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Scarpati, Claudio
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- PublicationOpen AccessThe petrogenesis of chemically zoned, phonolitic, Plinian and sub-Plinian eruptions of Somma-Vesuvius, Italy: Role of accessory phase removal, independently filled magma reservoirs with time, and transition from slightly to highly silica undersaturated magmatic series in an ultrapotassic stratovolcano(2022)
; ; ; ; ; ; ; ; ; A mineralogical, major, LA-ICP-MS trace element mineral chemistry and bulk-rock geochemical study of juvenile samples of the Mercato, Avellino, Pompeii and Pollena eruptions, collected in stratigraphically and volcano logically well-characterized sections of the Somma-Vesuvius stratovolcano (Roman Magmatic Province), along with reference data on the 1944 CE and the Pomici di Base eruptions, highlights the compositional variability of bulk-rock and glass from leucite phonotephrite to garnet-bearing phonolite. The latter products have extreme fractionation of trace elements (e.g., La/Ybn = 126, Zr/Y = 89, Zr/Hf =78, Nb/Ta = 40; Th/U = 2.3), very low Sc, V, Y, HREE and very high As, Tl, Cs, Pb, Th and U. The Pomici di Base products, older than the eruptions described above, range from leucite-bearing shoshonites to trachytes, are devoid of garnet and belong to an independent liquid-line-of-descent, having also different fractionation between trace elements (e.g., La/Ybn =15; Zr/Y = 12.4, Zr/Hf = 50, Nb/Ta = 15.6; Th/U = 3 in the Pomici di Base trachytes). A marked chemical variability of the observed phases is found. The geochemistry of garnet, amphibole, clinopyroxene and other phases shows wide variations of concentrations and elemental ratios (e.g., La/Ybn up to 520 in the sadanagaite coexisting with garnet). The magmatic evolution is dominated by low-pressure, oxidized, nearly closed-system fractional crystallization of clinopyroxene, plagioclase, leucite, ±magnetite, ±biotite, ±olivine and apatite in the transition tephrite-phonotephrite, and of potassic sanidine (±hyalophane), Fe-clinopyroxene, melanite garnet ±Fe-amphibole in the transition tephriphonolite-phonolite. Mineralogic and geochemical evidence and model ling points out the existence of independent, zoned magma batches throughout the activity of the stratovolcano, which possibly started to crystallize at similar depths. The Somma-Vesuvius magmas thus evolved in shallow independent reservoirs with respect to those of the neighbouring volcanic complexes (Campi Flegrei, Ischia) as shown, for instance, by the contrasting compositional trends of clinopyroxene and amphibole, and have very limited evidence of crustal contamination (and/or carbonate assimilation).68 2 - PublicationOpen AccessA roadmap for amphibious drilling at the Campi Flegrei caldera: insights from a MagellanPlus workshop(2019-12-02)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ;; ; ; ; ; ; ; ; ; ;; ; ;; ; ;; ;Large calderas are among the Earth's major volcanic features. They are associated with large magma reservoirs and elevated geothermal gradients. Caldera-forming eruptions result from the withdrawal and collapse of the magma chambers and produce large-volume pyroclastic deposits and later-stage deformation related to post-caldera resurgence and volcanism. Unrest episodes are not always followed by an eruption; however, every eruption is preceded by unrest. The Campi Flegrei caldera (CFc), located along the eastern Tyrrhenian coastline in southern Italy, is close to the densely populated area of Naples. It is one of the most dangerous volcanoes on Earth and represents a key example of an active, resurgent caldera. It has been traditionally interpreted as a nested caldera formed by collapses during the 100–200 km3 Campanian Ignimbrite (CI) eruption at ∼39 ka and the 40 km3 eruption of the Neapolitan Yellow Tuff (NYT) at ∼15 ka. Recent studies have suggested that the CI may instead have been fed by a fissure eruption from the Campanian Plain, north of Campi Flegrei. A MagellanPlus workshop was held in Naples, Italy, on 25–28 February 2017 to explore the potential of the CFc as target for an amphibious drilling project within the International Ocean Discovery Program (IODP) and the International Continental Drilling Program (ICDP). It was agreed that Campi Flegrei is an ideal site to investigate the mechanisms of caldera formation and associated post-caldera dynamics and to analyze the still poorly understood interplay between hydrothermal and magmatic processes. A coordinated onshore–offshore drilling strategy has been developed to reconstruct the structure and evolution of Campi Flegrei and to investigate volcanic precursors by examining (a) the succession of volcanic and hydrothermal products and related processes, (b) the inner structure of the caldera resurgence, (c) the physical, chemical, and biological characteristics of the hydrothermal system and offshore sediments, and (d) the geological expression of the phreatic and hydromagmatic eruptions, hydrothermal degassing, sedimentary structures, and other records of these phenomena. The deployment of a multiparametric in situ monitoring system at depth will enable near-real-time tracking of changes in the magma reservoir and hydrothermal system.759 109 - PublicationRestrictedNew proximal tephras at Somma-Vesuvius: evidences of a pre-caldera, large (?) explosive eruptionA ~ 5 m thick pyroclastic and volcaniclastic sequence, never reported before, comprising a pumice fall deposit has been recognized in a disused quarry near Pollena Trocchia, on the NW slope of Somma-Vesuvius. It is composed of three stratigraphic units: a pumice fall deposit that underlies a pyroclastic density current deposit; they are overlain by a volcaniclastic unit emplaced during a quiescent period of the volcano. The pyroclastic deposits are separated by a horizon of reworked material indicating the emplacement from two distinct eruptive events. The pumice fall deposit has been subject of a detailed investigation. It consists of an ash bed overlaid by a roughly stratified pumice fall layer. The presence of ballistic clasts indicates the proximal nature of this deposit and its stratigraphic position below the Pomici di Base (22 ka) Plinian deposit allows constraining its age to the pre-caldera period (22–39 ky) of activity of Somma-Vesuvius. Samples have been collected in order to perform sedimentological (grain size and componentry), geochemical and isotopic analyses. Samples range from moderately to poorly sorted and show a trachytic composition. The comparison with literature data of compatible deposits vented from Somma-Vesuvius (Schiava, Taurano and Codola eruptions as well as borehole data) allows excluding any correlation with already known Vesuvian products suggesting that the analysed products are ascribable to a new, pre-caldera, explosive eruption. We name this new event “Carcavone eruption”. Based on thickness, maximum lithic clasts and orientation of impact sags, showing a provenance from SE, we envisage the emplacement from a Plinian style eruption vented in the northern sector of the current caldera.
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