Fault systems impede incision of the Yarlung river into the Tibetan plateau

Abstract

It is widely accepted that tectonics generally enhances river incision. However, why rivers have not incised further into orogenic plateaus to destroy terrains over long-time scales remains ambiguous. Here we hypothesize that the diverse nature of regional tectonics could have impeded river erosion, taking Yarlung River in Tibetan Plateau as a case. We constrain the incision history and effect of a tectonic rift on fluvial incision by low-temperature thermochronology. Results show focused cooling near the rift, but markedly reduced cooling in the upstream and downstream regions since ~7 Ma. This coincides with an episode of rapid exhumation of Eastern Himalaya Syntaxis downstream. We propose that these two co-phased tectonic systems resulting from accelerated extension of southern Tibetan Plateau prevented upstream migration of river knickpoints. Our study highlights that the activity of fault systems may hinder regional erosion, thereby facilitating the preservation of topography and high plateaus in active orogenic belts.