藏北果芒错蛇绿岩中堆晶岩地球化学特征及其地质意义

发布时间：2018-04-06 21:03

本文选题：果芒错蛇绿岩　切入点：堆晶岩　出处：《现代地质》2017年03期

【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Mg O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。
[Abstract]:Gomangcha ophiolite in Tibet is located in the middle of the Shiquanhe-Namuo-Bormian ophiolite melange belt. It is mainly composed of mantle peridotite, ferromagnesis-ultraferromagnesian heap crystal complex, occipital lava, basic rock wall and siliceous rock.The petrological and geochemical characteristics of ultraferromagnesian heaps and basic rocks in the Gomangcao ophiolitic melange show that the Guomangcao superferromagnesian heap complex has a good stacking rhythm.The petrochemical characteristics reflect the continuous separation and crystallization process from bottom to top with the decrease of MgO content, the rare earth elements in the heap complex generally have the characteristics of LREE enrichment and slight EU anomaly, and the trace elements are rich in high field strength elements.The characteristics of depleted large ion lithophile elements and the good variation of compatible elements indicate that the rocks come from the mantle source where the enriched components are mixed and experienced subduction fluid action in the late stage.Guomangdislocation basic rocks have the geochemical characteristics of enriched mid-oceanic ridge basalt (E-MORBB) superimposed island arc basalt (IAB) and are influenced by subduction fluids in the late stage.Based on the geochemical properties of the gomangcao ophiolite and the distinguishing diagram of its tectonic environment, it is inferred that the ophiolite was formed in the tectonic environment of the extended back-arc basin in this area.As a part of the Shiquanhe-Namuco-Bomi ophiolite belt, the ophiolite exists in the form of the Bangong Lake-Nu River Tethys back-arc basin.
【作者单位】：中国地质大学(北京)地球科学与资源学院;中国地质科学院地质力学研究所;
【基金】：中国地质调查局计划项目(1212011120182)
【分类号】：P587

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