Study On Deep Electrical Structure Of The Northern Tibetan Plateau

Located at the northern edge of the Qinghai-Tibet Plateau,Kumukuli Basin is a secondary tectonic basin formed by the interaction of the plateau,Tarim and Qaidam basins,and is the leading-edge area that constitutes the expansion of the main part of the plateau.The study of the deep electrical structure in this area is of great value for the deep resources and tectonic movement mechanism of the northern Tibetan plateau.In this paper,the magnetotelluric sounding(MT)method was used to study the resistivity distribution characteristics of Kumukuli Basin from surface to 120 km underground.The research mainly focuses on two aspects: comprehensive qualitativequantitative processing and analysis of the measured data,including time-frequency conversion,regional dimensionality analysis,structural spindle determination and static displacement correction.Using advanced inversion methods,a series of two-dimensional inversion experiments are designed and realized,and a quasi-three-dimensional profile of apparent resistivity within 120 km of the working area is obtained.In summary,the MT research work carried out in the Kumukuli Basin in this paper mainly has the following conclusions:1.The underground of the basin is mainly two-dimensional structure,and there are a small number of three-dimensional structures in the deep part;The overall tectonic trend of the basin is NE80°.2.The deep electrical structure of Kumukuli presents the characteristics of horizontal division and vertical stratification.The region has high resistance at the edge and relatively low resistance in the middle.Above the earth’s crust,it can be divided into three electrical layers,the first electrical layer corresponds to the upper crust,showing high resistance,resistivity higher than 500 ohms,and the bottom interface is buried 20km;The second electrical layer corresponds to the middle crust,which is manifested as medium resistance,and the resistivity is slightly less than two hundred ohms;The third electrical layer corresponds to the middle crust,which shows a wide range of lowresistance anomalies,resistivity of less than 20 ohms,and the top surface is buried 40 km.There is a large-scale low-resistance layer within the burial depth of 40～100km,with a resistivity of ten ohms,extending from the north-north to southwest of the central Kumukuli to the upper mantle.The shell mantle structure in this region is in good agreement with the electrical stratification.3.According to the distribution characteristics of the low resistance layer,it is divided into low resistance in the shell and low resistance in the upper mantle,and it is found that the formation mechanism of the two is different.The low resistance in the shell may be caused by the shear action of the deep rock after being squeezed,and then graphitization leads to a smaller resistivity.The formation of the upper mantle low resistance may be related to partial melting of deep rocks or upwelling of upper mantle material.In this paper,it is believed that the mantle of the upper crust of the lower Kumukuli has certain rheology,and the deep low-resistance layer may be a "channel" carrying the flow of melt to the north and east of the central and northern plateau.