Settembre 2022

PubAIV 2022
(aggiornamento di Settembre 2022)

1) Magmi e sistemi di alimentazione (2 articoli) 
2) Dinamiche eruttive e di messa in posto (1 articolo)
3) Geologia e struttura dei vulcani (0 articoli)
4) Monitoraggio, pericolosità e rischio vulcanico (0 articoli)

Tematica 1: Magmi e sistemi di alimentazione
Spallanzani R., Koga K. T., Cichy S. B., Wiedenbeck M., Schmidt B. C., Oelze M., Wilke M. (2022)
Lithium and boron diffusivity and isotopic fractionation in hydrated rhyolitic melts.
Contributions to Mineralogy and Petrology 177, nr. 74
Data di pubblicazione: 22/07/2022
PubAIV-ID-00080 - Articolo in Rivista (open access)

Lithium and boron are trace components of magmas, released during exsolution of a gas phase during volcanic activity. In this study, we determine the diffusivity and isotopic fractionation of Li and B in hydrous silicate melts. Two glasses were synthesized with the same rhyolitic composition (4.2 wt% water), having different Li and B contents; these were studied in diffusion-couple experiments that were performed using an internally heated pressure vessel, operated at 300 MPa in the temperature range 700–1250 °C for durations from 0 s to 24 h. From this we determined activation energies for Li and B diffusion of 57 ± 4 kJ/mol and 152 ± 15 kJ/mol with pre-exponential factors of 1.53 × 10–7 m2/s and 3.80 × 10–8 m2/s, respectively. Lithium isotopic fractionation during diffusion gave β values between 0.15 and 0.20, whereas B showed no clear isotopic fractionation. Our Li diffusivities and isotopic fractionation results differ somewhat from earlier published values, but overall confirm that Li diffusivity increases with water content. Our results on B diffusion show that similarly to Li, B mobility increases in the presence of water. By applying the Eyring relation, we confirm that B diffusivity is limited by viscous flow in silicate melts. Our results on Li and B diffusion present a new tool for understanding degassing-related processes, offering a potential geospeedometer to measure volcanic ascent rates.
Zuccarello F., Schiavi F., Viccaro M. (2022)
The eruption run-up at Mt. Etna volcano: Constraining magma decompression rates and their relationships with the final eruptive energy.
Earth and Planetary Science Letters, 597
Data di pubblicazione: 27/09/2022
PubAIV-ID-00081 - Articolo in Rivista (non-open access)

Although explosivity is linked with high decompression rates induced by magma ascent, the quantitative relationships between decompression rate and eruption energy have yet to be properly assessed, especially for open-conduit basaltic volcanoes, where ordinary weak activity can rapidly evolve into more intense eruptions. Here, we selected three eruptions of different explosivity from Mt. Etna's recent activity to study the relationships between the observed explosive intensities and decompression rates determined through diffusion chronometry, which is based on modeling volatile diffusion along olivine-hosted melt embayments. The approach used in this study has provided important indications on differences in the timescales of decompression-driven degassing for magmas emitted with markedly distinct eruptive dynamics, starting from similar physical and chemical conditions of the magmas involved in the three eruptions. The intense paroxysmal activity at Voragine Crater on December 3, 2015, was fostered by high decompression rate (∼0.36-0.74 MPa/s), slightly higher than in the less energetic paroxysm that occurred on February 19, 2013, at New South-East Crater (NSEC) (∼0.14-0.29 MPa/s). Decompression rates of magmas emitted during lava fountaining are one order of magnitude greater than values obtained for the mild flank eruption that occurred in December 2018 (∼0.045-0.094 MPa/s). Our results indicate that degassing kinetics controlled the intensity of activity at Mt. Etna, thus suggesting that the explosivity does not depend exclusively on the degree of overpressurization of the shallowest reservoir due to injection of gas from the deepest levels of the plumbing system.
Tematica 2: Dinamiche eruttive e di messa in posto
Di Fiore F., Vona A., Costa A., Mollo S., Romano C. (2022)
Quantifying the Influence of Cooling and Shear Rate on the Disequilibrium Rheology of a Trachybasaltic Melt from Mt. Etna.
Earth and Planetary Science Letters, 594, 117725
Data di pubblicazione: 15/09/2022
PubAIV-ID-00082 - Articolo in Rivista (non-open access)

Magmas often experience severe disequilibrium conditions during their migration through the Earth’s crust and the subsequent emplacement on its surface. During their transport, magmas are subjected to a wide range of cooling (q) and deformation rates (γ ̇), generating physico-chemical perturbations in the magmatic system able to inhibit or promote crystallization processes. Quantifying the magnitude and timescale of kinetic effects is essential to correctly constrain the rheological evolution of magmas and their ability to flow. Here we present a suite of cooling deformation experiments (CDE) conducted on a basalt from Mt. Etna (Sicily, Italy) to disentangle and model the concurrent effects of q (from 1 to 10 °C/min) and γ ̇ (from 1 to 10 s-1) on the rheology of the system. The analysis of the temporal evolution of viscosity indicates that both q and γ ̇ strongly affect the onset of crystallization and achievement of a rheological cut-off over time, which represents the steep viscosity increase responsible for inhibiting magma flow. Both these rheological thresholds occur at lower T and earlier in time with increasing q, as well as at higher T and earlier in time with increasing γ ̇. To reproduce the observed effects of crystallization on the apparent viscosity, we adopt a stretched exponential function that identifies two main crystallization regimes: i) a first shear-induced crystallization regime, characterized by a gentle viscosity increase and ii) a second cooling-dominated regime, marked by a steeper viscosity increase. The relative extent of these crystallization regimes strictly depends on the interplay between q and γ ̇ on the crystallization kinetics and suggest a first order control of q and a subordinate role of γ ̇.
Tematica 3: Geologia e struttura dei vulcani
Tematica 4: Monitoraggio, pericolosità e rischio vulcanico
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