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现代地质 ›› 2017, Vol. 31 ›› Issue (03): 486-497.

• 岩石学与矿床学 • 上一篇    下一篇

藏北果芒错蛇绿岩中堆晶岩地球化学特征及其地质意义

王振1(), 叶培盛2(), 张绪教1, 杨星辰2, 陈宇鹏1, 祁洁1, 石剑岳1, 盛余应1   

  1. 1.中国地质大学(北京) 地球科学与资源学院,北京 100083
    2.中国地质科学院 地质力学研究所,北京 100081
  • 收稿日期:2016-04-19 修回日期:2016-09-20 出版日期:2017-06-10 发布日期:2017-06-27
  • 通讯作者: 叶培盛,男,研究员,1964年出生,地质矿产勘查专业,主要从事区域地质调查及岩石地球化学研究。Email:yepeisheng@263.net
  • 作者简介:王 振,男,硕士研究生,1990年出生,地质矿产勘查专业,主要从事岩石地球化学及大地构造学研究。Email:geosciences_wzh@163.com
  • 基金资助:
    中国地质调查局计划项目(1212011120182)

Geochemical Characteristics of Cumulates in the Guomangcuo Ophiolites, Northern Tibet and Its Geological Significance

WANG Zhen1(), YE Peisheng2(), ZHANG Xujiao1, YANG Xingchen2, CHEN Yupeng1, QI Jie1, SHI Jianyue1, SHENG Yuying1   

  1. 1. School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China
    2. Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China
  • Received:2016-04-19 Revised:2016-09-20 Online:2017-06-10 Published:2017-06-27

摘要:

西藏果芒错蛇绿岩位于狮泉河—纳木错—波密蛇绿混杂岩带的中段,主要由地幔橄榄岩、铁镁质-超铁镁质堆晶杂岩、枕状熔岩、基性岩墙和硅质岩等单元组成。对果芒错蛇绿混杂岩中超铁镁质堆晶岩、基性岩岩石学及地球化学特征的研究表明,果芒错超铁镁质堆晶杂岩具很好的堆晶韵律,岩石化学特征反映了随着MgO含量的降低其从底到顶的连续分离结晶过程;堆晶杂岩稀土元素总体上具LREE富集、Eu轻微异常特点,微量元素具有富集高场强元素、亏损大离子亲石元素的特征,且相容元素显示良好的变化规律,指示岩石来自受富集组分混染的地幔源区,并在后期经历了俯冲流体作用。果芒错基性岩具有富集型洋中脊玄武岩(E-MORB)叠加岛弧型玄武岩(IAB)的地球化学特征,并受到后期俯冲流体的影响。根据果芒错蛇绿岩地球化学属性及其构造环境判别图解,推断该地区蛇绿岩生成于扩张的弧后盆地构造环境。作为狮泉河—纳木错—波密蛇绿岩带的一部分,该区蛇绿岩以班公湖—怒江特提斯洋弧后盆地的形式存在。

关键词: 果芒错蛇绿岩, 堆晶岩, 地球化学, 富集型地幔源, 弧后盆地

Abstract:

The Guomangcuo ophiolite in the central Shiquanhe-Namco-Bomi ophiolitic mélange belt is composed of mantle peridotite,ultramafic-mafic cumulates,mafic lavas, dikes and siliceous rocks. Petrographic studies of the ultramafic cumulates show that the ultramafic cumulates has a well crystallization order. Trace elements analyses indicate that the ultramafic cumulates are enriched in HFSE,depleted in LILE,and that the compatible elements have a good change rule. The rare earth elements analyses also show a enriched LREE pattern with slight Eu anomaly,displaying that the rocks are formed from a enriched mantle source metasomatized by fluid in the slab subduction.Guomangcuo mafic rocks have both E-MORB and IAB affinity and are effected by the subduction fluids.We suggest that guomangcuo ophiolite likely developed in a back-arc basin,as a portion of Shiquanhe-Namco-Bomi ophiolitic mélange belt which is the Bangonghu-Nujiang Tethyan ocean back-arc basin.

Key words: Guomangcuo ophiolite, cumulate, geochemistry, enriched mantle source, back-arc basin

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