Geochemical Characteristics of Hydrothermal Volatiles From Southeast China and Their Implications on the Tectonic Structure Controlling Heat Convection

Abstract

Hot springs and igneous rocks are present widely in southeast China, influenced by the subduction of the Western Pacific and Philippine Sea Plates. This study reports on new data of chemical compositions and He–Ne–C isotopes for gas samples from representative hot springs and wells in the Guangdong and Fujian provinces to identify the origin of hydrothermal volatiles and provide insight into geothermal tectonic affinities. The primary hydrothermal volatile component from southeast China is atmospheric N2, with a volumetric percentage of 82.19%–98.29%. It indicates medium-low temperature geothermal systems where geothermal fluids suffered a shallow circulation in closed fracture systems. Low CO2 and CH4 contents and their depleted δ13C values confirmed the small number of deep-derived components in the study area. However, spatially discernible geochemical characteristics imply enhanced hydrothermal fluid convection in the adjacent area of the two provinces, including the Fengshun, Zhangzhou, Longyan, and Sanming geothermal fields. Specifically, the He–Ne isotopes from this area exhibit mantle He contribution of more than 10% and mantle heat flow accounts for more than half of the total heat flow. Moreover, according to the thermal background calculations, the highest heat flow value of 77.7 mW/m2 is indicated for the Zhangzhou geothermal area and the lowest value of 54.7 mW/m2 is indicated for the Maoming geothermal area. Given the epicenter distributions and the corresponding earthquake magnitudes, the NE-trending faults are heat-control tectonic structures and their intersections with the NW-trending faults provided expedite channels for geothermal fluids rising to the surface. Therefore, the preferred development potential of geothermal resources can be expected in the adjacent area of the two provinces where two sets of active faults crossed. This study provides critical information on understanding the geothermal distribution controlled by the tectonic structure in southeast China.

Magnetotelluric Evidence for Lithospheric Alteration Beneath the Wuyi‐Yunkai Orogen: Implications for Thermal Structure of South China

“…According to the final electrical resistivity structure, the thickness of the granitic rock mass beneath the geothermal system can reach 10 km, and the heat flow generated by radioactive elements in the upper crust is estimated to be approximately 40 mW/m 2 (Jaupart et al., 2016), while the average heat flow is 83.4 mW/m 2 in the geothermal system. The heat flow from the mantle is 43.4 mW/m 2 , accounting for more than half of the total heat flux, which is consistent with the heat flow quantified from the geochemical data of hydrothermal volatiles within the geothermal system (Tian et al., 2021).…”

First Estimates of Hydrothermal Helium Fluxes in Continental Collision Settings: Insights From the Southeast Tibetan Plateau Margin

“…The Southeast Tibetan Plateau margin has variable degrees of mantle helium degassing, as shown by the hydrothermal 3 He/ 4 He ratios varying between crustal value and upper mantle value (Tian et al., 2021; Wang et al., 2020; Zhang, Guo, et al., 2021; Zhou et al., 2020). Genetically, such helium degassing is closely correlated with regional volcanic and tectonic processes in response to southeastward expansion of the Tibetan Plateau (Zhang, Guo, et al., 2021).…”

Stable isotopes and hydrogeochemical evolutions of groundwater from a typical seismic fault zone in the Mt. Lushan region, Eastern China

“…Underground fluid is proved to be an important carrier for transmitting information of geological evolution within the Earth and thus its geochemical characteristics and genesis are widely studied (Zhang, 1992;Che et al, 1998;Du and Kang, 2000;Liu, 2006;Li et al, 2022;. Detailed researches involving the relationship between groundwater and surface runoff (Grasby et al, 1999;Su et al, 2009;Gu et al, 2017), the circulation process and waterrock interactions (He and Singh, 2019;Hosono and Masaki, 2020;Hosono et al, 2019;Nakagawa et al, 2020;Shi et al, 2020;Barberio et al, 2017;Skelton et al, 2014;Barberioet al, 2017;Zhou et al, 2020;Chen et al, 2015;Li et al, 2021;Martinelli and Dadomo, 2017;Skelton et al, 2019;Li et al, 2017;Bao et al, 2019;Du and Liu, 2003;Sun et al, 2016;Zhou et al, 2022;Tian et al, 2021;Song et al, 2006), the changes of chemical compositions before and after earthquakes (Tsunogai and Wakita, 1995;Claesson et al, 2004;He and Singh, 2019;Hosono and Masaki, 2020;Hosono et al, 2019;Nakagawa et al, 2020;Shi et al, 2020;Barberio et al, 2017;Skelton et al, 2014;Barberioet al, 2017;Zhou et al, 2020;…”