西藏东巧蛇绿岩的地球化学特征及其形成的构造环境

西藏东巧蛇绿岩主要由变质橄榄岩、辉长岩及玄武岩等组成。变质橄榄岩以富Mg、Fe、Cr,贫Ti、∑REE为特征。辉长岩和玄武岩的主量元素、微量元素特征显示其具有扩张洋脊拉斑玄武岩的地球化学特征,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;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。根据其地球化学属性,推测该区蛇绿岩形成于大洋盆地扩张的构造环境。

GEOCHEMICAL CHARACTERISTICS AND TECTONIC SETTING OF OPHIOLITE OF DONGQIAO,TIBET

Ophiolites exposed in Dongqiao are mainly composed of metamorphic peridotites, gabbros and basalts. Through the analysis of major and trace elements of ophiolite in Dongqiao, it is concluded that the geochemical characteristics of its metamorphic peridotites are high content in Mg,Fe,Cr, and low content in Ti and REE. The gabbros and basalts are the transitional MORB type basalt. According to the data of trace elements in the ophiolite, the gabbros and basalts show the same characteristics as the spreading MORB, such as the depletion of elements of Nb, Ta and its relative enrichment of Rb, Sr and Ba. Meanwhile, according to the REE distribution patterns with no Eu anomaly, the gabbros and basalts are similar to Mid-Ocean Ridge Basalt.On the basis of its geochemical attribute, it is concluded that the ophiolite of Dongqiao geotectonic setting is formed in spreading ocean basin.