The Breccia Museo is one of the most debated volcanic formations of the Campi Flegrei volcanic district. The deposit, made up of six distinctive stratigraphic units, has been interpreted by some as the proximal facies of the major caldera-forming Campanian Ignimbrite eruption, and by others as the product of several, more recent, independent and localized events. New geochemical and chemostratigraphical data and Ar-Ar age determinations for several units of the Breccia Museo deposits (~39 ka), correlate well with the Campanian Ignimbrite-forming eruption. The chemical zoning of the Breccia Museo deposits is interpreted here to be a consequence of a three-stage event that tapped a vertically zoned trachytic magma chamber.

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Abstract. The Campi Flegrei hosts numerous monogenetic vents inferred to be younger than the 15 ka Neapolitan Yellow Tuff. Sanidine crystals from the three young Campi Flegrei vents of Fondi di Baia, Bacoli and Nisida were dated using 40Ar/39Ar geochronology. These vents, together with several other young edifices, occur roughly along the inner border of the Campi Flegrei caldera, suggesting that the volcanic conduits are controlled by caldera-bounding faults. Plateau ages of ∼9.6 ka (Fondi di Baia), ∼8.6 ka (Bacoli) and ∼3.9 ka (Nisida) indicate eruptive activity during intervals previously interpreted as quiescent. A critical revision, involving calendar age correction of literature 14C data and available 40Ar/39Ar age data, is presented. A new reference chronostratigraphic framework for Holocene Phlegrean activity, which significantly differs from the previously adopted ones, is proposed. This has important implications for understanding the Campi Flegrei eruptive history and, ultimately, for the evaluation of related volcanic risk and hazard, for which the inferred history of its recent activity is generally taken into account

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The city of Naples can be considered part of the Campi Flegrei volcanic field, and deposits within the urban area record many autochthonous pre- to post-caldera eruptions. Age measurements were carried out using 40Ar–39Ar dating techniques on samples from small monogenetic vents and more widely distributed tephra layers. The 40Ar–39Ar ages on feldspar phenocrysts yielded ages of c. 16 ka and 22 ka for events older than the Neapolitan Yellow Tuff caldera-forming eruption (15 ka), and ages of c. 40 ka, 53 ka and 78 ka for events older than the Campanian Ignimbrite caldera-forming eruption (39 ka). The oldest age obtained is 18 ka older than previous dates for pyroclastic deposits cropping out along the northern rim of Campi Flegrei. The results of this study allow us to divide the Campi Flegrei volcanic history into four main, geochronologically distinct eruptive cycles. A new period, the Paleoflegrei, occurred before 74–78 ka and has been proposed to better discriminate the ancient volcanism in the volcanic field. The eruptive history of Campi Flegrei extends possibly further back than this, but the products of previous eruptions are difficult to date owing to the lack of fresh juvenile clasts. These new geochronological data, together with recently published ages related to young volcanic edifices located in the city of Naples (Nisida volcano, 3.9 ka) testify to persistent activity over a period of at least 80 ka, with an average eruption recurrence interval of ∼ 555 years within and adjacent to this densely populated city

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