Noble gases and nitrogen: mixing and temporal evolution in the fumarolic fluids of Vulcano, Italy

Since 1979, noble gases (He, Ne, Ar) and N2 in the medium-temperature fumaroles of Vulcano crater have been analyzed repeatedly. During these 10 years of surveillance, variations have been noticed in fluid composition. Until 1986, Ar-40/Ar-36 ratios up to 2000 were found, N2/Ar was 1600 and He/Ar was 1.9, indicating the presence of a deep component as the result of a mixing between mantle and crustal fluids. Since 1987, the atmospheric component has increased and the fluid composition has evolved towards an air-saturated groundwater (ASW). This change is considered to be the result of mixing between magmatic fluids and meteoric waters that release their atmospheric gases on entering the volcanic system. These gases thus mask the magmatic component which has remained more or less constant in the last decade.