The deep plumbing system of the Ischia island: a physico-chemical window on the fluid-saturated and CO2- sustained volcanism of Campania volcanoes (Southern Italy)

Ischia, a volcano island offshore Naples, is a densely populated active caldera as testified by the last eruption in 1302 AD, seismicity, fumaroles, and thermal springs. Ischia magmas record strong evidences for CO2-dominated gas fluxing, under very oxidized conditions. Volatile concentrations within Melt Inclusions require gas-melt equilibria between 3 and 18 km depth. Budgets of magma degassing show that at Ischia there is much less magma than that needed to justify the amount of released magmatic fluids, compatible with a deep CO2 degassing plume. Comparison with nearby volcanoes highlights the role of deep fluids in originating the Neapolitan volcanism. In fact, despite compositional and eruptive style differences, and variable occurrence of differentiation processes, the different kinds of volcanism are linked by supercritical CO2 fluids produced by the devolatilization of subducted terrigenous-carbonatic metasediments. The generation of supercritical fluids due to deep CO2-release represents thus a leitmotiv at Neapolitan volcanoes, within which, Ischia is a natural borehole probing the relatively most undisturbed supercritical CO2, and the deep physico-chemical conditions of magmas generated in a slab-contaminated mantle. Understanding the common volatile source for Neapolitan volcanism means understanding how magmas are produced at large depths and then transferred at shallow levels where they evolve, differentiate and mix/mingle in magma chambers supersaturated of volatiles.