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<p>Spring systems in tectonically active evaporite basins provide critical insights into groundwater circulation, solute sources, and geothermal potential. However, the processes controlling the hydrogeochemical evolution of springs in the Nangqian Basin, located in the southeastern Qinghai–Tibetan Plateau, remain insufficiently understood. In this study, we collected a comprehensive dataset of 20 spring and river water samples during both wet and dry seasons in 2022, encompassing saline, hot, and cold springs. Major and trace elements were analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS), while hydrogen, oxygen, tritium, and boron isotopes were determined through isotope ratio mass spectrometry and liquid scintillation counting. The results indicate that saline springs are characterized by high concentrations of Na<sup>+</sup>, Cl<sup>−</sup>, Ca<sup>2+</sup>, and SO<sub>4</sub><sup>2−</sup>, which suggest dominant evaporite dissolution. In contrast, hot springs exhibit significantly elevated silica contents and reservoir temperatures exceeding 130&#xa0;°C. The stable isotopic compositions plot near the local meteoric water line, and tritium activity (3.6–26.4 TU) indicate modern meteoric recharge, which is generally considered to have residence times of less than 60&#xa0;years. Most boron isotope ratios (−8.12‰ to intermediate values) suggest continental depositional characteristics, whereas isolated high ratios, such as +28‰, likely record marine evaporite influences; these variations also reflect isotopic fractionation during deep groundwater circulation. Estimated circulation depths range from approximately 1300&#xa0;m in cold springs to over 4200&#xa0;m in hot springs, reflecting contrasting flow paths and structural controls. Integrated geochemical and isotopic evidence supports a conceptual model wherein meteoric water infiltrates along faults and fractures, undergoes extensive water–rock interaction with evaporitic and silicate strata, and variably mixes with ascending geothermal fluids before discharge. These findings enhance the understanding of hydrogeochemical processes in high-altitude evaporite basins and provide a scientific basis for groundwater resource management and geothermal exploration in the Nangqian Basin.</p>

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Hydrogeochemical characteristics and circulation evolution of spring waters in the Nangqian Basin, Qinghai, China: Insights from multi-isotope (δ2H–δ18O–3H–δ11B) constraints

  • 期刊论文

  • 发表日期：

    2026年3月5日

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  • Pengcheng Zhang,
  • Wenhua Han,
  • Huaide Cheng,
  • Yongshou Li,
  • Haizhou Ma,
  • Binkai Li,
  • Xuehai Ma,
  • Huandi Li

摘要

Spring systems in tectonically active evaporite basins provide critical insights into groundwater circulation, solute sources, and geothermal potential. However, the processes controlling the hydrogeochemical evolution of springs in the Nangqian Basin, located in the southeastern Qinghai–Tibetan Plateau, remain insufficiently understood. In this study, we collected a comprehensive dataset of 20 spring and river water samples during both wet and dry seasons in 2022, encompassing saline, hot, and cold springs. Major and trace elements were analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS), while hydrogen, oxygen, tritium, and boron isotopes were determined through isotope ratio mass spectrometry and liquid scintillation counting. The results indicate that saline springs are characterized by high concentrations of Na+, Cl−, Ca2+, and SO42−, which suggest dominant evaporite dissolution. In contrast, hot springs exhibit significantly elevated silica contents and reservoir temperatures exceeding 130 °C. The stable isotopic compositions plot near the local meteoric water line, and tritium activity (3.6–26.4 TU) indicate modern meteoric recharge, which is generally considered to have residence times of less than 60 years. Most boron isotope ratios (−8.12‰ to intermediate values) suggest continental depositional characteristics, whereas isolated high ratios, such as +28‰, likely record marine evaporite influences; these variations also reflect isotopic fractionation during deep groundwater circulation. Estimated circulation depths range from approximately 1300 m in cold springs to over 4200 m in hot springs, reflecting contrasting flow paths and structural controls. Integrated geochemical and isotopic evidence supports a conceptual model wherein meteoric water infiltrates along faults and fractures, undergoes extensive water–rock interaction with evaporitic and silicate strata, and variably mixes with ascending geothermal fluids before discharge. These findings enhance the understanding of hydrogeochemical processes in high-altitude evaporite basins and provide a scientific basis for groundwater resource management and geothermal exploration in the Nangqian Basin.