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Giacomoni, Pier Paolo
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- PublicationOpen AccessMagma recharge and mush rejuvenation drive paroxysmal activity at Stromboli volcano(2022-12-13)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; Open-conduit basaltic volcanoes can be characterised by sudden large explosive events (paroxysms) that interrupt normal effusive and mild explosive activity. In June-August 2019, one major explosion and two paroxysms occurred at Stromboli volcano (Italy) within only 64 days. Here, via a multifaceted approach using clinopyroxene, we show arrival of mafic recharges up to a few days before the onset of these events and their effects on the eruption pattern at Stromboli, as a prime example of a persistently active, open-conduit basaltic volcano. Our data indicate a rejuvenated Stromboli plumbing system where the extant crystal mush is efficiently permeated by recharge magmas with minimum remobilisation promoting a direct linkage between the deeper and the shallow reservoirs that sustains the currently observed larger variability of eruptive behaviour. Our approach provides vital insights into magma dynamics and their effects on monitoring signals demonstrating the power of petrological studies in interpreting patterns of surficial activity.68 6 - PublicationOpen AccessThe Variscan subduction inheritance in the Southern Alps Sub-Continental Lithospheric Mantle: Clues from the Middle Triassic shoshonitic magmatism of the Dolomites (NE Italy)Although often speculated, the link between theMiddle Triassic shoshonitic magmatismat the NE margin of the Adria plate and the subduction-related metasomatismof the Southern Alps Sub-Continental Lithospheric Mantle (SCLM) has never been constrained. In this paper, a detailed geochemical and petrological characterization of the lavas, dykes and ultramafic cumulates belonging to the shoshonitic magmatic event that shaped the Dolomites (Southern Alps) was used tomodel the composition and evolution of the underlying SCLMin the time comprised between the Variscan subduction and the opening of the Alpine Tethys. Geochemical models and numerical simulations enabled us to define that 5–7% partial melting of an amphibole + phlogopite-bearing spinel lherzolite, similar to the Finero phlogopite peridotite, can account for the composition of the primitive Mid-Triassic SiO2- saturated to -undersaturated melts with shoshonitic affinity (87Sr/86Sri = 0.7032–0.7058; 143Nd/144Ndi = 0.51219–0.51235; Mg # ~ 70; ~1.1 wt% H2O). By taking into account the H2O content documented in mineral phases from the Finero phlogopite peridotite, it is suggested that the Mid-Triassic SCLM source was able to preserve a significant enrichment and volatile content (600–800 ppm H2O) for more than 50 Ma, i.e. since the slab-related metasomatismconnected to the Variscan subduction. The partialmelting of a Finero-like SCLM represents the exhaustion of the subduction-related signature in the Southern Alps lithosphere that predated the Late Triassic-Early Jurassic asthenospheric upwelling related to the opening of the Alpine Tethys.
43 32 - PublicationOpen AccessA micro-scale insight into a back-arc trans-crustal plumbing system: The case of Marsili volcano, Southern Tyrrhenian Sea(2024-06)
; ; ;Costa, Simone; ; ; ; ; ; ; ; The Marsili seamount is a submarine volcano in the Tyrrhenian Sea that originated in a back-arc setting. Aiming to define the complexity of its trans-crustal plumbing system, we explored the compositional and textural variations of crystal cargoes in basaltic to andesitic lavas collected from three different sectors of the volcano (northern, axial, and lateral). Lavas collected from the northern sector are basaltic in composition and contain minerals with a narrow and more primitive composition compared to basalt and basaltic andesitic lavas sampled at the lateral and axial sectors, hosting a crystal cargo characterized by a broader chemical variability. Crystal-poor andesitic lavas were only collected at the axial summit sector of the volcano. Glomerocrysts with diverse mineralogy are ubiquitous in lavas erupted from all sectors and testify to the presence of crystal mush domains in the whole trans-crustal system. Thermobarometric calculations performed on clinopyroxene coupled to mass-balance and thermodynamic modeling collectively point to a polybaric and spatially heterogeneous plumbing system. The relatively less differentiated basaltic magmas erupted in the northern and axial sectors reside at depth corresponding to the lower crust-mantle boundary (300–450 MPa, 1040–1080 °C). Basaltic and basaltic andesitic magmas extracted from this deep storage zone formed, over time, scattered magma storage zones in the 10–12 km-thick oceanic crust beneath the Marsili volcano. The shallower magma storage zones sourced the andesitic magmas (<250 MPa, 920–980 °C) erupted in the axial summit sector. In turn, basaltic and basaltic andesitic magmas erupted in the lateral sector testify to intermediate storage conditions (200–400 MPa, 980–1060 °C) and variable degree of evolution. The variable content of incompatible (TAl and Ti) and REE in clinopyroxene contained in basaltic lavas from the three sectors relates to different degrees of undercooling (∆T), with magmas erupted from the northern sector recording higher undercooling (∆T = 90 ± 39 °C) compared to those erupted from the lateral (∆T = 52 ± 27 °C) and axial (∆T = 30 ± 25 °C) sectors. The emerging scenario is that basaltic magmas erupted from the northern sector experienced a more rapid ascent (also testified by the occurrence of high-Fo olivine and dendritic clinopyroxene in the groundmass) compared to magmas erupted at the lateral and axial sectors, otherwise experiencing prolonged residence within the crust.29 4 - PublicationRestrictedExperimental constraints on the origin of pahoehoe “cicirara” lavas at Mt. Etna Volcano (Sicily, Italy)(2015)
; ; ; ; ; ; ; ; ; ;; ; ; ; ; ; ;We present results from phase equilibria experiments conducted on the most primitive pahoehoe "cicirara" trachybasaltic lava flow ever erupted at Mt. Etna Volcano. This lava is characterized by a pahoehoe morphology in spite of its high content of phenocrysts and microphenocrysts (> 40 vol%) with the occurrence of centimetre-sized plagioclases (locally named cicirara for their chick-pea-like appearance). Our experiments have been performed at 400 MPa, 1100-1150 degrees C and using H2O and CO2 concentrations corresponding to the water-undersaturated crystallization conditions of Etnean magmas. Results show that olivine does not crystallize from the melt, whereas titanomagnetite is the liquidus phase followed by clinopyroxene or plagioclase as a function of melt-water concentration. This mineralogical feature contrasts with the petrography of pahoehoe cicirara lavas suggesting early crystallization of olivine and late formation of titanomagnetite after plagioclase and/or in close association with clinopyroxene. The lack of olivine produces MgO-rich melt compositions that do not correspond to the evolutionary behaviour of cicirara magmas. Moreover, in a restricted thermal path of 50 degrees C and over the effect of decreasing water concentrations, we observe abundant plagioclase and clinopyroxene crystallization leading to trace element enrichments unlikely for natural products. At the same time, the equilibrium compositions of our mineral phases are rather different from those of natural cicirara phenocrysts and microphenocrysts. The comparison between our water-undersaturated data and those from previous degassing experiments conducted on a similar Etnean trachybasaltic composition demonstrates that pahoehoe cicirara lavas originate from crystal-poor, volatile-rich magmas undergoing abundant degassing and cooling in the uppermost part of the plumbing system and at subaerial conditions where most of the crystallization occurs after the development of pahoehoe surface crusts.97 7 - PublicationRestrictedThe nature of the West Antarctic Rift System as revealed by noble gases in mantle minerals(2019-06-18)
; ; ; ; ; ; ; ; ;; ;; ;The noble gases He, Ne and Ar in fluid inclusions from mantle xenoliths at three localities in Northern Victoria Land (Baker Rocks, Greene Point and Handler Ridge), spanning about 300 km, provide new constraints on the nature of the lithospheric mantle beneath the West Antarctic Rift System (WARS). Mantle xenoliths are anhydrous and hydrous spinel-bearing lherzolite and harzburgite samples. The 4He/40Ar* ratios (0.004–0.39) in olivines, two pyroxenes and amphiboles are much lower than those typical of fertile mantle (1–5), suggesting that this lithospheric domain are consistent with a variably depleted mantle, as also indicated by the major- and trace-element compositions of whole rock and minerals. The 3He/4He ratios vary from 2.30 to 19.79 Ra. However, the lowest and highest 3He/4He ratios are related to the post-eruptive accumulation of radiogenic 4He and cosmogenic 3He, respectively. After filtering the data for these secondary effects, we constrain the 3He/4He signature of the subcontinental lithospheric mantle below this area to 7.1 ± 0.4 Ra (mean ± standard deviation). This isotope signature results from mantle metasomatism by asthenospheric melts with a MORB (midocean ridge basalt)-type 3He/4He. The range of 7.1 ± 0.4 Ra is compatible with previous measurements in mantle xenoliths and lavas from other localities of the NVL, as far away as Mount Erebus, evidencing a homogeneous He-isotope signature beneath the entire rift. The He and Ne isotopes support the hypothesis that WARS origin is not related to a plume.740 10 - PublicationRestrictedThe 2011–2012 paroxysmal eruptions at Mt. Etna volcano: Insights on the vertically zoned plumbing systemThe activity ofMt. Etna volcano from January 2011 to April 2012 was characterized by 24 paroxysmal, short-duration (from a few to several hours) eruptions at the New South-East summit crater. Despite the violence of the activity, no appreciable geophysical signals were recorded during this period, except for an increase in seismic tremors just minutes/hours before the occurrence of the paroxysm. This type of activity represents a significant shift from the mainly effusive eruptions of 2004, 2006, and 2008/2009, as well as from the lateral rift-related events of 2001 and 2002/2003. The 2011–2012 paroxysmal activity thus represents an important opportunity to better understand the effects of different magmatic parameters (i.e., P-T-fO2) and magmatic H2O content on the crystallization and fractionation processes. To this aim the petrographic and geochemical features of lava and scoria clasts from 10 paroxysmal events have been investigated. Fractional crystallization modelling indicates that most of the eruptions are related to magmas rising along the vertically-developed feeding systemof the volcano, accompanied by one main recharge of a more primitive, deep-seated magma feeding the 4/3/2012 event. Olivine-, clinopyroxene-, and plagioclase-melt equilibria and thermobarometric calculations were performed in order to estimate the crystallization conditions of magmas. These calculations reveal that the erupted products contain different phenocryst populations in equilibrium with a spectrum of primitive to more evolved magma compositions. On the basis of crystal composition, crystal-melt equilibriumconditions and thermobarometric estimations, four main magmatic facies have been recognized: F1, 1600 MPa at 1270 °C (Ol Fo88); F2, 800 MPa to 600MPa at 1178 °C to 1151 °C (Ol Fo84–78); F3, 450 MPa to 250 MPa at 1139 °C to 1118 °C (Ol Fo79–74); F4, b250 MPa at b1120 °C (Ol Fo75–70). The overall geochemistry and thermobarometric data allowus to characterize the central feeding systemas continuous and vertically zoned. During the 2011–2012 activity the studied 30/7/11, 29/8/11, 8/9/11, 18/3/11 and 24/4/12 events were fed by magma residing at F3 and F4 facies. Mafic magma influx from deeper F2 facies occurred 18/2/11 and 20/8/11,with a major recharge event before the 4/3/12 eruption. The primitive magma is testified by rare olivine crystals equilibrated at the F1 facies, located at crust-mantle boundary depth and close to liquidus temperature.
103 2 - PublicationRestrictedClinopyroxene and titanomagnetite cation redistributions at Mt. Etna volcano (Sicily, Italy): Footprints of the final solidification history of lava fountains and lava flows(2015)
; ; ; ; ;Mollo, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Giacomoni, P. P.; Departimento di Fisica e Science della Terra, Università di Ferrara, Via Saragat 1, 44122 Ferrara, Italy ;Andronico, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Scarlato, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; ; For a better understanding of the final solidification history of eruptions at Mt. Etna volcano (Sicily, Italy), we have investigated cation redistributions at the interface between sub-millimetre-sized clinopyroxene and titanomagnetite crystal rims and coexisting melts. The studied products were scoria clasts from lava fountains and rock samples from pahoehoe and aa lava flows. Our data indicate that scoria clasts from lava fountaining were rapidly quenched at the contact with the atmosphere, preserving the original crystal textures and compositions inherited during magma dynamics within the plumbing system. Kinetics and energetics of crystallization were instantaneously frozen-in and post-eruptive effects on mineral chemistry were negligible. The nearequilibrium compositions of clinopyroxene and titanomagnetite indicate that lava fountain episodes were supplied by high-temperature, H2O-rich magmas ascending with velocities of 0.01–0.31 m/s. In contrast, magmas feeding lava flow eruptions underwent a more complex solidification history where the final stage of the crystal growth was mostly influenced by volatile loss and heat dissipation at syn- and post-eruptive conditions. Due to kinetic effects associated with magma undercooling, clinopyroxenes and titanomagnetites formed by crystal attachment and agglomeration mechanisms leading to intricate intergrowth textures. The final compositions of these minerals testify to closure temperatures and melt–water concentrations remarkably lower than those estimated for lava fountains. Kinetically-controlled cation redistributions at the crystal–melt interface suggest that the solidification of magma was driven by degassing and cooling processes proceeding from the uppermost part of the volcanic conduit to the surface.294 83 - PublicationOpen AccessCO2 storage in the Antarctica Sub-Continental Lithospheric Mantle as revealed by intra- and inter-granular fluids(2022)
; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ; ; ;The investigation of the role played by CO2 circulating within the mantle during partial melting and metasomatic/refertilization processes, together with a re-consideration of its storage capability and re-cycling in the lithospheric mantle, is crucial to unravel the Earth's main geodynamic processes. In this study, the combination of petrology, CO2 content trapped in bulk rock- and mineral-hosted fluid inclusions (FI), and 3D textural and volumetric characterization of intra- and inter-granular microstructures was used to investigate the extent and modality of CO2 storage in depleted and fertile (or refertilized) Sub-Continental Lithospheric Mantle (SCLM) beneath northern Victoria Land (NVL, Antarctica). Prior to xenoliths entrainment by the host basalt, the Antarctic SCLM may have stored 0.2 vol% melt and 1.1 vol% fluids, mostly as FI trails inside mineral phases but also as inter-granular fluids. The amount of CO2 stored in FI varies from 0.1 μg(CO2)/g(sample) in olivine from the anhydrous mantle xenoliths at Greene Point and Handler Ridge, up to 187.3 μg/g in orthopyroxene from the highly metasomatized amphibole-bearing lherzolites at Baker Rocks, while the corresponding bulk CO2 contents range from 0.3 to 57.2 μg/g. Irrespective of the lithology, CO2 partitioning is favoured in orthopyroxene and clinopyroxene-hosted FI (olivine: orthopyroxene = 0.10 ± 0.06 to 0.26 ± 0.09; olivine: clinopyroxene = 0.10 ± 0.05 to 0.27 ± 0.14). The H2O/(H2O + CO2) molar ratios obtained by comparing the CO2 contents of FI to the H2O amount retained in pyroxene lattices vary between 0.72 ± 0.17 and 0.97 ± 0.03, which is well comparable with the values measured in olivine-hosted melt inclusions from Antarctic primary lavas and assumed as representative of the partition of volatiles at the local mantle conditions. From the relationships between mineral chemistry, thermo-, oxybarometric results and CO2 contents in mantle xenoliths, we speculate that relicts of CO2-depleted mantle are present at Greene Point, representing memory of a CO2-poor tholeiitic refertilization related to the development of the Jurassic Ferrar large magmatic event. On the other hand, a massive mobilization of CO2 took place before the (melt-related) formation of amphibole veins during the alkaline metasomatic event associated with the Cenozoic rift-related magmatism, in response to the storage and recycling of CO2-bearing materials into the Antarctica mantle likely induced by the prolonged Ross subduction.496 25 - PublicationRestrictedReconstruction of magmatic variables governing recent Etnean eruptions: Constraints from mineral chemistry and P–T–fO2–H2O modeling(2015)
; ; ; ; ; ; ; ; ; ;; Petrological investigations of active volcanoes are often supported by mass balance, thermodynamic calculations and/or experiments performed at key conditions. Conversely, the compositions of mineral phases found in natural products are generally used as input data for predictive models calibrated to derive the intensive variables of the magmatic system. In order to evaluate the extent to which mineral chemistry records crystallization conditions, we have compared the compositions of olivine, clinopyroxene, plagioclase and titanomagnetite in 20012012 trachybasaltic lavas at Mt. Etna with those obtained through thermodynamic simulations and experiments conducted under anhydrous, water-undersaturated and water-saturated conditions. This systematic comparison allows us to track recent differentiation processes beneath Mt. Etna, as well as the P-T-fO(2)-H2O variables controlling the solidification path of magma. Two compositionally distinct populations of olivine and clinopyroxene phenocrysts are found in these lavas: Mg-rich and Mg-poor minerals formed at 600-1100 MPa and 11001250 degrees C, and 0.1-500 MPa and 1050-1175 degrees C, respectively. The oxygen fugacity varies by 1-2 log units suggesting water exsolution during magma ascent in the conduit and magma emplacement near the surface. The nucleation and growth of normally zoned plagioclases occur at P <100 MPa, when the amount of H2O dissolved in the melt abruptly decreases from about 3.0 to 0.2 wt.% due to magma decompression and degassing. This leads to the conclusion that Etnean magmas fractionate throughout the entire length of the vertically developed plumbing system where magma mixing, volatile exsolution and degassing are the most important processes driving eruptions. (C) 2014 Elsevier B.V. All rights reserved.63 1 - PublicationRestrictedClinopyroxene-melt element partitioning during interaction between trachybasaltic magma and siliceous crust: Clues from quartzite enclaves at Mt. Etna volcano(2017)
; ; ; ; ; ; ; ; ; ; ;; ; ; ;A peculiar characteristic of the paroxysmal sequence that occurred on March 16, 2013 at the New South East Crater of Mt. Etna volcano (eastern Sicily, Italy) was the eruption of siliceous crustal xenoliths representative of the sedimentary basement beneath the volcanic edifice. These xenoliths are quartzites that occur as subspherical bombs enclosed in a thin trachybasaltic lava envelope. At the quartzite-magma interface a reaction corona develops due to the interaction between the Etnean trachybasaltic magma and the partially melted quartzite. Three distinct domains are observed: (i) the trachybasaltic lava itself (Zone 1), including Al-rich clinopyroxene phenocrysts dispersed in a matrix glass, (ii) the hybrid melt (Zone 2), developing at the quartzite-magma interface and feeding the growth of newly-formed Al-poor clinopyroxenes, and (iii) the partially melted quartzite (Zone 3), producing abundant siliceous melt. These features makes it possible to quantify the effect of magma contamination by siliceous crust in terms of clinopyroxene-melt element partitioning. Major and trace element partition coefficients have been calculated using the compositions of clinopyroxene rims and glasses next to the crystal surface. Zone 1 and Zone 2 partition coefficients correspond to, respectively, the chemical analyses of Al-rich phenocrysts andmatrix glasses, and the chemical analyses of newly-formed Al-poor crystals and hybrid glasses. For clinopyroxenes fromboth the hybrid layer and the lava flow expected relationships are observed between the partition coefficient, the valence of the element, and the ionic radius. However,with respect to Zone 1 partition coefficients, values of Zone 2 partition coefficients show a net decrease for transition metals (TE), highfield strength elements (HFSE) and rare earth elements including yttrium(REE+Y), and an increase for large ion lithophile elements (LILE). This variation is associated with coupled substitutions on theM1, M2and T sites of the type M1(Al, Fe3+)+TAl=M2(Mg, Fe2+)+TSi. The different incorporation of trace elements into clinopyroxenes of hybrid origin is controlled by cation substitution reactions reflecting local charge-balance requirements. According to the lattice strain theory, simultaneous cation exchanges across the M1,M2, and T sites have profound effects on REE+Y and HFSE partitioning. Conversely, both temperature and melt composition have only a minor effect when the thermal path of magma is restricted to ~70 °C and the value of non-bridging oxygens per tetrahedral cations (NBO/T) shifts moderately from 0.31 to 0.43. As a consequence, Zone 2 partition coefficients for REE+Y and HFSE diverge significantly fromthose derived for Zone 1, accounting for limited cation incorporation into the newly-formed clinopyroxenes at the quartzite-magma interface.264 7