Longitudinal profile analysis of rivers draining edges of the Tibetan Plateau and its geomorphology implications

River systems are the main external driving force to transform the plateau landscape,and their morphological patterns record the growth of orogenic belt. The information of regional tectonics and climate can be obtained by extracting river geomorphology. At present,the study of river profiles around the margins of the Tibetan Plateau is mainly focused on the southern,southeastern and eastern edges. The similarities and differences in the development of rivers at different locations of the plateau edge have not been studied. In this study,we selected the major rivers in northern margin(West Kunlun-Altyn),northeastern margin(Qilian Mountain range),and southeastern margin(Sanjiang),and southern margin(Himalaya Mountain Range)to conduct a comparative study of river geomorphology,and to obtain quantitative regional tectonic and climatic information through longitudinal river profile analysis. The results show that the steepness of the rivers is associated with relief of the region: it increases significantly when they flow through the plateau edges,while the steepness is relatively low on both sides of the plateau edge. The rivers flowing through the northern edge have a steep increase in slope at the plateau edge,while the rivers in the northeastern,southeastern and southern edges are relatively gentle. Taken together,the knickpoints are mainly located at the plateau edge,indicating that the river incision is confined to the plateau edge and the migration of the knickpoints is limited. For a geomorphic unit as large as the Qinghai-Tibet Plateau,it is biased to analyze the timing of plateau uplift by river morphology under the steady-state assumption. The high-elevation,low-relief surfaces on the southeastern edge of the Tibetan Plateau may have formed under the action of gentler in stream flow systems and evolved to their present-day outflow state during subsequent river raids and other processes.