0000000000082433
AUTHOR
Antonio Paonita
New insights into magma dynamics during last two eruptions of Mount Etna as inferred by geochemical monitoring from 2002 to 2005
Two distinct eruptive events characterize the volcanic activity at Mount Etna during the 2002 to 2005 period. We identified signals of magma ascent preceding these eruptions by geochemical monitoring of both chemical composition and He-isotope ratio of gas emissions from five locations in the peripheral area of the volcano. The geochemical signals are interpreted using the models proposed by Caracausi et al. (2003a, 2003b) and allow identification of episodes of magma ascent and estimation of the pressures of degassing magma. As observed for the 2001 eruption (Caracausi et al., 2003b), magma ascent probably triggered the onset of the 2002–2003 eruption, and minor events of magma ascent were…
New evidence of mantle heterogeneity beneath the Hyblean Plateau (southeast Sicily, Italy) as inferred from noble gases and geochemistry of ultramafic xenoliths
Abstract We analyzed major and trace elements, Sr and Nd isotopes in ultramafic xenoliths in Miocenic age Hyblean diatremes, along with noble gases of CO2-rich fluid inclusions hosted in the same products. The xenoliths consist of peridotites and pyroxenites, which are considered to be derived from the upper mantle. Although the mineral assemblage of peridotites and their whole-rock abundance of major elements (e.g., Al2O3 = 0.8–1.5 wt.%, TiO2 = 0.03–0.08 wt.%) suggest a residual character of the mantle, a moderate enrichment in some incompatible elements (e.g., LaN/YbN = 9–14) highlights the presence of cryptic metasomatic events. In this context a deep silicate liquid is considered the me…
S, Cl and F degassing as an indicator of volcanic dynamics: The 2001 eruption of Mount Etna
[1] The recent eruption of Mount Etna (July 2001) offered the opportunity to analyze magma-derived volatiles emitted during pre- and syn-eruptive phases, and to verify whether their composition is affected by changes in volcanic dynamics. This paper presents the results of analyses of F, Cl and S in the volcanic plume collected by filter-packs, and interprets variations in the composition based on contrasting solubility in magmas. A Rayleigh-type degassing mechanism was used to fit the acquired data and to estimate Henry's solubility constant ratios in Etnean basalt. This model provided insights into the dynamics of the volcano. Abundances of sulfur and halogens in eruptive plumes may help …
Mount Etna: Geochemical signals of magma ascent and unusually extensive plumbing system
] FiveyearsofgasmonitoringfromselectedsitessuggestthatMtEtna’splumbingsystemismuchmoreextensivethanpreviously reported. It extends at least 40 km SW from thevolcano’s boundary along the NE-SW regional fault, whereit discharges about 200 tons/day of gas, containing heliumwith mantle-type isotopic composition. Synchronousvariations of
Melt inclusions track melt evolution and degassing of Etnean magmas in the last 15 ka
We present major elements compositions and volatiles contents of olivine-hosted melt inclusions from Etna volcano (Italy), which extend the existing database with the aim of interpreting the chemical variability of Etnean magmas over the last 15 ka. Olivine phenocrysts were selected from the most primitive Fall Stratified (FS) eruptive products of picritic composition (Mg# = 67–70, Fo 89–91 ), the Mt. Spagnolo eccentric lavas (Mg# = 52–64, Fo 82–88 ) and among the more recent 2002–2013 eruptive products (Mg# = 33–53, Fo 68–83 ). Crystal fractionation and degassing processes were modeled at temperatures of 1050–1300 °C, pressures <500 MPa, and oxygen fugacity between 1 and 2 log units abo…
Evidence of deep magma degassing and ascent by geochemistry of peripheral gas emissions at Mount Etna (Italy): Assessment of the magmatic reservoir pressure
[1] Five gas discharges in the area of Mount Etna volcano (Italy) and in the near Hyblean plateau have been monitored since 1996. All the emissions displayed low contributions from crustal fluids, whereas magmatic gases were the main component. Selective dissolution of these gases into hydrothermal aquifers has been recognized and modeled, allowing us to calculate the original composition of the magma-released gases. The inferred composition of the magmatic gases exhibits synchronous variations of He/Ne and He/CO2 ratios, which are coherent with the magma degassing process. On the basis of numerical simulations of volatile degassing from Etnean basalts we have computed the initial and final…
Magmatic degassing of multicomponent vapors and assessment of magma depth: application to Vulcano Island (Italy)
Degassing of magmatic H2O, CO2 and rare gases plays a major role in understanding large-scale Earth processes and in the assessment of volcanic activity. Here we describe a quantitative model for magmatic degassing of H2O–CO2–noble gas–N2 mixtures. Our modeling takes into account non-ideal behaviors by adopting recently developed approaches for the solubility of H2O–CO2 mixtures in silicate liquids and for noble gas partitioning in H2O–CO2 bearing magmas. This new approach allows quantitative treatment of inert gas fractionation throughout the degassing of any H2O–CO2 bearing natural magma in a wide range of thermo-baric conditions. Magma degassing simulations performed by our model have cl…
Magmas near the critical degassing pressure drive volcanic unrest towards a critical state
During the reawaking of a volcano, magmas migrating through the shallow crust have to pass through hydrothermal fluids and rocks. The resulting magma–hydrothermal interactions are still poorly understood, which impairs the ability to interpret volcano monitoring signals and perform hazard assessments. Here we use the results of physical and volatile saturation models to demonstrate that magmatic volatiles released by decompressing magmas at a critical degassing pressure (CDP) can drive volcanic unrest towards a critical state. We show that, at the CDP, the abrupt and voluminous release of H2O-rich magmatic gases can heat hydrothermal fluids and rocks, triggering an accelerating deformation …
Massive submarine gas output during the volcanic unrest off Panarea Island (Aeolian arc, Italy): Inferences for explosive conditions
The possibility of understanding natural processes leading to explosive events in volcanic systems provides advantages for a better management of possible volcanic crises. On account of the possibility of the occurrence of other phenomena, such as tsunamis, the explosions driven by submarine volcanic systems are of particular interest, although little investigated. The recent sudden increase in the degassing activity of the submarine geothermal system of Panarea Island (Aeolian arc), has allowed us to better understand the way in which the quiet degassing activity of a submarine hydrothermal system may develop if new magma or magmatic gases feed it. We focused our investigations on the crat…
Elemental and isotope covariation of noble gases in mineral phases from Etnean volcanics erupted during 2001–2005, and genetic relation with peripheral gas discharges
Abstract During 2001–2005, Mount Etna was characterized by intense eruptive activity involving the emission of petrologically different products from several vents, which involved at least two types of magma with different degrees of evolution. We investigated the ratios and abundances for noble-gas isotopes in fluid inclusions trapped in olivines and pyroxenes in the erupted products. We confirm that olivine has the most efficient crystalline structure for preserving the pristine composition of entrapped gases, while pyroxene can suffer diffusive He loss. Both the minerals also experience noble gas air contamination after eruption. Helium isotopes of the products genetically linked to the …
Geochemical heterogeneities in magma beneath Mount Etna recorded by 2001-2006 melt inclusions
We present a geochemical study on olivine and clinopyroxene-hosted melt inclusions (MIs) from 2001 to 2006 Etna basaltic lavas and pyroclastites. Three MI suites are distinguished on the basis of trace element fingerprinting. Type-1 MIs (from 2001 Upper South and 2002 Northeast vents) share their trace element signature with low-K lavas erupted before 1971. Critical trace element ratios (e.g., K/La, Ba/Nb), along with Pb isotope data of Type-1 MIs provide evidence for a heterogeneous mantle source resulting from mixing of three end-members with geochemical and isotopic characteristics of EM2, DMM, and HIMU components. Type-1 MIs composition does not support involvement of subduction-related…
Genesis of fumarolic emissions as inferred by isotope mass balances: CO 2 and water at Vulcano Island, Italy
We have developed a quantitative model of CO2 and H2O isotopic mixing between magmatic and hydrothermal gases for the fumarolic emissions of the La Fossa crater (Vulcano Island, Italy). On the basis of isotope balance equations, the model takes into account the isotope equilibrium between H2O and CO2 and extends the recent model of chemical and energy two-end-member mixing by Nuccio et al. (1999). As a result, the H2O and CO2 content and the δD, δ18O, and δ13C isotope compositions for both magmatic and hydrothermal end-members have been assessed. Low contributions of meteoric steam, added at a shallow depth, have been also recognized and quantified in the fumaroles throughout the period fro…
Geochemistry and isotope composition (Sr, Pb, δ66Zn) of Vulcano fumaroles (Aeolian Islands, Italy)
We present and discuss temperatures, major and trace element gas geochemistry, radiogenic isotopes (Pb, Sr) and the first Zn isotope data of fumarole condensates and altered rocks from the Vulcano fumarolic field. The fumaroles of the La Fossa cone, sampled on 5th May 2015, have temperatures ranging between 233 and 427 °C. They plot compositionally on the mixing trend between the magmatic and hydrothermal end-members defined by previous studies, but are strongly displaced towards the hydrothermal component. Correlations of radiogenic (Sr, Pb) and stable isotopes of Zn with δ13CCO2 and several trace elements of the fumarolic acid condensates support mixing between the above mentioned distinc…
Melt inclusions constrain S behaviour and redox conditions in Etnean magmas
Mount Etna is a complex magmatic system characterized by a continuous variability both in terms of eruptive style and composition of erupted products. Currently, its volcanic activity is marked by high gas fluxes (of above all SO2), both during eruptive and non-eruptive periods. In this study, we have studied the volatile contents and Fe speciation of olivine-hosted melt inclusions from 6 eruptions of the last 15 ky, mainly to investigate the behaviour of S during ascent and differentiation of Etnean magmas. Samples selected come from the FS eruption which is the oldest and most primitive (picritic composition, Fo91), the Mt Spagnolo and from more recent eruptions: 2002/3, 2006, 2008, and 2…
Genesis of chlorine and sulphur in fumarolic emissions at Vulcano Island (Italy): assessment of pH and redox conditions in the hydrothermal system
Chlorine- and sulphur-bearing compounds in fumarole discharges of the La Fossa crater at Vulcano Island (Italy) can be modelled by a mixing process between magmatic gases and vapour from a boiling hydrothermal system. This allows estimating the compounds in both endmembers. Magma degassing cannot explain the time variation of sulphur and HCl concentrations in the deep endmember, which are more probably linked to reactions of solid phases at depth, before mixing with the hydrothermal vapours. Based on the P–T conditions and speciation of the boiling hydrothermal system below La Fossa, the HCl and Stot contents in the hydrothermal vapours were used to compute the redox conditions and pH of th…
Plume chemistry provides insights into mechanisms of sulfur and halogen degassing in basaltic volcanoes
Abstract This paper deals with sulfur, chlorine and fluorine abundances in the eruptive volcanic plume of the huge October 2002–January 2003 eruption of Mount Etna, aiming at relating the relevant compositional variations observed throughout with changes in eruption dynamics and degassing mechanisms. The recurrent sampling of plume acidic volatiles by filter-pack methodology revealed that, during the study period, S/Cl and Cl/F ratios ranged from 0.1–6.8 and 0.9–5.6, respectively. Plume S/Cl ratios increased by a factor of ∼10 as volcanic activity drifted from paroxysmal lava fountaining (mid- and late November) to passive degassing and minor effusion (early January), and then decreased to …
New Insights into the Provenance of the Obsidian Fragments of the Island of Ustica (Palermo, Sicily)
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 isla…
The role of melt composition on aqueous fluid vs. silicate melt partitioning of bromine in magmas
International audience; Volcanogenic halogens, in particular bromine, potentially play an important role in the ozone depletion of the atmosphere. Understanding bromine behaviour in magmas is therefore crucial to properly evaluate the contribution of volcanic eruptions to atmospheric chemistry and their environmental impact. To date, bromine partitioning between silicate melts and the gas phase is very poorly constrained, with the only relevant experimental studies limited to investigation of synthetic melt with silicic compositions. In this study, fluid/melt partitioning experiments were performed using natural silicate glasses with mafic, intermediate and silicic compositions. For each co…
Changes in fluid geochemistry and physico-chemical conditions of geothermal systems caused by magmatic input: The recent abrupt outgassing off the island of Panarea (Aeolian Islands, Italy)
Abstract Hydrothermal systems and related vents can exhibit dramatic changes in their physico-chemical conditions over time as a response to varying activity in the feeding magmatic systems. Massive steam condensation and gas scrubbing processes of thermal fluids during their ascent and cooling cause further compositional changes that mask information regarding the conditions evolving at depth in the hydrothermal system. Here we propose a new stability diagram based on the CO2-CH4-CO-H2 concentrations in vapor, which aims at calculating the temperatures and pressures in hydrothermal reservoirs. To filter gas scrubbing effects, we have also developed a model for selective dissolution of CO2-…
Evidence of a recent input of magmatic gases into the quiescent volcanic edifice of Panarea, Aeolian Islands, Italy
- Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Naples, Italy. - Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Palermo, Italy. - Dipartimento Chimica e Fisica della Terra ed Applicazioni, Palermo, Italy.
A new set of standards for in–situ measurement of bromine abundances in natural silicate glasses: Application to SR-XRF, LA-ICP-MS and SIMS techniques
Measuring the low bromine abundances in Earth's materials remains an important challenge in order to constrain the geodynamical cycle of this element. Suitable standard materials are therefore required to establish reliable analytical methods to quantify Br abundances. In this study we characterise 21 Br-doped glasses synthesized from natural volcanic rocks of mafic to silicic compositions, in order to produce a new set of standards for Br analyses using various techniques. The nominal Br contents (amounts of Br loaded in the experimental samples) of 15 of 21 glasses were confirmed within 20% by instrumental neutron activation analysis (INAA). Using this new set of standards, we compare thr…
Active geodynamics of the central Mediterranean Sea: Tensional tectonic evidences in western Sicily from mantle-derived helium
[1] We report results on the measured high 3He/4He isotope ratio in western Sicily, interpreted together with the heat data. The study of this sector of the Europe-Africa interaction is crucial to a better understanding of the tectonics and the geodynamical evolution of the central Mediterranean area. The estimated mantle-derived helium fluxes in the investigated areas are up to 2–3 orders of magnitude greater than those of a stable continental area. The highest flux, found in the southernmost area near the Sicily Channel, where recent eruptions of the Ferdinandea Island occurred 20 miles out to sea off Sciacca, has been associated with a clear excess of heat flow. Our results indicate that…
A two-component mantle source feeding Mt. Etna magmatism; insights from the geochemistry of primitive magmas.
The major elements, trace elements and Sr and Nd isotopes of selected Etnean primitive rocks (b15 ky BP) were studied in order to characterize their mantle source. The noble-gas geochemistry of fluid inclusions in minerals fromthe same lavaswas also investigated. Themajor element compositions ofwhole rocks and minerals showed that these products are among the most primitive atMt. Etna, comprising 6.3–17.5 wt.% MgO. The variable LREE (Light Rare Earth Elements) enrichment relative to MORB (Mid-Ocean Ridge Basalt) (Lan/Ybn = 11–26), togetherwith the patterns of certain trace-element ratios (i.e., Ce/Yb versus Zr/Nb and Th/Y versus La/Yb), can be attributed to varying degrees of melting of a c…