Geologic model of the magmatic-hydrothermal system of Vulcano (Aeolian Islands, Italy)

This paper presents a model of the active magmatic-hydrothermal (high-sulfidation) system of La Fossa volcano, based on mineralogical and geochemical studies of hydrothermal alteration on the surface and in the subsoil (geothermal wells and lithic clasts from explosive eruptions). The main engine of this system is represented by the shallow magmatic feeding system of La Fossa, which produces substantial degassing of volatiles (H2O, S, Cl). The introduction of magmatic fluids into the conduit system causes high temperature recrystallisation and metasomatism of the volcanic and sub-volcanic rocks. Lateraly to the volcanic conduits, the magmatic fluids undergo a primary neutralization, forming neutral low permeability hydrothermal zones. During their rise to the surface, the magmatic vapours may condense in groundwater, forming acid solutions that react with rocks to form superficial hydrothermal alteration. Silicic, advanced argillic and intermediate argillic alteration facies develop. This reflects the progressive neutralisation of extremely acid fluids. High contents of trace elements, like Tl and Bi, supporting evidence for magmatic fluid transport, were found close to the high temperature fumaroles (up to 500 degrees C) in the silicic alteration zone of La Fossa.