Gases from mud volcanoes of western and central Caucasus

Abstract

AbstractNew data on He and C isotopes in gases from Caucasus mud volcanoes located in Taman Peninsula (TP, Russia) and Kakhety District (KD, Georgia) have been produced and included in a wider metadata‐set, allowing a comparison between gas geochemistry of the two regions. In TP, the 3He/4He (R) ratios are typical of radiogenic crustal helium (R/Ratm ∼ 0.03, on average). In KD, the helium isotopic ratio Rmax = 223 × 10−8 (R/Ratm = 1.59) indicates an admixture of mantle‐derived helium in gases from the central segment of the Caucasus. The repeated sampling showed that the 3He/4He values in both TP and KD mud volcano emanations are effectively constant through time, unlike δ13C values in accompanying CH4 and CO2. Moreover, δ13C values in these gases show lateral variations within the limits of volcanic edifice. Positive correlations found between the pairs (3He/4He)meas–(4He/20Ne) and (3He/4He)corr–[He] suggests that there are two helium end‐members in KD gases representing ‘near‐surface’ and ‘deep‐originated’ components. There is no correlation between methane and mantle‐derived helium in Caucasian mud volcano gases. CH4 and radiogenic helium are generated in Cenozoic molasse sequences that fill structural depressions.