Active Degassing of Deeply Sourced Fluids in Central Europe: New Evidences From a Geochemical Study in Serbia
Paolo Randazzo, Antonio Caracausi, Alessandro Aiuppa, Carlo Cardellini, Giovanni Chiodini, W. D’Alessandro, Lorenza Li Vigni, Petar Papić, Goranh Marinkovic, Artur Ionescu
Abstract
Abstract We report on the results of an extensive geochemical survey of fluids released in the Vardar zone (central‐western Serbia), a mega‐suture zone at the boundary between Eurasia and Africa plates. Thirty‐one bubbling gas samples are investigated for their chemical and isotopic compositions (He, C, Ar) and cluster into three distinct groups (CO 2 ‐dominated, N 2 ‐dominated, and CH 4 ‐dominated) based on the dominant gas species. The measured He isotope ratios range from 0.08 to 1.19 Ra (where Ra is the atmospheric ratio), and reveal for the first time the presence of a minor (<20%) but detectable regional mantle‐derived component in Serbia. δ 13 C values range from −20.2‰ to −0.1‰ (versus PDB), with the more negative compositions observed in N 2 ‐dominated samples. The carbon‐helium relationship indicates that these negative δ 13 C compositions could be due to isotopic fractionation processes during CO 2 dissolution into groundwater. In contrast, CO 2 ‐rich samples reflect mixing between crustal and mantle‐derived CO 2 . Our estimated mantle‐derived He flux (9.0 × 10 9 atoms m −2 s −1 ) is up to 2 orders of magnitude higher than the typical fluxes in stable continental areas, suggesting a structural/tectonic setting favoring the migration of deep‐mantle fluids through the crust.