Waters from mud volcanoes of Azerbaijan: Isotopic-geochemical properties and generation environments

New data on chemical and isotopic properties of waters from 35 mud volcanoes of Azerbaijan show that they are represented by two contrasting types characterized by different mineralization: Cl-Na (M = ∼30–80 g/L) and HCO3-Cl-Na (M = ∼8–15 g/L). Waters of the last type are usually enriched with alkaline metals, B, and Br. Waters of the Cl-Na type are similar in their Cl/Br coefficient with seawater. According to Mg-Li and Na-Li geothermometers, waters were formed at temperatures varying from ∼20 to ∼140°C. Taking into consideration these estimates, “roots” of the volcanoes under consideration should be located at depths of 6.0–7.5 km. The fluid generation temperatures exhibit a tendency for their growth toward the Greater Caucasus orogen. The δD, δ18O, and δ13C (TDIC) values in dissolved inorganic carbon vary from −32 to −12 and −0.6 to +10.4‰ (V-SMOW) or −12.9 to +37.3‰ (V-PDB), respectively. The highest δD, δ18O, and δ13C values are typical of HCO3-Na waters. It is shown that the growth of formation (Mg-Li) temperatures is accompanied by a significant increase of the δ18O(H2O) and δ13C(HCO 3 − ) values along with HCO 3 − concentrations. The degree of water enrichment with Br, B, and alkaline metals also increases. This allows the formation of soda waters from mud volcanoes with elevated 18O and 13C contents to be attribute to relatively high-temperature transformations of mineral and organic matter during the catagenic alteration sedimentary rocks.