Crustal structure and geothermal mechanism of Gonghe-Guide Basin based on EIGEN-6C4 satellite gravity and aeromagnetic data

Abstract

Abstract Gonghe-Guide Basin is situated in the northeastern edge of the Tibetan Plateau. one of China's main targets for geothermal research and exploitation. It is also a crucial region for studying the Tibetan Plateau's uplift mechanisms. Therefore, the elaborate crustal structure of the entire basin is essential for recognizing the geothermal mechanisms, geothermal source targets and even the uplift mechanisms of the Tibetan Plateau. However, these issues remain enigmatic, partly because it is difficult to depict the crustal structure of entire base by using the profile results of magnetotelluric and seismic data. To overcome the limitations of profile results, we present a new crustal structure of the entire Gonghe-Guide Basin by using EIGEN-6C4 satellite gravity and aeromagnetic data. The gravity and magnetic data were processed using the wavelet multi-scale decomposition method and the iterative compact depth from extreme points imaging method. Satisfactory residual anomalies and inversion results were obtained. The gravity inversion results reveal pronounced low-density regions at the depths of 15–35 km in the middle-upper crustal, most likely caused by partial melting from heating the overlying hot dry rocks. The results correspond well with the magnetotelluric and seismic results and are an effective supplement. The magnetic inversion results show negative or no magnetism within a similar depth range. But at shallow depths of the same horizontal positions, there is high positive magnetism, which can be interpreted as granite. To confirm and validate this conclusion, a 2D geologic model of a profile from a typical area is created to show the detailed tectonic. Based on the new crustal structure results, the suggested geothermal target is the low/negative density corresponding to low/negative magnetism located at deep depths and high/ positive magnetism located at shallow depths. These density and magnetism anomalies are primarily located near the town of Guide, Gonghe, Xinjie, Chaka, Wayuxiangka, Tanggemu, Xinhai, which can be considered geothermal source targets. The geothermal source is thought to be due to mantle material upwelling or faults activity causing partial melting in the crust, and heat flows from deep to shallow along the faults in the region. Then we established a geological conceptual model to illustrate this process. This indicates that tectonic movement is taking place in the deep part of the earth in Gonghe-Guide Basin. The research on the geological structure and geothermal heat source mechanism in the Gonghe-Guide Basin can provide a primary reference for research on geothermal resources in other areas with similar geological structures.