西藏纳木错西岸蛇绿岩的地球化学特征及其形成环境

西藏纳木错西岸蛇绿岩主要由变质橄榄岩、辉长辉绿岩及玄武岩等组成。变质橄榄岩以富Mg、贫Ti、贫REE元素为特征。辉绿岩和玄武岩的主量元素、微量元素特征显示其含有洋脊拉斑玄武岩和岛弧拉斑玄武岩的双重成分，其中高场强元素Nb、Ta、Zr、Hf等亏损．大离子亲石元素Rb、Sr、Ba等相对富集，具岛弧玄武岩的特点；在球粒陨石标准化稀土元素配分模式图上为LREE亏损的平坦型，无负Eu异常，与洋中脊玄武岩的特征类似。通过与典型地区作对比并应用构造环境判别图解，推测该区蛇绿岩形成于弧后盆地的构造环境。

GEOCHEMISTRY AND TECTONIC SETTING OF OPHIOLITES IN WEST OF NAMCO LAKE,TIBET

Ophiolites in west of the Namco Lake in Tibet are mainly composed of metamorphic peridotites, gabbro-diabases and basalts. From the analysis of major and trace elements of ophiolite in west of Namco, the characteristics of the metamorphic peridotite are high content in Mg, and low content in Ti and ∑REE. The diabases and basalts are the transitional IAB / MORB - type basalt, which have the characteristic of depletion in high field elements (Nb, Ta, Zr, Hf) and comparable enrichment in large ion lithosperic elements (Rb, Sr, Ba), and on the other hand, the REE/chondrite pattern displays a flat-model with LREE depletion and without Eu anomaly. It is concluded that the geotectonic setting of ophiolite in Namco is formed in back arc basin by the comparison with the ophiolite of typical areas and discrimination diagrams of the tectonic setting.