution history,strong magmatic underplating and crust-mantle magmatic mixing might be occur during the Eocene in the southern margin of Gangdese belt.

关 键 词：辉长岩 LA-ICP-MS锆石U-PB测年 岩石成因 冈底斯 西藏 

分 类 号：P58[天文地球—岩石学]