1.Key Laboratory of the Earths Deep Interior|Institute of Geology and Geophysics|Chinese Academy of Sciences|Beijing |100029；
2.Institute of Tibetan Plateau Research|Chinese Academy of Sciences|Beijing |100085
The southeastern Tibetan Plateau possesses unique low and continuous relief，where the Jinsha River，Yalong River and Dadu River are developed. Large quantities of lacustrine deposits，called Xigeda，are well preserved in the trunk and tributaries of the Jinsha River. Using cosmogenic nuclide burial age dating we determined the deposition age of the lacustrine deposits： 158～134 Ma. Studies of detrital zircon UPb age distribution related to the upstream of the Jinsha River show that the age spectrum is mainly derived from its course in the Qiangtang sedimentary block together with some characteristics of north China craton，which differs obviously from the provenance of the Yalong River. UPb age distributions related to Xigeda and underlying sand suggest westward stream flow from Panzhihua to Taoyuan，which was in the opposite direction of the current stream flow. The results further suggest changes of stream flow direction from Taoyuan to Panshihua accompanying with the drainage of the Xigeda paleolake，and the Jinsha River started to flow east.