Study Of Electrical Structure Of Continental Lithosphere

The study of lithospheric electrical structure can not only solve the problem of earth science service, but also is closely related to our life. The magnetotellurics is an important geophysical method to explore the structure of lithosphere.In this paper, we take three magnetotelluric profiles as foundation, including the Great Xing’an Range (400km), the northern margin of the North China Plate (600km) and the Qinling Orogen (350km). Through the robust estimation, remote reference, editing of the power spectrum and other processing methods, we get the high-quality magnetotelluric data. The Bahr skewness and GB are used for the qualitative analysis, the result shows the three profiles can be applied to the2D inversion. Subsurface electrical structure of the three profiles had been obtained through the nonlinear conjugate gradients algorithm method for the2D magnetotelluric inversion. In combination with other geological and geophysical data, the models of the electrical structure were analyzed. The main conclusions are as follows:The Great Xing’an Range, the electrical structure can be divided into three tectonic units, the Hailaer basin, the Great Xing’an Range and the Songliao Basin, which is consistent with the regional geology. The result shows that the eastern margin of the Hailaer basin and the western margin of the Songliao basin exhibit low resistivity feature in the shallow, but the latter has a complex electrical structure in the deep, meanwhile, the Great Xing’an Range exhibits an overall high resistivity feature. The eastern margin of the Hailaer basin may belong to the Xing’an Terrane, the relationship between the western margin of the Songliao basin and the Great Xing’an Range is complex. The upper crust of the Great Xing’an Range may be overlapping volcanic rocks and granites representing multi-periodic magmatic activities; extensive horizontal low resistivity bodies in the middle-lower crust reflects that the crust is non-rigid; the large high resistivity body in the lithospheric mantle imply the lower crust may have undergone delamination. There is a lithospheric scale of west-dipping structural transfer zone between the Great Xing’an Range and the Songliao Basin, inferring that the Songnen Terrane firstly subducted to the Xing’an Terrane, then sutured in the form of soft collision, and finally modified by strike-slip and volcanic activities later.The northern margin of the North China Plate, the electrical structure shows extensional tectonics after the convergence. The model indicates the Paleo-Asian Ocean has been closed along the Solonker suture; moreover, high resistivity in the upper crust of the profile may represent the large scale outcrop of granites, the north-dipping conductive layer in the middle-lower crust connected with the underlying conductive bodies may indicate the uptrend channel of the mantle, they are probably formed in post-orogenic extensional environment, reflecting the rising of the mantle material is the major impetus of the extension.The Qinling Orogen, the electrical structure can be divided into six tectonic units, the Sichuan basin, the Southern Daba Mountains, the Northern Daba Mountains, the South Qinling, the North Qinling and the Weihe basin, they have different electrical structural characteristics. There are large scale high-conductivity bodies in the middle-lower crust of the Qinling Orogen, indicating the Qinling may have experienced the underplating and delamination; the Southern Daba Mountains and the Northern Daba Mountains have different electrical structure that are divided by the strike slip indicating they have different tectonic evolution process; at last the northeastern margin of the Sichuan basin and the Weihe basin may have remnants of the ancient craton basement.