Cristina Perinelli

Eruptive styles are influenced by multiple factors, including magma chamber depth. At Ventotene volcano (Pontian Islands, Tyrrhenian Sea, central Italy), a transition at ~300 ka is observed from repeated ‘pure Plinian’ eruptions—i.e. without associated caldera collapse (Cala di Battaglia eruptions, UCB)—to a caldera-forming event (Parata Grande eruption, PGT). In the latter eruption, the initial Plinian phase is followed by the roof collapse and widespread pyroclastic currents. We characterize the pre-eruptive magmatic systems of Ventotene—defined as reservoirs immediately preceding eruption and directly feeding syn-eruptive exsolution and fragmentation—through integrated analyses of juvenile (pumice and scoria) clasts, including texture, mineral and bulk-rock chemistry, 87Sr/86Sr isotopic ratios, and experimental phase equilibria. These data provide new insights into contrasting deep vs shallow pre-eruptive magmatic systems that fed pure Plinian and caldera-forming eruptions, respectively, at Ventotene. UCB pumice clasts contain low phenocryst amounts (<3 vol %) and primary analcime microcrysts, whose crystallization is consistent with PH2O conditions higher than 150 MPa, as shown by experimental runs on Ventotene trachyte at PH2O = 150 and 600 MPa. The presence of analcime constrains the UCB pre-eruptive magmatic systems to the deep metapelitic basement, also indicated by higher 87Sr/86Sr ratios. In contrast, PGT juvenile clasts—from Plinian fall, welded spatter, lag breccia, pumice-rich, and hydromagmatic pyroclastic current deposits—contain abundant phenocrysts and antecrysts (10–25 vol %), while analcime is absent. This latter textural feature, coupled with the lower H2O content in glasses and clinopyroxene barometry, points to a shallow (P ≤ 180 MPa) PGT pre-eruptive magmatic system. Notable differences between phonolitic–trachytic groundmass glasses and shoshonitic to tephri-phonolitic/latitic bulk compositions reflect the occurrence of olivine and clinopyroxene antecrysts in the PGT pre-eruptive magmatic system. The presence of centimeter-sized clinopyroxenes lacking resorption textures suggests that this system was short lived. Consistently, the longevity of the PGT pre-eruptive magmatic system is estimated to be <2 years, based on experimentally calibrated clinopyroxene and amphibole growth rates and settling distances of ~1-cm-sized antecrysts. Homogeneous glass compositions but variable phenocryst assemblages suggest a crystal-zoned pre-eruptive magmatic system with antecryst-depleted (D), enriched (E), and mush (M) zones. The initial Plinian phase tapped the D zone, followed by spatter deposits rich in olivine and clinopyroxene antecrysts from the E zone, concurrent with caldera collapse onset. The low water content in these glasses indicates magma outgassing. This evolution is consistent with a transition from a central conduit (sustaining a Plinian column) to a multi-vent (fissural) system along ring faults, feeding spatter-, lithic-, and pumice-rich pyroclastic currents. We propose that pure Plinian scenarios at Ventotene—and likely in similar volcanic systems—are driven by polybaric differentiation of a magma batch ascending from depth and/or pre-eruptive storage in deep reservoirs with high roof aspect ratios. In contrast, isobaric differentiation in shallow, sill-like pre-eruptive magmatic systems with low roof aspect ratios favors caldera-forming eruptions. Here, decompression from initial Plinian magma withdrawal induces roof collapse, a hallmark of underpressure caldera scenarios. This has implications for active caldera systems such as Ischia and Campi Flegrei, which share similar magma compositions and eruptive style shifts—from early pure Plinian to later caldera-forming activity—throughout their histories.

Here, we report the discovery of silica- and sulfur-enriched deposits forming on the seafloor off Zannone Island (western Mediterranean Sea), where hydrothermal activity is ongoing. Our multidisciplinary investigation reveals that these deposits form through the interplay between hydrothermal processes and microbial activity. The deposits result from a dynamic equilibrium involving microbial mediation, sedimentation, and episodic lithification, driven primarily by two mineralization pathways: silica and sulfur precipitation. This study provides new insights into the bio-sedimentary processes shaping authigenic crusts in shallow submarine hydrothermal settings, contributing to a broader understanding of mineralization in marine environments influenced by both geological and biological factors.

This study examines element mobility in volcanic soils to evaluate the relationships between mineral assemblage and the uptake capacity of rootstocks. The Gravesac rootstock, which appears to have a low capacity to selectively absorb K, Ca, Mg, and Na relative to one another, was used for this study. We analysed the chemical composition of rootstocks and the adhering soils. These soils were also mineralogically characterised and subjected to leaching using water over variable time periods and ammonium acetate. Chemical weathering of minerals significantly controls the mobility of base cations in vineyard soils and this should strongly impact root absorption and plant nutrient content. In the scarcely evolved volcanic soils (hereafter pozzolanic soils), where clinopyroxene is not significantly weathered, Ca has low availability in soil solution compared to evolved volcanic soils (hereafter clay-bearing volcanic (CBV) soils), despite higher Ca content in pozzolanic soils. This indicates that in pozzolanic soils, Ca and Mg are less mobile due to the minimal weathering of clinopyroxene. Rootstock absorption of Ca and Mg mirrors these findings, with lower uptake in pozzolanic soils despite higher total element content. Leaching experiments show that the bioavailability of Ca and Mg obtained in H2O and ammonium acetate is inversely correlated with the uptake efficiency of rootstocks, which is instead positively correlated with the removal of Ca and Mg from the soils. In CBV soils, the intense chemical weathering of clinopyroxene increases the mobility and subsequent uptake of Ca and Mg by roots. On the contrary, leaching tests show that K bioavailability in pozzolanic soils, derived from leucite weathering, is higher than in CBV soils, which is consistent with their higher K content. The rapid dissolution of K in pozzolanic soils contrasts with its slower and more sustained release in CBV soils, linked to the weathering of phlogopite. This leads to higher K uptake in CBV soils despite their lower K content. The mineral assemblage in CBV soils, particularly the extent of phlogopite alteration, maintains high K activity in the soil solution, enhancing K bioavailability. The effect of mineral speciation (i.e., the solid solution range and weathered form of a particular mineral) on the uptake efficiency of rootstocks is confirmed by the distinct chemical compositions of musts from Merlot grapes grown in the two soils. Our results highlight the pivotal role of mineral assemblage in shaping nutrient availability and rootstock uptake dynamics in viticultural systems.

Microbial activity has been documented in various lacustrine environments, suggesting its fundamental role in mineral precipitation and, therefore, in the formation of organo-deposits such as microbialites. Many studies are currently focused on documenting how the association of microbes and extracellular polymeric substances (EPSs) may influence the authigenesis of Mg-rich clay minerals and the subsequent carbonate precipitation in growing microbialites in lacustrine environments. In this study, we investigate the present-day microbialites of the alkaline Bagno dell’Acqua lake (Pantelleria Island, Italy) using X-ray diffraction (XRD) scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Our results reveal the intimate association of Mg-smectite/carbonate minerals with the EPS and microbes, and, for the first time, we selected microbes belonging to phylum Firmicutes (Bacillus sp.), from natural microbialites, to carry out laboratory experiments that testify their direct role in the precipitation of clay and carbonate minerals.

The Bagno dell'Acqua lake is characterized by CO₂ 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.

Time-series experiments were carried out in a piston-cylinder apparatus at 0.8 GPa and 1030–1080 °C using a hydrous K-basalt melt as the starting material to determine the element partition coefficients between amphibole and silicate glass. Major, minor, and trace element compositions of amphibole and glass were determined with a combination of electron microprobe and laser ablation inductively coupled plasma mass spectrometry. Results show that the main mineral phase is calcic amphibole, and the coexisting glass compositions range from basaltic trachyandesite to andesite. We estimated the ideal radius, the maximum partition coefficient and the apparent Young’s modulus of the A, M1-M2-M3, and M4-M4′ sites of amphibole. The influence of melt and amphibole composition, temperature, and pressure on the partition coefficients between amphiboles and glasses has also been investigated by comparing our data with a literature data set spanning a wide range of pressures (0.6–2.5 GPa), temperatures (780–1100 °C), and compositions (from basanite to rhyolite). Finally, we modeled a deep fractional crystallization process using the amphibole-melt partition coefficients determined in this study, observing that significant amounts of amphibole crystallization (>30 wt%) well reproduce the composition of an andesitic melt similar to that of the calc-alkaline volcanic products found in Parete and Castelvolturno boreholes (NW of Campi Flegrei, Italy).

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 cm³ 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.