Spatiotemporal Characteristics Of Basin-wide Erosion Rates In The Northern Chinese Tian Shan And Its Controlling Factors

The geomorphological evolution and driving mechanism of active orogenic belts are one of the core contents of geomorphology.The quantification of erosion rates and its spatiotemporal characteristics are the key basis and prerequisite for research.Studying the spatio-temporal variation of erosion rate has always been a hotspot.In a sense,the key to controlling mountain evolution is erosion of mountains.The effect of surface erosion on the landforms of active orogenic belts varies greatly indifferent temporal and spatial scales.Therefore,quantifying erosion rates over various temporal and spatial scales is thus crucial for understanding the geomorphological evolution in active orogenic belts.Catchment-basin erosion rate helps to quantify the coupling relationship of topographic and landscape processes.The Tian Shan is one of the most important and large-scale young mountain in Central Asia.Due to long-term tectonic activities and surface erosion,the topography of the Tian Shan is complex and diverse.A series of north-south-flowing rivers developed in the northern Tian Shan.The rivers eroded the bedrock strata in the mountainous areas,and the debris transported by the rivers accumulated in the front of the mountain to form multi-stage alluvial fans.These rivers flow through similar stratigraphic units,tectonic units,and climate units.So they are ideal areas to explore the spatiotemporal characteristics and mechanisms of erosion rates in active orogenic belts.Nine rivers are selected as the research objects,as well as discuss the interannual scale erosion rate and its spatial characteristics of the northern Tian Shan.Based on the hydrological data from 1964 to 2011,we firstly estimate the sediment load in the basin(suspended load,bed load,solute load)and erosion rates.Furthermore,the main factors controlling the erosion of the northern Tian Shan catchment were further analyzed based on the characteristics of topography,vegetation,lithology and tectonics.Combined with the 10 thousand years and million years scale erosion/denudation/river incision rates in the northern Tian Shan.The spatiotemporal patterns of erosion rates in the study area and geomorphic evolution are discussed.The main understandings of this paper are as follows:(1)Through analysis of the hydrological data,the total sediment load of the 9rivers and catchment-basins in the the northern Tian Shan was obtained.The results are as follows:Sikeshu River(29.21×10~4 t/yr),Kuitun River(56.19×10~4 t/yr),Jingou River(89.82×10~4 t/yr),Manas River(368.14×10~4 t/yr),Taxi River(18.09×10~4 t/yr),Hutubi River(38.31×10~4 t/yr),Santun River(94.02×10~4 t/yr),Toutun River(31.24×10~4 t/yr),Urumqi Rive(11.5×10~4 t/yr).(2)Further based on the basin area and bedrock density of mountain catchments,the erosion rates of catchment-basins of 9 rivers were estimated,in order:Sikeshu River(0.12 mm/yr),Kuitun River(0.11 mm/yr),Jingou River(0.24 mm/yr),Manas River(0.30 mm/yr),Taxi River(0.11 mm/yr),Hutubi River(0.08 mm/yr),Santun River(0.22mm/yr),Toutun River(0.13 mm/yr),Urumqi River(0.05 mm/yr).The average erosion rate is 0.15 mm/yr.(3)Pearson correlation analysis of the climate,topography,lithology,vegetation,tectonics,and catchment-erosion rate,it was found that the catchment-basin erosion rate is more closely correlated with topographic factors(basin area and basin relief)and climatic variables(discharge,run off,run off depth,and mean temperature).These evidences indicate that topography and climate may be the main factors controlling erosion in the northern Tian Shan.(4)The results show that the average catchment-basin erosion rate of northern Tian Shan is?0.15 mm/yr.The erosion rates reported in this work are approximately consistent with the paleo-erosion rate of<0.5 mm/yr over the last 1.5 Myr derived from terrestrial in situ cosmogenic nuclide ¹⁰Be concentrations in the Kuitun catchment basin in the west part of the range.But these erosion rates are significantly smaller than the tectonic activity rate of several millimeters per year based on GPS measurements and geological and geomorphological records.This may indicate that the topographic evolution of the northern Tian Shan is far from equilibrium.Relatively arid climatic conditions may have limited surface erosion in the northern Tian Shan,resulting in a non-equilibrium state of mountain topography evolution.