罗布莎蛇绿混杂岩中堆晶辉长岩U-Pb定年、地球化学特征及其地质意义  

U-Pb dating,geochemical characteristics,and geological significance of cumulate gabbro in the Luobusha ophiolite mélange

作　　者：唐建科 刘育 张泽国 何林武 邓科 段炳鑫 王金贵 TANG Jianke;LIU Yu;ZHANG Zeguo;HE Linwu;DENG Ke;DUAN Bingxin;WANG Jingui(No.5 Geological Party,Xizang Bureau of Geology and Mineral Exploration and Development,Golmud 816099,Qinghai,China;Hebei Provincial Key Laboratory of Strategic Critical Mineral Resources,Shijiazhuang 050000,Hebei,China;Hebei Provincial Institute of Regional Geological Survey,Langfang 065000,Hebei,China)

机构地区：[1]西藏自治区地质矿产勘查开发局第五地质大队,青海格尔木816099 [2]河北省战略性关键矿产资源重点实验室,河北石家庄050000 [3]河北省区域地质调查院,河北廊坊065000

出　　处：《矿产勘查》2024年第6期928-937,共10页Mineral Exploration

基　　金：中国地质调查局项目(DD20160015)资助。

摘　　要：罗布莎蛇绿岩是雅鲁藏布蛇绿岩带东段的典型代表,但目前对其形成时代和构造环境有不同的认识。本文对蛇绿混杂岩中的堆晶辉长岩开展了LA-ICP-MS锆石U-Pb定年和岩石地球化学研究,以探究罗布莎蛇绿岩形成时代和构造环境。堆晶辉长岩锆石^(206)Pb/^(238)U年龄平均值为(144±3)Ma(MSWD=0.19,n=25),表明罗布莎蛇绿岩形成于早白垩世。堆晶辉长岩亏损高场强元素Nb、Hf以及轻稀土元素(LREE),且稀土配分曲线具有N-MORB的趋势特征,表明其形成于亏损地幔源区。Nb的负异常表明形成堆晶辉长岩的岩浆源区受到板片俯冲作用的影响,因此罗布莎蛇绿岩为SSZ型蛇绿岩。结合区域资料其形成的构造环境可能为弧后盆地。The Luobusha ophiolite is a typical site of the eastern part of the Yarlung Zangbo ophiolite belt,but so far there has been no consensus concerning its formation time and tectonic setting.We conducted LA-ICP-MS zircon U-Pb dating and geochemistry studies on the cumulate gabbro within the ophiolite mélange,aiming to explore the formation age and tectonic setting of the Luobusha ophiolite.The mean zircon^(206)Pb/^(238)U ages for the cumulate gabbro is(144±3)Ma(MSWD=0.19,n=25),suggesting that the Luobusha ophiolite was formed during the Early Cretaceous.The cumulate gabbro exhibits depletion in high field strength elements such as Nb and Hf,as well as light rare earth elements(LREE).Additionally,its rare earth element distribution curve shows characteristics consistent with N-MORB(Normal Mid-Ocean Ridge Basalt),indicating its formation in a depleted mantle source region.The negative Nb anomaly indicates that the magma related to the studied cumulate gabbro was influenced by plate subduction.This suggests that the Luobusha ophiolite is an SSZ-type ophiolite.Combined with regional data,the tectonic setting for the formation of the Luobusha ophiolite is likely a back-arc basin.

关 键 词：蛇绿岩 堆晶辉长岩 构造环境 锆石U-Pb年龄 地质年代学 

分 类 号：P597[天文地球—地球化学]