N sub(2), Ar, and He as a tool for discriminating sources of volcanic fluids with application to Vulcano, Italy

A detailed analysis of published data on the N sub(2), Ar, and He content and Ar and He isotopic composition of fumarolic fluids from Vulcano crater (south Italy) supports a model with two endmembers comprising magmatic and hydrothermal fluids with correspondingly low and high H sub(2)O content. The magmatic component with the highest super(3)He/ super(4)He and highest absolute concentrations of N sub(2), Ar, and He also has the lowest N sub(2)/Ar and N sub(2)/He ratios (300 and 500, respectively). In contrast, the hydrothermal endmember, with the lower super(3)He/ super(4)He and lower absolute N sub(2), Ar, and He abundances, has high N sub(2)/Ar (1,000) and high N sub(2)/He (>3,000) ratios. The hydrothermal component is also characterized by the highest super(40)Ar/ super(36)Ar ratios (>1,000) and is proposed to be the main carrier of metamorphic gases from the arc crust.