Ottobre 2021

PubAIV Visite: 469
PubAIV 2021
(aggiornamento Ottobre 2021)
TEMATICHE GENERALI:

1) Magmi e sistemi di alimentazione (7 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., Perinelli C., Gaeta M., Stagno V., Fabbrizio A., Mollo S., Hrubiak R. (2021)
High pressure experimental investigation of clinopyroxene dissolution in a K-basaltic melt.
Chemical Geology, 584, 120533
https://doi.org/10.1016/j.chemgeo.2021.120533
Data di pubblicazione: 21/09/2021
PubAIV-ID-00028 - Articolo in Rivista (non-open access)
Abstract
Dissolution of clinopyroxene (cpx) in a K-basaltic melt from the Campi Flegrei Volcanic District (Italy) has been investigated through dissolution and dissolution-crystallization experiments at pressure of 0.8 GPa, superliquidus temperature of 1350 °C, and dwell times between 0.5 and 1 h. The obtained dissolution rates range from 7.9·10-6 cm s-1 to 6.1·10-6 cm s-1 as a function of dwell time. In the dissolution-crystallization experiment (1300 °C; 0.8 GPa; 2 h), the formation of overgrowth rims accompanied by new cpx crystals suggests that the injection of recharge magmas in basaltic reservoir may lead to inverse or oscillatory zonation. The interaction between cpx and K-basaltic melt at ~1570 °C was studied by in situ radiography using synchrotron radiation combined with the Paris-Edinburgh press. This resulted in cpx resorption to occur depending on the temperature conditions with respect to the liquidus temperature of the cpx (TcpxL). The calculated cpx dissolution rates are ~5·10-3 cm s-1 at T ≤ TcpxL and ~3·10-2 cm s-1 at T ≥ TcpxL. The role of crystal dissolution in the estimation of magma residence times has been also tested for a natural magmatic system by interpolating the dissolution rates (~10-5-10-6 cm s-1) with the textural data of cpx phenocrysts from the Agnano-Monte Spina pyroclastic deposit at Campi Flegrei caldera (Campanian region, Italy). Results from calculations indicate that the time required for partial or complete resorption of phenocrysts varies from ~0.5 to ~40 h, and that the effect of crystal dissolution may be relevant to estimate magma residence times whether significant dissolution occurs during magma mixing processes.
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Costa S., Masotta M., Gioncada A., Pistolesi M. (2021)
A Crystal Mush Perspective Explains Magma Variability at La Fossa Volcano. (Vulcano, Italy)
Minerals, 11(10), 1094
https://doi.org/10.3390/min11101094
Data di pubblicazione: 05/10/2021
PubAIV-ID-00033 - Articolo in Rivista (open access)
Abstract
The eruptive products of the last 1000 years at La Fossa volcano on the island of Vulcano (Italy) are characterized by abrupt changes of chemical composition that span from latite to rhyolite. The wide variety of textural features of these products has given rise to several petrological models dealing with the mingling/mixing processes involving mafic-intermediate and rhyolitic magmas. In this paper, we use published whole-rock data for the erupted products of La Fossa and combine them in geochemical and thermodynamic modelling in order to provide new constrains for the in- terpretations of the dynamics of the active magmatic system. The obtained results allow us to picture a polybaric plumbing system characterized by multiple magma reservoirs and related crystal mushes, formed from time to time during the differentiation of shoshonitic magmas, to produce latites, trachytes and rhyolites. The residing crystal mushes are periodically perturbated by new, fresh magma injections that, on one hand, induce the partial melting of the mush and, on the other hand, favor the extraction of highly differentiated interstitial melts. The subsequent mixing and mingling of mush-derived melts ultimately determine the formation of magmas erupted at La Fossa, whose textural and chemical features are otherwise not explained by simple assimilation and fractional crystallization models. In such a system, the compositional variability of the erupted products reflects the complexity of the physical and chemical interactions among recharging magmas and the crystal mushes.
Di Fiore F., Mollo S., Vona A., MacDonald A., Ubide T., Nazzari M., Romano C., Scarlato P. (2021)
Kinetic partitioning of major and trace cations between clinopyroxene and phonotephritic melt under convective stirring conditions: New insights into clinopyroxene sector zoning and concentric zoning.
Chemical Geology 584 (2021) 120531
https://doi.org/10.1016/j.chemgeo.2021.120531
Data di pubblicazione: 05/12/2021
PubAIV-ID-00029 - Articolo in Rivista (non-open access)
Abstract
Within subvolcanic plumbing systems, along volcanic conduits and post-eruptive emplacement, mineral textures and compositions are governed by complex kinetic (undercooling) and dynamic (convective) processes that deviate from theoretical models and equilibrium criteria. In this perspective, we have investigated the partitioning of major and trace cations between clinopyroxene and phonotephritic melt under convective stirring conditions at high degrees of undercooling (−ΔTnominal = 30–60 °C) and atmospheric pressure. We have integrated this novel data set with conventional static (no physical perturbation) clinopyroxene-melt compositions obtained under interface- and diffusion-controlled growth regimes. Results show that clinopyroxene growth kinetics and diffusion boundary layers caused by melt supersaturation are partly mitigated by the homogenizing effects of stirring. Because of continuous supply of fresh melt to the advancing crystal surface, the partitioning of major and trace cations is governed by local equilibrium effects, which are interpreted as the extension of equilibrium thermodynamic principles to non-equilibrium bulk systems. Major cations are incorporated into the clinopyroxene structure via the coupled substitution [M1Mg, TSi] ↔ [M1Ti, TAl] and in conformity with the thermodynamic mixing properties of CaMgSiO2, CaAl2SiO6, and CaTiAl2O6 components. The complementary relationship between lattice strain (ΔGstrain) and electrostatic (ΔGelectrostatic) energies of heterovalent substitutions is the most appropriate thermodynamic description for the accommodation of trace cations in the clinopyroxene lattice site (i.e., ΔGpartitioning = ΔGstrain + ΔGelectrostatic). The excess energy of partitioning ΔGpartitioning changes principally with Al in tetrahedral coordination and determines the type and number of charge-balanced and -imbalanced configurations taking place in the structural sites of clinopyroxene. An important outcome from dynamic stirring experiments is that superimposition of convective mass transfer on melt supersaturation phenomena causes the formation of Cr-rich concentric zones under closed system crystallization conditions. However, these Cr-rich zones do not correlate with enrichment in other compatible elements and depletion in incompatible elements, as would be expected in natural open systems characterized by input of more primitive magmas. While the convective transport acts to reduce the diffusive length scale of chemical species in the experimental melt, fresh Cr cations are more easily incorporated into the concentric zones due to crystal field effects. Together, our findings reveal that during magma ascent and emplacement, convective stirring may promote clinopyroxene crystallization and minimize kinetic effects on clinopyroxene zoning.
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Deb P., Giordano G., Shi X., Lucci F., Clauser C. (2021)
An approach to reconstruct the thermal history in active magmatic systems: Implications for the Los Humeros volcanic complex, Mexico.
Geothermics 96, 102162.
https://doi.org/10.1016/j.geothermics.2021.102162
Data di pubblicazione: 23/06/2021
PubAIV-ID-00032 - Articolo in rivista (non-open access)
Abstract
Reconstructing the thermal history in active volcanic complexes characterized by multiple magmatic events is challenging due to the limited knowledge of the nature and extent of the transient heat sources. Although understanding of the geometry and architecture of a magmatic system is of prime importance for accurate temperature assessments, it is still one of the most uncertain parameters in numerical models. In this work, we presented a methodology for thermal assessment in active volcanic systems, whereby field-based geological, geochemical and petrological data are integrated to define the transient heat sources of a magma plumbing system. This time-varying heat source conceptual model is applied in the Los Humeros Volcanic Complex, an active Quaternary caldera complex in the Trans Mexican Volcanic Belt, for evaluating the thermal footprint related to the major volcanic events. The site is characterized by two caldera-forming eruptions, the Los Humeros (164 000 years ago) and the Los Potreros (69 000 years ago) and numerous episodes of post-caldera bi-modal volcanism during Holocene period (8 000 – 3 000 years old). The transient nature of the heat sources is implemented as time-varying temperature boundary conditions and the complete temporal evolution for a period of 182 000 years is simulated in 13 modeling stages. The thermal impact due to the voluminous caldera-forming events and the later short-lived magma pockets of Holocene ages is simulated by emplacing heat sources in the numerical model distributed heterogeneously in space and active at different instants of time. The depth, volume and age of the magma pockets are constrained from geochemical, petrological, geochronological and thermo-barometric analysis of erupted material. The present temperature state obtained from this approach agrees well with the temperature data recorded in the geothermal wells. The thermal footprint of the individual volcanic events indicates that almost 80 % of the present-day thermal contribution results from the massive caldera-forming events. The post-caldera Holocene magma pockets had additionally increased temperatures locally by 10 % - 20 % depending on the volumes and ages of the magma pockets. The present-day thermal regime of the younger Holocene magma pockets suggests existence of super-hot resources at shallow depths in the southern part of the geothermal field, making it a potential site for future exploration activities.
Lucci F., Saki A., Miri M., Rabiee A., White J.C. (2021)
Genesis of trondhjemite by low-pressure low-melt fraction anatexis of hornblende-gabbro at Alvand Plutonic Complex (Hamedan, NW Iran): insights from geochemical modelling.
Arabian Journal of Geosciences 14, 1788.
https://doi.org/10.1007/s12517-021-08104-0
Data di pubblicazione: 16/08/2021
PubAIV-ID-00031 - Articolo in rivista (open access)
Abstract
Amphibole-dominated dehydration melting of gabbro is the primary process responsible for the genesis of adakites, low-K tonalites, modern trondhjemites, and plagiogranites aswell as Archean tonalite-trondhjemite-granodiorite suites that represent the earliest examples of continental crust. Previous literature has mostly focused on the role of Al-rich amphibole during anatexis of a mafic source and many of these studies have investigated this process through experimental melting runs. However, due to experimental boundary conditions, little is known about partial melting of amphibole-bearing mafic rock at temperatures
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Pappalardo L., Buono G. (2021)
Insights Into Processes and Timescales of Magma Storage and Ascent From Textural and Geochemical Investigations.
In Crustal Magmatic System Evolution (eds M. Masotta, C. Beier and S. Mollo), Geophysical Monograph Series AGU.
https://doi.org/10.1002/9781119564485.ch10
Data di pubblicazione: 21/05/2021
PubAIV-ID-00027 - Capitolo di un libro (non-open access)
Abstract
The mechanisms and timescales of magmatic evolution during storage in crustal reservoirs and ascent in the volcanic conduit exert an important control on both the evolution of precursory phenomena recorded during volcanic crises as well as the style and intensity of the impending eruption. Improving our knowledge on this topic is therefore of paramount importance for better assessment of hazard for active high-risk volcanoes. The densely populated Neapolitan volcanic area (Italy) is one of the places most at risk of volcanic disaster in Europe. To reconstruct the magma plumbing system and its evolution toward critical conditions close to eruption, we employed petrological data on past eruptive products representative of the entire volcanic history. Our results are consistent with the possible existence of a long-term magmatic sill-shaped storage zone beneath the whole Neapolitan volcanic area, with its maximum volume under the Campi Flegrei supervolcano, where the largest eruptions occurred in the last 40 ka. Moreover, slow magma transfer, an open degassing regime, and stasis at a shallow level (ephemeral storage zones) characterize magma ascent during small-scale events, whereas fast magma rise and a continuous closed degassing mechanism drive violent large-scale eruptions. These distinctive dynamics could imply different time-depth patterns of precursory unrest.
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Saki A., Lucci F., Miri M., White J.C. (2021)
Trondhjemite leucosomes generated by partial melting of a hornblende-gabbro (Alvand plutonic complex, Hamedan, NW Iran).
International Geology Reviews, pp.1-34.
https://doi.org/10.1080/00206814.2020.1861554
Data di pubblicazione: 21/01/2021
PubAIV-ID-00030 - Articolo in rivista (non-open access)
Abstract
This work describes the petrogenesis of in situ and in-source trondhjemite leucosomes generated by low-degree partial melting of the Jurassic Cheshmeh-Ghasaban hornblende-gabbros in the northern Alvand batholith (Hamedan, NW Iran). These leucosomes occur in a metatexite migmatite as patches, net-structures, veinlets, and dikes at scales ranging from a few millimetres to a few metres. They have high SiO2 (mean ≈ 78 wt%) and Na2O (4–5 wt%) with low Al2O3 (<15 wt%), K2O (<1.5 wt%), Sr (33–267 ppm), Eu (0.31–0.62 ppm) and heavy REE (<4 ppm) contents similar to typical low-Al2O3 trondhjemites. Batch-melting models indicate these leucosomes are the result of ≈1-2% partial melting of the hornblende-gabbro, whereas thermobarometric modelling constrains their petrogenesis in the field of hornblende hornfels-facies metamorphism (pressure ≈3.0–4.5 kbar and temperature ≈700-750°C). On a wider scale, our results document natural trondhjemites generated in the upper crust by amphibole-dehydration melting of a mafic source at temperature conditions close to the solidus, filling the existing gap of data in low-pressure (P < 5kbar) and low-temperature (T < 800°C) amphibole-dominated partial melting experiments. The genesis of these trondhjemites is then discussed with respect to the Mesozoic evolution of the Alvand plutonic complex.
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Tematica 2: Dinamiche eruttive e di messa in posto
Tematica 3: Geologia e struttura dei vulcani
Tematica 4: Monitoraggio, pericolosità e rischio vulcanico
Lima A., Bodnar R.J., De Vivo B., Spera F. J., Belkin H.E. (2021)
Interpretation of Recent Unrest Events (Bradyseism) at Campi Flegrei, Napoli (Italy): Comparison of Models Based on Cyclical Hydrothermal Events versus Shallow Magmatic Intrusive Events.
Geofluids 2021, 2000255.
https://doi.org/10.1155/2021/2000255
Data di pubblicazione: 15/10/2021
PubAIV-ID-00034 - Articolo in rivista (open access)
Abstract
Several recent models that have been put forth to explain bradyseism at Campi Flegrei (CF), Italy, are discussed. Data obtained during long-term monitoring of the CF volcanic district has led to the development of a model based on lithological-structural and stratigraphic features that produce anisotropic and heterogeneous permeability features showing large variations both horizontally and vertically; these data are inconsistent with a model in which bradyseism is driven exclusively by shallow magmatic intrusions. CF bradyseism events are driven by cyclical magmatic-hydrothermal activity. Bradyseism events are characterized by cyclical, constant invariant signals repeating over time, such as area deformation along with a spatially well-defined seismogenic volume. These similarities have been defined as “bradyseism signatures” that allow us to relate the bradyseism with impending eruption precursors. Bradyseism is governed by an impermeable shallow layer (B-layer), which is the cap of an anticlinal geological structure culminating at Pozzuoli, where maximum uplift is recorded. This B-layer acts as a throttling valve between the upper aquifer and the deeper hydrothermal system that experiences short (1-102 yr) timescale fluctuations between lithostatic/hydrostatic pressure. The hydrothermal system also communicates episodically with a cooling and quasi-steady-state long timescale (103-104 yr) magmatic system enclosed by an impermeable carapace (A layer). Connectivity between hydrostatic and lithostatic reservoirs is episodically turned on and off causing alternatively subsidence (when the systems are connected) or uplift (when the systems are disconnected), depending on whether permeability by fractures is established or not. Earthquake swarms are the manifestation of hydrofracturing which allows fluid expansion; this same process promotes silica precipitation that seals cracks and serves to isolate the two reservoirs. Faults and fractures promote outgassing and reduce the vertical uplift rate depending on fluid pressure gradients and spatial and temporal variations in the permeability field. The miniuplift episodes also show “bradyseism signatures” and are well explained in the context of the short timescale process.
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