海原断裂带中东段地貌差异及其成因探讨

TOPOGRAPHIC VARIATION ALONG THE MIDDLE-EAST SEGMENT OF HAIYUAN FAULT ZONE AND ITS IMPLICATIONS

以定量化地形因子为切入点的构造地貌学方法已成为活动构造研究的有效手段,被广泛用于定性或半定量解析地貌对新构造运动的响应及其演化过程。针对海原断裂带中东段现今地貌差异,以SRTM 90m分辨率DEM为基础,利用ArcGIS软件和Matlab程序脚本,提取了海原断裂带中东段高程、坡度、地形起伏、地形侵蚀以及河流陡峭系数等地形因子。从空间分布上看,上述各项地形因子沿断裂走向均呈现"西高东低"的整体分布特征。西段海拔高、坡度陡、起伏大、侵蚀强、抬升快,中段和东段海拔低、坡度缓、起伏小、侵蚀弱、抬升慢,此外,在断裂带的东南尾端呈略微增加趋势,达到小范围内的峰值。在此基础上,通过对比分析地形因子与年降水量、基岩岩性,初步探讨了构造与降水、岩性等因素对地形地貌的控制作用,认为不同降水条件对地貌后期改造起显著作用,基岩岩性与现今地貌之间并无显著关系,该区域地貌类型主要受构造抬升差异所控制。沿断裂带走向上的现今地貌差异表明,西段处于相对快速的构造隆升和强挤压造山构造背景,中段由于受到黄河下切及河流冲积作用影响,地貌参数记录的抬升特征并不显著,而东段则反映出大型断裂带尾端挤压调整效应。

Tectonic geomorphology introduces the quantitative topographic factors to describe and characterize the landform in real world, which is accepted as one efficient approach in neotectonics study now. More and more qualitative and quantitative researches have been implemented to delve into the response of surface topography to tectonic activity, or discuss the further subsequent geomorphology evolution. The various topographic characteristics along the middle-east segment of the Haiyuan Fault, which is located on the northeastern margin of Tibet plateau, indicate the different geotectonic backgrounds and evolution processes. Five quantitative topographic factors （i.e. elevation, slope, local relief, residual relief and channel steepness）derived from 90-m-grid SRTM DEMs all demonstrate higher values on the western section, lower values on the eastern section and middle section as well. However, all factors slightly increase to local peak values at the southeastern tailing end. Combining with average annual precipitation and geologic mapping, we discuss the basic mechanism about how geotectonic, climate and bedrock type would impose and build up various landforms. As demonstrated by our analysis our analysis, the precipitation is thought to aggravate the surface erosion and accelerate the landform evolution, and there is no significant correlation between the distribution of topographic factors and the bedrock type. Statistic result indicates the relative strong extrusion uplift on the western section. The middle part is a transitional zone and affected by Yellow River incision and widespread fluvial terraces. The influence of compressive folding at the southeastern tail of large strike-slip fault is also revealed by topographic variations.