青藏高原东北缘清水河流域地貌特征及其构造意义

Geomorphic features of the Qingshui River Basin and their significance for the northeastern margin of the Qinghai-Tibet Plateau

新生代以来,受印度板块与欧亚板块剧烈碰撞汇聚的影响,青藏高原快速隆起,其构造变形不断向北东扩展、挤出,造就了清水河流域及其周缘独特的构造地貌格局。通过对清水河流域构造地貌的研究,可以揭示新生代晚期以来青藏高原东北缘变形机制和地貌演化过程。本文基于30 m分辨率DEM数据,利用ArcGIS 10.2软件对清水河流域地貌参数进行提取,精确计算了22条子流域的河长坡降指标(SL)及Hack剖面、面积-高程积分(HI)、流域不对称度(AF)以及盆地延伸率(Re)这4种地貌形态指数,定量获取了清水河流域的地貌形态特征,再结合4个参数求得各子流域的相对活动构造指数(Iat),对研究区的相对构造活动性程度进行分析。得到以下结论:(1)研究区SL值分布在70.1~353.9之间,表明整个流域内构造活动性存在区域差异且整体活动变形程度较高;(2)受海原断裂带和香山-天景山断裂带的影响,研究区西岸流域HI和AF指数的平均值大于东岸,Re指数的平均值小于东岸,表明西岸构造活动性大于东岸;(3)研究区相对活动构造指数(Iat)处于第一、二级的面积达到80%,主要分布在西岸,表明整个流域的构造活动性强烈,且展现由东向西活动性逐渐增强的趋势。同时结合相关地质资料综合评估流域构造活动状态,并据此对河流发育阶段以及构造运动进行分析。

Since the Cenozoic era,the Tibetan Plateau has risen rapidly under the influence of intense collisions and convergence between the Indian Plate and the Eurasian Plate.Its tectonic deformation has continued to expand and extrude to the northeast to create a unique tectonic geomorphological pattern of the Qingshuihe River Basin and surrounding areas.Research on the tectonic geomorphology of the Qingshuihe River Basin can reveal the mechanism of deformation and geomorphological evolution of the northeastern margin of the Tibetan Plateau since the late Cenozoic.In this study,we used DEM(digital elevation model)data at a resolution of 30 m with ArcGIS 10.2 software to extract the geomorphic parameters of the Qingshuihe River Basin.We accurately calculated the four geomorphologic indices of the stream length-gradient index(SL),Hack profile,hypsometric integral(HI),and the asymmetry factor(AF)and elongation ratio(Re)of the drainage basin to obtain its quantitative geomorphic characteristics.Following this,we obtained the index of relative active tectonics(Iat)of each sub-basin by combining these four parameters,and analyzed the degree of relative tectonic activity in the study area.The following conclusions were obtained:(1)The distribution of SL values in the study area ranged from 70.1 to 353.9,indicating that there were regional differences in structural activity,and large deformations were observed throughout the basin.(2)Under the influence of the Haiyuan fault zone and Xiangshan-Tianjingshan fault zone,the average values of the HI and AF indices in the west bank of the basin were higher than those in its east bank,while the average value of Re was lower than that in the east bank.This suggests that tectonic activity in the west bank was more intense than in the east bank.(3)The index of relative active tectonics(Iat)of the study area was of the first and second orders,80%of which was distributed in the west bank.This indicates that tectonic activity was strong in the entire basin,and gradually increased from east to west.Furthermore,we used the relevant geological data to comprehensively assess tectonic activity in the basin,and used it to analyze the development of the river and tectonic movement.