贺兰山构造带深部电性结构与动力学机制

    Deep electrical structure and dynamic mechanism of the Helanshan tectonic belt

    • 摘要: 贺兰山构造带是华北克拉通西部中生代以来的典型陆内构造变形区域。对野外采集的大地电磁数据进行分析与反演,获取贺兰山构造带的深部电性结构。结果揭示,贺兰山构造带上地壳发育逆冲推覆构造,中下地壳存在完整且厚实的地壳根。大地电磁测深剖面显示,贺兰山构造带西北部的河套盆地深部存在向NW方向上涌的低电阻率通道,东南部的银川地堑与鄂尔多斯盆地存在地幔物质上涌的特征。贺兰山构造带晚侏罗世WNW—ESE向挤压的褶皱冲断带与白垩纪以来的构造隆升过程和西太平洋板块俯冲作用相关,记录了早期深部地幔物质向NW方向上涌的现象。在新生代西太平洋板块持续俯冲与回撤过程中,以及青藏高原向东北缘扩展的联合控制下,贺兰山构造带的邻区深部地幔物质向地壳上涌,导致鄂尔多斯盆地深部岩石圈发生减薄,地幔物质与地壳发生交代作用,在刚性的贺兰山块体限制下,形成现今的盆山构造格局。

       

      Abstract: Helanshan tectonic belt is a typical intracontinental contractional deformation area of the western North China Craton since the Mesozoic. Based on the analysis and inversion of magnetotelluric data collected in the field, the deep electrical structure of the Helanshan tectonic belt was obtained. The results reveal that the Helanshan tectonic belt develops the thrust−nappe structure in the upper crust, and there are intact and thick crustal roots in the middle and lower crust. The magnetotelluric sounding profile shows that there is a low resistivity channel upwelling to the NW of the Helanshan tectonic belt, and there are mantle material upwelling characteristics in the Yinchuan Garben and Ordos Bain in the southeast. The Helanshan tectonic belt of the Late Jurassic WNW—ESE compressive fold−thrust belt and the Cretaceous tectonic uplift process are related to the subduction of the Western Pacific Plate, which records the early upwelling of deep mantle material in the NW direction. Controlling by the Cenozoic Western Pacific Plate subduction and rollback and the Tibetan Plateau growth northward, the adjacent area of the Helanshan tectonic belt deep mantle material upwelling into the crust. Then, the Ordos Basin deep lithosphere thinned, forming the present basin and mountain tectonic pattern.

       

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