Planation surface and valley shoulder elevation in different parts of the middle reaches of YZR from River capture in the middle reaches of the palaeo-Yarlung Zangbo River

There are 51 tributaries in the middle reaches of the Yarlung Zangbo River (YZR), and the confluences of 87% of the tributaries west of Jiacha Gorge are high-angle or perpendicular, reflecting the anomalous development of these tributaries. In this paper, field investigation and digital elevation model (DEM) methods were used to analyse the causes of this anomalous phenomenon, and it was found that there was a watershed in the area of the Jiacha Gorge. The palaeo-YZR west of the Jiacha Gorge flowed westward before the early Pleistocene into the Zada, Zhongba, Jilong and Gamba–Dingri palaeolakes, which featured a large amount of total accommodation space in the western Qinghai–Tibet Plateau; thus, this river was a continental river. With the intensification of the collision between the Indian plate and the Eurasian plate, the Qinghai–Tibet Plateau experienced rapid uplift and formed a landscape with high elevations in the west and lower elevations in the east, promoting the headward erosion of the eastward-flowing river. During the early Pleistocene, the river east of the Jiacha Gorge crossed the watershed and captured the palaeo-YZR, causing a reversal in the flow direction of the palaeo-YZR.

雅鲁藏布江（Yarlung Zangbo River, YZR）中游共计51条支流，佳加峡以西区域内87%的支流交汇角为高角度或垂直角度，反映出此类支流的发育存在异常特征。本文采用野外调查与数字高程模型（Digital Elevation Model, DEM）方法，对该异常现象的成因开展分析，研究发现佳加峡区域存在一处分水岭。早更新世之前，佳加峡以西的古雅鲁藏布江曾向西径流，注入札达、仲巴、吉隆及冈巴-定日古湖；彼时青藏高原西部具备充足的总沉积可容空间，因此该古河属于内陆河流。随着印度板块与欧亚板块碰撞作用加剧，青藏高原快速隆升，形成西高东低的地貌格局，推动了东向河流的溯源侵蚀。早更新世时期，佳加峡以东的河流穿越该分水岭，袭夺了古雅鲁藏布江，致使古雅鲁藏布江的流向发生反转。