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Abstract:
We reconstruct the incision history of bedrock rivers based on inverse modeling of the long profile of a river channel and the low-temperature thermochronological data. Our approach first infers an erodibility-dependent incision history through a linear inversion of the channel elevations of the river. Then to calibrate the reconstructed incision history in the geological timescale, we constrain the erosional efficiency by optimizing the erosion process of the river catchment using a Bayesian analysis, such that the exhumation and cooling paths of bedrocks in the catchment conform to the observed thermochronological ages. We apply this approach to estimate the incision history of the Three Gorges, Yangtze River in East Asia. We modeled the incision histories of three tributaries on the mainstem Yangtze River near the eastern end of the Three Gorges area, assuming that the gorge incision was driven by increased upstream drainage area of the Upper Yangtze (Scenario 1) or local tectonic uplift (Scenario 2). The results of both scenarios suggest an early Miocene onset of the incision of Three Gorges, that is, 18 ± 6 Ma or 21 ± 4 Ma, respectively. During the Pliocene, our models suggest a significant decrease in the gorge incision rate. By comparing the estimated gorge incision history to the late Cenozoic denudation of the eastern Tibetan Plateau and the regional climate change, we suggest that the incision of the Three Gorges has been heavily affected by the development of the Upper Yangtze River and the East Asian monsoon.
