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The Ora Ignimbrite (~275 Ma) is a crystal-rich (~40%), heterogeneous, supereruption-sized (~1300 km3) rhyolite in northern Italy and the final eruptive product of the Athesian Volcanic Group (289–274 Ma), the largest Permian volcanic district in Europe. Two key outcrops, an intracaldera vitrophyre and an outflow vitrophyre, contain well-preserved, glass-bearing juvenile material. We investigate at what scale heterogeneities existed in the Ora magmatic system by studying the geochemical and petrological characteristics of crystal-rich (20–50%) and crystal-poor (<20%) fiamme from the Ora vitrophyres, allowing us to reconstruct critical aspects of Ora's magmatic architecture and pre-eruptive history and granting us further insight into the storage and dynamic processes that occur in large, crystal-rich, silicic systems. Textural analysis of fiamme reveals four types: the intracaldera vitrophyre has very coarse-grained crystal-rich (VCCR) and fine-grained crystal-poor (I-FCP) fiamme, while the outflow vitrophyre has coarse-grained crystal-rich (CCR) and fine-grained crystal-poor (O-FCP) fiamme. The diversity of crystal-poor (I-FCP & O-FCP) fiamme glass trace-element compositions suggests that multiple small crystal-poor magma bodies were dispersed throughout the Ora magmatic system. Compositionally and texturally distinct glass types in single O-FCP fiamme preserve evidence of variable degrees of magma mixing and record different mingling to eruption timescales, revealing that the Ora magmatic system experienced multiple silicic recharge events. In the crystal-rich (VCCR & CCR) fiamme, high crystal contents (VCCR: 40–50%; CCR: 20–40%), large crystals (max grain size: VCCR: 4–10 mm; CCR: 3–4 mm), and interlocking growth textures suggest that these fiamme contain parcels of disaggregated magma mush. High-silica rhyolite glass compositions (77.2–78.3 wt.% SiO2) and extremely depleted Sr (VCCR: <20; CCR: <5 ppm) and Ba (VCCR: <70; CCR: <20 ppm) glass trace-element concentrations indicate that the crystal-rich fiamme glasses represent highly fractionated melts. Crystal-rich fiamme glass trace-element compositions also form discrete, tightly clustered populations, suggesting that multiple crystal-rich, melt-dominated magma bodies existed prior to eruption. We propose that the coexistence of large-scale heterogeneity (e.g. deposit-scale and outcrop-scale) with small-scale homogeneity observed in crystal-rich fiamme is resolved by a model in which at least two separate magma reservoirs, each containing multiple melt-dominant magma bodies, erupted to form the Ora Ignimbrite. [ABSTRACT FROM AUTHOR]

Geophysical data provide the chance to investigate a volcano's dynamics; considerable information can especially be gleaned on the stress and strain patterns accompanying the internal processes and the effect of magma ascent on the main structures triggering earthquakes. Here, we analysed in detail the seismicity recorded over the last two decades on Etna volcano (southern Italy), focusing on earthquakes distribution and focal mechanism clustering; the ground deformation pattern affecting the volcanic edifice with the inflation and deflation phases was also examined. Analysed data were compared in order to shed light on possible relationships with the volcanic activity and to better understand the internal dynamics of the volcano over time. Significant steps during or shortly before major eruptions in the seismic strain release and ground deformation temporal series highlight a straightforward relationship between seismicity occurring at shallow level, inflation/deflation and volcanism. Furthermore, at depths greater than 5–7 km, down to about 20 km, the orientation of the P- and T-axes clearly indicate the existence of a pressure source in the central part of the volcano. All the results underline that the stress field related to the volcano plumbing system interferes with the regional field, partly overriding it. [ABSTRACT FROM AUTHOR]

Mount Somma–Vesuvius is a stratovolcano that represents a geological hazard to the population of the city of Naples and surrounding towns in southern Italy. Historically, volcanic eruptions at Mt. Somma–Vesuvius (SV) include high-magnitude Plinian eruptions, such as the infamous 79 CE eruption that occurred after 295 years of quiescence and killed thousands of people in Pompeii and surrounding towns and villages. The last eruption at SV was in 1944 and showed a Volcanic Explosivity Index (VEI) of 3 (0.01 km 3 of volcanic material erupted). Following the 1944 eruption, SV has been dormant for the past nearly 79 years, with only minor fumarolic and seismic activity. During its long history, centuries of dormancy at SV have ended with Plinian eruptions (VEI 6) that signal the beginning of a new cycle of eruptive activity. Thus, the current dormancy stage demands a need to better understand the mechanism involved in high-magnitude eruptions in order to better predict future eruption magnitude and style. Despite centuries of research on the SV volcanic system, many questions remain, including the evolution of magmatic volatiles from deep primitive magmas to shallower more evolved magmas. Developing a better understanding of the physical and chemical processes associated with volatile evolution at SV can provide insights into magma dynamics and the mechanisms that trigger highly explosive eruptions at SV. In this study, we present new data for the pre-eruptive volatile contents of magmas associated with four Plinian and two inter-Plinian eruptions at SV based on analyses of reheated melt inclusions (MIs) hosted in olivine. We correct the volatile contents of bubble-bearing MIs by taking into account the volatile contents of bubbles in the MIs. We recognize two groups of MIs: one group hosted in high-Fo olivine (Fo 85–90) and relatively rich in volatiles and the other group hosted in low-Fo olivine (Fo 70–69) and relatively depleted in volatiles. The correlation between volatile contents and compositions of host olivines suggests that magma fractionation took place under volatile-saturated conditions and that more differentiated magmas reside at shallower levels relative to less evolved/quasi-primitive magmas. Using the CO 2 contents of corrected MIs hosted in Fo 90 olivine from SV, we estimate that 347 to 686 t d -1 of magmatic CO 2 exsolved from SV magmas during the last 3 centuries (38–75 Mt in total) of volcanic activity. Although this study is limited to only few SV magmas, we suggest that further study applying similar methods could shed light on the apparent lack of correlation between the volatile contents of MIs and the style and age of eruptions. Further, such studies could provide additional constraints on the origin of CO 2 and the interaction between the carbonate platform and ascending magmas below SV. [ABSTRACT FROM AUTHOR]

A key effect of subduction is the upward infiltration of slab-derived melts and fluids to create a chemically and lithologically heterogeneous region in the mantle wedge. Magmatism within the post-subduction setting of peninsular Italy is derived from a sediment-metasomatised lithospheric mantle source, with primitive products recording substantial temporal and spatial variations in the nature and extent of metasomatism. The Roman magmatic province, in central Italy, is host to ultrapotassic (HKS), leucite-bearing magmas that require source modification that is not yet well-constrained in terms of mineralogy and sediment provenance. Here, we present the chemistry and Sr-Nd-Pb isotope compositions of melt inclusions in forsterite-rich olivine (Fo 88−92) from three key Roman volcanic centres (Vulsini, Sabatini, Alban Hills) to characterise the metasomatic imprint of their mantle sources. The melt inclusion suites (Vulsini HKS, Vulsini melilite-bearing HKS, Sabatini HKS, Alban Hills HKS) have clear differences in major-element (K, Ca, Al, P, Ti), volatile (F, Cl, B, Be), trace-element (e.g., Rb, Sr/Y, Th/Nb), and radiogenic-isotope (87Sr/86Sr) compositions that reflect the diversity of the primary melts beneath the region. For each suite, the extraction of melt batches from different domains in a heterogeneous (veined) source rock with different compositions and mineralogies can explain the chemical characteristics of the melts. At least three metasomatic vein types are required to form the respective parental melts and we infer phase assemblages consisting of phlogopite + Ca-amphibole + clinopyroxene ± apatite. The Sr-isotope differences between Vulsini melilite-bearing HKS and Vulsini and Sabatini HKS require at least two distinct metasomatic events to have occurred beneath the Roman province. These events need not be associated with two distinct subduction systems. Instead, we infer that different metasomatic agents could have originated under different P-T-t conditions from different domains in the same subducting slab. [ABSTRACT FROM AUTHOR]

The liquid line of descent from trachyte to pantellerite is controlled primarily by fractional crystallization of alkali feldspar, with whole-rock compositions following a fractionation path along the 'thermal valley' in the peralkaline haplogranite system Qz-Ab-Or-Ac-Ns and terminating at a minimum on the feldspar-quartz cotectic. Although whole-rock compositions for different pantelleritic suites follow nearly identical paths in a Qz-Ab-Or projection that terminate near the experimental minimum (Qz40.5Or34.5Ab25 at 100 MPa, projected from Ac-Ns), matrix glass from samples with near-minimum compositions record extreme differentiation and form a 'cotectic delta' beyond the terminus of the 'thermal valley'. Although each glass trend shows a continuing increase in Zr to >3000 μg/g, the most evolved compositions in each suite differ in peralkalinity (mol [Na + K] / Al) and in the proportions of FeOT, Qz, Ab, Or, and other components, which are related to subtle variations in the mafic phases controlled mainly by differences in oxygen fugacity (f O2) and pressure (P). To determine the controls over mafic mineral crystallization in pantelleritic magmas and the various paths these suites take beyond the apparent (whole-rock) minimum, amphibole-phyric suites from the ~159 ka Cala dell'Altura and Cala Gadir volcanic centres and the ~8–10 ka Cuddia Mida volcanic centre on Pantelleria have been analyzed and compared with each other and with the well-characterized and amphibole-free, compositionally zoned Green Tuff, the ~46 ka caldera-forming ignimbrite of the Cinque Denti caldera. Differences between the extended fractionation trends may be ultimately attributed to variations in oxygen fugacity, depth of emplacement, and water saturation. Shallower (lower pressure) magma reservoirs such as the one for the Green Tuff are water-saturated and undergo degassing, which leads to an increase in relative oxygen fugacity. Deeper (higher pressure) magma reservoirs remain water-undersaturated and retain water in the melt, which both maintains lower relative oxygen fugacities and enables the crystallization of amphibole. Amphibole formation appears to require melt water contents >4 wt%, low oxygen fugacity (<ΔNNO-1.5), and low temperatures (<700°C), although fluorine may stabilize it at higher temperatures in some rocks. [ABSTRACT FROM AUTHOR]

The most frequent volcanic eruptions are of low-intensity and small magnitude. They produce abundant ash-sized (< 2 mm) clasts, which are too small to establish quantitative links between magmatic processes and eruptive dynamics using classic approaches. This inhibits our ability to study the past behaviour of frequently erupting volcanoes, essential to predict their future activity and mitigate their impact. The Palizzi unit (10–13th century, Vulcano, Italy) includes a prototype sequence of ash deposits resulting from prolonged Vulcanian eruptions punctuated by those of two larger sub-Plinian events. We apply Hierarchical Clustering to chemical analyses of clinopyroxene collected along the stratigraphy to decipher magma dynamics during this eruptive period. We identify periods of magma input and we link deep magmatic processes to eruptive dynamics, also showing that our approach can be used to connect magma and eruptive dynamics in any volcanic sequence. This is essential to track the processes occurring during frequent eruptions and to identify the build-up to larger explosive events. [ABSTRACT FROM AUTHOR]

This study provides the first micro‐thermometric data of fluid inclusions (FIs) in mafic loose (disaggregated) xenocrysts and ultramafic xenoliths in explosive products of the melilitite‐carbonatite Mt. Vulture volcano (southern Italy). Pure CO2 late stage FIs hosted in rock‐forming minerals of wehrlite xenoliths and clinopyroxene xenocrysts were trapped at the local crust‐mantle boundary (32 km). In contrast, trapping pressures within the loose olivine xenocrysts are from 3.2 to 4.5 kbar (8–13 km). Considering the ongoing degassing of mantle‐derived CO2 rich gases, together with seismic evidences of the presence of low amount of melts at depth, and the tectonic control of the past volcanic activity, our study opens new perspective about the hazardous nature of the "quiescent" melilitite‐carbonatite volcanoes. Plain Language Summary: The study of fluid inclusions (FIs) (small amount of fluid trapped within minerals) provides important information on variable environments and magmatological processes in which the host minerals were formed. Investigation of the FIs with respect to their composition, trapping pressure and temperature, allow us to constrain magma ascent history. To understand the last explosive volcanic activity of Mt. Vulture volcano (southern Italy), we investigated FIs in mafic minerals and mantle fragments brought to the surface by a melilitite‐carbonatite magma. Our results show the presence of CO2‐rich FIs with trapping pressure corresponding to a depth of 32 km in mantle fragments, and a shallower depth (8–13 km) in mafic mineral. Estimates on magma ascent rate show rapid ascent dynamics to the surface. Our study emphasizes the importance of a multidisciplinary approach that combine geochemistry and petrology to investigate a volcanic system even if the volcano is considered "quiescent," as is the case of Mt. Vulture volcano, where mantle degassing is still ongoing. Key Points: Micro‐thermometric analyses show the occurrence of high‐density CO2‐rich fluid inclusions hosted by minerals within wehrlite xenolithsAscent rate between melilitite‐carbonatite (≈20 m/s) and kimberlite (≈45 m/s) magma is comparableMelilitite‐carbonatite volcanoes can be hazardous even after long time of quiescence (>105 years) [ABSTRACT FROM AUTHOR]

Infrasound is increasing applied as a tool to investigate magma dynamics at active volcanoes, especially at open-vent volcanoes, such as Mt. Etna (Italy), which are prodigious sources of infrasound. Harmonic infrasound signals have been used to constrain crater dimensions and track the movement of magma within the shallow plumbing system. This study interprets the remarkable systematic change in monotonic infrasound signals preceding a lava fountaining episode at Mt. Etna on 20 February 2021. We model the changing tones (0.7 to 3 Hz fundamental frequency) as a rise in the magma column from 172 ± 25 m below the crater rim to 78 ± 8 m over the course of 24 h. The infrasonic gliding disappears approximately 4 h before the onset of lava fountaining as the magma column approaches the flare of the crater and acoustic resonance is no longer supported. The featured 20 February event was just one of 52 lava fountain episodes that occurred at Mt. Etna over the course of 9 months in 2021 and was the only lava fountain episode where dramatic gliding was observed as a subsequent partial collapse of the crater prevented future resonance. The results presented here demonstrate that analysis of infrasonic gliding can be used to track the position of the magma free surface and hence may provide information on the processes taking place within the plumbing system before eruptive activity. [ABSTRACT FROM AUTHOR]

Models of volcanic collapses proposed in the literature rely on combining field examples with analogue and numerical modelling to connect superficial observables to sub-surface volcano-tectonic processes. However, the behaviour of such collapses in an already faulted and fractured medium needs to be better explored. We studied a complex array of normal and reverse faults within the central sector of the active Campi Flegrei caldera, where faults with centimeters-to-meters displacements are hosted in the La Pietra tuff (∼13.5 ka) and the overlying pyroclastic succession of the last ∼5.5 kyr. We analyzed the attitude, kinematics and throw of these structures, employing a UAV-based digital outcrop model. The analysis shows that antithetic normal and reverse faults form in the hanging wall of a pre-existing WNW striking, NNE-dipping master normal fault. Moving northward, the strike of the antithetic faults rotates from WNW to NNW directions, with the latter showing a right-lateral oblique component. The simultaneity and coherence of both kinematics and attitudes are verified by the throw analysis. We associated the formation of this array with the caldera-collapse phase of the Agnano-Monte Spina eruption (∼4.55 ka), which caused off-caldera faulting beyond the main collapsed area. Based on field data, we suggest that during peak caldera-forming phases, wider areas beyond the main caldera scarps can be involved in volcano-tectonic collapses in the presence of a pre-existing fault network and complex tapped reservoirs. This highlights the role of inherited structures in weakening the crust above the magma reservoir that can potentially increase the magnitude and duration of caldera-forming eruptions, as they may induce a broader roof rock subsidence, pressurizing wider regions of the sub-caldera magma system. • We studied a complex array of normal and reverse faults at Campi Flegrei caldera. • These faults occur in the hanging wall of a reactivated master normal fault. • Both normal and reverse faults accommodate the overall displacement. • The array formed during the Agnano Monte Spina Plinian eruption collapse phase. [ABSTRACT FROM AUTHOR]

The Euganean Hills (NE Italy) magmatic district represents the final volcanic activity of the Veneto Volcanic Province. Alkaline to subalkaline magmatic suite dominated by intermediate to felsic volcanic rocks characterises the latest volcanic activity of the Euganean Hills. Magmatic (intrusive and volcanic) enclaves are common in Euganean Hills trachytes. We used the ability of clinopyroxene to record variations of P, T, and fO 2 to reconstruct the geological history of the volcanic enclaves and trachytic host. Despite similar major and trace elements composition, clinopyroxene from host is higher in Ca and Na (and Fe 3 + ) and lower in Mg than enclaves and is slightly enriched in trace elements but with the same pattern distribution. Minor differences in geochemistry and crystal structure of clinopyroxene from enclaves and trachytic host suggest similar parental magmas that differs by small degrees of fractional crystallisation. Clinopyroxene geobarometry performed combining X-ray diffraction with mineral geochemistry for volcanic enclaves–trachytic host combined with amphibole geobarometry for intrusive enclaves and crystal mushes points to a crystallisation pressure range between 4.8–2.0 kbars. Our data support the model of a complex system of magma chambers at intermediate to shallow crustal level where mafic magma accumulated, evolved by fractionation processes and mixed. [ABSTRACT FROM AUTHOR]

We present a new three‐dimensional (3D) image of attenuation beneath Mt. Etna volcano based on the coda normalization method. Mt. Etna is an ideal natural laboratory for the application of new or unconventional tomography techniques owing to high levels of seismicity spanning a wide range of epicentral distances and depths. We retrieved seismic waveforms from the database generated in the 2014 TOMO‐ETNA seismic experiment and performed a joint interpretation of tomographic and geophysical inversion models to better constrain interpretations of the volcanic structure. We compared the attenuation tomography results with seismic inversion models (two P wave seismic models and a 3D coda wave seismic attenuation model) and the literature to highlight and interpret structural elements and their impact on the volcano dynamics. We created a new image of the inner structure of Mt. Etna that will help to constrain present and future volcanic behavior. In particular, we focused on magma storage below the summit area and identified a large high‐attenuation volume that is characterized by physical properties compatible with the presence of magma and other fluids. The existence of such a large volume of magma in the shallow crust below Mt. Etna has implications for the eruptive potential of the volcano. Plain Language Summary: Mount Etna, Italy, is one of the world's most active volcanoes and presents an almost constant state of activity. To correctly interpretate potential volcanic hazards, there is a need to better understand the complex inner structure of the volcano. To this end, Mt. Etna is an ideal natural laboratory for the application of new or unconventional tomography techniques. We analyzed seismic attenuation, which measures the loss of energy of the seismic waves, to obtain a three‐dimensional attenuation model of Mt. Etna. We compared our attenuation tomography results with other geophysical data in order to interpret key structural elements and their impact on volcano dynamics. We identified a large volume below the summit area that is compatible with the presence of magma and other volcanic fluids, highlighting the continued eruptive potential of the volcano. Key Points: Three‐dimensional attenuation images over the first 10 km below Etna volcano obtained by coda normalization methodAttenuation images show partial melt body below Etna volcanoJoint interpretation of different models confirm the high heterogeneity below Etna volcano [ABSTRACT FROM AUTHOR]

Somma-Vesuvius (SV) is an active volcanic system in southern Italy that has generated Plinian eruptions during its history as the infamous 79 CE (Pompeii) eruption. Plinian eruptions produced airfall pumice deposits characterized by white pumice clasts in the lower half part, and by grey pumice clasts in the other upper half part. Plinian pyroclastic deposits are also characterized by the presence of skarn xenoliths. Previous studies on the fluid (FI) and melt inclusions (MI) in the Somma-Vesuvius (SV) skarn xenoliths have widely documented immiscibility between silicate melt and hydrosaline melt (±aqueous chloride-rich liquid‑carbonate/sulfate melt). In this study, we recognize a new type of MI namely composite melt inclusions (CMI) hosted in minerals of SV skarn xenoliths previously studied in the literature. In addition to a review of studies about skarn at SV, we present new microthermometric observations of CMI based on heating experiments using a heating stage. We heated CMI to complete homogenization at 1080 °C, and we cooled the CMI to simulate a natural sequence of phase appearances during magma cooling. At T around 1060 °C the CMI unmixes forming two different silicate melts. Upon further cooling at around 700 °C, the CMI show droplets of chloride immiscible liquids instantly nucleating. The cooling experiments of CMI from high-T are assumed to reproduce on a small scale the sequence of magma cooling prior to eruption below SV. In this case, magma could unmix before eruption forming two different silicate melts producing a chemically stratified reservoir. In support of our heating experiments results of CMI, the reprocessing of SV bulk rock compositions data highlights that magma feeding interplinian eruptions is Fe-and P-rich and Si-poor. In contrast, magma feeding Plinian eruptions is Si-rich and Fe-and P-poor. As experimental studies have demonstrated, immiscibility can occur when one melt is Fe-and P-rich and Si-poor, and the other is Si-rich and Fe-and P-poor and the transition between the two end members is not gradual, resulting in a gap of homogeneous intermediate melt. • Geochemical zonation of the Somma Vesuvius shallow magma chamber • Silicate liquid immiscibility in melt inclusions • Interactions occurring at the contact between magma and limestone country rocks • Magma differentiation by silicate liquids immiscibility • Syneruptive nucleation of unmixed droplets of nonsilicate liquids [ABSTRACT FROM AUTHOR]

Here, we report on the Quaternary Volsci Volcanic Field (VVF, central Italy). In light of new 40Ar/39Ar geochronological data and compositional characterization of juvenile eruptive products, we refine the history of VVF activity, and outline the implications on the pre-eruptive magma system and the continental subduction processes involved. Different from the nearby volcanic districts of the Roman and Campanian Provinces, the VVF was characterized by small-volume (0.01–0.1 km3) eruptions from a network of monogenetic centers (mostly tuff rings and scoria cones, with subordinate lava occurrences), clustered along high-angle faults of lithospheric depth. Leucite-bearing, high-K (HKS) magmas (for which we report for the first time the phlogopite phenocryst compositions) mostly fed the early phase of activity (∼761–539 ka), then primitive, plagioclase-bearing (KS) magmas appeared during the climactic phase (∼424–349 ka), partially overlapping with HKS ones, and then prevailed during the late phase of activity (∼300–231 ka). The fast ascent of primitive magma batches is typical of a tectonically controlled volcanic field, where the very low magma flux is a passive byproduct of regional tectonic strain. We suggest that the dominant compressive stress field acting at depth was accompanied by an extensional regime in the upper crust, associated with the gravity spreading of the Apennine chain, allowing the fast ascent of magma from the mantle source with limited stationing in shallow reservoirs. [ABSTRACT FROM AUTHOR]

Rising magma, dike intrusions, and flank collapse are observed at many volcanoes worldwide, but how they interact is still poorly documented. Extensive synthetic aperture radar interferometry and continuous global positioning system observations captured a sharp dike intrusion at Mount Etna, Italy, during the 2018 paroxysm that triggered a vigorous seaward sliding of the eastern flank connected with brittle failure and deep magmatic resourcing. We propose a feedback process between flank acceleration and magma intrusion that derives from the interaction between the long- and short-term deformation of the volcano. The flank sliding acts as a valve that modulates the emplacement and eruption of magma within the shallow system. Rapid flank acceleration could potentially evolve into sudden collapses and seismic release at shallow depth. In turn, flank slip events could act as a sentinel for changes in magma depth and paroxysmal eruptions at Mount Etna. [ABSTRACT FROM AUTHOR]

In this paper, we present results of the reconstruction of the total grain size distribution (TGSD) of the material erupted during explosive volcanic eruptions at Campi Flegrei (Italy) considering all components (juvenile, lithic and crystal clasts). To date, the few TGSDs made available have been mostly reconstructed by assuming that the tephra deposits consisted of only one component. This simplification can introduce substantial bias in the interpretation of magma fragmentation mechanisms and significantly affect ash dispersion forecasts, since each tephra component has specific aerodynamic characteristics. By means of field investigations and laboratory analyses on samples collected from deposits of the Agnano-Monte Spina and Astroni eruptions, we reconstructed the TGSDs of juvenile, lithic and crystal components via the Voronoi tessellation method. Our results show how the systematic reconstruction of a TGSD, from the component-specific to the bulk TGSD, can provide important information on magma fragmentation mechanisms and wall-rock erosion processes. Results confirm that the bulk TGSD is the combination of the merging of different component subpopulations, according to their own TGSD, density and relative mass proportions. In addition, the integration of component analysis, TGSD and settling velocity data allowed characterization of the aerodynamic behaviour of each component at variable distances from the vent, which can be related to their own parent grain size distribution. The integration of new data from distal tephra deposits for the considered eruptions has thus allowed a reassessment of the erupted volumes of eruptions considered in this research, which are now 3.17 and 0.63 km3, for Agnano-Monte Spina and Astroni, respectively. [ABSTRACT FROM AUTHOR]

Silicic volcanoes are increasingly understood to be underlain by crystal-rich and vertically extensive magma reservoirs within which disequilibrium is widespread. Observations from ignimbrite deposits demonstrate that silicic magma reservoirs are often compartmentalised and compositionally stratified. However, it is currently unclear whether the small (i.e., < 0.1 km3 dense rock equivalent) eruptions that dominate activity at many volcanoes, and peralkaline volcanoes in particular, are fed from similarly complex magma reservoirs as their larger counterparts. Here I report petrographic and geochemical observations from the products of a small peralkaline eruption on Pantelleria, Italy, with the aims of unravelling peralkaline magma assembly processes and evaluating the complexity of reservoirs feeding small silicic eruptions. Matrix glass and whole-rock compositions from the Khaggiar lava flow and Cuddia Randazzo pumice cone reveal that erupted magmas were assembled from at least three distinct magma types stored within a compartmentalised magma reservoir: trachytes, less-evolved pantellerites and evolved pantellerites. Chemical variability in the Khaggiar lava flow was created by at least three distinct processes: the accumulation of evolved macrocrysts into evolved pantellerites; the injection of trachytic magmas into less evolved pantellerites; and the accumulation of relatively primitive macrocrysts into trachytic magmas. Macrocryst textures indicate that both trachytic and pantelleritic domains of the magma reservoir experienced numerous recharge events prior to the one that ultimately triggered eruption. Overall, magmas forming the Khaggiar lava flow and Cuddia Randazzo pumice cone appear to have been assembled in analogous ways to those erupted in much larger events. My observations are in good agreement with those from other peralkaline volcanoes and confirm that magma mingling, crystal cannibalism and macrocryst entrainment are as ubiquitous in peralkaline systems as they are in their calc-alkaline counterparts. [ABSTRACT FROM AUTHOR]

Clinopyroxene growth rates were experimentally determined in a K-basaltic rock from Campi Flegrei Volcanic District (south Italy). The primary objective was to provide constraints on the clinopyroxene crystallization kinetics at high pressure: we carried out a series of experiments at 0.8 GPa, 1030–1250 °C, 1 ≤ H2O ≤ 4 wt.%, with durations of 0.25, 3, 6 and 9 h. Overall, growth rate reaches a maximum value in the shortest experiments (~ 3·10−7 cm·s−1), decreasing to ~ 1·10−8 cm·s−1 in the longest duration runs. Temperature and water content do not seem to significantly affect the growth rate. Moreover, partition coefficients based on the crystal-liquid exchange show that mineral chemistry progressively approaches equilibrium with increasing run duration. Furthermore, to estimate the magma recharge of the deep reservoirs, we combined the determined growth rates with data from thermobarometry and from crystal size distribution analyses of clinopyroxenes in the most primitive scoria clasts of the Campi Flegrei Volcanic District (CFVD). We obtained a minimum residence time of ~ 5 months for the larger clinopyroxene population, and an ascent velocity of ~ 0.5·10−4 m·s−1 for the CFVD K-basaltic magma. The smaller clinopyroxene phenocrysts and microlite populations, however, suggest that the late stage of Procida magma crystallization took place in disequilibrium conditions. [ABSTRACT FROM AUTHOR]

Phase relations, compositions, and modes of two natural primitive alkaline basalts were determined through experiments performed at 0.8 GPa, temperatures between 1000 and 1310 °C, and nominal water (H 2 O i) contents varying from <1 (natural water rock content) to 6 wt%. The two natural samples used as starting material are high-Mg, moderate-K, alkaline basalt scoria clasts (Mg# = 0.68–0.66, Σ alkalis = 4.4 wt%) dispersed within the hydromagmatic tuff of the Solchiaro eruption (Procida Island, southern Italy). These samples are considered representative of parental magmas feeding the Phlegraean Volcanic District, which includes the Campi Flegrei caldera and the Procida and Ischia islands. The composition of the experimental phases has been compared with that of natural rocks to constrain the early stages of crystallization of poorly differentiated magmas from the Phlegraean Volcanic District. Our study shows that the liquidus temperature at H 2 O i < 1 wt% is ~1300 °C whereas with water contents between 1.5 and 3 wt%, and between 4 and 6 wt%, the apparent liquidus temperature decreases of about 50–100 °C, respectively. Under natural water conditions (<1 wt%), the liquidus phase is clinopyroxene, followed by olivine and Cr-spinel and, then, by plagioclase. The increase of H 2 O content in the system enhances olivine stability along with clinopyroxene at the liquidus temperature. The 4–6 wt% water bearing experiments show evidence of H 2 O saturation at 1100 °C, with olivine being replaced by orthopyroxene later joined by pargasitic amphibole and minor amounts of oxide starting from 1080 °C. The composition of glasses in the experiments with low H 2 O i content is consistent with the trachybasaltic products of Procida; glasses obtained in the runs with 1.5–3 wt% water resemble the trend formed by the shoshonitic products of Campi Flegrei. The water-saturated experiments produced variably alkali-depleted residual glasses whose composition converges toward the subalkaline field. The compositions of the experimental clinopyroxenes match well those found in the Campi Flegrei products for which we have estimated crystallization conditions from 1140 to 1200 °C of temperature and from 0.6 to 0.9 GPa of pressure (22–33 km). Phase equilibria constraints and clinopyroxene compositions suggest that the parental magmas of Procida likely contained <2 wt% of H 2 O and were affected by an early stage of fractionation at a depth corresponding to the local Moho (~ 25 km corresponding to ~ 0.8 GPa assuming an average crustal density of 2.8 g/cm3). Based on our results, an early magmatic storage at this level could have caused a deep degassing process able to remove variable proportions of Na and K from the melt. • Phase relations of K-basalt at high-pressure and at anhydrous-hydrous conditions. • Piston cylinder experiments on the primitive Phlegraean magmas. • Differentiation of Phlegraean Volcanic District parental magmas at the Moho depth. • Deep degassing process removes variable proportions of Na and K from the melt. [ABSTRACT FROM AUTHOR]

• U-Pb CA-ID-TIMS dates of zircon from plumbing system of a Permian caldera. • Distribution of ages interpreted through a new zircon saturation model. • Relative decrease of zircon mass with time implies monotonic cooling. • Late peak in zircon crystallization indicates episodic increase in heat supply. • Evidence for open-system processes preserved in zircon record of super-eruptions. The emplacement history and thermal evolution of subvolcanic magma reservoirs determine their longevity, size, and ability to feed volcanic eruptions. As zircon saturation is dependent on melt temperature and composition, quantitative analysis of zircon age distributions provides insight into the timing and magnitude of intensive parameter variations during the lifetime of a magma reservoir. Here we present chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb zircon crystallization ages and in-situ zircon trace-element geochemistry for a suite of caldera-related, coeval plutonic and volcanic units of the Permian Sesia Magmatic System (northern Italy). This dataset documents the protracted growth and evolution (∼1 Myr) of a voluminous (>1000 km3), upper crustal (3.5–2.0 kbar) silicic magma reservoir. Systematic changes in zircon composition with time reveal episodic intrusions of new magma into a single, progressively differentiating reservoir which was dominantly kept at high crystallinity conditions (>60 vol.%). The volcanic and plutonic units both show dispersed and heterogeneous CA-ID-TIMS age distributions. A stochastic, thermodynamics-based zircon saturation model accounting for fractional crystallization, recharge and thermal rejuvenation effects on zircon growth and stability in a rhyolitic magma body reproduces the observed distributions of zircon U-Pb ages. Model results suggest that zircon compositional variability and crystallization age heterogeneity, characteristic of the Sesia and other large silicic systems, distinguish open- and closed-system magmatic processes. Specifically, an increase of the mass of crystallized zircons over time is the hallmark of thermally and chemically mature magma reservoirs, capable of producing voluminous eruptions upon changes in the thermal and mechanical state of the system. Conversely, a decrease in crystallized zircon mass over time characterizes systems where crystallization dominates over magma mobility, hindering substantial mass release during eruptive events. We suggest that quantitative analyses of dispersed zircon crystallization age distributions obtained with high-precision techniques can be applied to the plutonic and volcanic record to identify mature silicic magma reservoirs whose properties and storage conditions allowed for catastrophic caldera-forming eruptions. This work provides the petrologic community with a new tool to investigate the genesis and evolution of zircon-bearing intermediate to silicic intrusive magmatism and caldera-forming volcanism through time and across tectonic settings. [ABSTRACT FROM AUTHOR]

Despite the many scientific contributions and advances in our understanding of magmatic processes that have been derived from the analyses of melt inclusions (MI), it is difficult to find examples of chronologically constrained MI, tracking a magma mixing event before an eruption. Here, we studied a single, reversely zoned olivine phenocryst with multiple MI from the Solchiaro eruption on Procida Island (Phlegrean Volcanic District, Southern Italy) to understand both the order of appearance of basaltic versus trachybasaltic magmas and the reliability of MI to record a magma mixing event. Based on phosphorous X-ray mapping, MI are characteristic of three populations: early, intermediate, and late MI. Early MI represent trachybasaltic melts which differentiate by fractional crystallization to form the liquids that are represented by intermediate MI. Late MI are hosted within a forsterite-rich growth band near the olivine rim representing a mixing event between basalts and the pre-existing trachybasaltic magmas shortly before the eruption. The compositions of the three MI populations are compared to a database of bulk rocks and MI from the literature on the mafic products of the Phlegrean Volcanic District to test if the MI studied show same geochemical trends. In addition, in this study, the late MI represented a melt inclusion assemblage (MIA) sensu stricto that represents a group of MI trapped all along the same growth band of the olivine. This simultaneous entrapment offers the opportunity to study the reliability of MI based on Roedder's rules. Correlations between major element contents and the size of late MI suggest that MI ≥22 μm are the most reliable in recording the compositions of the melt at specific times and places in the plumbing system. • We analyze MI hosed in an individual reversely zoned olivine. • We used phosphorous X-Ray mapping technique to assess relative ages of MI. • We recognized three different populations of MI each showing specific compositions. • Late MI trapped simultaneously and those <22 μm are the most reliable. [ABSTRACT FROM AUTHOR]

Apatite, which has demonstrated to be useful for tracking volatile evolution in magmatic systems, is a common accessory in La Fossa active volcano (Vulcano island, Italy) products. We performed in situ geochemical (major and trace elements, Cl, F, S) analyses on apatite of La Fossa, and used the data to track the pre-eruptive magmatic volatile evolution for the La Fossa shoshonitic suite, to provide insights on magma evolution in the plumbing system and to investigate volatile fluxing. Our results confirm that apatite volatile chemistry is a valuable tool to give constraints on pre-eruptive volatile contents of magmas. For specific compositions, however, we obtained an underestimation of the water contents with respect to those estimated with plagioclase-liquid hygrometer in previous works. Vulcano apatite halogen composition also indicates that water saturation and pre-eruptive exsolution of a hypersaline aqueous fluid phase occurred when the magma reached rhyolitic composition. The high As, Bi and Cd contents found in apatite crystals belonging to shoshonite and high-K trachyte suggest that the magma reservoirs feeding these eruptions were affected by a deep volatile fluxing which was able to carry these trace elements up to shallow levels. This is in agreement with the occurrence of the deep degassing already demonstrated at La Fossa volcano on the basis of petrological and geochemical data, and supports the apatite geochemical approach to track deep volatile fluxing. • Apatite chemistry is used to assess volatile evolution in Vulcano magmas. • Apatite halogen composition indicates hypersaline fluid exsolution in rhyolites. • High As, Bi, Cd contents in apatite suggest deep volatile fluxing. [ABSTRACT FROM AUTHOR]

Crustal-scale magmatic systems act as filters between the mantle and the atmosphere, and can generate large volcanic eruptions that pose significant hazards while altering Earth's climate. Quantifying the growth rates, magma fluxes, and duration of storage at different crustal levels is crucial for understanding such systems, but these parameters are poorly constrained due to the scarcity of exposed crustal sections. Here we present the first detailed reconstruction of magma emplacement and differentiation time scales of a complete crustal-scale igneous system exposed in the southern Alps (Ivrea-Sesia region, northern Italy) to quantify the magma fluxes and duration of transcrustal magmatism. Integrated zircon U-Pb petrochronology and numerical modeling provides unprecedented evidence that the volcanic and plutonic bodies are directly related to each other both chemically and temporally, suggesting that the entire magmatic system grew rapidly from its deepest roots to the erupted products. In the entire crustal section, zircons record 4 m.y. of magma accretion, but the bulk of the magma was emplaced within approximately 2 m.y. during an episode of enhanced magma flux from the mantle. Our results show the synchronous growth and differentiation of discrete magma bodies at various crustal levels beneath silicic caldera volcanoes and reconcile modeling and geochronological results on crustal-scale heat and mass transfer. [ABSTRACT FROM AUTHOR]

Olivine phenocrysts in basaltic rocks carry valuable mineral-chemical information on early evolution processes in mafic magmatic systems. Fast intra-crystalline diffusion and re-equilibration weakens this potential for major cation constituents of olivine, but the relative immobility of phosphorous makes this element a promising tracer of early crystallization histories. Although phosphorous zoning patterns and underlying kinetic controls have been studied in recent years, little is known about compositional controls on phosphorous incorporation into igneous olivines. We have analysed olivine phenocrysts, hosting Mg-rich melt inclusions, from a range of mafic potassium-rich lavas from Quaternary volcanic centres in Italy for phosphorous and associated trace elements by laser ablation inductively coupled mass spectrometry (LA-ICP-MS), and intra-crystal zoning by electron probe micro-analysis (EPMA) using Kα X-ray elemental maps and quantitative traverses. The studied olivines are marked by low and variable phosphorous concentrations (generally ≤ 200 ppm, but up to 435 ppm in enriched zones). In most cases, phosphorous zoning is decoupled from zoning in any other element or forsterite content. From a comprehensive database of melt inclusions and host phenocrysts, we infer that the composition of the host melt (silica and phosphorous activities) and olivine crystallization dynamics (interplay between diffusion rate of cation constituents in the melt and crystal growth rate) largely regulate phosphorous incorporation in olivines. Melt composition is likely the most important control under near-equilibrium crystallization conditions, as apparent phosphorous partition coefficients tend to increase with increasing silica activity. A negative relationship between apparent partition coefficients and X PO2.5 indicates that phosphorous partitioning into olivine may deviate from Henry's law behaviour. Melt inclusions are virtually always surrounded by phosphorous-poor zones that are also depleted in Cr and enriched in Al and Ti, suggesting that supply-limited slow growth and coupled-substitution mechanisms largely govern phosphorous uptake here. Our results demonstrate the potential versatility of phosphorous as sensitive indicator of crystal-growth histories and magmatic evolution processes in mafic systems. [ABSTRACT FROM AUTHOR]

Abstract Textural evidence from occurrences of mingled magmas in lava flows often yields insights into chemical and thermal disequilibrium between multiple magma batches at depth. An understanding of these interactions is key as they can occur on short timescales and may act as eruption triggers, particularly important in very active volcanic settings. This paper focuses on the Pietre Cotte lava flow (Vulcano, Aeolian Islands, Italy), a short (<1 km in length), texturally-heterogeneous rhyolitic extrusion on the northern slope of the active Fossa Cone. The occurrence of (i) multiple magma compositions, (ii) distinct magmatic cumulates (as glomerocrysts) and (iii) mineral resorption textures within glomerocrysts and isolated feldspar phenocrysts in the Pietre Cotte lava flow highlight a complex pre-eruptive magmatic history, including crystal mush remobilisation. Petrographic observations and mineral, bulk rock and glass geochemistry suggest that multiple mingling events occurred during the evolution of the Pietre Cotte magmatic system, evidenced by the recognition of the following components: (1) a remobilised predominantly mafic crystal mush, evident as macrocrysts (crystals >500 μm), which form glomerocrysts within enclaves, (2) a microlitic (<100 μm) trachytic enclave groundmass with microcrysts (100–500 μm), and (3) a rhyolitic glass, which hosts both the enclaves and the glomerocrysts. The macrocrystic mafic assemblage includes clinopyroxene (En 38-47 Wo 45–50 ; Mg# 0.72–0.89), olivine (Fo 49–66) and magnetite (Usp 7–26), with plagioclase (An 40–63 Ab 5–50) and rare alkali feldspar (Or 41–57) also present. Enclaves are comprised of a groundmass of plagioclase (An 43–47) and alkali feldspar (Or 33–57) microlites, with clinopyroxene microcrysts (En 39-42 Wo 47–51 ; Mg# 0.75–0.81) and trachyte groundmass glass. The rhyolitic host is characterised by glass, spherulites, microlites and enclave-derived macrocrysts. Compositionally and texturally distinct magmas are attributed to storage and interactions of distinct magma batches and their cumulates at various temperatures and depths beneath the Fossa Cone. Compositions vary from basaltic-shoshonitic, through latitic-trachytic and rhyolitic magmas. The macrocrystic glomerocryst assemblage shows resorbed, chemically-zoned and cumulate textures; the glomerocrysts are attributed to a shoshonitic parent and remobilisation from a crystal mush. Macrocrysts formed at a pressure of 825 ± 80 MPa and temperatures of 789–1117 °C at around the Moho (~23–28 km). Pressure and temperature calculations of the shoshonitic mineral assemblage give average crystallisation conditions of 710 ± 80 MPa (above the Moho) and 1128 ± 25 °C, respectively. The trachytic magma crystallised at ~640 ± 75 MPa and 1000–1130 °C. The average liquidus of the rhyolitic magma has been calculated at 970 ± 7 °C, at depths of <5 km (<60 MPa). New textural observations and intensive variable calculations permit the development of a new pressure and temperature-constrained model of the magmatic evolution of the Pietre Cotte system prior to eruption, with useful insights into the interactions of different magmatic components prior to and during the rapid onset of eruptions linked to magma mingling/mixing. Highlights • Disequilibrium textures in the Pietre Cotte lava flow signify a complex evolution. • Petrography and geochemistry highlight several magmatic mingling events. • Crystal mush, trachyte and rhyolite magmas interacted at various crustal depths. • Shallow magmatic interactions may trigger eruptions following migration from depth. [ABSTRACT FROM AUTHOR]

Vulcano is part of the Aeolian volcanic arc in the southern Tyrrhenian Sea. Its products were emplaced through multiple episodes of edifice building and collapse since about 120 ka B.P. to present. A major discontinuity in the activity occurred after about 28 ka, while the focus of volcanism moved from SE to NW. The older products are basalts to shoshonites, and have lower K2O than the younger ones, shoshonites to rhyolites. Between these two groups, Lentia latites-rhyolites, Spiaggia Lunga basalts, and Quadrara shoshonite-trachytes, erupted along the western side of Vulcano Island. The Spiaggia Lunga basalts (i) are the most primitive magmas erupted at Vulcano after 28 ka (ii) mark the change between older and younger phases, and (iii) overlap geochemically with a monzogabbroic intrusion of similar age. This work focuses on the Spiaggia Lunga products, discussed within a large dataset of geochemical and radiogenic isotope analyses on the entire Vulcano sequence. Older products have more primitive geochemical and isotope characteristics, and lower incompatible element contents, than younger ones. The Spiaggia Lunga basalts exhibit intermediate geochemical characteristics between the older and the younger groups, and can likely be regarded as a third magmatic phase, which represents a distinct mantle reservoir active during the magmatic history of Vulcano. Significant variations of Sr, Nd, and Pb isotope ratios, and isotopic disequilibrium between phenocrysts and groundmass, are present among the Vulcano products. This variability suggests crustal assimilation in shallow-level magma chambers, which also accounts for the formation of evolved products by combined assimilation and fractional crystallization, particularly in the younger series. Considering only the mafic products, incompatible element patterns with high LILE/HFSE and enriched signatures of Sr, Nd, and Pb isotope ratios, indicate enriched mantle sources. Besides, chemical and isotope variability among older, younger, and Spiaggia Lunga mafic rocks, suggests an origin from geochemically diverse primary melts, derived from distinct mantle reservoirs. Their parent magmas, based on geochemical and isotope patterns, were from both MORB- and OIB-type mantle sources, subject to variable degrees of metasomatism by subducted sediments. [ABSTRACT FROM AUTHOR]

Abstract The Campi Flegrei caldera in Southern Italy is one of the most populated active volcanoes on Earth. It has an unprecedented record of historical unrest and eruption that dates back to 2.2 ka BP and provides key insights for understanding the dynamic evolution of large calderas. Since 1950, it has undergone four episodes of caldera-wide uplift and seismicity, which have raised the coastal town of Pozzuoli, near the centre of unrest, up to 4.5 m and triggered the repeated evacuation of some 40,000 people. After about 20 years of subsidence, following the uplift peak reached in 1984, the caldera started a new, low rate uplift episode, accompanied by low magnitude seismicity and marked geochemical changes in fumaroles. In this area it is crucial to discriminate episodes of shallow magma intrusion from hydrothermal perturbations, which are both able to generate unrest signals. In this paper, by a critical review of previous literature and some new results, we discriminate, in the unrest episodes, the relative contributions of hydrothermal effects and shallow magma intrusions. Our review is aimed also to show the different behavior of the largest unrest episodes, such as the 1982–1984, and the present, ungoing unrest characterized by smaller rate but longer lasting uplift. We show that for the former, larger uplift of the 80's, there is clear evidence for shallow magma intrusion, and we are able to compute the amount of intruded magma volume. For the present, on-going uplift, on the contrary, there is no evidence for magmatic activity at shallow depth. As a main result of our analysis, we demonstrate here the present unrest, characterized by much lower uplift rates and seismicity, is only interpretable as due to large gas fluxes coming from the deeper magma reservoir; without any appreciable contribution from shallow magma or recent magmatic intrusion. Our results shed new light on the interpretation of caldera unrest worldwide, and clearly indicate the most constraining data and the most rigorous procedures of data analysis for a correct interpretation of volcanic unrest. [ABSTRACT FROM AUTHOR]

Abstract We combined literature and experimental data to determine the role of magma mixing in the pre-eruptive dynamics of the Aeolian Islands volcanoes. As a first step, we systematically reviewed the evidence supporting the hypothesis of mixing-triggered eruptions in the Aeolian archipelago, providing textural, chemical, and rheological constraints. The existing data highlighted the significant role of magma mixing in many eruptions within the Aeolian archipelago. Examples include the Upper Pollara and Porri volcano eruptions at Salina, Monte Guardia, and the AD 1230 Monte Pilato eruption at Lipari, as well as the present-day activity at Stromboli. Then, we focused on Vulcano Island, chosen as a case study because it represents one of the volcanoes posing the highest risk in the Aeolian archipelago. At Vulcano Island, we highlighted the role of magma mixing in the AD 1739 and 1888–90 eruptions. Finally, we investigated mixing-to-eruption timescales for the AD 1739 eruption, performing mixing experiments, and evaluated the progressive decay of the chemical concentration variance with time. Results pointed to mixing-to-eruption timescales of the order of 29 ± 9 h and magma ascent rates ranging between 3×10−2 and 5×10−2 m s−1. We finally emphasized that the presented results may have significant implications in the context of volcanic hazard mitigation and planning of emergency activities. Highlights • Magma mixing plays a key role in magmatic feeding systems of Aeolian volcanoes. • Magma mixing plays a key role in the AD 1739 eruption at Vulcano Island. • Mixing experiments are a valid proxy to constrain mixing-to-eruption timescales. [ABSTRACT FROM AUTHOR]

Magma transfer between lower and upper continental crust is a fundamental process linking the dominantly mafic composition of the lower crust with the more felsic composition of the upper crust. We explored the mechanisms of mafic magma ascent and emplacement in the middle crust by studying a midcrustal gabbroic to dioritic magmatic system (Sondalo complex, eastern central Alps, northern Italy). We characterized the structure and anisotropy of magnetic susceptibility (AMS) fabric of concentric gabbroic to dioritic intrusions. The significance of AMS fabrics is discussed using anisotropy of anhysteretic remanent magnetization (AARM) and crystallographic preferred orientation (CPO) data acquired on different test sites. The magmatic and magnetic fabrics of the pluton were acquired during its emplacement in the Permian and were not subsequently tilted: The fabrics are essentially vertical, indicating vertical magma transfer through the crust with a two-phase intrusion history. (1) The concordant orientation between the magmatic foliation and the host-rock xenoliths in the center of the pluton suggests that the first magma ascent phase occurred along pathways subparallel to the vertical fabric of the host metasedi-mentary rocks. (2) The second magma ascent phase was controlled by a change in the rheology of the host rock and the mafic magma. Heat dissipation to the contact aureole induced partial melting, thereby lowering the mechanical strength of the host rocks, whereas the viscosity of the mafic magma increased due to cooling and associated fractional crystallization. This caused an en-masse rise of the pluton, resulting in the formation of a structural aureole, i.e., a vertical foliation in the contact aureole and a weaker but concordant magmatic foliation at the rim of the pluton. This ascent phase accounts for the pressure-temperature evolution recorded by metasedimentary rocks in the contact aureole of the pluton. [ABSTRACT FROM AUTHOR]

Puffing, i.e., the frequent (1 s ca.) release of small (0.1-10 m), over-pressurized pockets of magmatic gases, is a typical feature of open-conduit basaltic volcanoes worldwide. Despite its non-trivial contribution to the degassing budget of these volcanoes and its recognized role in volcano monitoring, detection and metering tools for puffing are still limited. Taking advantage of the recent developments in high-speed thermal infrared imaging, we developed a specific processing algorithm to detect the emission of individual puffs and measure their duration, size, volume, and apparent temperature at the vent. As a test case, we applied our method at Stromboli Volcano (Italy), studying 'snapshots' of 1 min collected in the years 2012, 2013, and 2014 at several vents. In all 3 years, puffing occurred simultaneously at three or more vents with variable features. At the scale of the single vent, a direct relationship links puff temperature and radius, suggesting that the apparent temperature is mostly a function of puff thickness, while the real gas temperature is constant for all puffs. Once released in the atmosphere, puffs dissipate in less than 20 m. On a broader scale, puffing activity is highly variable from vent to vent and year to year, with a link between average frequency, temperature, and volume from 136 puffs per minute, 600 K above ambient temperature, 0.1 m, and the occasional ejection of pyroclasts to 20 puffs per minute, 3 K above ambient, 20 m, and no pyroclasts. Frequent, small, hot puffs occur at random intervals, while as the frequency decreases and size increases, an increasingly longer minimum interval between puffs, up to 0.5 s, appears. These less frequent and smaller puffs also display a positive correlation between puff volume and the delay from the previous puff. Our results suggest an important role of shallow bubble coalescence in controlling puffing activity. The smaller and more frequent puffing at 'hotter' vents is in agreement with the rapid rise of small gas pockets with only limited coalescence, while slower rise, allowing more time for coalescence, leads to larger but less frequent puffing at 'colder' vents. This link between puffing style and vent thermal state points to a feedback between gas flux and magma temperature (and viscosity), where higher gas flux stirs and heats the magma, which, by getting less viscous, becomes a preferential way for bubble rise. Such a link has implications for the monitoring of the state of the shallow conduit at open-vent volcanoes as well as for determination of their total gas budget, relevant for hazard forecast and environmental studies. [ABSTRACT FROM AUTHOR]

The active volcano of Ischia, an island off-shore the city of Naples, Southern Italy, has a discontinuous volcanic activity characterized by caldera-forming paroxysmal eruptions, lava flows, and lava domes, and thus offers the opportunity to study the complexity of magma storage, differentiation, and extraction mechanisms in a long-lived magma reservoir. The overall geochemical composition of erupted magmas varies from shoshonite to latite and trachyte/trachyphonolite. Their Sr and Nd, isotope composition variation is typical of subduction-related magmas, akin to other potassic magmas of the Neapolitan District, and there is a complete overlap of radiogenic isotope composition among shoshonite, latite, and trachyte/trachyphonolite. The lack of systematic radiogenic isotope covariation during differentiation suggests that the radiogenic isotope variability could be a signature of each magma pulse that subsequently evolved in a closed-system environment. Erupted magmas record a recurrent evolutionary process consisting of two-step fractional crystallization along similar liquid lines of descent for each magma pulse, suggesting near steady-state magma chamber conditions with balanced alternating periods of replenishment, differentiation, and eruption. The dominant role of fractionating feldspars determines a significant depletion of Sr (<10 ppm) coupled with high Rb/Sr (>200) in the residual trachyte magma. Several more-evolved trachytes have anomalous radiogenic 87Sr/86Sri (>0.707) coupled with high 87Rb/86Sr (>50), all other geochemical and isotopic characteristics being similar to normal 87Sr/86Sri trachytes at the same degree of evolution. This radiogenic Sr isotope signature is not consistent with assimilation of crustal material and demands for a time-related in-growth of 87Sr during storage within the magma chamber. Rb-Sr isochrons on separated mineral-groundmass pairs provide robust constraints on a prolonged pre-eruptive history ranging from a few tens to hundreds of thousands of years at relatively low temperature (~750 °C). Remarkably, also normal trachytes with high 87Rb/86Sr (>200) yield a magma residence time from some 4 to 27 kyr, implying that the long-lived history of Ischia magmas is not limited to the anomalous 87Sr/86Sri trachytes. This long-lived history could be a characteristic feature of the magma chamber reservoir of this active volcano, which other volcanic products (i.e., shoshonite and latite) cannot disclose due to their lower Rb/Sr (i.e., low 87Sr in-growth rate) and higher magma storage temperature (>900 °C) (i.e., rapid Sr isotope homogenization via diffusion). The magma chamber dynamics of the active volcano of Ischia, probed on the basis of geochemical and radiogenic isotope tools, is consistent with recent models of complex magma chamber reservoirs made up of multiple discrete melt pockets, isolated by largely crystalline mush portions, maintained in a steady-state thermal flux regime with no mass exchange, and with reactivation shortly before eruption. [ABSTRACT FROM AUTHOR]

The aim of this paper is to discuss a novel approach to provide insights on the probability of vent opening in calderas, using a dynamic model of sill intrusion. The evolution of the stress field is the main factor that controls the vent opening processes in volcanic calderas. On the basis of previous studies, we think that the intrusion of sills is one of the most common mechanism governing caldera unrest. Therefore, we have investigated the spatial and temporal evolution of the stress field due to the emplacement of a sill at shallow depth to provide insight on vent opening probability. We carried out several numerical experiments by using a physical model, to assess the role of the magma properties (viscosity), host rock characteristics (Young's modulus and thickness), and dynamics of the intrusion process (mass flow rate) in controlling the stress field. Our experiments highlight that high magma viscosity produces larger stress values, while low magma viscosity leads to lower stresses and favors the radial spreading of the sill. Also high-rock Young's modulus gives high stress intensity, whereas low values of Young's modulus produce a dramatic reduction of the stress associated with the intrusive process. The maximum intensity of tensile stress is concentrated at the front of the sill and propagates radially with it, over time. In our simulations, we find that maximum values of tensile stress occur in ring-shaped areas with radius ranging between 350 m and 2500 m from the injection point, depending on the model parameters. The probability of vent opening is higher in these areas. [ABSTRACT FROM AUTHOR]

Evaluating mechanisms and rates for magma transport and emplacement in the upper crust is important in order to predict the thermal and rheological state of the crust, and understand the relationship between plutonism and volcanism. U–Pb geochronology on zircon is commonly used to constrain magma emplacement and storage time in the crust, but interpreting complex zircon age populations in terms of in-situ crystallization versus crystallization at a deeper level is not trivial. This study focuses on the Mt. Capanne pluton in Elba (Italy), a well-documented example of arc-related laccolith emplaced in the upper continental crust. Previous studies proposed that the Mt. Capanne intrusion was accreted in less than 10 000 yr by distinct and mappable magma pulses. Here, we couple high-precision ID-TIMS U–Pb zircon geochronology with numerical thermal simulations to evaluate emplacement rates, test different emplacement models, inform zircon age interpretations and evaluate the potential for melt storage during construction of the Mt. Capanne pluton. Our results require that the Mt. Capanne intrusion was built in at least 250 000 yr by multiple magma injections. A variety of emplacement scenarios show that melt was preserved for <60 000 yr after each pulse and that the maximum eruptible volumes were approximately equal to the volume of each pulse. Our results also require that the majority of zircon crystallization occurred in zircon saturated reservoirs at deeper crustal levels prior to final magma emplacement and cooling, which has implications for using zircon U–Pb geochronology to infer upper crustal magma residence times. [ABSTRACT FROM AUTHOR]

Intra-caldera settings record a wealth of information on caldera-forming processes, yet field study is rarely possible due to lack of access and exposure. The Permian Ora Formation, Italy, preserves > 1000 m of vertical section through its intra-caldera succession. This provides an excellent opportunity to detail its mineralogical and geochemical architecture and gain understanding of the eruption evolution and insight into the pre-eruptive magma system. Detailed juvenile clast phenocryst and matrix crystal fragment point count and image analysis data, coupled with bulk-rock chemistry and single mineral compositional data, show that the Ora ignimbrite succession is rhyolitic (72.5–77.7% SiO 2 ), crystal-rich (~ 25–57%; average 43%) and has a constant main mineral population (volcanic quartz + sanidine + plagioclase + biotite). Although a seemingly homogeneous ignimbrite succession, important subtle but detectable lateral and vertical variations in modal mineralogy and bulk-rock major and trace elements are identified here. The Ora Formation is comprised of multiple lithofacies, dominated by four densely welded ignimbrite lithofacies. They are crystal-rich, typically lithic-poor (< 2%), and juvenile clast-bearing (average 20%). The ignimbrite lithofacies are distinguished by variation in crystal fragment size and abundance and total lithic content. The intra-caldera stratigraphic architecture shows both localised and some large-scale lithofacies correlation, however, it does not conform to a ‘layer-cake’ stratigraphy. The intra-caldera succession is divided into two depo-centres: Southern and Northern, with proximal extra-caldera deposits preserved to the south and north of the system. The Southern and Northern intra-caldera ignimbrite successions are discriminated by variations in total biotite crystal abundance. Detailed mineralogical and chemical data records decreases across the caldera system from south to north in biotite phenocrysts in the groundmass of juvenile clasts (average 12–2%), matrix biotite (average 7.5–2%) and plagioclase crystal fragments (average 18–6%), and total crystal fragment abundance in the matrix (average 47–37%); a biotite compositional change to iron-rich (0.57–0.78 Fe); and bulk-rock element decreases in Fe 2 O 3 , MgO, P 2 O 5 , Ce, Hf, V, La and Zr, and increases in SiO 2 , Y and Nb, with TiO 2 . Together, the changes enable subtle distinction of the Southern and Northern successions, indicating that the Northern deposits are more evolved. Furthermore, the data reveals discrimination within the Northern succession, with the northwestern extra-caldera fine-crystal-rich lithofacies, having a distinct texture, componentry and composition. The componentry variation, mineralogical and chemical ranges identified here are consistent with an eruption from a heterogeneous magma system. Our results suggest that the Ora magma was likely stored in multiple chambers within a genetically related magma reservoir network. The mineralogical and chemical architecture together with stratigraphic relationships, enable interpretation of eruption sequence. Caldera eruption is proposed to have commenced in the south and progressed to the north, forming the two pene-contemporaneous caldera depressions. Moreover, this data illustrates heterogeneity and local zonation from base-to-top of the main intra-caldera and extra-caldera successions. These variations together with crystal fragment size variations between ignimbrite lithofacies support the hypothesis of a multi-vent eruption process, incremental caldera in-filling by subtly compositionally different pyroclastic flow pulses, and a lower intensity eruption style ( Willcock et al., 2013, 2014 ). [ABSTRACT FROM AUTHOR]

Faults in volcanic areas can have different origins and can form due to several volcano-tectonic processes. In this work, by means of detailed field observations, we analysed a fault array cutting through a recent pyroclastic succession in the Campi Flegrei caldera of southern Italy to investigate its origin. Geometric and kinematic data indicate that the fault array consists of steeply dipping faults with both normal and reverse senses of movement. Displacement data suggest that these faults with opposed kinematics acted together , in agreement with what was previously described from analogue and numerical experiments for faults formed in response to gravitational collapses in volcanic areas. By integrating these results with considerations of the recent volcano-tectonic evolution of the Campi Flegrei caldera, we propose a model in which the studied fault array developed to accommodate a gravitational collapse triggered by an underground magma migration predating the 1538 CE historical Monte Nuovo eruption. This work is, to our knowledge, the first thorough field description of faults developed to accommodate gravitational collapses in volcanic areas. • Detailed field description and throw analysis of a volcano-tectonic fault array. • Normal and reverse faults of the array acted simultaneously. • The fault array accommodated a gravitational collapse triggered by an underground magma migration. [ABSTRACT FROM AUTHOR]

Dissolution of clinopyroxene (cpx) in a K-basaltic melt from the Campi Flegrei Volcanic District (Italy) has been investigated through dissolution and dissolution-crystallization experiments at pressure of 0.8 GPa, superliquidus temperature of 1350 °C, and dwell times between 0.5 and 1 h. The obtained dissolution rates range from 7.9·10−6 cm s−1 to 6.1·10−6 cm s−1 as a function of dwell time. In the dissolution-crystallization experiment (1300 °C; 0.8 GPa; 2 h), the formation of overgrowth rims accompanied by new cpx crystals suggests that the injection of recharge magmas in basaltic reservoir may lead to inverse or oscillatory zonation. The interaction between cpx and K-basaltic melt at ~1570 °C was studied by in situ radiography using synchrotron radiation combined with the Paris-Edinburgh press. This resulted in cpx resorption to occur depending on the temperature conditions with respect to the liquidus temperature of the cpx (T cpxL). The calculated cpx dissolution rates are ~5·10−3 cm s−1 at T ≤ T cpxL and ~ 3·10−2 cm s−1 at T ≥ T cpxL. The role of crystal dissolution in the estimation of magma residence times has been also tested for a natural magmatic system by interpolating the dissolution rates (~10−5–10−6 cm s−1) with the textural data of cpx phenocrysts from the Agnano-Monte Spina pyroclastic deposit at Campi Flegrei caldera (Campanian region, Italy). Results from calculations indicate that the time required for partial or complete resorption of phenocrysts varies from ~0.5 to ~40 h, and that the effect of crystal dissolution may be relevant to estimate magma residence times whether significant dissolution occurs during magma mixing processes. • Piston cylinder experiments on the primitive Phlegraean magmas. • Clinopyroxene dissolution rates at high pressure. • Dissolution-crystallization processes. • In situ observation of clinopyroxene dissolution rate at high pressure and temperature through X-ray synchrotron radiography. • Dissolution times of zoned clinopyroxenes from the Campi Flegrei. [ABSTRACT FROM AUTHOR]

The eruptive products of the last 1000 years at La Fossa volcano on the island of Vulcano (Italy) are characterized by abrupt changes of chemical composition that span from latite to rhyolite. The wide variety of textural features of these products has given rise to several petrological models dealing with the mingling/mixing processes involving mafic-intermediate and rhyolitic magmas. In this paper, we use published whole-rock data for the erupted products of La Fossa and combine them in geochemical and thermodynamic modelling in order to provide new constrains for the interpretations of the dynamics of the active magmatic system. The obtained results allow us to picture a polybaric plumbing system characterized by multiple magma reservoirs and related crystal mushes, formed from time to time during the differentiation of shoshonitic magmas, to produce latites, trachytes and rhyolites. The residing crystal mushes are periodically perturbated by new, fresh magma injections that, on one hand, induce the partial melting of the mush and, on the other hand, favor the extraction of highly differentiated interstitial melts. The subsequent mixing and mingling of mush-derived melts ultimately determine the formation of magmas erupted at La Fossa, whose textural and chemical features are otherwise not explained by simple assimilation and fractional crystallization models. In such a system, the compositional variability of the erupted products reflects the complexity of the physical and chemical interactions among recharging magmas and the crystal mushes. [ABSTRACT FROM AUTHOR]

Leucititic rocks, K-foiditic in composition are volumetrically important in the Colli Albani (also known as Alban Hills) volcanic district (Central Italy) especially during the most explosive phases of activity (>200 km3). The Colli Albani tephra in distal (>500 km) deposits indicates that K-foiditic magma chambers fed large explosive eruptions (i.e., tens of km3 of pyroclastic rocks). Major oxides, trace elements and Raman spectra were measured on the glasses and minerals occurring in the K-foiditic scoria clasts of the ~530 kyr-old Tufo del Palatino, erupted in the Colli Albani volcanic district. The Colli Albani pre-eruptive magmatic system is characterized by the a H2O < 1 and high CO 2 activity in the melt, as testified by the CO 3 in the clinopyroxene melt inclusions, by the early crystallization of CO 3 -bearing apatite and by the high CO 2 activity in the free volatile phase that led to crystallization of calcium carbonate in the scoria clast vesicles. The K-foiditic magmas plot on the Cpx + Lc + melt divariant surface of the Ol-Cpx-Lc-Mel-H 2 O-CO 2 , P ≥ 0.2 GPa and T ≤ 1100 °C. The assimilation of cold carbonate by hot magmas is an important open-system process allowing the establishment of a H20 < 1 condition in the volatile-rich, Colli Albani magma chambers where the stability fields of the olivine and phlogopite are reduced in favor of clinopyroxene and leucite. Trace element modelling indicates large amount of carbonate assimilation (~12.4 wt%) involved in the differentiation process that origins the K-foiditic magmas starting from a K-rich, phonotephritic parental magma. The large amount of assimilate carbonate is consistent with the peculiar distribution of the latent heat across the crystallization interval of the phonotephritic parental magma. The isenthalpic assimilation process is very efficient in the phonotephritic magma because the crystallization of clinopyroxene and leucite in equilibrium with a K-foiditic melt proceeds over a relatively large temperature interval (>200 °C) and the K-foiditic melt shows low viscosity (104Pa·s at 1000 °C). Actually, the low melt viscosity, that increases the growth rate, and the large temperature interval of crystallization are intrinsic factors that increase the release of the latent heat of crystallization from the phonotephritic parental magma. Extrinsic factors enhancing the assimilation process efficiency are the thickness (>4 km) and the depth (down to 5–7 km) of the carbonate substrate in the Colli Albani volcanic district. [ABSTRACT FROM AUTHOR]

We present a textural investigation of compositionally homogeneous alkaline tube pumices from the plinian fallouts of the Agnano Monte Spina eruption (ca. 4.1 ka), Campi Flegrei, Italy. The pumice clasts present strong textural complexity from hand specimen to microscopic scale of inspection. The clasts are characterized by large vesicle tubes that extend up to several millimetres along the clast main axis. They also exhibit small and elongated vesicles arranged in stretched bands around textural domains of larger, sub-spherical vesicles associated with pyroxene, feldspar, and biotite phenocrysts. Clasts, vesicle tubes, vesicle deformation, major axes of pyroxene phenocrysts and crystals with size ≤100 μm align in the same direction. In addition, we observe chains of gradually smaller stretched vesicles likely generated from break-up of a larger parent vesicle (i.e., tip-streaming phenomenon). We use image analysis to quantify the heterogeneity of vesicle sizes and shapes. Then, we deduce the Capillary number (Ca) of the each single vesicle, which represents the ratio between the deforming viscous stress on a bubble and the restoring stress supplied by surface tension, and obtain the spatial distribution of Ca values within pumice clasts. As Ca depends on strain-rate and viscosity, the spatial distribution of Ca values provides us with a snapshot of the sub-millimetre scale variation in magma strain-rate and rheology before fragmentation. Ca in highly stretched vesicles is close to values (0.45 to 0.6) required for bubble-breakup induced by tip-streaming. Instead, low Ca values (0.3 to 0.45) are calculated for large sub-spherical vesicles mostly distributed around phenocrysts. We suggest that sub-millimetre heterogeneities in vesicle sizes and shapes recorded in tube pumices are caused by a combination of tip-streaming, heterogeneous bubble nucleation and second-boiling processes prior to fragmentation. The heterogeneous spatial distribution of Ca values may be the result of local micrometric shear localisation and consequent deformation upon break-up experienced by magma while ascending in the conduit. This deformation suggests that a variation of magma strain-rate and viscosity occurred before fragmentation at the clast microscale and this is likely to affect magma dynamics and fragmentation. Our results claim for future experimental and numerical modelling studies that investigate and consider the effect of such micrometric heterogeneities on magma rheology and flow condition variations inside volcanic conduits. • Tube pumices are diagnostic of conditions in silicic explosive eruptions. • Clast length, vesicle stretch, prismatic phenocrysts and acicular microlites align. • Tube pumices record a heterogeneous capillary number distribution of vesicles. • Texture and capillary number of vesicles suggest magma instability by tip-streaming. • Sub-millimetre textural heterogeneities influence magma rheology. [ABSTRACT FROM AUTHOR]

The mineralization potential of arc magmas depends, among other factors, on the timing of sulfide melt saturation relative to magma differentiation and to exsolution of a magmatic fluid phase. In fossil mineralized or barren systems, understanding the evolution of metals along the magma differentiation path is often hindered by late magmatic processes and hydrothermal alteration. To better understand the process of metal evolution "caught in the act" in crustal reservoirs, we analyzed magmatic sulfides and melt inclusions found within eruptive products from the active arc volcano, La Fossa (Vulcano Island, Italy), for the basalt to rhyolite compositional spectrum. We found that, in case of sulfide-undersaturated and volatile-rich arc basalts, metals are scarcely subtracted by degassing during ascent to shallow crustal reservoirs and reach the highest abundances in intermediate magmas (250 ppm Cu). At sulfide saturation the sulfide melt has 34–66 wt% Cu, leading to a dramatic decrease in chalcophile metals dissolved in the silicate melt. After fractionation of only 0.2–0.3 wt% of sulfide in the solid assemblage, the exsolved sulfide is a monosulfide solid solution (pyrrhotite) containing <3 wt% Cu. Metals that do not partition in sulfides (Pb, Zn) increase their concentrations during magmatic evolution until they are sequestered by a Cl-rich aqueous fluid phase exsolved at the rhyolitic stage. The absolute and Cu-normalized concentrations of metals in sulfide inclusions are similar to sulfide accessories in magmatic rocks associated with world-class porphyry Cu systems. Our results demonstrate that the mechanisms governing metal evolution inferred for the magmatic stage in porphyry Cu environments can be also tracked at an active arc volcano, using eruptive products as snapshots of the magmatic evolution. Arc volcanoes can thus be viewed as ideal active analogues when studying these crucial processes for the formation of porphyry Cu deposits. • We tracked metal evolution in the plumbing system of La Fossa active volcano. • Sulfide saturation is achieved in intermediate composition magmas. • Two types of Cu-bearing magmatic sulfides were identified. • Cu and Pb evolution during magmatic differentiation is modeled. • Metal evolution gives insights into the mineralizing potential of arc magmas. [ABSTRACT FROM AUTHOR]

Hydrothermal regions are affected by a wide variety of phenomena, including ground inflation and deflation episodes. Among them, calderas offer the opportunity to study the complex interactions between magmatic processes at depth and permeable rocks saturated with fluids in the upper sedimentary layers. One of such regions is the Campi Flegrei caldera in southern Italy, where several source models have been applied over the years to reproduce the ground displacement and seismicity observed during the most recent phase of major unrest (1982–1984). The present work aims at introducing a new source model consisting of a thermo-poro-elastic inclusion embedded in a homogeneous poroelastic half-space. The inclusion is meant to represent a permeable rock layer stressed and strained by hot and pressurized volatiles released upward by an underlying magmatic reservoir and is modeled as a thin horizontal disk inside which a sudden change of temperature and pore pressure occurs. We provide semi-analytical solutions for the displacement and stress fields both within and outside the source and check them by comparison with those obtained through a fully numerical approach. Results provided by our model are compared with two other deformation source models often used to describe volcanic environments in terms of pressurized cavities describing a spherical magma chamber (Mogi source) or a sill-like magma intrusion (Fialko source). For the Campi Flegrei 1982–84 unrest, our model provides a better reproduction of ground deformation data and manages to explain the widespread presence of compressive focal mechanisms, since the stress field promoted both inside and outside the thermo-poro-elastic inclusion is very different from pressurized cavities. • We model strain and stress due to a disk shaped thermo-poro-elastic inclusion. • We compare our model with other popular deformation source models. • Displacement and stress fields are provided both within and outside the source. • The modeled source provides strong compressive stress regime inside it. • It accounts for the heterogeneity of seismic mechanisms observed at Campi Flegrei. [ABSTRACT FROM AUTHOR]

The Onano eruption (~ 0.17 Ma) is the second to last caldera-forming eruption of the Latera volcano, in the northernmost sector of the Roman Comagmatic Province (Latium, Italy). The stratigraphic sequence, from base to top, includes ash and pumice-rich flow deposits, spatter-rich flow deposits and lag breccias associated with ash-rich flow deposits. By combining major and trace element compositions of the bulk rocks, matrix glasses and minerals of juvenile components from the different depositional units, we reconstruct the pre-eruptive evolution of the magma chamber and the syn-eruptive magma dynamics. Juvenile clasts with heterogeneous glass composition and/or mineral assemblage are a ubiquitous feature of the Onano eruption. The products cover a large compositional range from phonotephrite to phonolite. They are crystal poor, with felsic paragenesis associated to Mg-rich olivine (Fo82–90) and diopside (Fs4–7), these last not in equilibrium with the erupted melts. The mafic mineral assemblage suggests that the pre-eruption magma reservoir was periodically perturbed by the arrival of a primitive magma carrying on Mg-rich minerals and/or remobilizing a mafic crystal mush at the bottom of the reservoir. According to the results obtained from both rhyolite-MELTS and Rayleigh crystal fractionation modeling, we infer that the system evolved from phonotephrite to phonolite both via crystal fractionation and magma mixing between the two end members. Crystallization mostly proceeded at the wall of the reservoir, while magma mixing in the middle zones of the chamber generated the intermediate tephriphonolitic melts. The pre-eruptive chemical zoning was disrupted during the course of the eruption due to the simultaneous withdrawal of magma from different portions of the reservoir. During the first phase of the eruption, high-silica tephriphonolitic to phonolitic melts, residing in the upper part of the reservoir, were emitted with less involvement of the deeper phonotephrite. Phonotephritic magmas, with only a minor contribution of evolved melts, were later erupted as spatter-rich pyroclastic flows that preceded the main caldera collapse. During the caldera collapse, the whole reservoir was involved, leading to extensive and intimate syn-eruption mingling of the different melts. A comparison between the Onano eruption and other eruptions of the Italian high potassic volcanism provides new insights into the evolution of the Roman Comagmatic Province magmas and their eruptive processes. [ABSTRACT FROM AUTHOR]

Late-Variscan metaluminous/weakly peraluminous (quartz-diorites and tonalites) and strongly peraluminous (two mica porphyritic granodiorites and granites) granitoids represent two magmatic associations making up the Capo Vaticano Promontory (central Calabria, Italy). They characterize a portion of a complete continental crustal section exposed in continuity from NW to SE in the adjacent Serre Batholith. In this paper, we deal with geochemical modelling trying to understand the evolutionary processes responsible for the CVP granitoid genesis. We have investigated the main processes such as fractional crystallization, variable entrainment of peritectic mineral phases in the melt (Stevens et al., 2007; Clemens and Stevens, 2012), restite-unmixing (White and Chappell, 1977) and magma mixing to explain the geochemical variability in major and trace elements of these magmatic suites. The quartz-diorites and tonalites, representing the deepest seated rocks, are constituted by various amount of Pl + Bt + Amph + Qtz. Bt-rich and Pl-rich quartz-diorite are characterized by cumulus of Bt and Pl, respectively. A multi-step articulated fractional crystallization process was able to reproduce the quartz-diorite/tonalitic trends. Starting from a tonalitic parental magma, three different cumulates were produced: a mafic (Bt-rich) cumulate (75 % Bt, 10 % Pl and 5 % Ap) after F = 10 %, a second cumulate composed by Pl (45 %), Bt (30 %) and Amph (5 %) after F = 20 % and Pl-rich quartz-diorite (60 % Pl, 20 % Bt and 20 % Amph) as the third cumulates, after F = 30 %. Among the source-related models, restitic unmixing could have played a minor role in the quartz-diorite and tonalite genesis, defining them as products derived from partial melting of I-type sources. Pl + Kfs + Qtz + Bt + Ms are the main phases constituting the porphyritic granodiorites and granites. A simple fractional crystallization from less evolved granodiorites sample (KA2) has reproduced the more evolved liquid composition (PA27), after F = 27 %. In addition, PAE modelling is consistent with partial melting of a metapelitic source with entrainment of 20 to 5 % vol. of a peritectic assemblage made of orthopyroxene and garnet. Magma mixing modelling with mafic end-members (a basalt, a basaltic andesite and the MME of CVP) excluded any additional contribution from the mantle. Finally, geochemical modelling highlights the fractional crystallization as the main responsible process in the CVP granitoids differentiation, whereas PAE and restite unmixing processes do not provide evidence about source contributions. This study supports the idea that granitoid rocks represent recycled crustal material in the Capo Vaticano Promontory. [ABSTRACT FROM AUTHOR]

• Hafnium isotopes on zircon trace protracted mantle-crust interaction. • Thermal modelling quantifies magma flux and melting of various lower crustal lithologies. • Late stage mafic rejuvenation governed by changing magma flux towards the end of recorded magmatic activity. • "In situ" development of isotopic variation during development of a lower crustal to upper mantle hot zone. • New high precision zircon U-Pb ID-TIMS data of the Middle Triassic magmatic province of the Southern Alps (northern Italy). Tracing the origin and evolution of magmas on their pathway through the lithosphere is key to understanding the magmatic processes that eventually produce eruptions. For ancient magmatic provinces, isotope-geochemical tracers are powerful tools to probe the source regions and magma-crust interaction during ascent and storage. Here we present hafnium isotopic compositions of ID-TIMS dated zircons to trace the evolution of the Middle Triassic magmatic province in the Southern Alps (northern Italy) at high temporal resolution. Systematic changes in hafnium isotopic composition with time record progressively stronger crustal assimilation over 3.5 million years, followed by a rapid increase in ε Hf towards more juvenile compositions for the major pulse of mafic intrusions and post-intrusive volcanic ash beds within one million years. We interpret these trends to reflect variations in mantle-crust interaction through time. Initial intrusions of basaltic dykes into the relatively cold lower crust cause only limited crustal melting and assimilation but an ensuing magma injection into progressively hotter crust results in more extensive partial melting and assimilation of crustal material. Subsequent intrusions into the magmatic lower-crustal roots cannibalize previous intrusions with progressively less isotopic contrast due to dilution with mantle-derived magmas. This is potentially accompanied by an increase in magma flux due to delamination of dense lower crustal cumulates into the subcontinental lithospheric mantle. The observed trends in hafnium isotopic composition therefore do not necessarily require tectonic re-organizations or changes in mantle sources. Instead these trends may trace variations in mantle-crust interaction during thermally induced chemical maturation of the lower crustal magmatic roots progressively replacing ancient pelitic to mafic lower crustal lithologies by juvenile cumulates. [ABSTRACT FROM AUTHOR]

The 4.5 ka trachytic Plinian eruption of Agnano-Monte Spina is the largest magnitude event of the past 5 ka at Campi Flegrei caldera. The complete eruptive sequence consists of six members, three of which, named A, B and D, are characterized by the association of fallout and pyroclastic density current (PDC) deposits well preserved at proximal locations. In this study, we analyze the textural characteristics of the pumice clasts of the three major fallout deposits (A1, B1, D1) and of their associated PDC deposits (A2, B2, D2), and link them to the physical properties of magma in order to investigate conduit fluid dynamics. A combination of data (field work, grain-size and density measurements, vesicle number densities and size distributions, crystal content, water content) is used to set up the source term conditions for numerical simulations. Each fall/PDC transition is accompanied by distinctive changes in textural properties of the juveniles, recognized by a lowering in vesicle number densities of about one order of magnitude (from 108 to 107 cm−3), indicating a significant decrease in the magma ascent rate. Melt inclusions show a marked decrease in volatile content recurrent at each fall/PDC transition and indicate that the three main pulses of the eruption were fed by distinct and progressively deeper magma batches. Numerical simulations, taking into account magma properties derived from the textural analyses, and variations in initial water content, show decreases in the exit velocities and Mass Discharge Rate (MDR) consistent with such fall/PDC transitions. Different initial water contents together with changes in conduit diameters allow us to simulate the different column heights reconstructed for the three Plinian phases. The reconstructed scenario for the Agnano-Monte Spina eruption involves a stop-start behavior and a top-down trigger for the most voluminous and intense eruptive episode D. [ABSTRACT FROM AUTHOR]