The Genesis and Circulation of Geothermal Water in the Riduo–Cuona Rift, Eastern Tibetan Plateau, Based on Hydrochemistry and Stable Isotopes Geochemistry

Abstract

Studying initial geothermal fluids and tectonic active zones is crucial for exploiting intermediate high-temperature geothermal resources. This study aims to investigate the genesis, circulation and environmental implications of geothermal water in the Riduo–Cuona Rift (RCR) of the eastern Tibetan Plateau. By integrating hydrochemical analysis, stable isotope geochemistry (δ²H, δ¹⁸O and ⁸⁷Sr/⁸⁶Sr), and noble gas isotope characteristics, the research seeks to develop comprehensive geothermal circulation models in the RCR. (M1) The spatial distribution of geothermal waters near the molten magmatic domes indicated ⁸⁷Sr/⁸⁶Sr ranges consistent with those of the rock, respectively. The high Ca, Mg ‘hardness’ spring waters were attributed to strata surrounding the dome resulting from the last leaching, as confirmed by the estimated higher hydraulic head, mainly located in ‘immature water.’ (M2) The spatial distribution of geothermal waters corresponding to an orogenic belt revealed HCO₃·SO₄–Na as the dominant hydrochemical facies in the northern RCR. Research suggests that springs exhibit greater circulation depths and that spring solute SO₄ is related to the Gangdise magmatic arc leaching. (M3) However, the active tectonic zone's springs ⁸⁷Sr/⁸⁶Sr (0.705763–0.709754) indicated evaporite characteristics. The thermal reservoir temperature in this structural junction zone is the highest (256.75°C–287.03°C). The high trace alkali element concentrations, particularly of B, F and As, exceeded the WHO guideline; the drainage system analysis indicates regional nonnegligible environmental risks in the Gudui. Establishing these models can clarify the relationships between geothermal fluids, tectonic structures and regional faults, providing insights into geothermal resource potential, environmental risks and possible strategies for sustainable resource exploitation in the region.