Fluid-induced and vapor-sustained magma production at the Stromboli and Campania Province volcanoes (Southern Italy)

Abstract The Italian territory is subject to widespread deep degassing, characterized by large carbon dioxide emissions. The peri-Tyrrhenian area of southern Italy is where these emissions are accompanied by active volcanism, with magmas displaying K-alkaline affinity and covering a wide compositional spectrum. It has long been debated whether such CO 2 production is related to decarbonation of crustal limestones or to other deep sources. However, a global view of melt inclusions and plume data from southern Italian volcanoes suggests that magmas are produced under CO 2 -rich, fluid-buffered conditions that begin in the mantle. Nevertheless, what we can “see” when “looking at” these data depend on the reliability of multicomponent saturation models for volatile-melt systems. Using an accurate non-linear thermodynamic model, I process relevant melt inclusion data and infer that volcanic plumbing systems are steadily infiltrated by deep mantle-derived fluids with a CO 2 /H 2 O molar ratio between 0.5 and 1, which increases southward. Furthermore, melt inclusions show variable degrees of CO 2 -enrichment (fluxing), related to (1) increasing CO 2 /H 2 O vapor (gas) ratio and flux within the ascending mantle-derived fluid or (2) cross-sectional variations of the ascending flow. The first scenario depends on variations in the mantle source, particularly its composition (mainly alkali content) and the pressure/depth of early fluid release. The second scenario accounts for the fact that molten layers retain water and release a relatively CO 2 -enriched fluid upward, resulting in an effective H 2 O-CO 2 chromatography-like separation as long as melting goes on. The two scenarios are likely to operate in combination over time and space. This study suggests that activity and evolution at nearby volcanoes are driven more by structurally guided fluid pathways and the development of local chambers than by the persistence of a single deep magma chamber.