A new approach to Kırşehir (Turkey) geothermal waters using REY, major elements and isotope geochemistry

Kırşehir geothermal area is located in Central Anatolia and is controlled mainly by NW–SE and NE–SW faults belonging to Seyfe Fault Zone. This paper examines the geochemistry, particularly trace elements and isotopes of geothermal fluids in relation to regional tectonics and discusses the geothermal potential of the Kırşehir. The cold and thermal fluids forming the Kırşehir sources are Ca–Mg–HCO₃ and Ca–Na–HCO₃–Cl, respectively. According to Giggenbach diagram, the cold waters are located in the partially equilibrated water region whilst other samples are located in the immature water region. Besides, the semi-logarithmic Schoeller diagram shows that cold and hot waters come from different aquifers because cold and thermal fluids exhibit similar ion concentrations in themselves. Cation and SiO₂ geothermometers show that the reservoir rock temperatures range from 58 to 98 °C. According to δ¹⁸O and δ²H values, the thermal fluids in the study area are located between the Mediterranean meteoric water line and global meteoric water line; this suggests that the geothermal sources are of meteoric origin and the colder aquifers are recharged by precipitation at lower attitudes, whereas the geothermal reservoir is recharged by precipitation at higher altitudes and from inland environments. The Rare Earth Elements and Yttrium results show that the waters have remarkable negative Cerium (Ce), Europium (Eu) and Yttrium (Y) anomalies. The negative Ce anomaly indicates that the colder aquifers of Kırşehir are close to oxygen-rich surface waters and thermal fluids interact with granites. The Eu anomalies in groundwater are controlled by the preferential mobilization of Eu²⁺ during water–rock interaction compared to Eu³⁺ and negative Eu anomalies, which show that geothermal fluids have leached from granites. Y/Ho values between 25 and 33 of the thermal fluids at Kırşehir result from the active contribution of fluorine during mobilization of REE as either fluoride or fluorocarbonate ligand complexes, causing Y to act as a heavy pseudolanthanide.