The 40Ar/36Ar Isotope Ratio in Spontaneous Gases of Mineral Waters in the Caucasian Region

Regularities in the distribution of ⁴⁰Ar/³⁶Ar values in spontaneous gases were examined for the Caucasian region. It was revealed that the maximal values of this parameter are characteristic for methane water seepages located along the periphery of this mountain structure (Dagestan Wedge and southern and northwestern slopes of the Greater Caucasus). The excess ⁴⁰Ar here is probably genetically related to active tectonic processes (nappes, high seismicity, stresses, and others) rather than mantle source. By contrast, the carbon dioxide of recent volcanic areas is characterized by nearly atmospheric (296) and lower (up to 285) ⁴⁰Ar/³⁶Ar values. In such springs in the Elbrus region, an inverse correlation was revealed between the ⁴⁰Ar/³⁶Ar ratio in gases and concentrations of geothermometer elements (Li, K, Rb, and Cs) in water. This suggests that the Ar isotopic signature is governed by thermal conditions of the gas–water fluid circulation. The contribution of mantle gases with high ⁴⁰Ar/³⁶Ar values turns out to be undetectable against the background of these processes.