A model of sulphur solubility for hydrous mafic melts: application to the determination of magmatic fluid compositions of Italian volcanoes

We present an empirical model of sulphur solubility that allows us to calculate f S2 if P, T, fO2 and the melt composition, including H2O and S, are known. The model is calibrated against three main experimental data bases consisting in both dry and hydrous silicate melts. Its prime goal is to calculate the f S2 of hydrous basalts that currently lack experimental constraints of their sulphur solubility behaviour. Application of the model to Stromboli, Vesuvius, Vulcano and Etna eruptive products shows that the primitive magmas found at these volcanoes record f S2 in the range 0.1-1 bar. In contrast, at all volcanoes the magmatic evolution is marked by dramatic variations in f S2 that spreads over up to 9 orders of magnitude. The f S2 can either increase during differentiation or decrease during decompression to shallow reservoirs, and seems to be related to closed versus open conduit conditions, respectively. The calculated f S2 shows that the Italian magmas are undersaturated in a FeS melt, except during closed conduit conditions, in which case differentiation may eventually reach conditions of sulphide melt saturation. The knowledge of f S2, fO2 and fH2O allows us to calculate the fluid phase composition coexisting with magmas at depth in the C-O-H-S system. Calculated fluids show a wide range in composition, with CO2 mole fractions of up to 0.97. Except at shallow levels, the fluid phase is generally dominated by CO2 and H2O species, the mole fractions of SO2 and H2S rarely exceeding 0.05 each. The comparison between calculated fluid compositions and volcanic gases shows that such an approach should provide constraints on both the depth and mode of degassing, as well as on the amount of free fluid in magma reservoirs. Under the assumption of a single step separation of the gas phase in a closed-system condition, the application to Stromboli and Etna suggests that the main reservoirs feeding the eruptions and persistent volcanic plumes at these volcanoes might contain as much as 5 wt% of a free fluid phase. Consideration of the magma budget needed to balance the amounts of volatiles emitted in the light of these results shows that the amount of nonerupted magma could be overestimated by as much as one order of magnitude

Petrography, mineralogy and geochemistry of a primitive pumice from Stromboli: implications for the deep feeding system

We describe the field relations, petrographic, mineralogical and geochemical characteristics of an exceptional “golden” pumice belonging to a tephra layer exposed on the summit area of Stromboli volcano, Italy. Pumice sample PST-9 comes from a fallout deposit older than a spatter agglutinate sequence emplaced during the twentieth century. The eruption that produced it had a size exceeding that of intermediate paroxysms but was smaller than large-scale, spatter-forming, paroxysms from the sixteenth century and 1930 A.D. Lapilli are strongly vesicular and crystal-poor, similar to other “golden” pumices. Modal proportions include 89 vol% glass, 8 vol% clinopyroxene, 1–2 vol% olivine and 1–2 vol% plagioclase. Plagioclase is represented by reacted crystals coming from the shallow resident magma and incorporated in the pumice during eruption. A total of 74 and 44 crystals of olivine and clinopyroxene, respectively, were examined and 187 and 99 electron microprobe analyses obtained. Fo in olivine ranges between 70 and 92 mol% and Fs in clinopyroxene between 3 and 13 mol%. PST-9 hosts a higher proportion of Fo-rich olivine and Fs-poor clinopyroxene than the other “golden” pumices. Groundmass glasses are basaltic (Mg# = 66–69), as are most rim glasses around olivine and clinopyroxene, and glass inclusions in clinopyroxene. They are more primitive than in the other “golden” pumices. A few rim glasses and glass inclusions are shoshonitic (Mg# = 45–50). Most glass inclusions in olivine have CaO/Al2O3 higher than the other glasses and the whole-rock. PST-9 has the highest bulk MgO, CaO, Mg# and CaO/Al2O3 and the lowest FeOt of all “golden” pumices analysed to date. Analysis of Fe-Mg partitioning between olivine, clinopyroxene and melt allows three crystallization stages to be recognized. The first involves primitive mantle-derived melts (Mg# = 74–80), the second basaltic melts represented by groundmass glasses and the third is associated with more evolved melts represented by the shoshonitic glasses. The population of crystals in “golden” pumices is heterogeneous not only because of crystal incorporation from the shallow resident magma, but also because of pre-eruptive recharge of the deep reservoir with primitive melts. Differences between PST-9 and the other “golden” pumices in terms of groundmass glass composition and distribution of olivine and clinopyroxene compositions reflect contrasted replenishment rates of the deep reservoir with primitive liquids. Gabbroic inclusions in a clinopyroxene crystal provide a direct illustration of melt wall-rock interaction and stress the variability of the deep reservoir in terms of temperature, crystallinity and phase assemblages. Deep crystallization of plagioclase should be considered as a possibility at Stromboli. PST-9 is exceptionally well representative of the early magmatic evolution of “golden” pumices

Carbonatite Melts and Electrical Conductivity in the Asthenosphere

Electrically conductive regions in the Earth mantle have been interpreted to reflect the presence of either silicate melt or water dissolved in olivine. On the basis of laboratory measurements we show that molten carbonates have electrical conductivities that are 3 orders of magnitude higher than those of molten silicate and 5 orders of magnitude higher than those of hydrated olivine. High conductivities in the asthenosphere probably indicate the presence of small amounts of carbonate melt in peridotite and can therefore be interpreted in terms of carbon concentration in the upper mantle. We show that the conductivity of the Oceanic asthenosphere can be explained by 0.1 volume % of carbonatite melts on average, which agrees with the CO2 content of Mid Ocean Ridge Basalts

Role of non-mantle CO2 in the dynamics of volcano degassing: The Mount Vesuvius example

International audienceMount Vesuvius, Italy, quiescent since A. D. 1944, is a dangerous volcano currently characterized by elevated CO2 emissions of debated origin. We show that such emissions are most likely the surface manifestation of the deep intrusion of alkalic-basaltic magma into the sedimentary carbonate basement, accompanied by sidewall assimilation and CO2 volatilization. During the last eruptive period (1631-1944), the carbonate-sourced CO2 made up 4.7-5.3 wt% of the vented magma. On a yearly basis, the resulting CO2 production rate is comparable to CO2 emissions currently measured in the volcanic area. The chemical and isotopic composition of the fumaroles supports the predominance of this crust-derived CO2 in volatile emissions at Mount Vesuvius

Melt inclusions track changes in chemistry and oxidation state of Etnean magmas

Mount Etna (Italy) is a stratovolcano, located near the convergent boundary between African and European plates. Since its appearance, it was characterized by continuous variability of eruptive style and magma composition, though more subtle. Currently, its volcanic activity consists of effusive and explosive eruptions marked by high gas fluxes. Olivine hosted melt inclusions (MIs), belonging to products of the last 15 ky, were analysed for their chemical composition, volatiles contents and Fe speciation, in order to interpret the chemical variability and to evaluate the oxidation state of Etnean magmas and its eventual evolution. Olivine phenocrysts were selected from the most primitive Fall Stratified (FS) eruption of picritic composition (Fo91), from the oldest Mt. Spagnolo and from more recent eruptions: 2002-2003, 2006, 2008-2009, and 2013; the MIs of some of these eruptions (Mt Spagnolo, 2008-2009 and 2013) are here investigated for the first time. The variability of the major elements contents in the MIs designates a continuous differentiation trend, marked by the decrease of MgO and CaO/Al2O3 ratio and the increase of alkalis. The volatiles content in etnean magmas is extremely variable. The highest H2O (5-6 wt.%) and CO2 (~0.5 wt.%) contents are found in FS magma entrapped at depth of 16-18 km (below crater level). S content achieves 4150 ppm in the older Mt. Spagnolo inclusions, completely H2O and CO2\u2013free. Fe3+/\u3a3Fe ratios obtained from XANES spectra for some melt inclusions, generally decrease from the most primitive and volatile-rich FS to the most evolved and degassed melts, suggesting changing in the oxidation state of etnean magmas. Petrological arguments coupled to modelling of fractional crystallization and degassing processes concur to suggest that the magmas of Mt. Spagnolo and of the recent eruptions may be produced by differentiation from the most oxidized and hydrous pristine FS magma along highly variable P-T paths, occasionally accompanied by mixing processes

Granite magmatism and mantle filiation

Current granite magma generation models essentially reduce to two groups: (1) intra-crustal melting and (2) basaltic origin. A mixed, crustal, and basaltic origin and therefore a mantle filiation has been proposed for most granite magma types. In contrast, strongly peraluminous silicic magmas such as two-mica leucogranites have been classically interpreted as products of pure crustal melting. In this paper, we re-examine this interpretation and the evidence for considering leucogranites as unique among granite types. In the first part, some key aspects of the intra-crustal melting model are reviewed. Classical assumptions are discussed, such as the use of migmatites to infer granite generation processes. Our knowledge of crustal melt production is still incomplete, and fluid-present H2O-undersaturated melting should be considered in addition to mica dehydration melting reactions. The source rock remains essential as a concept despite difficulties in the identification of source lithologies from their geochemical and mineralogical signatures. Incorporating spatial and temporal variability at the source and the possibility of external inputs (fluids, magmas) would represent useful evolutions of the model. Thermal considerations bring strong constraints on the intra-crustal melting model since the absence of mafic magmas reduces possible external heat sources for melting. In the second part, the origin of a strongly peraluminous silicic volcanic suite, the Macusani Volcanics (SE Peru), is detailed. Magmas were generated in a mid-crustal anatectic zone characterized by high temperatures and heat fluxes. Crustal metamorphic rocks (metapelites) were dominant in the source region, although Ba-, Sr- and La-rich calcic plagioclase cores and some biotite and sanidine compositions point to the involvement of a mantle component. The heat necessary for melting was supplied by mafic mainly potassic–ultrapotassic magmas which also partly mixed and hybridized with the crustal melts. The Macusani Volcanics provide an example of a crustal peraluminous silicic suite generated with a contribution from the mantle in the form of mafic magmas intruded in the source region. This, as well as the limitations of the intra-crustal melting model, establishes that a mantle filiation is possible for peraluminous leucogranites as for most other crustal (S-, I- and A-type) peraluminous and metaluminous granites. This stresses the critical importance of the mantle for granite generation and opens the way for unification of granite generation processes.</p

The discovery of potent, selective, and reversible inhibitors of the house dust mite peptidase allergen Der p 1: an innovative approach to the treatment of allergic asthma.

Blocking the bioactivity of allergens is conceptually attractive as a small-molecule therapy for allergic diseases but has not been attempted previously. Group 1 allergens of house dust mites (HDM) are meaningful targets in this quest because they are globally prevalent and clinically important triggers of allergic asthma. Group 1 HDM allergens are cysteine peptidases whose proteolytic activity triggers essential steps in the allergy cascade. Using the HDM allergen Der p 1 as an archetype for structure-based drug discovery, we have identified a series of novel, reversible inhibitors. Potency and selectivity were manipulated by optimizing drug interactions with enzyme binding pockets, while variation of terminal groups conferred the physicochemical and pharmacokinetic attributes required for inhaled delivery. Studies in animals challenged with the gamut of HDM allergens showed an attenuation of allergic responses by targeting just a single component, namely, Der p 1. Our findings suggest that these inhibitors may be used as novel therapies for allergic asthma

The helminth product, ES-62, protects against airway inflammation by resetting the Th cell phenotype

We previously demonstrated inhibition of ovalbumin (OVA)-induced allergic airway hyper-responsiveness in the mouse using ES-62, a phosphorylcholine-containing glycoprotein secreted by the filarial nematode, Acanthocheilonema viteae. This inhibition correlated with ES-62-induced mast cell desensitisation, although the degree to which this reflected direct targeting of mast cells remained unclear as suppression of the Th2 phenotype of the inflammatory response, as measured by eosinophilia and IL-4 levels in the lungs, was also observed. We now show that inhibition of the lung Th2 phenotype is reflected in ex vivo analyses of draining lymph node recall cultures and accompanied by a decrease in the serum levels of total and OVA-specific IgE. Moreover, ES-62 also suppresses the lung infiltration by neutrophils that is associated with severe asthma and is generally refractory to conventional anti-inflammatory therapies, including steroids. Protection against Th2-associated airway inflammation does not reflect induction of regulatory T cell (Treg) responses (there is no increased IL-10 or Foxp3 expression) but rather a switch in polarisation towards increased T-bet expression and IFNγ production. This ES-62-driven switch in the Th1/Th2 balance is accompanied by decreased IL-17 responses, a finding in line with reports that IFNγ and IL-17 are counter-regulatory. Consistent with ES-62 mediating its effects via IFNγ-mediated suppression of pathogenic Th2/Th17 responses, we found that neutralising anti-IFNγ antibodies blocked protection against airway inflammation in terms of pro-inflammatory cell infiltration, particularly by neutrophils and lung pathology. Collectively, these studies indicate that ES-62, or more likely small molecule analogues, could have therapeutic potential in asthma, in particular for those subtypes of patients (e.g. smokers, steroid-resistant) who are refractory to current treatments

Clinical and genetic characterisation of dystrophin-deficient muscular dystrophy in a family of Miniature Poodle dogs

Four full-sibling intact male Miniature Poodles were evaluated at 4–19 months of age. One was clinically normal and three were affected. All affected dogs were reluctant to exercise and had generalised muscle atrophy, a stiff gait and a markedly elevated serum creatine kinase activity. Two affected dogs also showed poor development, learning difficulties and episodes of abnormal behaviour. In these two dogs, investigations into forebrain structural and metabolic diseases were unremarkable; electromyography demonstrated fibrillation potentials and complex repetitive discharges in the infraspinatus, supraspinatus and epaxial muscles. Histopathological, immunohistochemical and immunoblotting analyses of muscle biopsies were consistent with dystrophin-deficient muscular dystrophy. DNA samples were obtained from all four full-sibling male Poodles, a healthy female littermate and the dam, which was clinically normal. Whole genome sequencing of one affected dog revealed a >5 Mb deletion on the X chromosome, encompassing the entire DMD gene. The exact deletion breakpoints could not be experimentally ascertained, but we confirmed that this region was deleted in all affected males, but not in the unaffected dogs. Quantitative polymerase chain reaction confirmed all three affected males were hemizygous for the mutant X chromosome, while the wildtype chromosome was observed in the unaffected male littermate. The female littermate and the dam were both heterozygous for the mutant chromosome. Forty-four Miniature Poodles from the general population were screened for the mutation and were homozygous for the wildtype chromosome. The finding represents a naturally-occurring mutation causing dystrophin-deficient muscular dystrophy in the dog

Upward migration of Vesuvius magma chamber over the past 20 thousand years

International audienceForecasting future eruptions of Vesuvius is an important challenge for volcanologists, as its reawakening could threaten the lives of 700,000 people living near the volcano1,2. Critical to the evaluation of hazards associated with the next eruption is the estimation of the depth of the magma reservoir, one of the main parameters controlling magma properties and eruptive style. Petrological studies have indicated that during past activity, magma chambers were at depths between 3 and 16km (refs 3– 7). Geophysical surveys have imaged some levels of seismic attenuation, the shallowest of which lies at 8–9km depth8, and these have been tentatively interpreted as levels of preferential magma accumulation. By using experimental phase equilibria, carried out on material from four main explosive events at Vesuvius, we show here that the reservoirs that fed the eruptive activity migrated from 7–8km to 3–4km depth between the AD 79 (Pompeii) and AD 472 (Pollena) events. If data from the Pomici di Base event 18.5 kyr ago9 and the 1944 Vesuvius eruption7 are included, the total upward migration of the reservoir amounts to 9–11 km. The change of preferential magma ponding levels in the upper crust can be attributed to differences in the volatile content and buoyancy of ascending magmas, as well as to changes in local stress field following either caldera formation10 or volcano spreading11. Reservoir migration, and the possible influence on feeding rates12, should be integrated into the parameters used for defining expected eruptive scenarios at Vesuvius