Hydrogeochemical origin and circulation of spring waters along the Karakorum fault, Western Tibetan Plateau: Implications for interaction between hydrosphere and lithosphere

Abstract

Geochemical investigation on the origin and circulation of geothermal water is crucial for better understanding the interaction between hydrosphere and lithosphere. Previous studies on the Himalayan geothermal belt mainly distributed in the central and eastern Tibetan Plateau. In this study, water samples (8 hot springs and 1 cold spring) from the Karakorum fault (KKF) zone of western Tibetan Plateau were analyzed for the hydrogeochemical characteristics and isotopic compositions. Three types of spring water along the KKF were classified on basis of ionic concentration and Sr isotopic composition: type A water (HCO3–Mg or Ca), type B water (HCO3–Na) and type C water (Cl–Na). Type A water is originated from the infiltration of meteoric water and the dissolution of silicate/evaporite. Type B water is mainly leached from the metamorphic and granitoid rocks. Type C water is formed by the dissolution of chlorides and sulphates. δD and δ18O isotopes indicate that geothermal fluid along the fault zone was mainly recharged by local precipitation. Moreover, reservoir temperatures of 144.2–208.6°C were estimated by the silica–enthalpy mixing model, and the thermal waters have a relatively deep circulation depth (≥ 7.0 km). Meanwhile, the thermal waters are characterized by extremely high Li, B, Fe and As concentrations and earthquakes frequently happened in the vicinity, suggesting that the KKF is a deep and active fault, which also indicates that the thermal fluids are strongly associated with seismicity. Therefore, thermal fluid can potentially be used as continuous monitoring sites for earthquake forecasting.

Hydrothermal Degassing Through the Karakoram Fault, Western Tibet: Insights Into Active Deformation Driven by Continental Strike-Slip Faulting

“…Modeling results show that calcite precipitation probably occurred at temperatures of ~90−170 o C (Figure 3d), or within an expected pH of 6−8 (Gilfillan et al, 2009). Assuming a geothermal gradient of 30 o C km −1 for the western Tibet, carbonate minerals may start to precipitate at ~5−6 km depth, consistent with groundwater circulation of the KKF (Wang et al, 2022). The possibility of calcite precipitation is supported by travertine surrounding spring mouths and calcite veins in exhumed fault rocks (Wallis et al, 2013).…”

“…Model of calcite precipitation (CP) is after Barry et al (2020). Groundwater circulation depth is after Wang et al (2022) and the brittle-ductile transition zone is assumed to be at ~30 km depth for western Tibet.…”

Hydrogeochemical Characteristics of Earthquake-Related varied-temperature Springs along the Eastern Kunlun Fault Zone, China

“…Since the Tazang segment is predominantly composed of carbonate lithology containing high levels of Ca 2+ , and the pH of springs in the area is weakly alkaline, it favors the enrichment of Sr [60]. Li exhibits high chemical reactivity and strong migration ability, making it more prone to enrichment in springs, which indicates deep fluid upwelling [61,62]. The solubility of B in groundwater rises as depth and pressure increase [63].…”

The Hydrogeochemistry of and Earthquake-Related Chemical Variations in the Springs along the Eastern Kunlun Fault Zone, China

“…Since the Tazang segment is predominantly composed of carbonate lithology, containing high levels of Ca 2+ , and the pH of springs in the area is weakly alkaline, this favors the enrichment of Sr [47]. Li exhibits high chemical reactivity and a strong migration ability, making it more prone to enrichment in springs, which indicates deep fluid upwelling [48,49]. The solubility of B in groundwater rises as the depth and pressure increase [50].…”