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In the Tyrrhenian back‐arc basin, the Ventotene Volcanic Ridge (VR) represents a NW‐SE‐oriented morphological high, located 25 km north of Ventotene Island in the Eastern Pontine Islands. It is considered part of an alignment of volcanic edifices developed in the central‐eastern Tyrrhenian Sea, from the western Pontine Islands (WPI) to the Campanian Volcanic Region. The samples dredged along the VR are basalts to trachybasalts belonging to the transitional (TR) rock‐series, with a 40Ar‐39Ar age of 2.760 ± 0.039 Ma. Petrological and geochronological data link the VR basalts to the TR peralkaline rhyolites cropping out at the WPI (∼1.6‐1.1 Ma); here, during a time span of ∼4.5‐1.0 Ma highly differentiated products of high‐potassium calc‐alkaline (HKCA, ∼4.5‐2.9 Ma) and K‐alkaline (KA, ∼1 Ma) series were also erupted. Notably, the parental melts of the three rock‐series were recognized in the continental slope close to the WPI (TR, HKCA) and eastward, namely in eastern Pontine Islands (KA), at the VR (TR), and in the Campanian Plain (HKCA). All the parental melts show typical orogenic geochemical signatures being originated from a similar heterogeneous suprasubduction mantle source, without the involvement of anorogenic sources. Tectonically, the faults bordering the VR, associated to the Pliocene E‐W directed rifting stage of the Tyrrhenian back‐arc basin were characterized by a more intense activity during the time span ∼5.0‐2.0 Ma (the emplacement time of HKCA and TR series), while KA products are related to a later stage of extension deformation (<∼2.0 Ma) when the extensional direction changed to NW‐SE and the VR fault activity decreased. Key Points: Under‐investigated seafloor sectors controlled by complex geodynamic processesThe Ventotene Volcanic Ridge emplacement in a context of extensional deformations related to the opening of the Tyrrhenian back‐arc basinCoexistence in space and time of high‐K calc‐alkaline, transitional and K‐alkaline rock‐series sharing orogenic‐type signatures [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]

The Colli Albani volcanic district emplaced huge pyroclastic-flow deposits up to 20 m thick in the southeastern suburbs of the City of Rome. The soil quality onto the gentle slopes of the Colli Albani has certainly contribute to the growth of Ancient Rome, a city with one million inhabitants as early as 2000 years ago. Interestingly, the Colli Albani soils developed on K-foiditic pyroclastic rocks with peculiar low silica, high alkali and high CaO composition. In the past, the productivity of the Colli Albani soils was maximized without the understanding of the unique physical, chemical, and mineralogical properties of these soils; now an in-depth knowledge of the Colli Albani soils is necessary to respond to the current and increasingly demand of sustainable soil use. Textural, mineralogical and chemical data indicate that the evolutionary stages of soil development are bedrock →leucite (Lct)-bearing soils→quartz (Qz)-bearing soils. The bedrock is made up mainly of leucite, clinopyroxene, phlogopite, zeolites and K-foiditic glass that is turned in an amorphous phase characterized by the Al-rich, cations base-poor and hydrated composition (i.e. halloysite-like chemistry). This reaction occurs in the syndepositional conditions (i.e. temperature up to ∼600 °C) and causes the absence of glass and the abundant crystallization of halloysite in the Colli Albani soils. The Lct-bearing soils are organic matter-poor, weakly weathered volcanic matter, comparable to the vitric andosols, showing incipient halloysite crystallization. As the degree of weathering increases, i) grain size decrease, ii) pH remain neutral, iii) highly soluble leucite, analcime and other zeolites, are rapidly dissolved, iv) alkali, Ca and Mg are leached, v) silica, Al and Fe activities increase and vi) halloysite stability field enlarges. The resulting Qz-bearing soils are made up mainly of halloysite, quartz, oxy-phlogopite and calcic clinopyroxene showing a lower cation exchange capacity (CEC) compared to the Lct-bearing soils. However, in Qz-bearing soils the CEC it is rarely <20 cmol (+)kg−1 because K Ex , Mg Ex and Ca Ex are released from the oxy-phlogopite and the strongly weathered clinopyroxenes characterized by the "gothic" texture. • Evidences of authigenic quartz in volcanic soils developed on silica-poor pyroclastic rocks. • Incipient halloysite formation in volcanic soils from high-temperature, cations base depleted glasses. • Gothic texture of clinopyroxenes in the Colli Albani soils. [ABSTRACT FROM AUTHOR]

The Bagno dell'Acqua lake is characterized by CO 2 emissions, alkaline waters (pH = 9) and Eh values which indicate strongly oxidizing conditions. A typical feature of the lake is the presence of actively growing microbialites rich in calcium carbonates and silica precipitates. Mineralogy, petrography and morphology analyses of the microbialites were coupled with the analysis of the microbial community, combining molecular and cultivation approaches. The DNA sequencing revealed distinct patterns of microbial diversity, showing pronounced differences between emerged and submerged microbialite, with the upper layer of emerged samples exhibiting the most distinctive composition, both in terms of prokaryotes and eukaryotes. In particular, the most representative phyla in the microbial community were Proteobacteria, Actinobacteriota, and Bacteroidota, while Cyanobacteria were present only with an average of 5%, with the highest concentration in the submerged intermediate layer (12%). The role of microorganisms in carbonate mineral formation was clearly demonstrated as most of the isolates were able to precipitate calcium carbonate and five of them were characterized at molecular level. Interestingly, when microbial isolates were cultivated only in filtered water, the precipitation of hazenite was observed (up to 85%), opening new prospective in P (phosphate) recovery from P depleted environments., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Mazzoni, Piacentini, Di Bella, Aldega, Perinelli, Conte, Ingrassia, Ruspandini, Bonfanti, Caraba, Falese, Chiocci and Fazi.)

Volcanic eruptions are shallow phenomena that represent the final stage of density- and viscosity- driven processes of melt migration from source rocks at upper mantle depths. In this experimental study, we investigated the effect of pressure (0.7-7.0 GPa) and temperature (1335-2000 °C) on the viscosity and the atomic melt structure of a synthetic anhydrous primitive alkaline basalt, an analogue of the pre-eruptive magma that likely feeds the Campi Flegrei Volcanic District at present day. Obtained viscosities (0.5-3.0 Pa s), mobility (0.1-0.4 g cm 3  Pa -1  s -1 ) and ascent velocity (1.5-6.0 m yr -1 ) are presented to support geochemical and geophysical observations of Campi Flegrei as a critical volcanic district currently undergoing gradual magma recharge at depth., (© 2022. The Author(s).)