DIFFERENTIAL UPLIFT ANALYSIS OF THE DOWNSTREAM REACHES OF YARLUNG ZANGBO RIVER BASED ON ASTER-DEM

The Yarlung Zangbo River in Tibet is the core area of the eastern tectonic knot. This paper aims to study the current uplifting status of the Big Bend Region at Yarlung Zangbo River. It uses the ArcGIS platform. The research teams calculate the ASTER-DEM30m area-elevation integral value of the Big Bend Region at the lower Yarlung Zangbo River. The Hypsometry Index is a method based on the digital elevation model to obtain the characteristics of river evolution and the corresponding response index of tectonic activity. It examines the uplift difference in the study area in combination with the basic data of structure, lithology, climate, Quaternary depositsand rivers. The results show that the uplift area with HI>0.43 is mainly located outside the Big Bend suture zone and its distribution is well coupled with the Ⅲ-grade planation plane in each block. While the distribution range of Lhasa fault uplift area with HI>0.60 is the largest, and the distribution area of the Gyalha Bair fault uplift area is the smallest, which is only distributed in a small range of the Big Bend Region. The eroded cutting area with HI < 0.43 is located at the Ⅰ and Ⅱ grade valley shoulders of the river and the mature area of rivers. The Linzhi-Paizhen section with HI < 0.35 mainly manifests as erosion and down cut. It is concluded that the tectonic compressive action still exists in the study area, and the influence of climate, rivers and fault zone density are generated under the tectonic setting. The above factors would gradually inhibit the tectonic uplift with the passage of time, and the promotion effect of erosion is different in different regions. When the tectonic effect plays a major role, fault block is dominated by uplift with HI>0.43. The influence of climatic action led to the uplift stagnation for Gyalha Bair and Namjagbarwa Mountains, with HI < 0.43. The Linzhi block with HI < 0.35 indicates that the intensity of erosion will increase under the influence of climate, rivers and fault zone density. So the area mainly manifests as erosion and down cut, with no sign of uplift. Therefore, under the combined influence of tectonics, climate, river development and fault zone density, the uplift function is gradually weakened from the outside to the inside of the lower reaches of the Yarlung Zangbo River Basin, and the differences in the local area are determined by the difference in the role of the influencing factors.