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Di Piazza, Andrea
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Di Piazza, Andrea
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andrea.dipiazza@ingv.it
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- PublicationRestrictedThe complex rheology of megacryst-rich magmas: The case of the mugearitic “cicirara” lavas of Mt. Etna volcanoMultiphase magma rheological properties play a fundamental role on lava flow transport, emplacement and morphology. To date, however, the three-phase (melt + crystals + bubbles) rheology of natural magma remains relatively understudied. We present here a series of high-temperature experiments designed to investigate the multiphase rheology of a mugearitic megacryst-bearing lava from Mt. Etna. A peculiar textural feature of this magma is the abundance of cm-size plagioclase crystals (megacrysts) together with smaller size crystals (phenocrysts and microlites), yielding a very wide crystal size distribution. We combined different experimental techniques (rotational and compressional rheometry) to investigate the rheology of this natural lava under different degrees of partial melting at subliquidus conditions. Results indicate that natural megacryst-bearing mugearite magmas from Mt. Etna display a wide range of behaviors as a function of temperature (T = 1000–1200 °C) and crystal content (ϕX = 0.2–0.7). In the investigated T range, the deformation mechanism of these magmas varies from mainly brittle (T < 1050 °C) to mainly ductile (T > 1085 °C). At T = 1075 °C, both ductile and brittle behavior have been observed. In the ductile regime, these magmas behave as non-Newtonian fluids (at least up to T = 1100 °C) showing marked apparent shear thinning behavior. The observed rheological behavior is due to a complex response related to a non-homogenous deformation of the natural sample (e.g. viscous and/or brittle shear localization), favored by the presence of bubbles. Consequently, the obtained flow parameters can be considered as representative of the bulk rheology of natural magmas, commonly characterized by similar non-homogeneous deformation styles. We applied the obtained data to discuss the flow and emplacement conditions of these peculiar lava flows. We demonstrated that at eruptive temperatures, the presence of a pre-eruptive crystal cargo and bubbles facilitates the achievement of critical crystal content during flow and cooling, ultimately controlling lava transport and emplacement. Flow conditions can be maintained in the presence of an efficient insulation and, importantly, of deformable vesicles promoting and enhancing shear localization.
84 2 - PublicationRestrictedNew insights on the provenance of obsidian fragments of Ustica Island (Palermo, Sicily).(2017)
; ; ; ; ; ; ; ;Foresta Martin, F.; Museo di Ustica ;Di Piazza, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;D'Oriano, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Carapezza, M. L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Paonita, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Rotolo, S. G. ;Sagnotti, l.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; ; ; ; ; ; In this study we applied a multidisciplinary approach, coupling geophysical and geochemical measurements, to unveil the provenance of 170 obsidian flakes, collected on the volcanic island of Ustica (Sicily). On this island there are some prehistoric settlements dated from the Neolithic to the Middle Bronze Age. Despite not having geological outcrops of obsidian rocks, the countryside of Ustica is rich in fragments of this volcanic glass, imported from other source areas. The study of obsidian findings was carried out first through visual observations and density measurements. At least two different obsidian families have been distinguished, probably imported from Lipari and Pantelleria islands. Analysing the magnetic properties of the samples, these two main sources were confirmed, but the possibility of other provenances was inferred. Finally, we characterized the geochemical signature of the Ustica obsidians by performing microchemical analyses through electron microprobe (EMPA) and laser ablation (LA–ICP–MS). The results were compared with literature data, confirming the presence of the Lipari and Pantelleria sources (Sicily) and indicating for the first time in this part of Italy a third provenance from Palmarola island (Latium). Our results shed new light on the commercial exchanges in the peri-Tyrrhenian area during the prehistoric age.929 17 - PublicationRestrictedGeochemistry of the mantle source and magma feeding system beneath Turrialba volcano, Costa Rica(2015-07-31)
; ; ; ; ; ; ; ;Di Piazza, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Rizzo, A. L; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Barberi, F.; Università Roma Tre ;Carapezza, M. L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;De Astis, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Romano, C.; Università Roma Tre ;Sortino, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; ; ; ; ; ; Turrialba volcano lies in the southern sector of the Central American Volcanic Front (CAVF) in Costa Rica. The geochemistry of major and trace elements, and Sr and Nd isotopes of a selected suite of volcanic rocks ranging in composition from basaltic andesite to dacite and belonging to the last 10 ka of activity of Turrialba volcano is described, together with the He-, Ne-, and Ar-isotope compositions of fluid inclusions hosted in olivine and pyroxene crystals. Most of the variability in the rock chemistry is consistentwith typical trends of fractional crystallization, but there is an outlying group of andesites that displays an adakite-like composition (with a consistent depletion in high-field-strength elements and a marked enrichment in Sr) and low 3He/4He ratios (7.0–7.2 Ra). The trace-element composition of these rocks is typical of subduction-related magmas influenced by an OIB-like component at the source associated with the subduction of the Galapagos seamounts. The 87Sr/86Sr (0.703612–0.703678) and 143Nd/144Nd (0.512960–0.512984) ratios of the bulk rocks vary within narrowranges, and are among the least-radiogenic isotope signatures of the CAVF volcanoes. The 3He/4He ratios measured in fluid inclusions hosted in olivine crystals (up to 8.1 Ra) are among the highest for the CAVF, and indicate that radiogenic 4He from fluids derived fromthe subducting slab contribute negligibly to the mantle wedge. The difference in He isotopes between most of studied rocks and those showing adakite-like features reasonably reflects two distinct components in the local mantle: (1) a MORB-like component, characterized by the highest He-isotope ratios (7.8–8.1 Ra), and (2) an OIB-like component, characterized by lower He-isotope ratios (7.0–7.2 Ra), coming from the subduction of the Galapagos seamounts. An overview at the regional scale indicates that high He-isotope ratios are peculiar to the two extreme sectors of the CAVF (Costa Rica to the south and Guatemala to the north), whereas in the central sector (Nicaragua) the magma source is probably contaminated by slab fluids. For the past few years Turrialba volcano has been in a volcanic unrest phase that has included a series of explosions, the most recent of which occurred between October 2014 and May 2015. The volcano is subject to an ongoing safety alert due to the possibility of a magmatic eruption. One of the crucial questions to be addressed is the kind of eruption that can be expected, and hence what type of magma is likely to be involved. The high 3He/4He ratios (7.8–8.0 Ra) measured during 2011 at high-temperature fumaroles of Turrialba craters are comparable to those measured in fluid inclusions of basaltic andesites that erupted in 1864–1866, suggesting that the magma currently feeding the shallow plumbing system has similar geochemical characteristics to the most recently erupted magma.379 58 - PublicationOpen AccessEruptive activity at Turrialba volcano (Costa Rica): Inferences from 3He/4He in fumarole gases and chemistry of the products ejected during 2014 and 2015(2016-10-17)
; ; ; ; ; ; ; ;Rizzo, Andrea Luca; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Di Piazza, Andrea; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;de Moor, J. Maarten; Observatorio Vulcanol ogico y Sismol ogico de Costa Rica (OVSICORI) ;Alvarado, Guillermo E.; Instituto Costarricense de Electricidad, Apdo ;Avard, Geoffroy; Observatorio Vulcanol ogico y Sismol ogico de Costa Rica (OVSICORI) ;Carapezza, Maria Luisa; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Mora, Mauricio M.; Escuela Centroamericana de Geolog ıa, Universidad de Costa Rica; ; ; ; ; ; A new period of eruptive activity started at Turrialba volcano, Costa Rica, in 2010 after almost 150 years of quiescence. This activity has been characterized by sporadic explosions whose frequency clearly increased since October 2014. This study aimed to identify the mechanisms that triggered the resumption of this eruptive activity and characterize the evolution of the phenomena over the past 2 years. We integrate 3He/4He data available on fumarole gases collected in the summit area of Turrialba between 1999 and 2011 with new measurements made on samples collected between September 2014 and February 2016. The results of a petrological investigation of the products that erupted between October 2014 and May 2015 are also presented. We infer that the resumption of eruptive activity in 2010 was triggered by a replenishment of the plumbing system of Turrialba by a new batch of magma. This is supported by the increase in 3He/4He values observed since 2005 at the crater fumaroles and by comparable high values in September 2014, just before the onset of the new eruptive phase. The presence of a number of fresh and juvenile glassy shards in the erupted products increased between October 2014 and May 2015, suggesting the involvement of new magma with a composition similar to that erupted in 1864–1866. We conclude that the increase in 3He/4He at the summit fumaroles since October 2015 represents strong evidence of a new phase of magma replenishment, which implies that the level of activity remains high at the volcano.270 130 - PublicationRestrictedUnsteady magma discharge during the “El Retiro” subplinian eruption (Turrialba volcano, Costa Rica): Insights from textural and petrological analyses(2019-01)
; ; ; ; ; ; ; ; ; ; ; Turrialba is an active volcano of the Cordillera Volcánica Central in Costa Rica, which is currently experiencing a renewal of the eruptive activity after ~150 years of eruptive quiescence. Because of its explosive eruptive records in the recent geological history and the proximity with the metropolitan area of San José, this volcano poses serious threats to the population and economy of the area. In this study, we investigated the andesitic products of an explosive event (VEI 4) that occurred at Turrialba volcano ~2 ka, which we referred to as “El Retiro” eruption. Results fromfield observations, textural and chemical analyses indicate that the El Retiro eruptionwas characterized by two main pulses separated by a low energy activity. The eruption was fed by a homogeneous andesitic magma batch that crystallized along a P-T path of 0.1–400 MPa and 1050–1145 °C. The vesicle number density of pumiceous clasts ranges between 107 and 108 cm−3, in agreement with previous data from subplinian eruptions. The magma batch underwent decompression rates and pre-fragmentation velocities of 0.40–0.95 MPa s−1 and 23–37 m s−1, respectively. A marked textural variability within each stratigraphic layer has been also observed. This potentially suggests a horizontal zonation of the magma column, a condition that may have induced velocity gradients and high viscosity contrasts in the conduit leading to magma fragmentation. The observed pulsating behavior translates into mass eruption rate fluctuations that can be related to changes in magma volatile contents. Further explosive eruptions with characteristics similar to those observed for El Retiro, cannot be excluded at Turrialba volcano. This denotes the importance of investigating eruption dynamics at the conduit, providing key information to rigorously assess the volcanic risk in populated areas.71 2 - PublicationRestrictedLike a cannonball: origin of dense spherical basaltic ejecta(2017)
; ; ; ; ; ; ; ; ; ; ;Cannonballs are rare spherical to sub-spherical eruptive products associated with basaltic explosive activity. The origin of cannonballs is still debated and subjected to a wide spectrum of different interpretations. In order to better understand the physicochemical mechanisms controlling the formation of these explosive products, we investigated the textural and chemical features of cannonballs from the Cerro Chopo monogenetic volcano (Costa Rica). These explosive products ubiquitously show a core domain with coalesced bubbles (30–36% porosity) wrapped in a dense rim domain with small, isolated bubbles (20–27% porosity). Both domains are identical in terms of bulk rock composition and mineral chemistry and are portions of the same magma batch. Results from combined petrological and thermodynamic modeling indicate that a low-viscosity (~20 Pa s) melt containing early-formed olivine phenocrysts (~9 vol.%) ascended from storage at a decompression rate of 0.5 MPa s−1 until it reached a depth of 4.5 km (equivalent to a pressure of ~150 MPa). While rising from depth to 4.5 km, the melt underwent rapid decompression (0.5–2.6 MPa s−1) and H2O exsolution, driving late-stage crystallization of the groundmass. The fast ascent velocity (21–110 m s−1) while rising between 4.5 km and the surface induced turbulent (Re >103), annular flow development in the uppermost region of the conduit. We propose that cannonballs represent blebs of fluid magmas that underwent shear-driven detachment from the annulus of magma lining the conduit walls at depths lower than 4.5 km. The formation of such cannonballs is dictated by magma transport dynamics of low-viscosity, phenocryst-poor, and volatile-rich melts that rapidly accelerate within the shallow conduit.167 2 - PublicationOpen Access3He/4He Signature of Magmatic Fluids from Telica (Nicaragua) and Baru (Panama) Volcanoes, Central American Volcanic ArcConstraining the magmatic 3He/4He signature of fluids degassed from a magmatic system is crucial for making inferences on its mantle source. This is especially important in arc volcanism, where variations in the composition of the wedge potentially induced by slab sediment fluids must be distinguished from the effects of magma differentiation, degassing, and crustal contamination. The study of fluid inclusions (FIs) trapped in minerals of volcanic rocks is becoming an increasingly used methodology in geochemical studies that integrates the classical study of volcanic and geothermal fluids. Here, we report on the first noble gas (He, Ne, Ar) concentrations and isotopic ratios of FI in olivine (Ol) and pyroxene (Px) crystals separated from eruptive products of the Telica and Baru volcanoes, belonging to the Nicaraguan and Panamanian arc-segments of Central America Volcanic arc (CAVA). FIs from Telica yield air corrected 3He/4He (Rc/Ra) of 7.2–7.4 Ra in Ol and 6.1–7.3 in Px, while those from Baru give 7.1–8.0 Ra in Ol and 4.2–5.8 Ra in Px. After a data quality check and a comparison with previous 3He/4He measurements carried out on the same volcanoes and along CAVA, we constrained a magmatic Rc/Ra signature of 7.5 Ra for Telica and of 8.0 Ra for Baru, both within the MORB range (8 1 Ra). These 3He/4He differences also reflect variations in the respective arc-segments, which cannot be explained by radiogenic 4He addition due to variable crust thickness, as the mantle beneath Nicaragua and Panama is at about 35 and 30 km, respectively. We instead highlight that the lowest 3He/4He signature observed in the Nicaraguan arc segment reflects a contamination of the underlying wedge by slab sediment fluids. Rc/Ra values up to 9.0 Ra are found at Pacaya volcano in Guatemala, where the crust is 45 km thick, while a 3He/4He signature of about 8.0 Ra was measured at Turrialba volcano in Costa Rica, which is similar to that of Baru, and reflects possible influence of slab melting, triggered by a change in subduction conditions and the contemporary subduction of the Galapagos hot-spot track below southern Costa Rica and western Panama.
474 18 - PublicationRestrictedNew mafic magma refilling a quiescent volcano: Evidence from He-Ne-Ar isotopes during the 2011–2012 unrest at Santorini, Greece(2015-02-26)
; ; ; ; ; ; ; ;Rizzo, A. L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Barberi, F.; Università di Roma Tre ;Carapezza, M. L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Di Piazza, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Francalanci, L.; Università degli Studi di Firenze ;Sortino, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;D'Alessandro, W.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; ; ; ; ; ; n 2011-2012 Santorini was characterized by seismic-geodetic-geochemical unrest, which was unprecedented since the most-recent eruption occurred in 1950 and led to fear an eruption was imminent. This unrest offered a chance for investigating the processes leading to volcanic reactivation and the compositional characteristics of involved magma. We have thus analyzed the He-Ne-Ar-isotope composition of fluid inclusions in olivines and clinopyroxenes from cumulate mafic enclaves hosted in cogenetic dacitic lavas of the 1570–1573 and 1925–1928 eruptions of Nea Kameni. These unique data on Aegean volcanism were compared with those of gases collected in quiescent periods and during the unrest. The 3He/4He-ratios (3.1–4.0Ra) are significantly lower than the typical arc-volcano values (R/Ra~7–8), suggesting the occurrence of magma contamination in Santorini plumbing system, which would further modify the 3He/4He-ratio of parental magmas generated in the local metasomatized mantle. The 3He/4He-values of enclaves (3.1–3.6Ra) are comparable to those measured in gases during quiescent periods, confirming that enclaves reflect the He-isotope signature of magma residing at shallow depths and feeding passive degassing. A significant increase in soil CO2 flux from Nea Kameni and anomalous compositional variations in the fumaroles were identified during the unrest, accordingly with previous studies. Simultaneously, 3He/4He-ratios up to 4.0Ra were also measured, demonstrating that the unrest was due to the intrusion into the shallow plumbing system of a more-primitive 3He-rich magma, which is even volatile richer and less contaminated than mafic magma erupted as enclaves. This new intrusion did not however trigger an eruption.305 30