| Abstract |
An area of the Eskisehir Province has been investigated with the aim of constraining its geothermal potential by a hydro-geochemical approach. A total of 19 samples vented over the study area were collected and analyzed for their geochemical features including the chemical and isotopic composition of waters, bubbling, and dissolved gases. The waters can be grouped as calcium and magnesium bicarbonate, calcium and sodium bicarbonate, and sodium bicarbonate-type waters. The isotopic composition varies in the range of -11.48 and -7.69‰ for 18O; -83.1 and -57.6‰ for D, and 0-7.2 ± 0.31 TU (tritium units) and revealed that all the waters were derived from continental meteoric precipitations. The gases (both bubbling and dissolved) are mostly N2-dominated with a significant amount of CO2. The helium isotopic ratios, well above the typical crustal signature of 0.05 Ra (Ra= atmospheric 3He/4He ratio), imply a contribution from mantle-derived products showing they are a mixture of shallow (atmospheric) and deep components (crust and mantle originated). The geological setting of the area reveals it is made by a complex sequence of different rock types including metamorphic (mainly schist and marble) and ophiolitic rocks (Triassic age), granites (Paleocene), sedimentary and volcanic rocks (Miocene and Pliocene), and alluvial materials in (Quaternary). The Miocene and Pliocene units have been considered as cap rocks while the metamorphic units act as reservoir for the thermal fluids. Because of the low permeability of the cap rocks, thermal waters cannot move upward unless connected by faults. Electrical prospections (vertical sounding and self-potential method -SP) were performed to find out low-resistivity zones connected to the high permeability due to the fault and considered as productive zones. The springs are natural indications that a fault connection with deeply buried geothermal water existence. Combining the results of geochemical, geophysical and geological studies, we propose that the heat source of the geothermal system for the eastern sector of the study area can be found in the radioactive decay of U and Th from the granite and granodiorite rocks, although the mantle component in the vented volatiles may indicate heat transfer from deep levels, probably due to the presence of lithospheric structures. Finally, for those areas, according to the silica/chalcedony geothermometry, we roughly estimated water equilibration temperatures in the range of 40–100 °C. |