A study of the deep electrical structure of the northern segment of the Tan-Lu fault zone, NE China

摘要

We studied a magnetotelluric transect from Tongliao, Inner Mongolia, to Baishan, Jilin, that crosses the northern segment of the Tan-Lu fault zone. Based on the profiling data, we calculated and analyzed the two-dimensional (2D) deviation degree and the tectonic strike, inverted the data using the 2D nonlinear conjugate gradient inversion method, and obtained an electrical structure model of the crust and upper mantle along the transect. Our analysis reveals that the western portion of the transect is within and at the margin of a typical sedimentary basin, and a high-conductivity layer is present in the lower crust. In comparison, the eastern portion of the transect is in the Jihei fold zone and has a relatively stable electrical structure, but its resistivity is one to two orders of magnitude higher than that of the western portion. A distinct electrical anomaly exists between the western and eastern sides. The Yilan-Yitong Fault of the northern segment of the Tan-Lu fault zone dips to the northwest, has strike-slip characteristics, extends to a depth of 40-50 km, and induces upwelling of upper mantle materials. The Dunhua-Mishan Fault of the northern segment of the Tan-Lu fault zone has a clear electrical gradient, and similar to the Yilan-Yitong Fault, it also dips to the northwest. However, the Dunhua-Mishan Fault is mostly fractured, extends to a depth of approximately 20 km and is slightly smaller than the Yilan-Yitong Fault. The inferred distribution of deep resistivity values indicates that the lithosphere is generally thinner at the center of the transect and thicker at the edges: the lithosphere is approximately 150 km thick on the western end, thins eastward to approximately 60 km thick near the Tan-Lu fault zone and then gradually thickens eastward to 100 km thick.