内蒙古乌海断陷岗德尔山西麓断裂晚第四纪特征分析

岗德尔山西麓断裂是乌海断陷的一条控盆边界断裂。通过野外地质调查、构造剖面解析结合浅层物探、地球化学探测,综合对断裂的第四纪活动特征进行分析和研究。结果显示,岗德尔山西麓断裂整体走向NNE,倾角60°~80°,具有成束成带发育特点,是一条全新世活动断裂,表现出以拉张为主的活动特征。

Late Quaternary Activity Characteristics of Western Piedmont Fault of Gangdeershan in the Wuhai Fault Depression, Inner Mongolia

The western piedmont fault of Gangdeershan is a basin-controlled fault in the Wuhai fault depression. Based on field geological surveys, structural section analysis, and shallow geophysical and geochemical explorations, we analyzed the characteristics of the late Quaternary activity of this fault. Through field geological investigation, fault tracing, and structural profile analysis, we determined that the western piedmont fault of Gangdeershan extends north to south, with the northern end at Guanyinsi, Wuhai city, the southern end at Sandaokan, and further south the presence of a hidden fault. The overall strike of the fault is NNE, the dip angle is 60°~80°, the fault throw is 10~100 cm, and it has both bundle formation and zone formation characteristics. The tectonic activity is strong in the study area, and the elevation difference between the sides of the basin and the mountain is about 400 m. We found the Holocene alluvial sand and gravel deposits to be faulted. The study area is located in the earthquake-free zone and the stress-adjustment transition zone between the northern and southern earthquake areas, and there is a possibility of moderate earthquake activity in the future. Shallow geophysical and geochemical explorations also reveal obvious abnormal changes in the location of faults, and confirm the existence of the fault. The shallow geophysical exploration results show obvious stratigraphic position change and the fault characteristics of bundle formation and zone formation. In addition, most of the faults are high-angle normal faults, and the faults tend to be western. Geochemical surveys mainly employ two methods:soil radon and soil mercury analysis. Based on the above results, we consider the western piedmont fault of Gangdeershan to be a Holocene active fault characterized by tension.