西藏西部札达县东北部帮果日—波库蛇绿岩带的发现及其地质意义  

The discovery of Banguori-Boku ophiolite belt in northeastern Zanda County of west Tibet and its geological significance

作　　者：王行军[1,2] 王根厚[1] 李广栋[3] 吴连亨 李金和[3] 高雄[3] 张双增 专少鹏 班长勇 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]中国人民武装警察部队黄金地质研究所,河北廊坊065000 [3]河北省区域地质矿产调查研究所,河北廊坊065000

出　　处：《中国地质》2013年第6期1749-1761,共13页Geology in China

基　　金：中国地质调查局地质调查项目(200213000010)资助

摘　　要：帮果目—波库蛇绿岩带位于雅鲁藏布江缝合带的最西段，由帮果日蛇绿岩和波库混杂岩构成，呈北西展布，长128km，宽5～10km。帮果日蛇绿岩由方辉橄榄岩和二辉橄榄岩构成，岩石由橄榄石（Fo=85．2～88．0，平均86．6）、顽火辉石（Mg^#=89．3～94．3，平均91．2）、透辉石（Mg^#=92．0～94．9，平均93．1）构成，以高铝（Al2O3=0．96％～2．10％）、高钛（Ti=173～261μg／g）为特征，微量元素含量与MOR地幔岩的接近，亏损REE，∑REE仅为球粒陨石的33％~71％．估算其为原始地幔经过6％～12％部分熔融的产物。波库混杂岩基质由板岩、粉砂质板岩构成，岩块有橄榄岩、辉长岩、硅质岩、砂岩、灰岩等。通过对帮果日蛇绿岩同位素测年结果、波库混杂岩之中硅质岩岩块放射虫化石的研究．确定帮果日一波库蛇绿岩带形成于晚白垩世，是新特提斯洋俯冲消减的产物：帮果日蛇绿岩代表了新特提斯洋洋壳的残留，属典型的MoR型蛇绿岩．Located at the westernmost end of Yarlung Zangbo suture zone, the Bangguori-Boku ophiolite belt is composed of NW-striking Bangguori ophiohte and Boku melange 128 km in length and 5-10 km in width. Bangguori ophiohte consists of harzburgite and lherzohte comprising ohvine （Fo=85.2～88.0, 86.6 on average）, enstatite （Mg# =89.3～94.3, 91.2 on average）, and diopside （Mg#=89.3～94.3, 93.1 on average）, characterized by high Al2O3 （0.96%～2.10%） and Ti （173～261μ g/g）, close to the trace element content of MOR mande rock, and depletion of REE with ∑REE being 0.33～0.71 times that of chondrite. Moreover, major and trace element characteristics indicate that Bangguori ophiohtes are restites resulting from 6%～12% partial melting of the primitive mande. Boku melange consists of groundmass of slate and silty slate, and rock mass of peridotite, gabbro, siliceous rock, sandstone and hmestone. Studies show that Baoguori-Boku ophiohte belt was formed during Late Cretaceous, as evidenced by isotope dating of Bangguori ophiohte and radiolarians fossils from the silicohte rock mass of Boku melange. The results obtained by the authors demonstrate that Bangguori-Boku ophiohte belt resulted from Neotethys ocean subduction, and Bangguori ophiohte represents the residuum of Neotethys ocean hthosphere and belongs to the typical MOR-type ophiohte.

关 键 词：蛇绿岩 MOR 混杂岩 新特提斯洋 帮果日 波库 

分 类 号：P588.125[天文地球—岩石学]