Hydrogeochemical Characteristics and Geothermometry of Hot Springs in the Tensile Tectonic Region Leizhou Peninsula and Hainan Island in South China

Hydrochemistry and isotopes are studied for characterizations of geothermal waters, groundwaters, surface waters in Leizhou Peninsula (LZ) the northern part Hainan Island (HN) across tensile-tectonic Qiongzhou Strait, southern China. Water chemistry results showed that most alkaline HCO3-Na types, while shallow groundwater samples were significantly different with HCO3-Ca, HCO3-Mg, HNO3-Ca types. Stable isotope data indicated source LZ is atmospheric precipitation, HN water has a slight “oxygen drift”. Cation geothermometers silica could appropriately predict reservoir temperatures. Based on multicomponent mineral equilibria quart geothermometer without steam loss, temperatures estimated to be range 65.0°C 165.0°C at an average circulation depth 2023 m, substantiated from thousand-meter-depth borehole. The saturation indexes (SI) simulated by PHREEQC Na-K-Mg triangle diagram revealed chemical components possibly derived water-rock interactions high Four simulation paths established calculate mass flux minerals program. hydrothermal process volcanic rocks both sides Strait was similar, but water-mineral reactions more intense. During high-temperature deep central Island, molar transfer low degree reaction weak. Finally, genetic mechanism study area extensional geostructure proposed. findings mark characteristics region shift”, values 87Sr/86Sr possible mantle, higher shallower depths.