Search

We report composition, grain size, and rheological data related to the mud emitted as a consequence of the maximum moment magnitude (Mw max = 6.5) on 30 October 2016, commonly referred to as the Norcia earthquake (central Italy), and on the activity of pre-existent mud volcanoes affected by the central Italy seismic sequence started on 24 August 2016. The emission sites were located at Monteleone di Fermo and Santa Vittoria in Matenano, two municipalities near the town of Fermo (Marche Region, Italy). We sampled, measured, and analyzed the products of mud emissions 3 days after the mainshock to characterize the mud by geochemical, mineralogical, and rheological analyses. The muds' geochemical composition and low electrical conductivity suggest a continental origin, likely belonging to the Colombacci Formation. The collected muds are silt–sand–water-rich suspensions characterized by a Bigham rheology with viscosity values between 6.3∙107 and 6.9∙105 Pa∙s. The calculated minimum fluidization velocity of the mud suspensions is between 0.05 m/s (grain size of 2 μm) and 0.74 m/s (grain size of 8 μm). Water-rich mud suspensions flowing on a slope move faster as the water content increases up to 30 wt.%. At higher values, the velocity remains almost constant due to the disaggregation of bonds among the solid particles in the mixtures. [ABSTRACT FROM AUTHOR]

Large igneous provinces (LIPs) whose magma plumbing systems intersect sedimentary basins are linked to upheavals of Earth's carbon and sulfur cycles and thus climate and life history. However, the underlying mechanistic links between these phenomena are elusive. We address this knowledge gap through short time-scale petrological experiments (1200°C and 150 MPa) that explore interaction between basaltic melt and carbonaceous shale (mudstone) using starting materials from the Canadian High Arctic LIP and the Sverdrup Basin in which it intrudes. Here we show that entrainment of shale xenoliths in basaltic melt causes shale to shatter due to incipient thermal stress and devolatilization, which accelerates assimilation by increasing reactive surface area. Shale assimilation therefore facilitates transfer of sediment-derived volatile elements to LIP magma plumbing systems, whereupon carbon dominates the vapor phase while sulfur is partitioned into sulfide melt droplets. This study reveals that although carbon and sulfur are efficiently mobilized as a consequence of shale assimilation, sulfides can sequester sulfur—an important climate cooling agent—thus enhancing net emissions of climate warming greenhouse gases by shale-intersecting LIPs. [ABSTRACT FROM AUTHOR]

The solubility of [H.sub.2]O-C[O.sub.2] fluids in a synthetic analogue of a phono-tephritic lava composition from Alban Hills (Central Italy) was experimentally determined from 50 to 500 MPa, at 1200 and 1250 [degrees]C. Contents of [H.sub.2]O and C[O.sub.2] in experimental glasses were determined by bulk-analytical methods and FTIR spectroscopy. For the quantification of volatile concentrations by IR spectroscopy, we calibrated the absorption coefficients of water-related and carbon-related bands for phono-tephritic compositions. The determined absorption coefficients are 0.62 [+ or -] 0.06 L/(mol x cm) for the band at ~4500 [cm.sup.-1] (OH groups) and 1.02 [+ or -] 0.03 L/(mol x cm) for the band at ~5200 [cm.sup.-1] ([H.sub.2]O molecules). The coefficient for the fundamental OH-stretching vibration at 3550 [cm.sup.-1] is 63.9 [+ or -] 5.4 L/(mol x cm). C[O.sub.2] is bound in the phono-tephritic glass as C[O.sup.2.sub.3] exclusively; its concentration was quantified by the peak height of the doublet near the 1500 [cm.sup.-1] band with the calibrated absorption coefficient of 308 [+ or -] 110 L/(mol x cm). Quench crystals were observed in glasses with water contents exceeding 6 wt% even when using a rapid-quench device, limiting the application of IR spectroscopy for water-rich glasses. [H.sub.2]O solubility in the ultrapotassic melts (7.52 wt% [K.sub.2]O) as a function of pressure is similar to the solubility in basaltic melts up to 400 MPa (~8 wt%) but is higher at 500 MPa (up to 10.71 wt%). At 500 MPa and 1200[degrees]C, the C[O.sub.2] capacity of the phono-tephritic melt is about 0.82 wt%. The high C[O.sub.2] capacity is probably related to the high [K.sub.2]O content of the melt. At both 200 and 500 MPa, the [H.sub.2]O solubility shows a non linear dependence on [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] in the whole [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] range. The variation of C[O.sub.2] solubility with [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] displays a pronounced convex shape especially at 500 MPa, implying that dissolved [H.sub.2]O promotes the solubility of C[O.sub.2]. Our experimental data on C[O.sub.2], solubility indicate that the interaction between phono-tephritic magma and carbonate rocks occurring in the Alban Hills magmatic system may result in partial dissolution of C[O.sub.2] from limestone into the magma. However, although the C[O.sub.2 solubility in phono-tephritic melts is relatively high compared to that in silicic to basaltic melts, the capacity for assimilation of limestone without degassing is nevertheless limited to Keywords: [H.sub.2]O, C[O.sub.2], solubility, ultrapotassic magmas, Alban Hills, infrared spectroscopy

The oxidation state of Fe in hydrous ultrapotassic (phono-tephritic) melts coexisting with mixed [H.sub.2]O-C[O.sub.2] fluids was studied experimentally at 1200 and 1250[degrees]C and pressures from 50 to 500 MPa. The oxygen fugacity ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) varied from NNO-2.9 to NNO+2.6 in log [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], relative to the Ni-NiO oxygen buffer (NNO), as imposed by external redox conditions in experimental vessels and internal variations in water activity from 0.05 to 1 inside the capsules. The Fe redox state of the quenched melts was determined by colorimetric wet-chemical analysis. This analytical method was optimized to measure the [Fe.sup.2+]/[SIGMA]Fe ratio of milligram-sized samples within [+ or -] 0.03 (2[sigma]). The accuracy and precision was tested with international reference materials and with standards analyzed by other methods. The [Fe.sup.2+][SIGMA]Fe ratio of the experimental glasses covered a range of 0.41 to 0.85. A small negative effect of dissolved water on [Fe.sup.2+]/[SIGMA]Fe at given [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] was found, consistent with the thermodynamic model of Moretti (2005). No effect of pressure and temperature on the redox state of Fe was resolvable in the investigated P-T range. Compared to hydrous ferrobasaltic melts that were studied previously under similar conditions, systematically lower [Fe.sup.2+]/[SIGMA]Fe ratios were found for the phono-tephritic melts, in particular at low oxygen fugacities. This effect is attributed to the much higher [K.sub.2]O contents of the phono-tephrite (7.5 compared to 0.3 wt%), but the difference in Fe[O.sub.T] (7.8 wt% in the phono-tephrite and 12.9 wt% in the ferrobasalt) may have an influence as well. Comparison of the experimentally obtained relationship between log [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and [Fe.sup.3+]/[Fe.sup.2+] for the studied hydrous ultrapotassic melts with commonly used empirical and thermodynamic models suggest that these models can be successfully applied to phono-tephritc melts, although such compositions were not implemented in the model calibrations. Furthermore, the new data can be used to improve the models with respect to the effects of compositional variables, such as [H.sup.2]O or [K.sub.2]O, on the redox state of Fe in silicate melts. Keywords: Fe oxidation state, FeO determination, oxygen fugacity, water activity, phono-tephrite, ultrapotassic hydrous silicate melt, Alban Hills

The April to May 2010 eruption of Eyjafjallajökull (Iceland) volcano was characterized by a large compositional variability of erupted products. To contribute to the understanding of the plumbing system dynamics of this volcano, we present new EMPA and LA-ICP-MS data on groundmass glasses of ash particles and minerals erupted between April 15 and 22. The occurrence of disequilibrium textures in minerals, such as resorption and inverse zoning, indicate that open system processes were involved in determining the observed compositional variability. The variation of major and trace element data of glasses corroborates this hypothesis indicating that mixing between magma batches with different compositions interacted throughout the whole duration of the eruption. In particular, the arrival of new basaltic magma into the plumbing system of the volcano destabilized and remobilized magma batches of trachyandesite and rhyolite compositions that, according to geophysical data, might have intruded as sills over the past 20 years beneath the Eyjafjallajökull edifice. Two mixing processes are envisaged to explain the time variation of the compositions recorded by the erupted tephra. The first occurred between basaltic and trachyandesitic end-members. The second occurred between trachyandesite and rhyolites. Least-squares modeling of major elements supports this hypothesis. Furthermore, investigation of compositional histograms of trace elements allows us to estimate the initial proportions of melts that interacted to generate the compositional variability triggered by mixing of trachyandesites and rhyolites. [ABSTRACT FROM AUTHOR]

We experimentally investigate the major and trace elements behavior during the interaction between two partially molten crustal rocks (meta-anorthosite and metapelite) and a basaltic melt at 0.5-0.8 GPa. Results show that a hybrid melt is formed at the basalt-crust contact, where plagioclase crystallizes. This contact layer is enriched in trace elements which are incompatible with plagioclase crystals. Under these conditions, the trace element diffusion coefficients are one order of magnitude larger than those expected. Moreover, the HFSE diffusivity in the hybrid melt is surprisingly higher than the REE one. Such a feature is related to the plagioclase crystallization that changes the trace elements liquid-liquid partitioning (i.e. diffusivity) over a transient equilibrium that will persist as long as the crystal growth proceeds. These experiments suggests that the behaviour of the trace elements is strongly dependent on the crystallization at the magma-crust interface. Diffusive processes like those investigated can be invoked to explain some unusual chemical features of contaminated magmatic suites. [ABSTRACT FROM AUTHOR]

Abstract: Viscosity of hydrous trachytes from the Agnano Monte Spina eruption (Phlegrean Fields, Italy) has been determined at 1.0 GPa and temperatures between 1200 and 1400 °C using the falling sphere method in a piston cylinder apparatus. The H2O content in the melts ranged from 0.18 to 5.81 wt.%. These high-temperature hydrous viscosities, along with previous ones determined at low-temperature (anhydrous and hydrous) and at high-temperature (anhydrous), at 1 atm on the same melt composition, represent the only complete viscosity data set available for K-trachytic melts, from magmatic to volcanic conditions. Viscosity decreases with increasing temperature and water content in the melt. At constant temperature, viscosity appears to significantly decrease when the first wt.% of H2O is added. At H2O content higher than 3 wt.% the effect of temperature on viscosity is slight. Moreover, the deviation from Arrhenian behaviour towards greater “fragility” occurs with increasing water content. We combined low- and high-temperature viscosities (also from literature) and parameterized them by the use of a modified Vogel–Fulcher–Tamman equation, which accommodates the non-Arrhenian temperature dependence of melt viscosity. Moreover, in order to explore the extent to which the improved knowledge of Agnano Monte Spina trachyte viscosity may affect simulation of volcanic eruption at Phlegrean Fields, we included our viscosity models in numerical simulations of magma flow and fragmentation along volcanic conduits. These simulations show that the new parameterizations (and hence the new equations) give stronger predictions in the temperature interval relevant for magmatic and eruptive processes. [Copyright &y& Elsevier]

Water distribution in the deep Earth represents one of the most important topics in the field of geodynamics due to its large impact on the physical and chemical properties of the Earth's mantle, such as electrical conductivity, seismic anisotropy, diffusion, and rheology. In this study, we synthesized hydrous forsterite at 1100 °C and up to 4 GPa with either a piston-cylinder or multianvil apparatus. As a starting material, we used synthetic forsterite, unbuffered by SiO2, obtained by thermo-mechanical activation of talc and magnesium carbonate hydroxide. Hydration was carried out using liquid H2O as hydrogen source. Samples were polycrystalline in an effort to distribute H2O throughout the sample both rapidly and homogeneously. Using the Paterson calibration, we observed total water content concentrations ranging between 100 and 500 ppm wt H2O. Multiple absorption bands are found in the frequency range between 3400 and 3650 cm−1, identifying at least seven peaks in all samples. Vibrational bands were centered at 3476, 3535, 3550, 3566, 3578, 3605, and 3612 cm−1, in good agreement with experimental studies conducted on both hydrous forsterite and single crystals of olivine. The stronger OH stretching peaks can be attributed to vibrational modes associated with the hydrogarnet defect 4 H Si x in which four protons occupy a vacant tetrahedral site. None of the OH bands observed are found at frequencies associated with hydrogen occupying vacant octahedral sites. High-temperature FTIR spectroscopy was used to evaluate the evolution of IR spectra as a function of temperature, up to 500 °C. The complete reversibility of peak absorption vs. temperature in the OH stretching region confirms that no water loss occurred during heating. We observe an overall a decrease in total absorption with increasing temperature, and a prominent decrease in the relative intensities of the higher frequency bands (>3600 cm−1) with respect to lower frequency bands. We have assigned a series of equilibrium expressions based on the variation of relative peak areas with temperature and find that enthalpies of these processes range between 0.047–0.068 eV (4.5–6.5 kJ/mol), very low in comparison to activation energies observed for electrical conduction in hydrous olivine. Major changes in the vibrational spectrum are expected to be related to configurational changes of the same fully protonated hydrogarnet defect species. However, the complexity of the FTIR spectra may also be related to partially protonated defects, such as the associate defect 3 H Si ′ + H i • generated by a dissociation reaction of the hydrogarnet species. [ABSTRACT FROM AUTHOR]

ESCAPE VOLCANO: a new game on volcanic hazardsValeria Misiti, Maria Di Nezza, Francesca Di Laura, Lili Cafarella, Giuliana D'AddezioIstituto Nazionale di Geofisica e Vulcanologia (INGV)The game we propose here is called "Escape Volcano" and aims to teach the basic notions about volcanoes and different kind of eruptions. It is intended for middle and high school students. The game has been realized with some high school students in the frame of Alternanza Scuola Lavoro project. The visual impact of the game and its own actions in the dynamics of play allows the students to improve easily the knowledge of complex concepts, refining the abstract thought e developing solutions. The game, in general, can be see also as occasion to improve relationship between students. The game is not only evasion and entertainment but a way to know each other and confront themselves. In particular, this game is composed by a plastic billboard (160*200cm2), that represents a volcano with its magmatic chambers, four plastic pawns, one dice and four deck of cards.The game is for teams of 2/4 players. The aim of the game is to reach the crater, starting from the magmatic chamber, before the volcano erupts.Each player can try to reach the top jumping from the magmatic chamber to the minor chambers, answering the questions reported in the cards. There are four different types of cards, each corresponding to a die face:Tabù, mime, multiple answer and draw cards. The dice has two more faces: the BOMB, which forcesthe team go back one chamber, and the X2, which means the team has to answer two more questionsbefore moving to the next chamber. However, the way out is not so simple to reach, there are many insidious traps along the way!The game has been presented in some public meetings and has been very successful. [ABSTRACT FROM AUTHOR]

Abstract: The main effect of magma–carbonate interaction on magma differentiation is the formation of a silica-undersaturated, alkali-rich residual melt. Such a desilication process was explained as the progressive dissolution of CaCO3 in melt by consumption of SiO2 and MgO to form diopside sensu stricto. Magma chambers emplaced in carbonate substrata, however, are generally associated with magmatic skarns containing clinopyroxene with a high Ca-Tschermak activity in their paragenesis. Data are presented from magma–carbonate interaction experiments, demonstrating that carbonate assimilation is a complex process involving more components than so far assumed. Experimental results show that, during carbonate assimilation, a diopside–hedenbergite–Ca-Tschermak clinopyroxene solid solution is formed and that Ca-Tschermak/diopside and hedenbergite/diopside ratios increase as a function of the progressive carbonate assimilation. Accordingly, carbonate assimilation reaction should be written as follows, taking into account all the involved magmatic components: CaCO3 solid +SiO2 melt +MgOmelt +FeOmelt +Al2O3 melt →(Di–Hd–CaTs)ss solid +CO2 fluid The texture of experimental products demonstrates that carbonate assimilation produces three-phases (solid, melt, and fluid) whose main products are: i) diopside–hedenbergite–Ca-Tschermak clinopyroxene solid solution; ii) silica-undersaturated CaO-rich melt; and iii) C–O–H fluid phase. The silica undersaturation of the melt and, more importantly, the occurrence of a CO2-rich fluid phase, must be taken into account as they significantly affect partition coefficients and the redox state of carbonated systems, respectively. [Copyright &y& Elsevier]