Hydrogeochemical characteristics and formation of the hot springs occurring in the plunging ends of an anticline in Chongqing, Eastern Sichuan Basin, China

Hot springs occurring in two plunging ends of a very long and narrow anticline is unique. This study focuses on the hydrogeochemical characteristics and formation of the anticline-controlled thermal groundwater which may provide a perspective for geothermal resources potential. The low-to-middle temperature thermal groundwater of the Taozidang anticline in the Sichuan Basin, China, was examined to estimate the temperature of the deep reservoir and identify the main hydrogeochemical processes affecting the composition of hot water during circulation and evolution. The occurrences of thermal groundwater of these springs strongly controlled by anticline are in the two plunging ends of the anticline and differ from that of the more common deep-fault circulation controlled by faults or by faults and anticlines. Incongruent dissolution of the gypsum or anhydrite of the Lower Triassic Jialingjiang and Middle Triassic Leikoupo Groups is affected by the anticline structures and results in hot water of SO₄–Ca type. Meteoric water infiltrates through the karst channels and fissures at the outcropping area of carbonates to feed the groundwater. Part of the groundwater flows to depth and circulate along the two flanks of the anticline after heated. It issues in the form of hot springs or wells in the plunging ends of the anticline. Another part of the groundwater undergoing a shallow circulation forms the normal temperature spring near the hot springs. This study of the anticline-controlled thermal groundwater is important for exploitation and utilization of geothermal energy (tourism) and provides a perspective for the anticline-controlled geothermal resources potential.