Factors Controlling of Thermal Water Hydrogeochemical Characteristics in Tatun Volcano Group, Taiwan

Abstract

The Tatun geothermal system is located in Northern Taiwan and is hosted by the Tatun volcano group (TVG). The variation in the geochemical composition of thermal waters is considered to be an important indicator of volcanic activity. In this study, we analyzed the chemical and isotopic compositions of hot springs in the TVG. A chemical and multicomponent geothermometer was used to estimate the reservoir temperature, and hydrogen and oxygen isotopes were used to determine the source of the thermal water. The presence of thick andesite and fractures allowed the formation of different type of springs in the center close each other with lower temperatures and acidic springs with higher temperatures at the northeast and southwest sides of the Tatun geothermal field. The saturation index showed that the concentration of SiO2 in the thermal water was controlled by quartz. The multicomponent geothermometer indicated a reservoir temperature between 130 °C and 190 °C, and the geothermal water in Longfengku, Lengshniken, Matsao and Szehuangping may have mixed with shallow groundwater. Isotope data indicated that the stream water and groundwater originated from meteoric water, and the spring water showed a significant oxygen shift, due to water–rock interaction and evaporation. The isotopes of the fluid in the TVG are also affected by the seasonal monsoon. These results can serve as a reference for designing a conceptual model of the spring in the Tatun geothermal system.