The geothermal resources in sedimentary basins have high potential for development and utilization, and have become an important research topic globally. This study focuses on the geothermal system in the northwestern Songliao Basin. Water chemistry and isotopic signatures of geothermal fluids and shallow groundwater are analyzed. Water–rock interactions, recharge sources, and the ages of geothermal fluids are revealed and recharge elevation, circulation depth, and the reservoir temperature of the geothermal fluids are estimated. This article proposes deep heat sources and genetic mechanism for geothermal system. The results are as follows: The hydrochemical types of geothermal water mainly included Cl·HCO₃-Na, HCO₃·Cl-Na, and Cl-Na, and the TDS gradually increased from the margin to the center of the basin and from anticlines to the depression on both sides. The geothermal water was recharged by paleo-atmospheric precipitation in the northwest mountainous area at an elevation of 300–700 m. The ¹⁴C ages showed that the geothermal water flowed at an extremely low rate (millennial scale) and had a low circulation rate. The temperature of the geothermal reservoirs was estimated to be 45.19–83 °C using a quartz geothermometer. The geothermal water had a genetic model of stratum-controlling geothermal reservoirs, lateral runoff recharge, and heat supply by terrestrial heat flow. The underlying reasons for the high geothermal gradient and terrestrial heat flow in the basin include the uplift of the Moho, the uplift of the upper mantle, and the presence of a high-electrical-conductivity layer in the crust.

Compared to the southern Tibetan Plateau, the northern part has been regarded as relatively lacking geothermal resources. However, there is no lack of natural hot springs exposed in beads along large-scale fracture systems, and research on them is currently limited to individual hot springs or geothermal systems. This paper focuses on the Wahongshan-Wenquan Fracture Zone (WWFZ), analyzes the formation of five hydrothermal activity zones along the fracture zone in terms of differences in hot water hydrochemical and isotopic composition, and then explores the hot springs’ hydrothermal control in the fracture zone. The results show that the main fractures of the WWFZ are the regional heat control structures, and its near-north–south- and near-east–west-oriented fractures form a fracture system that provides favorable channels for deep hydrothermal convection. Ice and snow meltwater from the Elashan Mountains, with an average elevation of more than 4,500 m above sea level, infiltrates along the fractures, and is heated by deep circulation to form deep geothermal reservoirs. There is no detectable mantle contribution source heat to the hot spring gases, and the heat source is mainly natural heat conduction warming, but the “low-velocity body (LVB)” in the middle and lower crust may be the primary heat source of the high geothermal background in the area. The hot springs’ hydrochemical components show a certain regularity, and the main ionic components, TDS, and water temperature tend to increase away from the main rupture, reflecting the WWFZ controlling effect on hydrothermal transport. In the future, the geothermal research in this area should focus on the hydrothermal control properties of different levels, the nature of fractures, and the thermal contribution of the LVB in the middle and lower crust.

Hydrogeochemical research on fluids is an effective method to understand the formation mechanism, occurrence environment, and circulation process of groundwater. The groundwater sampling sites are located in the town of Dachaidan on the northeastern edge of the Tibetan Plateau, which was selected as the study object. Samples were collected from hot and cold springs and surface water in the area. This study is based on the analysis of water chemistry and isotopes, and aims (1) to discuss the chemical characteristics of groundwater in Da Qaidam, (2) to estimate the deep reservoir temperatures, recharge elevation and circulation depth of geothermal waters, and (3) to figure out the heat source beneath the geothermal area and its genetic mechanism. The result showed the following: The hydrochemical type of the hot spring is Cl·SO₄-Na and Cl-Na, and the hydrochemical type of cold spring is SO₄·HCO₃-Na·Ca and Cl·HCO₃·SO₄-Ca·Na. The main source of groundwater recharge is snow and ice melt water. The recharge elevation ranges from 4666.8 m to 5755.9 m. The geothermal reservoir temperature is about 119.15–126.6 °C. Ice and snow melt water infiltrate into the high mountainous areas on the north side of Da Qaidam and circulate underground through the developed deep and large fractures. Part of the groundwater migrates upwards under the water conduction of the Da Qaidam fault fracture zone to form cold springs, while another part is heated by deep circulation and exposed to the surface in the form of medium to low temperature tectonic hot springs. The research results can provide a scientific basis for geothermal resource exploitation and utilization in Qinghai Province.