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

The Italian territory is heavily invested by widespread deep degassing characterized by huge emissions of carbon dioxide. The peri-Thyrrenian area of southern Italy is where these emissions are accompanied by active volcanism, with magmas displaying alkalic affinity and covering a wide compositional spectrum. It has long been debated whether such a production of CO ₂ is related to decarbonation of crustal limestones or to other deep source features. However, a global look at melt inclusions and plume data from southern Italian volcanoes suggests that magmas are produced under CO ₂ -rich and fluid-buffered conditions that initiate in the lithospheric mantle. Nevertheless, what we can “see” when “looking at” these data depend on the reliability of multicomponent saturation models for the volatile-melt systems. Using an accurate non-linear thermodynamic model, here 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 ratio between 0.5 and 1 (molar), increasing 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 in the ascending mantle-derived fluid or 2) cross-sectional variations of the ascending flow. The first scenario is related to variations occurring in the mantle source that are about its composition (mainly the 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, determining 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.