Propagating uplift controls on high-elevation, low-relief landscape formation in Southeast Tibetan Plateau

High-elevation, low-relief surfaces are widespread in many mountain belts. However, the origin of these surfaces has long been debated, with previous studies proposing that they either represent a relict low-relief surface, uplifted and eroded by a wave of upstream incision instigated by a Cenozoic increase in rock uplift, or that they formed by tectonic shortening and consequent drainage reorganization. In particular, the Southeast (SE) Tibetan Plateau has extensive low-relief surfaces perched above deep valleys and in the headwaters of three of the world’s largest rivers (Salween, Mekong and Yangtze). Various geologic data, synthesized low-temperature thermochronologic data, and geodynamic models show that many mountain belts grow first to a certain height and then laterally in an outward propagation sequence. By translating this information into a kinematic propagating uplift function in a landscape evolution model, we propose that the high-elevation, low-relief surfaces in the SE Tibetan Plateau are simply a consequence of mountain growth and do not require a special process to form. The propagating uplift forms an elongated river network geometry with broad high-elevation, low-relief headwaters and interfluves that persist for tens of millions of years, consistent with the observed geochronology. We suggest that the low-relief interfluves can be long-lived because of their unusually/unproportionally small drainage area in comparison with the large mainstem rivers. The propagating uplift also produces spatial and temporal exhumation patterns and river profile morphologies that match observations. Our modeling therefore reconciles geomorphic observations with geodynamic models of uplift of the SE Tibetan Plateau, and provides a simple mechanism to explain low-relief surfaces observed in several mountain belts on Earth.