Hydrogeochemical and seismic activity characteristics of hot springs in Daocheng area, Sichuan Province

Daocheng area is located in the northern part of Sichuan-Yunnan block on the southeastern margin of Qinghai-Tibet Plateau. In order to reveal the geochemical characteristics of hot spring fluid and the relationship between the fluid and seismic activity in this area, hot spring water samples and gas samples from six hot springs in Daocheng area were collected, and the ion components and concentrations in hot spring water, gas components and gas isotopes of hot spring were tested. The following conclusions are obtained: the chemical types of hot spring water in the study area are mainly HCO₃-Na and HCO₃-Na·Ca types. The Reservoir temperature is estimated to be between 74℃ and 159℃ by cationic temperature scale, and the circulation depth is between 2.2 km and 5.0 km. The CO₂ in the hot spring gas is mainly generated by the decomposition or dissolution of the carbonate rocks in the reservoir, and the proportion of helium from the mantle component is relatively low, ranging from 0.4% to 2.4%. The hot spring in the study area is formed by the heating of the deep crustal heat source caused by the atmospheric precipitation penetrating along the fault zone. In Daocheng area, the geochemical characteristics of hot spring fluid such as circulation depth and contribution rate of mantle-derived gas have a good correlation with seismic activity, and the seismic activity of the study area is weaker than that of deep fluid upwelling areas such as the surrounding Xianshuihe fault area. At the same time, in the regional scale, the future seismic activity in the Zhongdui hot spring area of Daocheng, located at the intersection of faults, is the most noteworthy.