西藏班公湖蛇绿岩地质特征及形成时代

The geological characteristics and the forming time of ophiolites in the region of the Bangong Lake, Tibet

西藏班公湖蛇绿岩由变质橄榄岩、超基性-基性堆晶岩、辉长岩墙群和枕状熔岩组成。其地球化学特征为:超基性岩以富Mg,贫Ti、A l、Ca,低S i为特征;基性岩以ω(S iO2)、ω(MgO)偏高,稀土配分模式多数与洋岛玄武岩的稀土配分模式相类似为特征;火山岩以Th、Nd元素富集,球粒陨石标准化稀土配分模式可分为二类:一类为LREE亏损的直线型,与洋中脊玄武岩的特征类似,另一类为LREE富集型,与洋岛碱性玄武岩特征类似;蛇绿岩时代为晚三叠世晚期-早侏罗世早期开始,结束于晚白垩世晚期;形成于洋中脊相对扩张的构造环境。

The ophiolites in the ultrabasic - basic layered rocks are characterized by region of Bangong Lake are mainly composed of metamorphic peritonitis, crystallized rocks, groups of gabbros rich in Mg, depleted in Ti and a low wall and pillow lava. Ultrabasic content in Si. Basic rocks have a higher content in ω（ SiO2 ）and ω（MgO） and most of their models of REE distribution are similar to that of OIB. Volcanic rocks are rich in Th, Nd, whose models of REE distribution standardized by chondrite can be classified into two types： a linear model with LREE depleted, which is similar to the that of ORB; a model rich in LREE, which is similar to the that of OIAB . The ophiolites occurred in a tectonic expansion environment of the Ocean Ridge from the late Triassic - early Jurassic to the late Cretaceous.