Timing of the Yangtze initiation draining the Tibetan Plateau throughout to the East China Sea: a review

The question of the Yangtze’s origins has been extensively researched by geologists and geomorphologists for more than a century, and a widely-accepted answer is still pending. Evidence of river piracy, diversion and incision in the upper river segment from Shigu town in Yunnan Province to Yichang City has been used to reconstruct the history of the Yangtze drainage system, and constrain the timing of the upper Yangtze diversion from south flowing to east, debouching into the East China Sea. There is much diversity in fluvial deposits and landforms even over small spatio-temporal scales in tectonic highly active regions. They are also liable to latter reworking by external forces, making their paleo-geographical interpretation a more complex and controversial matter. Based on evidence from fluvial strata and landforms, various hypotheses have been proposed with considerable discrepancies for the timing of the Jinsha River diversion from the south flowing into the east, and the timing of the upper Yangtze channeling through the Three Gorges area. The Yangtze was controversially assumed to be: (1) a very old river in existence since the Cretaceous and earlier, (2) a very young river that came into being only during the past several hundred thousand years, or (3) any age in between these two extremes. Techniques in microprobe dating of single crystalline grains have greatly improved, and they have been widely and successfully used in provenance studies, drainage evolution reconstruction, and tectonic history restoration through dating detrital zircon/monazite grains from the onshore/offshore deposits. The timing of the Yangtze formation was estimated at ca. 2.58 Ma based on analyses of time-series variation of EMP (electron microprobe) monazite ages in the late Cenozoic strata of the Yangtze delta. By revisiting fluvial deposits and landforms in the upper Yangtze drainage basin, some references also state the initiation time of the Yangtze at between the late Pliocene and early Pleistocene. This indicates that microprobe dating of single detrital mineral grains is an effective tool to study sedimentary provenance and reconstruct the evolution history of large rivers, like the Yangtze. Laser ablation-ICPMS, a newly-developed microprobe dating technique characterized by minimal sample preparation, low cost and high throughput, and high precision, makes it possible to date large volumes of single detrital mineral grains for provenance studies. Its application is expected to increase the precision of the timing of the Yangtze formation. __________ Translated from Marine Geology and Quaternary Geology, 2007, 27(2): 121–131 [译自: 海洋地质与第四纪地质]