Hydrochemical Characteristics and the Genetic Mechanism of Low–Medium Temperature Geothermal Water in the Northwestern Songliao Basin

Abstract

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.