Incision of the Three Gorges, Yangtze River: Inversion of River Profiles and Low-Temperature Thermochronological Data

Abstract:

Incision of the Three Gorges has been suggested to create the link between the Upper and Middle Yangtze River, and therefore was potentially a key event during the drainage network reorganisation in East Asia. However, when the gorge incision started remains ambiguous. To estimate the age of the gorge incision, we modelled the uplift history of the channels of three tributaries relative to the mainstem Yangtze River in the Three Gorges area. Our approach assumes that the low-relief planation surface in the upper reaches of the tributaries represent the pre-incision landscape, which was in a topographic steady state. Time scale of the reconstructed channel elevation history is constrained by optimising the rock exhumation and cooling histories in the catchment, such that they conform to the observed thermochronological ages in the catchment. We tested two model scenarios of topographic history by fixing the elevations for either the tributary headwaters or base levels, and the results of both scenarios suggest an Early Miocene onset of the incision of Three Gorges, i.e., 18±6 Ma or 21±4 Ma, respectively. Considering the tectonic stability of the Three Gorges, we suggest that the incision was most likely driven by the drainage capture and flow reversal in the Sichuan Basin. Our estimate of the incision of the Three Gorges is coeval with the Early Miocene denudation of the eastern Tibetan Plateau, implying that incision of the Three Gorges was part of the drainage reorganisation of the Upper Yangtze River triggered by uplift of the eastern Tibetan Plateau.