基于GIS技术研究贺兰山、罗山洪积扇特征与山脉抬升关系

The Relationship between Alluvial Fans and Mountain Uplift in Helanshan and Luoshan Mountains in Northwestern China based on GIS Technique

西北是我国洪积扇发育的典型区域,特别是青藏高原东北缘,由于独特的气候条件,洪积扇保存良好,同时受高原隆起影响,此处构造多样,是研究洪积扇与构造运动关系的天然实验室。基于3S系统在地学应用中的发展,通过遥感图像解译。GIS空间分析等手段,探讨了青藏高原东北部地区典型山脉的洪积扇地貌特征:贺兰山山前洪积扇宽长比、扇顶角大,山麓弯曲明显,扇面坡度陡;罗山山麓平直,扇坡度陡,宽长比小。利用MATLAB、GRAPHER等统计分析了洪积扇细部特征与构造运动,特别是均衡抬升的响应发现:山前盆地沉降越剧烈,洪积扇扇面积与流域面积之比越小;构造活动年代越老,均衡抬升量越大,扇面宽长比越小,扇体横剖面越平直,洪积扇扇面积与扇高差之比越大,扇面积增长至75 km2,不再受控于流域情况;构造活动年代越新,山麓弯曲度、沟口间距越小,沟口与沟口高地高差越小,扇宽越大;就构造活动强度来说,山体构造抬升越剧烈,扇面坡度越大,扇面积越小。

In recent years, more and more technology was applied to the study of geomorphology. Because of its progressiveness and effectiveness, GIS has become an important part of the alluvial fan research. In this paper, the geomorphological features of the alluvial fans in aortheast margin of the Tibetan Plateau have been analyzed with remote sensing image interpretation, GIS spatial analysis, et al. Based on the tectonics and geomorphological features, we found that in Cenozoic era, the Helan Mountain underwent a strong tectonic activity in Eocene, the mountain uplifted and the Yinchuan Basin sank simultaneously. The closer to the fault, the more obviously the mountain uplifted. As a consequence, there was differential tectonic uplifting between the east and the west pediments of Helan Mountain： the uplifting in western part was weaker than the eastern one. Alluvial fans at Helan Mountain often have larger size, bigger width to length ratio, and the fan angle is bigger than others, also, the fan slopes are steeper, and the feet of the mountain are more bending. When it comes to Luoshan Mountain, the research shows that in the Quaternary, Luoshan Mountain, where there is no basin in front of, uplifted intensively, alluvial fans at Luoshan Mountain have steep slopes and small width to length ratio. The feet of the mountain are straighter relatively. Research on alluvial fans at basins reveals how alluvial fans are affected by faulted basins, with matlab, grapher and other statistical analysis methods, it is found that the more the Piedmont Basin sinks, the bigger the radio of catchment area to the fan area is, At the same time, the later uplift is, the straighter the foot of the mountain results. In the meantime, the spacing of the ravine and the width of the fan is shorter than others. The geomorphologic features of the alluvial fan are influenced by both the tectonic uplifting and the isostatic uplifting of the mountain ： the more intense tectonic activity is, the steeper the slope of the fan is, the smaller the fan area exhibits. As the isostatic up has a larger the width to length lifting increase with time, the fan cross-section bends more obviously, and the fan radio, while the amount of isostatic uplifting grows to a certain extent, the height difference will be stable, the area of the fan increases seldom by the increased catchment areas. Only the length and width are the key factors. With the fan area increasing, a new alluvial fan forms in the direction away from the mountain.