Carbon and oxygen stable isotope study of the Majdar travertine deposits, southeast of Ardabil

Freshwater carbonates differ from each other according to isotopic geochemical properties. The study of carbon and oxygen stable isotopes is one of the most important study tools for carbonates, including travertine deposits. In Majdar area, which is located in the western Alborz-Azerbaijan tectonic zone, Quaternary travertine deposits are located in the Eocene porphyry andesite volcanic units. Based on mineralogical studies, travertines are mainly composed of aragonite. The mean values of δ13C and δ18O isotopes of travertines in the study area are + 6.47 and -8.77, respectively, which indicates the thermogenic origin of travertines. Also, the mean value of δ13C (CO2) is -2.73, which suggests an inorganic and endogenic origin for CO2. It is thought that CO2-rich hydrothermal fluids have provided the calcium bicarbonate ions needed to form travertine after circulation within the calcareous unit in the area and reacting with it. Then, these fluids ascended through the fault systems and deposited travertine on the surface.