The Indication of Geothermal Events by Helium and Carbon Isotopes of Hydrothermal Fluids in South China

Helium and carbon isotopes are important indicators for identifying the origin of volatiles dissolved in groundwater. Four thermal springs and another twelve normal springs are hosted by local deep faults in south China, which are considered to have significant connection to deep geothermal activity. Between 4% and 6% mantle He in thermal springs reveals that significant mantle He migration in deep faults can bring a certain amount of energy, along with thermal volatiles, and contribute to thermal spring formation according to 3He/4He. While δ13C reveals that dissolved inorganic carbon in thermal springs is from rock metamorphism that occurred in certain deep crust as geothermal activity, which is potentially the main energy source of the thermal springs.