CONSTRAINTS ON THE YANGTZE RIVER RUNNING-THROUGH TIME,USING Th(U)-Pb DATING OF MONAZITE

Neogene Yangtze drainage adjustment and timing of the Yangtze River running due east and due west have attracted great attention at home and abroad.Complexities of Yangtze drainage evolution have been well acknowldeged after studies of fluival sedimentology and geomorphology over a century,but the timing of the Yangtze formation is not well constrained.31 monazite samples from late Cenozoic deposits in the Yangtze River estuary were analyzed with electron microprobe dating technique.The statistical treatment of Th(U)-Pb ages revealed that the Yangtze River extended its drainage westward to the upper reach,especially through the Tibetan Pleteau around 2.58 MaBP.Following great progress in micro-analysis techniques of single detrital minerals,geochronology and micro-features of zircon and monazite will become a major method to study large drainage evolution and tectonic activities in the drainage basins.