Do fault systems impede fluvial incision in active orogens?

AbstractIt is widely accepted that tectonism generally enhances the incision of river drainage systems. However, the question as to why on a global-scale, rivers have not incised further or more deeply into orogenic plateaus to destroy terranes over long-timescales remains ambiguous. Here we hypothesize the diverse nature of regional tectonics could have impeded river erosion to maintain plateau topography, taking Yarlung River in southern Tibetan Plateau as a case. We constrain the incision history and effect of a N-S trending tectonic rift on the evolution of fluvial incision by the low-temperature thermochronology. Results show a fast cooling since ~ 7 Ma focused near the rift structures, but markedly reduced cooling in upstream and downstream regions. This indicates that the steep flank fault of the rift controlled local rapid exhumation as a knickpoint since that time. This coincides with an episode of rapid exhumation of Eastern Himalaya Syntaxis downstream. We propose that these two co-phased tectonic systems with the accelerated late Miocene extension of southern Tibet prevented upstream migration of river knickpoints, and impeded fluvial incision. Our study highlights that the activity of fault systems may hinder regional erosion, thereby facilitating the preservation of topography and high plateau in active orogenic belts.