关键词: 蛇绿岩, 地球化学特征, 构造环境, 边缘海盆地, 泽当―罗布莎, 雅鲁藏布江缝合带, 西藏

Abstract:

The Zedang-Luobusha ophiolite in Tibet is an important component part of the Yarlung Zangbo ophiolite belt and controlled by the plate junction zone. It may be well correlated with some typical sequential ophiolites at home and abroad.Ophiolites exposed from Zedang to Luobusha are mainly composed of metamorphic harzburgites, gabbros and basalts. From the analysis of major and trace elements of ophiolite in ZedangLuobusha, the characteristics of its metamorphic harzburgites have low Al₂O₃, CaO contents, high MgO contents and Mg* values, and are lower in Ti and ∑REE, and belong to the depleted oceanic lithosphere mantle. They are consistent with those of harzburgites from the typical ophiolites of the world. The diabases and basalts are the transitional MORB/OIT-type basalt. According to the trace elements in the ophiolite, on one hand, the gabbros and basalts show the same characteristics as the island arc basalt, for the depletion elements of Nb, Ta and its relative enrichments of Rb, Sr and Ba. Meanwhile, according to the REE distribution patterns with no Eu anomaly, the gabbros are similar to mid-ocean ridge basalt. It is concluded that the geotectonic setting of ophiolite of Zedang-Luobusha is formed in marginal sea or small oceanic basin by the comparison with the ophiolites of typical areas and discrimination diagrams of the tectonic setting. This indicates that ophiolite complex of Zedang-Luobusha has a more complex evolution history than hitherto considered

Key words: ophiolite, geochemical characteristic, tectonic setting, marginal sea basin, Zedang-Luobusha, Yarlung Zangbo suture zone, Tibet