关键词: 青藏高原, 北羌塘盆地, 蛇绿岩, 甘孜—理塘缝合带, 洋盆环境

Abstract:

The Chayong ophiolite is a part of the northern extension of Ganze-Litang suture zone in Zhiduo area of the North Qiangtang basin in Qinghai-Tibet Plateau,it consists of basic cumulates,diabase dyke swarms,basic lavas and sedimentaryorigin cherts，but mantle peridotites are absent.Due to the effect of structures after the ophiolite formed，they are strongly metamorphized and deformed, and mostly dismembered to tectonic blocks and slabs. The cumulates comprise altered olivine pyroxenite and gabbro. The former is characterized by low SiO₂，TiO₂，P₂O₅ and high MgO contents，significant enrichment of Rb，Th，Cr and depletion of Sr，Nb，Y . In contrast, the latter is characterized by low SiO₂ and K₂O contents，high MgO，TiO₂ and Al₂O₃ contents. The diabase dykes are geochemically characterized by significant enrichment of Rb，Ba，Th and slight depletion of Y and Yb coupled with similar trace element spidergrams to midocean ridge basalts. The basalts exhibit high TiO₂ and low K₂O contents, typical feature of a low potassium tholeiite series. Additionally, they display fractionation of LREE from HREE fractionation, i.e,enrichment of LREE no significant Eu anomalies and near flat REE curves,resembling oceanic basalts. In combination with geochemical characteristics, regional geology and tectonic environment, we propose that the Chayong ophiolite was possibly produced in an ocean basin setting.

Key words:  Qinghai-Tibet Plateau, the North Qiangtang basin, ophiolite, Ganze-Litang suture zone, ocean basin setting