Electrical conductivity in the mantle transition zone beneath Mongol-Okhotsk suture: revealed by the geomagnetic signals of ground observatories

Abstract. The closure of the Mongo-Okhotsk ocean has a strong influence on the tectonic evolution of Northeast China. However, the dynamic mechanism in the Mongol-Okhotsk suture area is controversial. This paper intends to obtain the deep structure of beneath Northeast China based on geomagnetic depth sounding, and constrain the subduction of Mongol-Okhotsk Ocean from the perspective of electrical properties. This paper collects and processes the data of geomagnetic stations in China and adjacent areas, and obtains stable C-response data. The staggered grid finite difference method is used for forward modeling, and the finite memory quasi Newton method based on L₁-norm is used for inversion. The three-dimensional inversion of geomagnetic data is carried out in spherical coordinates. The intensive model testing stations can obtain high-resolution underground electrical structures. The measured data show that there are obvious high conductivity anomalies in the mantle transition zone in Northeast China, especially in the west of the Great Xing’an Range, showing an area of high conductivity anomalies. Combined with the regional tectonic background of the region, we speculate that the high conductivity anomaly body is related to the southward subduction of the Mongol-Okhotsk Ocean. The Mongol-Okhotsk Ocean subducted under the Eurasian plate at a small angle in the southward direction. With the closing of the Okhotsk Ocean and the extension environment after the termination of subduction, the subducted oceanic crust plate has been faulted and depressed and partially stopped in the mantle transition zone.