Petrogeochemical characteristics and tectonic setting of the Wandaohu ophiolite mélange, Jinshajiang sutnre, Tibet
金沙江缝合带弯岛湖蛇绿混杂岩带的岩石地球化学特征及其构造背景

The Wandaohu ophiolitic mélange is an essential component of the western part of Jinshajiang suture zone. The ophiolites are mixed in the Upper Triassic metaclastic rocks which interlayered by metavolcanic rocks. The main components of ophiolites are mafic-ultramafic complexes, in which metaperidotites, metacrystal-stacking gabbros and concomitant island-arc granites are included. Geochemical data indicate that most of the ophiolitic mélange are tholeiites of low-Ti (island arc-back arc) type and enriched middle-ridge type (E-MORB). The basic extrusive rocks, diabase veins accompanied with above mentioned ophiolites could be classified as interplate rift-type alkaline basalts and other transitional series. Metagabbro, dated at 232±11Ma with Sm-Nd isochron, represents the formation age of the mafic-ultramafic complexes and initial metamorphic age of the subduction of oceanic crust. The radiolarites were found in the sillcalites which overlained ophiolite. The age of the radiolarites is between Late Latin stage of Middle Triassic and Early Kaning stage of Late Triassic, indicating that the Wandaohu mafic-ultramafic complexes may form in the Middle-Triassic poly-islands oceanic basin or back-arc basin tectonic setting.