银川盆地东缘黄河断裂展布特征新认识

    New understanding of the distribution characteristics of the Yellow River fault on the eastern margin of Yinchuan Basin

    • 摘要: 作为宁夏北部重要的区域性断裂之一,黄河断裂控制了银川新生代断陷盆地形成与演化,是研究银川平原地震活动及地热资源富集规律不可避免的关键点之一。目前,专项针对黄河断裂的研究较少,以地表调查为主,局部地区开展了浅层地球物理勘探。本文以地质露头资料为线索,基于区域1:20万重力资料,利用小波分界、斜导数等地球物理数据处理技术,清晰刻画出黄河断裂具有“雁行式平面展布特征,据此将断裂划分为灵武段、临河段、月牙湖段与礼和段4个亚段;临河段与灵武段的CSAMT资料揭示黄河主断裂及其次级断裂由东向西呈逐级下掉的“阶梯状,具有明显的“分级特征。黄河主断裂下切深度直抵上地壳,剖面上与次级规模断裂组合形态呈现典型的“扫帚状,各条断裂“上陡、中缓、下陡的“座椅式空间赋存形态明显。与已有研究成果对比发现,二者之间存在展布特征、展布位置、展布关系3方面的差异。

       

      Abstract: As one of the important regional faults in northern Ningxia, the Yellow River fault has controlled the formation and evolution of Yinchuan Basin. This fault is one of the inevitable key points for studying the law of seismic activity and geothermal resource enrichment in Yinchuan plain. At present, the study of the Yellow River fault is very insufficient, and the work is mainly concentrated on surface survey with shallow geophysical exploration in some areas. In this paper, the authors used geological outcrop data as clues and, based on regional 1:200000 gravity data, used advanced geophysical data processing techniques such as wavelet demarcation and oblique derivative to clearly depict the phenomenon that the Yellow River fault has obvious characteristics of "flying geese" plane distribution. The fault is divided into four sub-segments: Lingwu section, Linhe section, Yueyahu section and Lihe section. The CSAMT data of Linhe section and Lingwu section reveal that the main fault and its secondary faults of the Yellow River descend gradually from east to west, i.e., "staircase", with obvious "grading" characteristics. The undercut depth of the Yellow River main fault reaches the upper crust, and the combination of the secondary-scale faults on the profile exhibits a typical "broom" shape. The "seat-like" space of "upward steep, moderately gentle, and downward steep" of each fault is obviously present. Compared with the existing research results, it is found that there are three differences between them, i.e., spreading characteristics, spreading position, and spreading relationship.

       

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