Akademik Veri Yönetim Sistemi
Geothermics, cilt.136, 2026 (SCI-Expanded, Scopus)
The Kepekler-Ilıcaboğazı geothermal field is located in northwest Anatolia, within Balıkesir Province, and comprises both thermal waters and therapeutic clay mud (Peloids). The thermal waters emerge as springs with a temperature range from 30 to 56 °C, with discharge rates of 0.01−4 L/s along a secondary fault in the North Anatolian Fault Zone (NAFZ). Only one (BK-1) production well was drilled to a depth of 390.30 m by General Directorate of Mineral Research and Exploration of Türkiye (MTA), which has a water temperature of 64 °C and a discharge rate of 15 L/sec. This study investigates the chemical and isotopic characteristics of thermal and cold waters using the major ion and trace element contents as well as environmental isotope compositions. The thermal waters belong to the alkaline NaCl-type, and are characterized by pH values of 6.35 and 7.90, generally higher EC (3149–3856 µS/cm), and relatively high concentrations of Cl, Na, B, As, Rb, Li, Cs, and Sr, in contrast to the cold waters, which are primarily of the CaHCO3 type. Carbonate and silicate dissolution, ion exchange, and energy loss through heat conduction are processes responsible for the origin and evolution of NaCl-type water. Thermal waters tend to have lower B/Cl ratios and strong correlations between (Cl and B, Li, and Rb) trace alkali metals and Cl due to rapid, efficient upflow pathways. These features align with high vertical permeability networks that promote efficient upflow and meteoric mixing, delineating the systems of the Kepekler-Ilıcaboğazı area. By estimating reservoir temperatures using chemical geothermometers and saturation indices, reservoir temperature estimates (75–100 °C) may be affected by conductive cooling, mixing, or partial equilibration—especially as most waters plot as "immature" on Giggenbach diagrams. Chemical equilibrium studies show that the thermal waters are in equilibrium with respect to calcite, aragonite, and quartz, while undersaturated with respect to albite, anorthite, K-feldspar, and gypsum. Thermal waters are meteoric in origin as suggested by the isotope (δ18O, δ2H, 3H) composition. Carbon in thermal waters is likely to originate from metamorphic CO2 or marine carbonates whereas carbon in cold waters is derived from an organic source. δ34S sulfur is derived from bacterial sulfate reduction and the dissolution of marine carbonates and sulfide minerals. The study area features a fault-controlled convection deep circulation geothermal system. Thermal waters are sourced from a resource base in the upper crust, which consists of thick granitic and metamorphic rocks that reach the surface. Using the results of hydrogeology and hydrogeochemistry, a conceptual hydrothermal model of recharge, mixing, and discharge has been proposed for the formation of the thermal waters in the study area. This is the first comprehensive geochemical and isotope-based investigation of the Kepekler–Ilıcaboğazı geothermal system, providing new insights into its genesis and evolution.