Growing attention has been focused on the extensive igneous rocks in eastern Tethyan Himalaya，southeastern Tibet．A suite of bimodal volcanics assemblage composed of dacite and dolerite are distributed in the Sangxiu formation in the Longzi area，south Tibet by the author．SHRIMP U Pb zircon age of 134.9±2.3 Ma has been obtained from dacite．the geological age of the dacite is Early Cretaceous，coeval with the peak age of the Comei—Bunbury LIP．Geochemical analysis indicates that the dolerites are enriched in TiO2，TFeO and P2O5，HFSE loss is not obvious，and the dacite are characterized by Th，Nb，Zr，Y ，enrichment and P，Ti trough，obvious loss of Eu．These dolerites could be the products of interaction between lithosphere and mantle plume，and the dacite originated from the anatexis ensialic continental crust．This proposes that this interaction could play an important role in understangding the key geological problems concerned with tectonic evolution of Yarlung Zangbo Oceanic Basin．