| The the Junggar Basin is located in the north of Xinjiang,and the Ulungu depression on its northern edge is NW trending.In order to study the characteristics of deep underground electrical structure in the the Junggar Basin,this paper uses the magnetotelluric sounding(MT)method to obtain the magnetotelluric sounding observation data within the 213 km range of a survey line in the Wulungu Sag area on the northern edge of the Junggar Basin.Through data refinement processing,impedance tensor GB decomposition,electrical axis analysis,and underground media dimensional analysis,the structural dimensional characteristics and electrical axis direction of the study area are obtained,Comparative analysis of different parameters was conducted under TM polarization mode.Finally,one-dimensional Occam inversion was conducted in the shallow 10 km range of the study area,and two-dimensional nonlinear conjugate gradient(NLCG)inversion with a regularization factor of Tau of 30 was conducted in the deep 100 km range.The inverted electrical structure model was obtained and verified.The results showed that the study area generally had good electrical structure characteristics,The shallow and central underground regions have good one-dimensional and two-dimensional characteristics.Although the electrical structure of the deep region is complex,it has certain two-dimensional structural characteristics.In combination with relevant geological and geophysical data,the results obtained are as follows:1.Inverted electrical structure model within 10 km of the shallow part of the study area,and inverted electrical structure model within 100 km of the deep part of the study area.2.The inversion electrical structure model within 10 km of the shallow part of the study area can intuitively display the distribution of shallow underground strata in Wulungu Sag in the northern margin of the Junggar Basin,which is in good agreement with the seismic data.The distribution of the shallow Carboniferous top interface in the study area is clearly revealed;The Carboniferous formation is characterized by a high resistivity formation with a resistivity greater than 50 ohmmeters.From the perspective of electrical characteristics,there are high resistivity bodies in the northwest and southeast ends of Wulungu Depression,with a large range.Secondly,low resistivity areas are found in the Carboniferous basement.3.The inversion electrical structure model in the depth of 100 km in the study area has obvious layering of electrical structure in the deep underground,which reflects the electrical characteristics of geological structures at all levels in the Wulungu Sag area on the northern edge of the the Junggar Basin,and can be mutually verified with other geological methods obtained by predecessors in the the Junggar Basin.From the perspective of electrical characteristics,the study area can be divided into four sets of electrical layers,the second set of electrical layers is the Carboniferous folded basement,and the third set of electrical layers is the Precambrian crystalline metamorphic basement rock series,with obvious layered structure,which corresponds to the "two-layer structure" of the basement properties of the Junggar Basin studied by previous researchers.The ultrahigh conductivity layer existing 15 km underground between survey points 30 and 80 is inferred to be a partially molten body;The high resistivity anomalies on the left and right sides are presumed to be igneous rock intrusions.The depth of 40～50km is speculated to be the location of the Moho surface in the study area,below the Precambrian basement rock series.Below a depth of 50 km is the upper mantle.The electrical structure model obtained from this 2D inversion has the general characteristics of the Junggar Basin... |
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