Febbraio 2022

PubAIV Visite: 299
PubAIV 2022
(aggiornamento Febbraio 2022)
TEMATICHE GENERALI:

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

Tematica 1: Magmi e sistemi di alimentazione
Bonechi B., Stagno V., Kono Y., Hrubiak R., Ziberna L., Andreozzi G.B, Perinelli C., Gaeta M. (2022)
Experimental measurements of the viscosity and melt structure of alkali basalts at high pressure and temperature.
Scientific Reports, 12, 2599
https://doi.org/10.1038/s41598-022-06551-7
Data di pubblicazione: 16/02/2022
PubAIV-ID-00053 - Articolo in Rivista (open access)

Abstract
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.
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Braschi E., Mastroianni F., Di Salvo S., Casalini M., Agostini S., Vougioukalakis G., Francalanci L. (2022)
Unveiling the occurrence of transient, multi-contaminated mafic magmas inside a rhyolitic reservoir feeding an explosive eruption (Nisyros, Greece).
LITHOS 410–411 (2022) 106574
https://doi.org/10.1016/j.lithos.2021.106574
Data di pubblicazione: 18/12/2021
PubAIV-ID-00050 - Articolo in Rivista (open access)

Abstract
The investigation of heterogeneous magma systems enhances the understanding of magma differentiation and transfer processes in active volcanoes, thus constraining the dynamics driving the eruptions and the related hazard. Magma heterogeneity is generally preserved in the coeval juvenile products of explosive eruptions, as it occurs in the Upper Pumice sequence, emplaced by the last sub-Plinian explosive eruption at Nisyros volcano (Greece). The deposit comprises a basal fallout, overlaid by pyroclastic density current units, followed by a lag- breccia level. White-yellow, porphyritic, rhyolitic pumices constitute the main juvenile component. Grey, crystal- rich juvenile clasts (CRCs) are less abundant (up to 10–15%), and are characterised by three different texture types (Type-A, -B and -C), with specific recurrence in the different depositional units and well correlated to the magma evolution. In the basal unit CRCs occur as andesitic to dacitic lapilli with Type-A and -B vesicular textures associated with highly variable trace element and isotopic compositions. In the lag-breccia deposit, the juvenile clasts occur as bombs with crenulated or bread-crust surfaces, displaying diktytaxitic Type-C textures and less evolved andesitic compositions, covering a larger Nd-isotope range at lower Sr-isotopes compared to the others.
The CRCs are interpreted as the result of the rapid cooling of more mafic magma blobs sequentially intruded in the cooler rhyolitic host magma, in which they attained variable textures by different undercooling conditions, due to their variable compositions. We suggest that a two-stage AFC (Assimilation plus Fractional Crystallisation) process occurred at different pressures, before intrusion in the host magma, accounting for their heterogeneous chemical and isotopic characteristics. Firstly, the most primitive melts variably assimilated gneissic wallrock at depth, acquiring a variable Nd-isotope signature. On the way to the surface, they later experienced shallow AFC processes within different small magma reservoirs, involving heterogeneous carbonate-rocks such as pure limestone, metasomatised marble and skarn. Sequential dynamics of ascent and intrusion into the rhyolitic magma chamber lead the more evolved and skarn-contaminated Type-A and -B melts to firstly move in the upper part of the reservoir to be erupted in the early fallout deposits. Type-C more mafic melts later intruded the rhyolitic reservoir and were erupted in the lag-breccia deposit. The lowest Nd-isotopes recorded by CRCs, with respect to all the volcanic products of the Kos-Nisyros volcanic field, reveal the peculiar transient history for these magmas at relatively shallow levels in the crust. The CO2 release from the carbonate-rock assimilation has also possibly contributed to trigger the explosive eruption, discharging a large amount of CO2 into the atmosphere.
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Godoy B., Taussi M., González-Maurel O., Hübner D., Lister J., Sellés D., le Roux P., Renzulli A., Rivera G., Morata D. (2022)
Evolution of the Azufre volcano (northern Chile): Implications for the Cerro Pabellón Geothermal Field as inferred from long lasting eruptive activity.
Journal of Volcanology and Geothermal Research Volume, 423, 107472
https://doi.org/10.1016/j.jvolgeores.2022.107472
Data di pubblicazione: 01/03/2022
PubAIV-ID-00051 - Articolo in Rivista (non-open access)

Abstract
Azufre volcano (21°47′S, 68°15′W) is part of the Pleistocene NW-SE trending Azufre-Inacaliri Volcanic Chain, located in the Chilean Central Volcanic Zone of the Andes, near the currently exploited Cerro Pabellón Geothermal Field. Geochronological data and geomorphological features indicate that Azufre was constructed between ~1300 and ~ 120 ka through four magmatic Stages (namely Stage I, II, III and IV), with eruptions from different vents that generated the Northern (Stages II and IV) and Southern (Stages I and III) edifices. Whole rock geochemical data indicates that lavas erupted in Stage II (700–500 ka) and Stage IV (300–120 ka) mainly show lower Al2O3, Na2O and Sr concentrations, and higher FeO, MgO and Ti2O concentrations at similar SiO2 contents than those of Stage I (1,300–700 ka) and Stage III (500–300 ka). These differences suggest dominant plagioclase and Fe–Mg rich mineral phases (i.e. olivine and orthopyroxene) fractionations in the Northern edifice with respect to the Southern one. This is in agreement with petrographic characters that reveal more olivine and orthopyroxene contents in less evolved (hermal Field. This possibly unravels a long lasting (more than 1 Ma) active magmatic system in the northeastern-most sectors of the Azufre-Inacaliri Volcanic Chain and new constraints on the longevity of the heat source regions of the high-enthalpy Cerro Pabellón Geothermal Field, possibly opening new perspectives in the geothermal exploration of this area.
Tematica 2: Dinamiche eruttive e di messa in posto
Tematica 3: Geologia e struttura dei vulcani
Tematica 4: Monitoraggio, pericolosità e rischio vulcanico
Schito A., Pensa A., Romano C., Corrado S., Vona A., Trolese M., Morgavi D., Giordano G. (2022)
Calibrating Carbonization Temperatures of Wood Fragments Embedded within Pyroclastic Density Currents through Raman Spectroscopy.
Minerals. 2022; 12(2):203
https://doi.org/10.3390/min12020203
Data di pubblicazione: 05/02/2022
PubAIV-ID-00052 - Articolo in Rivista (open access)

Abstract
The study of the structural order of charcoals embedded in pyroclastic density currents provides information on their emplacement temperature during volcanic eruptions. In the present work, a set of charcoals from three distinct pyroclastic density currents deposits whose temperatures have been previously estimated by charcoal reflectance analyses to lie between 250 °C and 550 °C, was studied by means of Raman spectroscopy. The analyses reveal a very disordered structural ordering of the charcoals, similar to kerogen matured under diagenetic conditions. Changes in Raman spectra at increasing temperatures reflect depolymerization and an increase of aromaticity and can be expressed by parameters derived from a simplified fitting method. Based on this approach, a second order polynomial regression with a high degree of correlation and a minimum error was derived to predict paleotemperatures of pyroclastic deposits. Our results show that Raman spectroscopy can provide a reliable and powerful tool for volcanological studies and volcanic hazard assessment given its advantage of minimum samples preparation, rapid acquisition processes and high precision.
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