In the present study, we combined stable isotopes and anthropogenic tracers to investigate the origin, residence times, and evolution of thermal waters in the Lonquimay-Tolhuaca Volcanic Complex (LTVC) of the southern Chilean Andes. A total of 20 water samples from springs discharging at a broad range of temperatures (8–96 °C) were collected and analyzed for major ion geochemistry, stable isotope ratios (δ²H, δ¹⁸O, δ¹³C_TDIC), dissolved chlorofluorocarbons (CFCs) and sulfur hexafluoride (SF₆). In addition, we compiled all available data on the isotopic composition of precipitation in the region to derive the local meteoric water line. Coupled with a Rayleigh-fractionation model of precipitation, we provide constraints on the elevation at which infiltration and recharge to the system is produced. δ¹³C_TDIC values are consistent with the bulk of dissolved inorganic carbon being derived from the addition of soil CO₂ to an atmospheric source, while magma degassing and boiling processes are evidenced in samples discharging directly on the flanks of volcanoes. The isotopic composition of thermal water, once heated at depth, is further modified by CO₂ degassing and carbonate precipitation during ascent. All geothermal samples contain low but detectable concentrations of CFC-11, CFC-12, CFC-113, and SF₆, suggesting the addition of only a small fraction (2–22%) of modern meteoric water. The discharge temperature of naturally outflowing springs in the LTVC correlates directly with the age distribution of the water samples. This difference in residence times is attributed to the distinct subsurface circulation pathways of each water type—i.e., the shallow, diffuse flow of cold groundwater vs. the deep, focused circulation of thermal water along fault zones. Conduit flow along high vertical permeability networks allows hydrothermal fluid to remain relatively unmixed with shallow meteoric water during ascent. Data from this study confirm that fault-fracture meshes with different orientations exert a first order control on the residence times, ascent, and mixing rates of thermal waters in this segment of the Andean Cordillera, thus modulating their chemical and isotopic signature. Additionally, our results show that the combined use of conventional hydrogeochemical and isotopic data with environmental tracers, including anthropogenic CFCs and SF₆, is a powerful tool to better understand the dynamics of geothermal systems.

在本研究中，我们结合了稳定的同位素和人为示踪剂，研究了智利安第斯山脉南部朗基梅-托尔瓦卡火山综合体（LTVC）中热水的起源，停留时间和演化。从弹簧在一个宽的温度范围（8-96℃）的放电总共20水收集样品并用于主要离子地球化学分析，稳定同位素比率（δ ² H，δ ¹⁸ O，δ ¹³ Ç _TDIC），溶解氯氟烃（CFC）和六氟化硫（SF ₆）。此外，我们汇总了该地区降水同位素组成的所有可用数据，以得出当地的大气水位线。结合降水的瑞利分馏模型，我们对产生渗透和补给系统的海拔高度提供了限制。δ ^13个Ç _TDIC值与溶解的无机碳的堆积从加法土壤CO被衍生一致₂到大气压源，而岩浆脱气和沸腾过程中直接在火山的侧面排出的样品证明。深度加热后，热水的同位素组成会进一步被CO ₂改性上升过程中脱气和碳酸盐沉淀。所有地热样品均含有低浓度但可检测到的CFC-11，CFC-12，CFC-113和SF ₆，表明仅添加了少量（2–22％）的现代大气水。LTVC中自然流出的弹簧的排放温度与水样的年龄分布直接相关。停留时间的这种差异归因于每种水类型的不同的地下循环路径，即，冷的地下水的浅而分散的流动与沿断层带的热水的深而集中的循环。沿高垂直渗透率网络的管道流使热液在上升过程中与浅流水保持相对不混合的状态。这项研究的数据证实，不同方向的断层-断裂网格对安第斯山脉山脉这一段的热水的停留时间，上升率和混合率具有一级控制，从而调节它们的化学和同位素特征。此外，我们的结果表明，常规水文地球化学和同位素数据与环境示踪剂（包括人为CFC和SF）的结合使用₆是一个强大的工具，可以更好地了解地热系统的动力学。