Hydrogeochemical and isotopic assessment and geothermometry applications in relation to the Karahayıt Geothermal Field (Denizli Basin, SW Anatolia, Turkey)

Abstract

The Karahayit Geothermal Field (KGF) is located at the northern margin of the Denizli Basin in SW Anatolia (Turkey) where thermal waters discharge along the Quaternary normal fault segments locally displaced by conjugate transfer faults. Major and trace element contents and stable isotopes (δ18O, δ2H, δ3H and δ13C) of the KGF thermal and cold waters were analyzed in order to determine their origin and evolution and reservoir temperatures. Two main thermal waters, indicated as being fed by steam-heated aquifers, are recognized: (1) Ca-HCO3 and (2) Ca-SO4 types. All thermal waters have shown non-equilibrium chemical conditions, indicating mixing processes. According to the δ18O (−9.14 to −8.07‰) and δ2H (−59.50 to −51.80‰) data, the KGF thermal waters are meteoric in origin and originated from precipitation in the northern piedmont of Yenice Horst with elevation of 900 m asl. Various geothermometers yield the reservoir temperatures of 80–130 °C. A conceptual flow model for the KGF was suggested as follows: the thermal waters were derived from a regional flow system with high recharge areas and deep circulation depth. The NW- and NE-trending conjugate fault segments (the Pamukkale Fault Zone) serve as features of hydraulic channelling, magmatic heat source and fluid convection in the extensional settings. This fault system is characterized by migration of a large amount of CO2-rich gas from the deep geothermal reservoir. Consequently, the KGF is characterized by a fault-hosted geothermal system affected by magmatism and active extensional tectonics, the same as other geothermal fields in this crustal extensional setting.