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We applied Ba diffusion chronometry to sanidine phenocrysts from the trachytic Agnano-Monte Spina eruption (A-MS ~4.7 ka) in order to constrains the time between reactivation and eruption of magma batches in the Campi Flegrei caldera (CFc, Napoli, southern Italy), one of the most hazardous volcanic areas on Earth. The A-MS products display variable 87Sr/86Sr and trace elements features that suggest magma mixing between two magma end-members. Resulting zonation patterns in phenocryst minerals are an ideal case to study timescales of magma mobilization at the CFc. Ba zonation profiles of 50 sanidine phenocrysts (Fig. 1) have been determined through combined energy-dispersive and wavelength-dispersive electron microprobe analyses (EDS-WDS-EMPA). We focused on compositional breaks near the rim of the crystals that represent the last mixing event prior to eruption. Profiles were measured by approaches: (1) quantitative BaO point-measurements at 10 μm spatial resolution, (2) gray-scale swath profiles from accumulated BSE images and (3) Ba X-ray scans. Since Ba dominates the backscattered electron intensities in sanidines, grayscale gradients extracted from the images using ImageJ® are a diffusive tracer proxy. Each profile from the different approaches was interpolated through a non-linear Boltzmann fit curve with Mathematica® software. We always choose the steepest gradients close to the crystal rims. However, any effects from cutting angles or crystal orientation always give longer apparent diffusion times. Our diffusion time estimates are thus minimum values. Gray-scale swath profiles and X-ray scans modelled for 930°C give short diffusion times of

Melt inclusions in phenocrysts from some shoshonite to latite eruptive products of Ischia Island (Southern Italy) provide a window on the deep magmatic feeding system. Together with similar products from the other Neapolitan volcanoes (Procida, Campi Flegrei and Somma-Vesuvius), they probe the deep physico-chemical conditions of magmas generated in a mantle contaminated by slab derived fluids/melts largely dominated by CO2. The analyzed melt inclusions bear clear evidence for CO2 dominated gas fluxing and consequent dehydration of magma portions stagnating at major crustal discontinuities. In general, magma differentiation at Ischia takes place under very oxidized conditions determined by an unusual, nearly equimolar, proportion of divalent and trivalent iron in the melt. Budgets of magma degassing show that at Ischia there is much less magma than that needed to directly supply the amount of magmatic fluids released at surface, thus constraining the role of CO2 rich deep fluids in originating the volcanism and generating caldera resurgence. The acquired data, together with those from the other Neapolitan volcanoes, show that, despite the compositional and eruptive style differences within the poorly extended Neapolitan Volcanic area, the different kinds of volcanism are linked by supercritical CO2 fluids produced by devolatilization of subducted terrigenous-carbonatic metasediment, that infiltrate the mantle wedge, generate magmas and control their ascent up to eruption. In particular, fluid upraise and accumulation at crustal levels beneath Neapolitan volcanoes occurs with different flow-rates that depend on the major geological structures, particularly NW-SE normal and NE-SW transfer regional fault systems

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.

The Campi Flegrei caldera collapsed 39 ka in the Neapolitan area (southern Italy) after the Campanian Ignimbrite eruption. This eruption, recognized as the largest and the most cataclysmic volcanic event in the Mediterranean area over the past 200 ka, extruded not less than 300 km3 of trachytic magma. Controversy exists over the timescales required to assemble a such large volume of silicic melt and thus whether large magmatic reservoirs can actually persist below active volcanic systems over prolonged periods of time. Uranium-series analyses have been performed on Campanian Ignimbrite whole-rocks, glass matrixes and separated minerals. The compositionally most evolved sample which is most radiogenic with respect to Sr isotopes records a reference age of 71 ka. By contrast, U-Th internal isochrones of the three compositionally least evolved samples give identical initial Th isotope ratios and yield consistent ages predating the eruption by up to 6.4 ka. Therefore the time preceding this large caldera-forming eruption during which the large volume of Campanian Ignimbrite magma assembled and mixed is 6.4 ± 2.1 ka. The highest Pb and Nd isotopic ratios and 230Th/232Th activity ratios together with the oldest reference age of the most evolved samples suggest the existence of a resident magma body possibly related to a magmatic system that is known to have fed earlier magmatic activity in the Campi Flegrei area. Conversely, the younger age of the least evolved and least radiogenic magma dates the crystallization/differentiation event of a chemically and isotopically new magma batch entering the reservoir of the resident magma some few thousand years before the cataclysmic eruption. The progress of crystallization yielded high-water contents (up to 6-7 wt%), thus producing an overpressurized gas cap. The onset of the eruption tapped this cap, with consequent depressurization and fast volume decrease that facilitated or even drove the caldera collapse, and allowed the water-rich magma to be discharged during the pyroclastic current phase.

The late Pleistocene trachytic Campanian Ignimbrite (CI; 300 km3 DRE) covers the Campanian Plain near Naples, and is found behind ridges more than 1,000 m high at 80 km from source, the Campi Flegrei caldera (CFc). Distal ignimbrite deposits reveal downhill and/or downvalley flow directions prior to deposition, whereas in the absence of significant topography, deposition came from a flow moving in a roughly radial direction. These features point to very dilute currents, that together with the huge amount of discharged magmatic material, suggest a magma reservoir highly enriched in volatiles, rather than fluid entrainment from hydrothermal bodies or seawater. Petrologic and geochemical modelling of erupted products and their chemical and textural zoning, together with MI-based studies of gas-melt saturation, corroborate this view and show that the CI huge volume differentiated and mixed at shallow depth (6-3 km). With respect to compositionally similar but also smaller CFc eruptions (e.g. Agnano-Monte Spina, A-MS), the large amount of volatiles discharged by IC was likely due to fractional crystallization and longer residence times of volatiles sourced by the subducting Appennininc slab. This yielded high-water contents (up to 6-7 wt%), as well as high void fractions (~70-80% for IC, ~45% for A-MS) and also produced an overpressurized CO2-dominated gas cap (about 150 km3), uniformly distributed at the top of the magma chamber. The onset of the eruption tapped this cap, with consequent depressurization and fast volume decrease that facilitated or even drove the caldera collapse, and allowed the water-rich magma to be discharged during the pyroclastic current phase. The gas saturation-based estimates of the tapped foamy magma are compatible with the extent of magma chamber roof collapse, strong expansion revealed by textural data and transport and deposition mechanisms, reflecting depressurization and magma inflation within the collapsed and laterally confined caldera.

The late Pleistocene trachytic Campanian Ignimbrite (CI; 300 km3 DRE) covers the Campanian Plain near Naples, and is found behind ridges more than 1,000 m high at 80 km from source, the Campi Flegrei caldera. Distal ignimbrite deposits reveal downhill and/or downvalley flow directions prior to deposition, whereas in the absence of significant topography, deposition came from a flow moving in a roughly radial direction. These features point to very dilute currents, that together with the huge amount of discharged magmatic material, suggest a magma reservoir highly enriched in volatiles, rather than fluid entrainment from hydrothermal bodies or seawater. Petrologic and geochemical modelling of erupted products and their chemical and textural zoning, together with MI-based studies of gas-melt saturation, corroborate this view and show that the CI huge volume differentiated and mixed at shallow depth (6-3 km). The progress of crystallization yielded high-water contents (up to 6-7 wt%), thus producing an overpressurized CO2-dominated gas cap (about 150 km3), uniformly distributed at the top of the magma chamber. The onset of the eruption tapped this cap, with consequent depressurization and fast volume decrease that facilitated or even drove the caldera collapse, and allowed the water-rich magma to be discharged during the pyroclastic current phase. The gas saturation-based estimates of the tapped foamy magma are compatible with the extent of magma chamber roof collapse, strong expansion revealed by textural data and transport and deposition mechanisms, reflecting depressurization and magma inflation within the collapsed and laterally confined caldera.

Ischia, a volcano island located 18 miles NW offshore Naples (Southern Italy), is a densely populated active caldera (last eruption 1302 A.D.). Melt inclusions (MIs) in phenocrysts of the Vateliero and Cava Nocelle shoshonite-latite eruptive products (VI-IV century B.C.) constrain structure and nature of the Ischia deep magmatic feeding system. The volcanic rocks of Ischia bear clear evidence for CO2 dominated gas fluxing, under very oxidized conditions, and consequent dehydration of magma portions stagnating at major crustal discontinuities. The geochemical features of the studied products make Ischia a natural borehole probing the deep physico-chemical conditions of magmas generated in a mantle contaminated by slab derived fluids largely dominated by CO2.Volatile concentrations in MIs require gas-melt equilibria between 3 and 18 km depth. MI-based evidence for CO2 fluxing is further supported by selective enrichment of K and related trace elements during magma differentiation. Accordingly, the budgets of magma degassing show that at Ischia there is much less magma than that needed to directly supply the amount of released magmatic fluids, thus constraining the role of CO2 rich deep fluids in originating the volcanism and generating caldera resurgence. The acquired data, together with those from the other Neapolitan volcanoes (Procida, Campi Flegrei –CF-, and Somma-Vesuvius –SV- ) show that, despite the compositional and eruptive style differences within the poorly extended Neapolitan Volcanic area, the different kinds of volcanism are mostly linked by supercritical CO2 fluids produced by devolatilization of subducted terrigenous-carbonatic metasediment, that infiltrate the mantle wedge, generate magmas and control their ascent up to eruption. Geochemical features of Ischia and the other volcanoes reveal that the ,extent of fluid contamination of the pre- subduction asthenospheric-mantle was similar at Ischia, Procida, CF and SV. However, the different isotopic composition (more enriched in radiogenic Sr at Ischia, CF, SV with respect to Procida) and water amount in the source (almost double at Ischia, CFc and SV than at Procida), reflect the different flow-rate of deep slab-derived fluids through the mantle wedge that, in turns, controls the amount of magma generation. The high bulk permeability below Ischia, CFc and SV, determined by the intersection of regional NW-SE normal and NE-SW transfer fault systems, favours fluid upraise and accumulation at crustal levels, with consequent magma production and storage larger than at Procida, that is located along the NE-SW system.

Assessment of time and space relationships among magmatism, volcanism, and resurgence of mediumsize calderas is a necessary tool to formulate a general model for their dynamics which also permits to forecast their evolution. To define a general hypothesis for the Campi Flegrei caldera, in a persistent state of unrest, the Ischia and Pantelleria medium-size resurgent structures, in variable stages of evolution, have also been investigated. In particular some parameters such as the structural and volcanological evolution, with emphasis on resurgence dynamics and coeval volcanism, and the evolution, present state and role of the magmatic system in resurgence, have been defined. For the Campi Flegrei caldera, the data collected during unrest episodes have also been taken into account, together with those from past eruptions. They corroborate the hypothesis that the unrest episodes are transient short-term events within the long-term deformation related to caldera resurgence. The geometry of the short-term deformation is strictly related to the structural setting of the caldera. The sub-surface processes have been dominated by joint degassing of two magmatic bodies, at 3-4 and 8 (or more) km depth, with the shallower formed by magma ascending from the deeper body. Both bodies contribute to the hydrothermal system, but the shallow magma is fluxed by the continuous upstream of CO2-richer gas released by the deep body. The two-layer degassing magma allows explaining geochemical and petrological features of unrest and volcanism. The joined interpretation of geological, geodetic, and geochemical data on the three calderas is an innovative approach that adds a time-perspective on how resurgent calderas behave. The proposed general hypothesis will help in long- and short-term volcanic hazards assessment and will support Civil Defence Authorities in elaborating actions devoted to volcanic risk reduction.

Volcanic calderas are affected by unrest episodes usually dominated by hybrid magmatic-hydrothermal system dynamics. Unrest episodes can evolve to eruptions of variable intensity, up to Plinian. Campi Flegrei caldera (CFc) is a type-location for this kind of activity escalation. CFc offers unique opportunity to join volcanological information to a long record of geochemical parameters. This allows understanding the role that magmatic system plays on variations displayed by the hydrothermal system. We model uneruptive unrest episodes as driven by i) the shallow emplacement (~4 km depth) of one volatile-rich magma batch ascending from a deep (≥ 8 km) magmatic body of regional extent, ii) subsequent gas separation with degassing driven by crystallization and iii) fluxing from the deep magmatic body. Our model matches three decades of geochemical constraints from fumarole discharges, as well as data from melt inclusions of past CFc eruptions. Besides, magma physical properties demanded for modeled degassing conditions are in good agreement with existing geophysical data. Our results open new perspectives to the definition of unrest scenarios at highly-populated CFc, as well as other resurgent calderas (e.g., Orsi et al., This Assembly).

The Pomici Principali Tephra (10.3 ka) is one of the two highest-magnitude eruptions of the Campi Flegrei caldera over the past 15 ka. This caldera is active and largely inhabited, consequently it is one of the most dangerous volcanic areas on Earth. Stratigraphic and stratimetric studies carried out on an area of about 1000 km2 allowed us to reconstruct both eruption sequence and dynamics. On the basis of both lithological characteristics and dominant emplacement mechanisms, the sequence has been divided in five members: A) a basal ash fallout member, produced by a phreatomagmatic opening phase; B) a second member composed of coarse fallout layers deposited by a pulsating Plinian column; C) a third member which includes an alternation of ash and coarse pumice layers, generated during a magmatic-phreatomagmatic explosion phase; D) a fourth member composed of three thick coarse fallout layers separated by ash layers and generated by a mainly magmatic phase, during which a pulsating column reached the maximum height of about 22 km; E) an upper and fifth member, composed of fine- to coarse-ash surge beds, produced by a phase dominated by phreatomagmatic explosions. During this final phase pyroclastic surges flowed both inside and outside the caldera depression. The Pomici Principali erupted products were investigated through geochemical and isotope analyses and glass inclusion studies in order to shed light on the processes operating in the plumbing system. Whole rocks and glasses, representative of the complete stratigraphyc sequence, have a fairly homogeneous chemical composition. The isotope data on whole rocks, glasses and mineral phases suggest that at least two isotopic components were extruded during the course of the eruption. One of these components, the least radiogenic one, is represented by light-green pyroxenes. The most radiogenic component is represented by glasses and the majority of the separated minerals. Glass inclusion data were collected to highlight the pre-eruptive storage conditions of the erupted magma

Volcanic calderas are affected by unrest episodes usually dominated by hybrid magmatic-hydrothermal system dynamics. Unrest episodes can evolve to eruptions of variable intensity, up to Plinian. Campi Flegrei caldera (CFc) is a type-location for this kind of activity escalation. CFc provides unique opportunity to build-up a volcanological model in which geochemical, geological and geophysical data are interpreted together to understand how degassing following magma emplacement drives the caldera resurgence. Uneruptive unrest episodes reflect i) a sudden increase of the CO2 magmatic fraction following the shallow emplacement of one single volatile-rich magma batch, ii) voluminous gas separation in a nearly single-step process, and iii), on longer times scales of 10-20 years, degassing driven by crystallization and deep gas fluxing. Our volcanological model matches three decades of geochemical constraints from fumarole discharges, as well as data from melt inclusions of past CFc eruptions. Besides, magma physical properties demanded for modeled degassing conditions are in good agreement with existing geophysical data. Our results open new perspectives to the definition of unrest scenarios at highly-populated CFc.