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滇东南八布杨万铜矿床硫化物Re-Os同位素年龄及其地质意义
Re-Os geochronology of the Babu copper deposit in southeast Yunnan Province and its geological implications
投稿时间:2020-06-01  修订日期:2020-08-04
中文关键词:Re-Os同位素定年  金属硫化物  蛇绿岩  杨万铜矿床  滇东南
英文关键词:Re-Os geochronology  sulfides  ophiolite  Yangwan copper deposit  Southeast Yunnan
基金项目:国家自然科学基金青年科学基金(41102141);中国地质调查局项目(DD20160122-7);自然资源部深地动力学重点实验室自主研究课题(J1901-20-8);中国地质科学院地质研究所基本科研业务费(J1515)
作者单位
向忠金 中国地质科学院 地质研究所, 北京 100037
自然资源部深地动力学重点实验室, 北京 100037 
闫全人 中国科学院 大学地球与行星科学学院, 北京 100049 
夏磊 云南大学 地球科学学院, 云南 昆明 650500 
夏文静 北京航空航天大学学生处, 北京 100191 
李超 国家地质实验测试中心, 北京 100037 
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中文摘要:
      滇东南八布地区发育一套晚古生代超镁铁质-镁铁质杂岩,是认识古特提斯分支洋构造演化的重要窗口,而其中以火山岩为赋矿围岩的杨万铜矿床,被视作区域找矿的突破点。目前,对这套超镁铁质-镁铁质杂岩的构造属性及赋存铜矿床的成矿时代及成因联系还存在争议。通过对杨万铜矿床中黄铜矿和黄铁矿进行Re-Os同位素定年,获得Re-Os等时线年龄为269±3 Ma,表明该矿床形成于早中二叠世,与火山岩(~270 Ma)大致同时;而初始187Os/188Os值为0.31±0.17,暗示成矿时存在热液流体与古海水的相互作用。区内玄武岩围岩和其它超镁铁质-镁铁质岩石的地球化学特征对比分析显示,八布超镁铁质-镁铁质杂岩为一套N-MORB型蛇绿岩组合,代表了古特提斯分支洋盆的洋壳残片。杨万铜矿床应划归为与古特提斯分支洋裂解有关的火山成因块状硫化物(VMS)矿床,其周边地区具有较好的找矿潜力。
英文摘要:
      Babu ultramafic-mafic rocks, located in the southeastern Yunnan Province, provide researchers a good opportunity to investigate the tectonic evolution of the branch of Paleotethys Ocean. The Yangwan copper deposit, which is hosted by basalts and breccia in Babu area, is considered as a good metallogenic prospective zone. However, the petrogenesis of the Babu ultramafic-mafic rocks and the age of Yangwan copper deposit are still controversial. In order to get the age of ore deposit, the authors applied Re-Os isotope dating to sulfides from the Yangwan deposit. Chalcopyrite and pyrite were picked out for Re-Os isotope analysis. Re-Os isotope dating yielded an isochron age of 269±3 Ma, with an initial 187Os/188Os ratio of 0.31±0.17. The well-defined Re-Os isochron, excluding the possible mixed isochron, represents the depositional age of sulfides, which means they were formed at the same time as ultramafic-mafic rocks (~270 Ma). The high initial 187Os/188Os ratio was interpreted as entrainment of seawater into pristine hydrothermal fluid. The characteristics of ore and the age of sulfides indicate that the Yangwan copper deposit is a VMS deposit. Though a comparative research on geochemistry between wall rock basalts and other rocks, it is held that all the data support the argument that the Babu ultramafic-mafic rocks are normal middle ocean ridge basalt (N-MORB)-type ophiolites at present. They probably represent the relics of the branch of Paleotethys Ocean.
向忠金,闫全人,夏磊,夏文静,李超,2020,滇东南八布杨万铜矿床硫化物Re-Os同位素年龄及其地质意义[J].岩石矿物学杂志,(5):583~595.
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