Search

Sulfur is an essential volatile component of basaltic magmas and it is mostly dissolved as S6+ and/or S2- depending on the redox conditions. Mt. Etna continuously discharges enormous quantity of SO2 (~3563 t/d [1]). However these high flows are not fully understood in terms of S origin (magmatic or crustal) and of its behavior during magmatic evolution (fractional crystallization, magma mixing, vapor/melt fractionation [2]). Our research combines the study of sulfur in natural olivine hosted melt inclusions with an experimental study on S solubility in hydrous alkali basalts at magmatic conditions. We report new data of S in melt inclusions, belonging to six of the most characteristic Etnean eruptions of the last 14 ky, from the oldest and most primitives (Mt Spagnolo and FS eruptions) up to the recent paroxysm event of April 2013. These melt inclusions were entrapped at different depths inside the magmatic system (up to ~ 18 km, corresponding to a pressure of almost 5 kbar) as defined by H2O-CO2 contents. Sulfur content, evaluated by EMP and SIMS methods, reach 3600-4100 ppm in the most primitive melt inclusions of Mt Spagnolo and 2006 eruptions (Fo87 and Fo80). Sulfide globules were observed in some melt inclusions of 2002/3, 2008 and 2013 products, but also in host olivine crystals, probably reflecting sulfide saturation of the melt during the entrapment of the melt inclusions. We therefore carried out IHPV experiments in Etnean mafic melts at sulfide saturation in order to investigate how the variations in S content observed in melt inclusions can be explained by the changes in magma

Objectives The study was designed to compare sibling and best friend relationships engaged by adolescents with autism spectrum disorder (ASD). Methods Twenty adolescents with ASD, aged 15–18 years ((M = 16.80, SD = 0.95), and their typically developing (TD) siblings (n = 20), aged 18 to 24 years (M = 20.05, SD = 1.67), were recruited for the current study. Behaviors underpinning attachment, caregiving and affiliative systems were evaluated as well as negative interaction behaviors in sibling relationships and friendships. Non-parametric statistical analyses (the Wilcoxon signed-ranks test and the Mann–Whitney U-test) were carried out to verify the differences in sibling and best friend relationships. Results Adolescents with ASD referred a higher presence of negative interaction behaviors in sibling relationships compared to friendships. However, when mixed and non-mixed friendships were distinguished, the descriptions of typically developing (TD) siblings and (TD) best friends overlapped for caregiving behaviors, revealing as both of them were depicted as a source of support and comfort by adolescents with ASD. A lower presence of behaviors underpinning attachment, caregiving and affiliations characterized relationships with best friends with disability compared to TD best friends. Conclusion This study highlighted that TD siblings provided a strong support for their siblings with ASD. The same role was also played by TD best friends.

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

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 2013. S concentrations in glass inclusions are extremely variable, from a few hundreds ppm in recent lavas up to 4000 ppm in the older Mt Spagnolo products (Fo88). This variation broadly correlates with the degree of differentiation of the melt, as expressed by the major element (SiO2, K2O) chemistry. However, both degassing and variations in redox conditions influence the S behaviour, as revealed by variations in volatile concentrations, sulfide saturation and Fe speciation in melt inclusions. Fe3+/ΣFe spectra in some glass inclusions were collected by XANES synchrotron radiation. Results span a large range of Fe3+/ΣFe ratios, generally decreasing from the most primitive (FS) to the most recent (2013) melts. Fe3+/ΣFe ratios were used for estimating the redox conditions of Etnean magma, yielding quite oxidizing and fairly variable fO2. Interpretation of the glass inclusion data (notably S content and Fe speciation) uses hydrous and S-bearing basaltic experimental glasses synthesized in the range of conditions (P, T, fO2) relevant to the Etnean system. Results corroborate an important control of fO2 and of the melt Fe concentration on the S concentration of Etnean glasses.

International audience; A 4-year geochemical survey of some fumaroles at the Voragine summit crater of Mt Etna was performed in combination with synchronous monitoring of peripheral gas emissions at the base of the volcano. This was the first geochemical study at Mt Etna to have included the abundances of Ar, He, and C isotopes. Once the effects of postmagmatic shallow processes were identified and quantitatively removed, the He-Ar-CO2 systematics of the Voragine crater fumaroles and peripheral gas emissions described the same degassing path. Combining the carbon-isotope composition with information about noble gases provided evidence that the crater fumaroles are fed from a two-endmember mixture composed of a deep member coming from pressures between 200 and 400 MPa (depending on time), and a shallower one exsolved at ~130 MPa. Similar mixing processes probably also occur in gases from peripheral vents. The simultaneous assessment of 13CCO2 and He/Ar values of crater fumaroles over time has identified simple changes in the mixing proportion between the two endmembers and, moreover, periods during which the exsolution pressure of the deep fluid increased. These periods seem to be linked to pre-eruptive phases of the volcano. The identified open-system degassing processes are indicative of efficient bubble-melt decoupling at depth, whereas the mixing process requires a convective transfer of the deeply exsolved fluids toward shallower levels of magma where further vapor is exsolved. In agreement with the most recent geophysical and petrological data from Mt Etna, these observations allow inferences about a deep portion of the plumbing system (5 to 12 km b.s.l.), comprising sill-like reservoirs connected by small vertical structures, and a main reservoir at 2-3 km b.s.l. that is probably fluxed by magmatic volatiles.

International audience; New experimental data of Ar and Ne solubility at pressures up to 360 MPa in alkali-basaltic (Mt. Etna, Italy) and rhyolitic (Vulcano Island, Italy) melts are presented. Solubility experiments have been conducted in internally heated pressure vessels at 1200 °C under nominally anhydrous conditions. Ar and Ne contents dissolved in the experimental glasses were then measured by quadrupole mass spectrometry. Over the pressure range investigated, Ar and Ne solubilities vary linearly with Ar and Ne pressures and can be described by Henry's constant (kAr,Ne = PAr, Ne / xAr, Ne, where PAr, Ne is the partial pressure of Ar or Ne and xAr, Ne is the molar fraction of Ar or Ne in the melt) of 7.6 ± 0.8 × 105 and 1.9 ± 0.4 × 105 MPa, respectively for Ar and Ne in the basaltic melt and 1.5 ± 0.2 × 105 and 3.8 ± 0.2 × 104 MPa, respectively for Ar and Ne in the rhyolitic melt. In accordance with existing models, rhyolitic melts show higher noble gas solubilities than basaltic melts, Ne solubility being higher than that of Ar in a given composition. We propose a semi-empirical model of noble gas (Ar, Ne and He) solubility calibrated on a very large set of measurements in natural and synthetic silicate melts. The model expands the concept of ionic porosity in terms of porosity accessible for noble gas dissolution in melt, taking into account the large-scale structural effects of cations, as well as temperature and pressure. The model is valid over a wide range of temperatures (800–1600 °C), pressures (up to 3 GPa) and compositions, being useful for both geological and physico-chemical studies.