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Somma-Vesuvius is one of the most dangerous active Italian volcanoes, due to the explosive character of its activity and because it is surrounded by an intensely urbanized area. For mitigating the volcanic risks, it is important to define how the Somma-Vesuvius magmatic system worked during the past activity and what processes took place. A continuous coring borehole drilled at Camaldoli della Torre, along the southern slopes of Somma-Vesuvius, allowed reconstructing its volcanic and magmatic history in a previous study. In this work, the wide range of chemical (Mg# = 92–69) and isotopic (87Sr/86Sr = 0.70781–0.70681) compositions, collected on single clinopyroxene crystals separated from selected lava flow units of the Camaldoli della Torre sequence, have been integrated with the already available bulk geochemical and Sr-isotopic data. The detected chemical and isotopic signatures and their variation through time allow us to better constrain the behavior of the volcano magmatic feeding system, highlighting that mixing and/or assimilation processes occurred before a significant change in the eruptive dynamics at Somma-Vesuvius during a period of polycyclic caldera formation, starting with the Pomici di Base Plinian eruption (ca. 22 ka).

The eruptions of Campi Flegrei (Southern Italy), one of the most studied and dangerous active volcanic areas of the world, are fed by mildly potassic alkaline magmas, from shoshonite to trachyte and phonotrachyte. Petrological investigations carried out in past decades on Campi Flegrei rocks provide crucial information for understanding differentiation processes in its magmatic system. However, the compositional features of rocks are a palimpsest of many processes acting over timescales of 100–104 years, including crystal entrapment from multiple reservoirs with different magmatic histories. In this work, olivine, clinopyroxene and feldspar crystals from volcanic rocks related to the entire period of Campi Flegrei’s volcanic activity are checked for equilibrium with combined and possibly more rigorous tests than those commonly used in previous works (e.g., Fe–Mg exchange between either olivine or clinopyroxene and melt), with the aim of obtaining more robust geothermobarometric estimations for the magmas these products represent. We applied several combinations of equilibrium tests and geothermometric and geobarometric methods to a suite of rocks and related minerals spanning the period from ~59 ka to 1538 A.D. and compared the obtained results with the inferred magma storage conditions estimated in previous works through different methods. This mineral-chemistry investigation suggests that two prevalent sets of T–P (temperature–pressure) conditions, here referred to as “magmatic environments”, characterized the magma storage over the entire period of Campi Flegrei activity investigated here. These magmatic environments are ascribable to either mafic or differentiated magmas, stationing in deep and shallow reservoirs, respectively, which interacted frequently, mostly during the last 12 ka of activity. In fact, open-system magmatic processes (mixing/mingling, crustal contamination, CO2 flushing) hypothesized to have occurred before several Campi Flegrei eruptions could have removed earlier-grown crystals from their equilibrium melts. Moreover, our new results indicate that, in the case of complex systems such as Campi Flegrei’s, in which different pre-eruptive processes can modify the equilibrium composition of the crystals, one single geothermobarometric method offers little chance to constrain the magma storage conditions. Conversely, combined methods yield more robust results in agreement with estimates obtained in previous independent studies based on both petrological and geophysical methods.

The 56 ka Monte Epomeo Green Tuff (MEGT) resulted from the largest volume explosive eruption from Ischia island (south Italy). Its tephra is one of the main stratigraphic markers of the central Mediterranean area. Despite its importance, a detailed characterisation of the petrography and mineral chemistry of MEGT is lacking. To fill this gap, we present detailed petrographic description and electron microprobe mineral chemistry data on samples collected on-land from the MEGT. Juvenile clasts include pumice, scoria, and obsidian fragments with porphyritic/glomeroporphyritic, vitrophyric, and fragmental textures. The porphyritic index is 13–40 vol.%, and phenocryst phases include alkali-feldspar, plagioclase, clinopyroxene, ferrian phlogopite, and titano-magnetite, in order of decreasing abundance; accessory phases include sphene, hydroxy-fluor-apatite, and rare edenite. Plagioclase varies from predominant andesine to subordinate oligoclase, whereas alkali-feldspar is more variable from sanidine to anorthoclase; quasi-pure sanidine commonly occurs as either rim or recrystallisation overgrowth of large phenocrysts due to hydrothermal alteration. Secondary minerals include veins and patches of carbonate minerals, Fe-Mn oxyhydroxides, clay minerals, and zeolites. Clinopyroxene is ferroan diopside (En45–29Fs7–27) and never reaches Na-rich compositions. This feature allows the discrimination of MEGT from aegirine-bearing, distal tephra layers erroneously attributed to MEGT, with implications for the areal distribution of Ischia explosive deposits.