鄂尔多斯地块北部至阴山造山带深部电性结构特征研究

Study of deep electrical structure along a profile from northern Ordos block to Yinshan orogenic belt

在SinoProbe-01项目的资助下,完成了一条跨越鄂尔多斯地块北部、河套断陷盆地和阴山造山带的大地电磁剖面,剖面长约440 km,共包括24个宽频测点和4个宽频一长周期联合测点.采用NLCG算法对TE和TM模式数据进行了二维反演,获得了该剖面的二维电性结构模型.结果表明:鄂尔多斯地块北部由浅至深电性结构比较简单,成层性较好,大体可分为低阻沉积盖层-高阻上地壳-低阻下地壳和上地幔顶部三层;河套断陷盆地和阴山造山带电性结构相对复杂,电阻率高低相间.鄂尔多斯地块北缘、河套断陷盆地以及阴山造山带区域的壳幔高导体可能与硫化物和部分熔融作用有关,而鄂尔多斯地块内部大规模的壳幔高导层可能是由高导矿物引起的.河套断陷盆地的沉降、阴山造山带的地势抬升和鄂尔多斯地块北缘东胜一杭锦旗一带的的隆起之间有着紧密的关系,它们的形成可能与区域伸展构造环境条件下的软流圈物质上涌有关.

Under the support of the SinoProbe-01 program in China, a magnetotelluric （MT） profile up to 440 km was deployed across the northern Ordos block, Hetao rift basin and Yinshan orogenic belt, which consists of 24 broadband MT sites among which 4 sites acquired simultaneously long period data. After inverting TM and TE data with NLCG algorithm,typical 2D electrical features of this profile are outlined. The results show that the electrical structure of northern Ordos block is relatively simple from top to bottom and are generally layered,which can be roughly distinguished into three layers as sedimentary cover of low resistivity, upper crust of high resistivity and lower curst and upper mantle of low resistivity; the electrical structure of Hetao rift basin and Yinshan orogenic belt are relatively complex, where the resistors and the conductors alternate with each other. Large scale bodies of high-conductivity in crust-mantle beneath the Ordos block probably represent high-conductivity minerals. However, the high- conductivity bodies in crust-mantle beneath the north margin of Ordos block, Hetao rift basin and Yinshan orogenic belt may be caused by sulphides and partial melting. The sedimentation of Hetao rift basin,uplifting of Yinshan orogenic belt and the rise of Dongsheng and Hanjin Banner area which lie in the north margin of Ordos block must be closely related with each other. Their formation may be highly relevant to the upwelling of asthenosphere material under the extensional tectonic background.