Three-dimensional electrical structure and deep dynamics of the Khondalite Belt and adjacent areas in the Western Block of the North China Craton

Abstract

The Khondalite Belt is an important orogenic belt in the Western Block of the North China Craton that was formed by the collision of the Ordos and Yinshan blocks in the Paleoproterozoic. In the background to the Mesozoic multi-plate convergence, the Western Block lithosphere was activated along with magma and tectonic activity. Being an important collision zone, the Khondalite Belt is a key area where the modification and destruction of the Western Block can be studied. In this study, 440 sets of magnetotelluric array data were used to obtain a three-dimensional resistivity model of the study area. The resulting model revealed that the crust in the study area could be divided into three layers. The first layer exhibited an overall low-resistivity anomaly with some regional high-resistivity anomalies, while the second and third layers exhibited high- and low-resistivity anomalies, respectively. Furthermore, the model elucidated obvious boundaries between the Khondalite Belt and the Yinshan Block. The area controlled by the western and eastern Helanshan faults may be the western boundary of the Khondalite Belt. However, there was no obvious boundary to the south or east, as the bounding area exhibited low resistivity, possibly caused by a severely modified lithosphere. As a result of the characteristics of the magmatic rocks’ xenoliths, magnetic anomalies, and low S-wave velocities, low-resistivity anomalies developed in the lower crust and upper mantle, which were related to the partial melting. The scale of the partial melting did not cover the entire collision zone. Rather, it only covered the structural weak zone, especially the Jining area in the eastern Khondalite Belt. Therefore, the eastern section of the lithosphere was potentially modified by the Paleo-Pacific Plate subduction.