藏北果芒错蛇绿岩中堆晶岩地球化学特征及其地质意义  

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

作　　者：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 盛余应 

机构地区：[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

出　　处：《现代地质》2017年第3期486-497,507,共13页Geoscience

基　　金：中国地质调查局计划项目(1212011120182)

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。The Guomangcuo ophiolite in the central Shiquanhe-Namco-Bomi ophiolitic m61ange belt is composed of mantle peridotite, uhramafic-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 com- patible elements have a good change rule. The rare earth elements analyses also show a enriched LREE pat- tern with slight Eu anomaly, displaying that the rocks are formed from a enriched mantle source metasoma- tized by fluid in the slab subduetion. Guomangcuo mafic rocks have both E-MORB and IAB affinity and are effected by the subduction fluids. We suggest that guomangeuo ophiolite likely developed in a back-arc basin, as a portion of Shiquanhe-Namco-Bomi ophiolitic m61ange belt which is the Bangonghu-Nujiang Tethyan ocean back-arc basin.

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 

分 类 号：P588.12[天文地球—岩石学]