Gases from mud volcanoes of western and central Caucasus

摘要

New data on He and C isotopes in gases from Caucasus mud volcanoes located in Taman Peninsula (TP, Russia)nand Kakhety District (KD, Georgia) have been produced and included in a wider metadata-set, allowing a com-nparison between gas geochemistry of the two regions. In TP, the 3nHe ⁄n4nHe (R) ratios are typical of radiogenicncrustal helium (R ⁄ Ratm u0002 0.03, on average). In KD, the helium isotopic ratio Rmax = 223 · 10)8n(R ⁄ Ratm = 1.59)nindicates an admixture of mantle-derived helium in gases from the central segment of the Caucasus. Thenrepeated sampling showed that the 3nHe ⁄n4nHe values in both TP and KD mud volcano emanations are effectivelynconstant through time, unlike d13nC values in accompanying CH4 and CO2. Moreover, d13nC values in these gasesnshow lateral variations within the limits of volcanic edifice. Positive correlations found between the pairsn(n3nHe ⁄n4nHe)meas–(n4nHe ⁄n20nNe) and (n3nHe ⁄n4nHe)corr–[He] suggests that there are two helium end-members in KD gasesnrepresenting ‘near-surface’ and ‘deep-originated’ components. There is no correlation between methane andnmantle-derived helium in Caucasian mud volcano gases. CH4 and radiogenic helium are generated in Cenozoicnmolasse sequences that fill structural depressions.