THE PRIMARY STUDY OF GEOCHEMICAL CHARACTERISTICS AND TECTONIC SETTING OF OPHIOLITE IN YONGZHU-NAMUHU,TIBET

From the analysis of the major elements of ophiolite in YongzhuNamuhu of Tibet, the characteristics of its metamorphic peridotite are high Mg content. And the characteristic of its basalt and gabbro is not the one of MidOcean Ridge Basalt (MORB) and Island Arc Basalt (IAB), for the percentage of TiO2 is very low, no more than 15%. According to the trace elements in the ophiolite, on one hand, the basalt shows the same characteristic as the Island Arc Basalt, for the depletion elements of Nb and Ta. On the other hand, the characteristic of basalt is not the same as the IAB's, for its high enrichment of Th and the nondepletion of Zr, Hf. The ∑REE of the ophiolite is low. Meanwhile, according to the REE distribution patterns, the basalt is of the characteristic of protomagma for its evenness form with no Eu anomaly. And the gabbro shows evenness form with Eupositive anomaly. It is concluded that the ophiolite of YongzhuNamuhu tectonic setting is formed in back arc basin by the comparison with the ophiolite of typical areas and discrimination diagrams of the tectonic setting.