REVIEWS ON RESEARCHES OF TIMING OF THE YANGTZE DRAINING THE TIBETAN PLATEAU TO THE EAST CHINA SEA

"When the Yangtze was formed" has become a century question both to geologists and geomorphologists, but a well-constrained answer is still on its way. Enormous geomorphological and sedimentary features, left by river piracy, reversal, and incision in the river section from Shigu town in Yunnan to Yichang City, have been widely studied to reconstruct Yangtze drainage evolution history and timing of the capture of the upper Yangtze from south-flowing into east-flowing. However, the river sedimentation and geomorphology are very complicated by themselves, and exposed to external reformation, leading to great difference in paleo-geological and paleo-geomorphological interpretations. There is no consensus on timing of the capture of the Jinsha River from south-flowing into east-flowing, and timing of the Yangtze channeling through the Three Gores area. It was therefore deduced that the Yangtze could be a very old river having existed since the Tertiary or the Cretaceous, or a very young river only hundreds of thousand years old.
Microprobe dating of single detrital minerals, particular zircon and monazite, is considered to be a powerful tool in provenance study. Lots of successful case studies have been reported in foreign literatures to reconstruct drainage evolution history and tectonic activities in the drainage basins through detailed studies of zircon/monazite geochronology of the sedimentary succession in the river-mouth or marine realm. The dating method of electron microprobe (EMP) is rapid and inexpensive, although its resolution is relatively low, and can be widely applied to primary study of drainage evolution. EMP Th(U)-Pb ages of monazite grains of the late Cenozoic strata in the Yangtze River mouth, provide a key constraint on timing of the Yangtze formation in~2.58 MaBP, which follows within the initiation time of the Yangtze in late Pliocene to early Pleistocene and is proposed by lots of river sedimentological and geomorphological studies. Laser ablation-ICPMS is a newly developed microprobe dating method of minimal sample preparation, low cost and high resolution, and thus can possibly date large volume of single detrital minerals for provenance study. The perspective should be promising when the method is applied to provenance and tectonic correlation to reconstruct the drainage evolution of the Yangtze, a big and complex drainage basin.