Isotopic Hydrogeochemical Study Of Geothermal Fluids In Volcanic Geothermal System

In this paper,the groundwater of volcanic thermal storage is taken as the research object,and the method of isotopic hydrogeochemistry is used to systematically study the groundwater and underground hot water of volcanic geothermal systems such as Wudalianchi,Changbai Mountain,Aershan,Tengchong and Fujian.The comparison of thermal fields(sedimentary geothermal systems)provides a scientific basis for the sustainable development and utilization of geothermal resources in China.Studies have shown that the chemistry characteristics of groundwater and underground hot water in the volcanic geothermal system in China are diverse,and the TDS of each study area varies greatly.The main types of hydrochemistry are HCO₃-Na water,HCO₃-Ca?Na water,and HCO₃?Cl-Na type water,HCO₃?SO₄-Na type water.According to the ion proportional coefficient of the sampling point,the thermal storage environment of groundwater and underground hot water is relatively open,and the replenishment mainly comes from atmospheric precipitation.In the study of the environmental isotopes of groundwater and underground hot water in volcanic geothermal systems,the water samples of Tianchi and Maer Lake formed by the volcanic eruption area showed obvious?¹⁸O drift phenomena,and their groundwater mineralization was low and ¹⁴C dating The low value of ³⁴S and the small value of ³⁴S suggest that Tianchi and Maer Lake are not the same water supply source.The investigation also found that all the Tianchi and Maer Lakes have the phenomenon that the water level does not fall during the dry season and the water level does not rise during the flood period,indicating that the replenishment water sources of Tianchi and Maer Lake also have volcanic craters and volcanoes in addition to the surrounding atmospheric precipitation Geothermal fluid rising from the mouth.The sampling points of the non-volcanic eruption area all fell on the atmospheric precipitation line,and there was no?¹⁸O drift phenomenon,and its TDS value was low,indicating that its groundwater recharge was mainly from atmospheric precipitation.The volcanic thermal storage lithology is dominated by broken metamorphic rocks and granite,with well-developed fissures and joints,and the volcanic crater and surrounding structure as the thermal storage space;the volcanic thermal storage is more open than the sedimentary basin thermal storage environment.The layers are more complex,mostly basalt and granite;in terms of structure,the volcanic and sedimentary types are controlled by large-scale fault structures,the volcanic type thermal reservoirs have frequent Cenozoic tectonic activities,and crater lakes(Tianchi and Maer Lake)Mostly caused by multiple volcanic tectonic activities since the early days.In terms of heat sources,volcanic geothermal systems generally use uncooled magma sacs as the geothermal fluid heat source;sedimentary basins generally have geothermal anomalies due to the shallow Moho depth.