Spatial and temporal pattern of erosion in the Three Rivers Region, southeastern Tibet

- 54 new thermochronometric ages from southeastern Tibet are presented.
- Inferred erosion rates decrease from west to east.
- Inferred erosion rates show spatial and temporal variations from south-to-north.
- Locus of fast erosion migrates northwards along the Salween and Mekong.
- An active coupling between river incision and tectonics is inferred.

Convergence and collision between India and Eurasia have produced the Tibetan Plateau, which stands 5 km high over a region of 3 million km2. Its southeastern margin lies in the restraining bend between the Sichuan basin and the Eastern Himalayan Syntaxis. In this region three parallel rivers, the Salween, the Mekong and the Yangtze, carve gorges up to 3 km deep. Along the longitudinal profiles, large-scale knickzones, defined by very high steepness, correspond to the gorges of the Salween and Mekong. The Yangtze, instead, has a nearly linear profile upstream from its first big bend. New low-temperature thermochronometric data reveal a complex pattern of erosion in the Three Rivers Region. From the Salween in the west to the Yangtze in the east the magnitude and rate of erosion decrease. From south-to-north erosion rates exhibit variable gradients in space and time. Along the Salween and the Mekong a northward increase of erosion rate is followed by a decrease with additional distance to the north. Variations of erosion rate in time are characterized by a deceleration along the Salween and a general deceleration with local acceleration along the Mekong. This pattern, together with river profile analysis, is best explained by active coupling between tectonics and river incision related to the indentation and northward migration of the corner of the Indian continent.