Abstract This study aims to hydrochemically characterise three CO2-bearing springs representing distinct hydrofacies in NW Gorveh (western Iran) and interpret them in the light of their geological setting. The results of laboratory measurements of elemental concentrations, stable oxygen, carbon and hydrogen isotopes, dissolved and particulate organic and inorganic carbon (DIC, DOC, POC, PIC) and alkalinity are combined with in situ measurements of pH and temperature. Parameters such as alkalinity, DIC, Ca2+ and pCO2 concentration display strong, positively correlated values, with systematic decrease from the spring vent in down-flow direction for the three spring systems. The inverse correlation of pH and δ13CDIC is caused by CO2 degassing. The δ18O and δD values show no significant variation, related to minor or no evaporation due to normal ambient temperatures. The low concentration of POC, PIC and DOC compared to that of DIC and the lack of correlation between them reflect predominant inorganic carbon in these fluids. Spring I is oversaturated in calcite with additional dissolution of CO2, and despite high concentrations of Na+ and Cl−, undersaturated in halite, indicating a fluid of geothermal origin and/or reflecting steady state dissolution. This is related to water-rock interaction processes with carbonate and evaporitic rocks, that affected the isotopic signature of δ18O, which is shifted to the right of the global meteoric water line. Spring I also represents a partially equilibrated and mature (deep) chloride type water. Spring II and III are less saline and represent a different fluid circulation and/or shorter residence time. The two latter springs are characterized by peripheral (shallow) dilute chloride-bicarbonate type waters. Decreasing key parameters especially in Spring III during the winter suggest that superficial mixing with rain and meteoric water results in high temporal variations. Cation and stable carbon isotope geothermometry applied to the studied springs reveals an average reservoir temperature of ~210, 110 and 90 °C for Spring I and II and III, respectively. The geochemical and isotopic data allowed to depict a conceptual model where the hydrothermal reservoir for Spring I is residing in carbonate and evaporitic rocks (most likely the Qom Formation) situated at a depth of 3–4 km whereas those of Spring II and III are likely sourced from a shallower depth (1–2 km) in correspondence with carbonate and porous and permeable volcanic rocks. Integration of hydrofacies with conceptual hydrological and geological models forms the base towards a proper understanding of water circulation patterns, increasingly important for sustainable water management and geothermal applications.

中文翻译：

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伊朗西部含 CO2 热泉的水文地球化学、稳定同位素地球化学和地球测温：其起源、演化和时空变化的证据

摘要 本研究旨在对代表 NW Gorveh（伊朗西部）不同水相的三个含 CO2 泉水进行水化学表征，并根据其地质环境对其进行解释。元素浓度、稳定氧、碳和氢同位素、溶解和颗粒有机和无机碳（DIC、DOC、POC、PIC）和碱度的实验室测量结果与 pH 值和温度的原位测量结果相结合。碱度、DIC、Ca2+ 和 pCO2 浓度等参数显示出很强的正相关值，三个弹簧系统从弹簧通风口沿向下流动方向系统性降低。pH 值和 δ13CDIC 的负相关是由 CO2 脱气引起的。δ18O 和 δD 值无显着变化，与由于正常环境温度导致的轻微蒸发或无蒸发有关。与 DIC 相比，POC、PIC 和 DOC 的低浓度以及它们之间缺乏相关性反映了这些流体中主要的无机碳。Spring I 在方解石中过度饱和，CO2 额外溶解，尽管 Na+ 和 Cl- 浓度很高，但在岩盐中不饱和，表明流体起源于地热和/或反映了稳态溶解。这与碳酸盐岩和蒸发岩的水-岩相互作用过程有关，影响了 δ18O 的同位素特征，δ18O 移动到全球大气水线的右侧。Spring I 也代表部分平衡和成熟（深）氯化物类型的水。Spring II 和 III 含盐量较少，代表不同的流体循环和/或较短的停留时间。后两个泉水的特点是外围（浅）稀氯化物-碳酸氢盐类型的水。减少关键参数，尤其是在冬季的春季 III 期间，表明雨水和大气水的表面混合会导致高度的时间变化。应用于研究泉水的阳离子和稳定碳同位素地球测温法显示，泉 I、II 和 III 的平均储层温度分别为~210、110 和 90 °C。地球化学和同位素数据可以描述一个概念模型，其中第一泉的热液储层位于碳酸盐岩和蒸发岩（最有可能是库姆组）中，深度为 3-4 公里，而第二泉和第三泉的热液储层可能位于源自较浅的深度（1-2 公里），对应于碳酸盐岩和多孔和可渗透的火山岩。水相与概念性水文和地质模型的整合构成了正确理解水循环模式的基础，这对于可持续水资源管理和地热应用越来越重要。