The Tectonic Landform Features And Evolution Of The Middle Reaches Of The Yalong River

The middle reaches of Yalong River is located in the Western Sichuan Ganzi district andLiangshan district, its landforms belongs to Sichuan Plateau,which is the easternQinghai-Tibet Plateau to the Sichuan Basin of the country second rungs，its tectoniclandforms is complex.based on the work of former people on the region and mentor research topic，via thefield observation and analysis of the DEM of this district and synthenize neotectonicsmaterials， the author has a regionalization of the tectonic landforms,which is divided intosub zones of northern Yajiang graben tectonic landforms and southern radial ladder tectoniclandforms.Each sub region develops three planation surfaces and wide valleies, five to seventerraces.three planation surface s， of4800m、4400-4700m、4000-4300m in elevation,takes shape around20Ma、 N₁³、 N₂²。T hree wide valleys,of different elevation，takeshape in Q12、Q₁³、Q₂¹。Terraces in Yajiang sub zone are accumulation terrace,some arerock-seated terrace; in jiu long sub zone are rock-seated and erosional terrace，few areaccumulation terrace.they developed in Q41、Q₃³、Q₃³、Q₃²、Q₃¹、Q₃¹、Q₂³。Other layered landform developed in this area are glaciers near the top of the mountainand five bedrock cavern in Jinping areaThrough the comparison of the planation surface、terrace and their times、uplift andrising rate，the author has found that tectonic movements in these zone are synchronized,butthe uplift and rising rate of Ya jiang sub zone significantly below the jiu long area,while T6,T7terrace did not develop in Yajiang district。It indicates that the tectonic movementfrequency and strength in Ya jiang district is far less than the jiu long area, at the same timetwo tectonic movement has exacerbated the trend。Via the analysis of the time、the elevation and neo tectonic of the stratified relieve in the middle reaches of The Yalong River，the author establishes the tectonic evolution of thearea，from the disintegration of the unified planation surface in3.6Ma to the end ofNeogene，three planation surfaces developed in this area. Then to the early MiddlePleistocene，t hree wide valleys formed； since the early Pleistocene epoch to today, five toseven terraces are developed.