Crustal Structure and Geothermal Mechanism of the Gonghe-Guide Basin Based on EIGEN-6C4 Satellite Gravity and Aeromagnetic Data

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 di cult to depict the crustal structure of entire base by using the pro le results of magnetotelluric and seismic data. To overcome the limitations of pro le 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 con rm and validate this conclusion, a 2D geologic model of a pro le 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 ows 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.

Fluid Chemical and Isotopic Signatures Insighting the Hydrothermal Control of the Wahongshan-Wenquan Fracture Zone (WWFZ), NE Tibetan Plateau

“…Seismic profiles along the Gonghe Basin-Yushu highway indicate vertical stacking of high-and lowvelocity crustal bodies in Wenquan Township, with the Chabcha area and the LVB buried at depths of 15-43 km and with S-wave velocities below 3.4 km/s [47]. Recently, scholars studying the seismicity of the Gonghe Basin in light of deep hot dry rock exploration generally attribute the phenomenon to a young (Quaternary) intrusion of mantle-derived melt into the crust [48][49][50][51]. Therefore, the release of gases from the melt offers the potential for the occurrence of mantle-derived helium in surface hot springs.…”

“…The He isotopes of the gases fall into the helium domain of the crust, i.e., the gases are mainly generated by α-decay of the natural radioactive systems of 238 U, 235 U, and 232 Th in the crust, with no additional heat contribution from the mantle source. Low-velocity bodies of unknown nature in the lower and middle crust of the region may have provided an additional source of heat to the high-temperature thermal background of the study area [16,19,[47][48][49][50][51], where hot springs were formed by deep circulation heating of snow and ice meltwater.…”

Fluid Chemical and Isotopic Signatures Insighting the Hydrothermal Control of the Wahongshan-Wenquan Fracture Zone (WWFZ), NE Tibetan Plateau

“…Natural seismic profiles along the Gonghe Basin-Yushu highway show that the high-velocity and lowvelocity bodies in the crust of Gonghe Basin are stacked vertically in the Wenquan Township, and the Chabcha area and the LVB are buried at a depth of 15-43 km in the Wenquan Township with the S-wave velocity of fewer than 3.4 km/s [32]. In recent years, in response to the exploration of the deep Hot Dry Rock in the Gonghe Basin, many scholars have studied the seismicity of the crust in this area, and most of them recognize it as a young (Quaternary) mantle-derived melt intruding into the crust [33][34][35][36][37]. Thus, degassing of the melt provides the possibility of the presence of the mantle component He in the surface hot springs.…”