Evidences from Geochemistry and Zircon U-Pb Geochronology of Volcanic Rocks of Yeba Formation in Demingding Area,the East of Middle Gangdise,Tibet

Abstract

The dacite of the Yeba Formation in Demingding,Tibet is dated(192.7±1.3) Ma by zircon SHRIMP U-Pb dating,representing the age of the formation in the area.The dacite of the Yeba Formation was formed in Early Jurassic,nearly the same time as that of volcanic rocks of the Yeba Formation in Dazi regions.The study of the features of rock combination and geochronology shows that the Yeba Formation is made up of shallow andesite,dacite,rhyolite,acid tuff with little clastic rock and carbonate rocks,and can be divided into upper,middle and lower parts.Geochemical characteristics illustrate that the rock of the Yeba Formation is the acidic volcanic rock,and may be a product of the northward subduction and reduction of the Yarlungzangbo ocean,and formed in the island arc environment.