Isotope and chemical compositions of thermal fluids at Tekman Geothermal Area (Eastern Turkey)

Abstract

The aim of this study was to understand geochemistry of thermal fluids circulating in the basin at the southwest of Tekman (Erzurum, Turkey) Geothermal Province in Eastern Anatolia as well as to estimate reservoir temperature and its heat source by assessment of helium and carbon isotopic compositions of liquid and gas samples. Deep thermal and cold shallow groundwaters are NaCl type (Cerme and Ilipinar springs) and Ca-Mg-HCO₃ type, respectively. The discharge temperatures of thermal waters vary between 29 and 57°C. The reservoir temperatures were estimated by solute silica and cation geothermometers vary from 80 to 110°C. CO₂ is the dominant gas in geothermal fluids with variable amounts of nitrogen, helium and CH₄. The isotopic ratios of helium that range from 1.03 to 1.54Ra_c show a range crustal to magmatic-type values. The isotopic composition of carbon (CO₂) obtained from the bubbling and dissolved gases shows the variation from -0.2 to 3.4‰ vs. PDB. The mantle derived fluids interact at shallower levels with circulating meteoric waters and originate geothermal systems from which equilibration temperatures were estimated up to 192°C by gas geothermometers.