祁连山东段石羊河流域及邻区地貌特征及其构造意义

摘要

Objectives:Because of the strong uplift of the Qilian Mountains since late Cenozoic,the drainage basins that derived from the mountain have undergone strong tectonic deformation,so the typical geomorphology characteristics of these drainage basins may indicate the strong tectonic movement in the region.Controlled by north Qilian Mountains fault and Qilian—Haiyuan fault,the eastern margin of Qilian Mountains which developed Gulang thrust nappe have undergone strong tectonic deformation and formed unique geomorphological characteristics,previous researchers studied the study region from the geological and geophysical view,while little concern was payed to the eastern Qilian Mountain from the geomorphological view.Methods:Based on ArcGIS spatial analysis,this study takes advantage of Digital Elevation Model (DEM) to extract macro landscape factors (such as Hypsometric Integral and Swath profiles) in the study area and combines rainfall and lithologic data to give systematic analysis to its geological significances.Results:The study shows it is the tectonic movement of the active fault but the lithologic factors and precipitation conditions that has strongly influenced on the regional geomorphic evolution;in addition,controlled by Huangcheng—Shuangta fault,Lenglongling fault and Lianhuaqiao fault,Gulang thrust nappe brings out high HI value,Hexibao—Sidaoshan fault,which lies on the east side of the Longshou hill,shows high HI value on its south side and relatively low HI value on its north side.Furthermore,the seven swath profiles indicated that the macrotopography is largely controlled the activities of the range—front faults.Conclusions:The results show that all the macro geomorphologic factors indicate that the eastern margin of the Qilian Mountains,even Xizang (Tibet) Plateau has been extending northward,and this study provide the geomorphic evidence that the north Qilian Mountains fault has extended into Hexi Corridor.%受祁连山北缘断裂和广义海原断裂等构造活动的控制和影响,祁连山东段发育了由多条挤压逆冲断裂组成的古浪推覆体构造,形成地貌起伏大并向北逐级降低的独特构造地貌特征.本文基于ArcGIS空间分析技术,利用数字高程模型(DEM)系统提取了祁连山东段(造山带内部与河西走廊盆地)的宏观地貌因子(如面积—高程积分和条带状剖面)并综合分析其所蕴含的地质意义.研究结果表明,区域地貌演化过程主要由构造变形控制,而并非岩性差异和降雨条件等因素.研究区内的皇城—双塔断裂、冷龙岭断裂以及武威盆地南缘断裂所控制的古浪推覆体具有较高的HI值,龙首山东段的河西堡—四道山断裂南侧显示HI高值、北侧显示HI低值,表明祁连山东段存在由南向北的挤压扩展演化过程,这可能与祁连山北缘大断裂向北的扩展以及阿拉善块体向南俯冲作用有关;提供了祁连山东段向河西走廊内部挤压扩展的地貌证据.