Isotopic composition of mud-volcanic waters from the Taman Peninsula (Russia) and from Kakheti (Eastern Georgia)

d18O and dD values in mud-volcanic waters of the Taman Peninsula and Kakheti vary from +0.7 to +10.0 per mil and from -37 to -13 per mil, respectively. These values increase as the Greater Caucasus is approached. Increase in d18O and dD also positively correlates with fluid generation temperatures based on hydrochemical geothermometers. This is accompanied by changes in chemical composition of waters, in which concentrations of alkali metals, HCO3- ion, and boron increase, while concentrations of halogen ions (Cl-, Br-, J-) decrease. Changes in isotopic composition of water are also accompanied by increase of d13C in methane and decrease of d11B in clays. Analysis of formal models of evolution of isotopic composition of mud-volcanic waters shows that mud volcanoes are recharged by freshened water from the Maikop paleobasin with inferred isotopic composition of dD~-40 per mil and d18O~-6 per mil. Based on this assumption, d18O and dD values observed in mud-volcanic waters can be explained not only by processes of distillation and condensation in a closed system, but also by combined processes of isotopic re-equilibration in the water-illite-methane system.