西藏仁布蛇绿岩壳层熔岩的岩石地球化学及成因

西藏仁布蛇绿岩壳层玄武岩基本上属高铝低钛的拉斑玄武岩，富集Ba、Rb、Sr等大离子亲石元素以及Th、Ta、Nb、Zr和Hf等高场强元素，具典型的洋岛玄武岩地球化学特征，结合REE配分曲线，可以认为该蛇绿岩可能形成于伸展应力体制下的边缘洋盆的构造环境，是新特提斯大洋岩石圈在俯冲消亡过程中的残片。

Lithogeochemical Characteristics and Origin for Basaltic Lava from Renbu Ophiolite from Xizang (Tibet), China

The basaltic lavas from Renbu ophiolite from Xizang (Tibet) are composed of fine- grained plagioclase basaltic porphyrite, coarse-grained plagioclase basaltic porphyrite, and amyg- daloidal pyroxene basalt. The analytical data show that their contents of potassium and natrium are relatively higher, and those of iron and phosphorus are also higher, but calcium and magne- sium are comparatively deficient. Meanwhile, they have higher aluminum and lower titanium contents and belong to tholeiite rock series. LILE, such as Ba, Rb, Sr and HFSE, including Th, Ta, Nb, Zr and Hf are rich, but Cr, Ni and the other trace elements are relatively poor. The to- tal abundances of rare earth elements are comparatively high and they display the enriched distri- bution patterns of LREE, which shows that the basalts possess the characteristics of the typical oceanic island-arc. The Th/Ta ratios are between 1.03 and 1.53 and the average value is 1.19. The La/Ta ratios are between 10.08 and 13.26 and the average value is 12.2. The Th/Ta, La/ Ta ratios and the distribution patterns of spidergrarns indicate that the Renbu lavas are oceanic non-SSZ basalts. Intergrating with the field geology and comparing with MORB, OIB and the other typical ophiolites, we can draw a conclusion that Renbu ophiolite was probably formed in an initial marginal basin tectonic environment under the extension stress dynamics during the Neo- Tethys periods.