Description: Glass stability (GS) indicates the glass reluctance or ability to crystallise upon heating and it can be characterised by several methods and parameters. GS is frequently used to retrieve glass-forming ability (GFA) of corresponding liquids: the likelihood of obtaining a crystal-free glass through melt-quenching. In the present study, GS has been determined for the first time on six sub-alkaline glasses having complex (natural) compositions, the most widespread and abundant on Earth. The two end-members are a basalt and a rhyolite, B100 and R100, plus intermediate compounds B80R20, B60R40, B40R60, B20R80. Each glass was heated in a differential scanning calorimetry (DSC) at a rate of 10 °C/min (600 °C/h) to measure in-situ Tg (glass transition), Tx (onset of crystallization) and Tm (melting) temperatures, from ambient to their liquidus temperatures. The ex-situ run-products quenched at Tm have been characterised by scanning electron microscope (SEM) and electron probe micro-analyzer (EPMA) techniques, in order to quantify textures and compositions of phases, respectively. R100 and B20R80 do not shown any DSC peaks, whereas B40R60, B60R40, B80R20 and B100 thermograms display progressively more resolvable peaks. As SiO2 (wt%) in the melt increases from B100 to B40R60, Tx linearly increases, Tm first decreases and then levels off, whereas Tg weakly changes. R100 and B20R80 run-products are completely glassy, while from B100 to B40R60 the amount of glass (gl) increases from 48.5 to 97 area%, counterbalanced by a decrease of clinopyroxene (cpx) content from 47.7 to 16 area%. The spinel (sp) content is constrained within a narrow range of 0.9–3.8 area%. Conversely, plagioclase (plg) crystallizes heterogeneously on the Al2O3 holders only in B100 and B80R20 and at distance 〈 100 μm from it. R100, B20R80, B40R60 and B60R40 ex-situ glasses exhibit chemistries very close to their starting compositions, according to the absence (or scarcity) of crystals formed during heating. Instead, B100 and B80R20 glasses are enriched in Si, Al, and Na but depleted in Fe, Mg, and Ca due to internal crystallization of sp and mostly cpx. Specifically, the composition of cpx from B100 is enriched in M2Ca, M1Mg, M2,M1Fe, and M1,TAl. The values of KT, KH, KW, KLL, and w2 (as GS parameters) increase linearly and monotonically as a function of SiO2, showing high correlation coefficients (R2 = 0.93–0.95). Moreover, Tx values and GS parameters highly correlate with GFA via Rc (critical cooling rate), as previously determined by ex-situ cooling-induced experiments. This leads to the conclusion that GS scales with GFA for natural silicate compositions. In addition, the in-situ Rc value of B100 measured with DSC is 〉 45 °C/min (〉 2700 °C/h), corroborating the value of Rc of ~ 150 °C/min (9000 °C/h) determined by ex-situ experiments. In turn, relevant solidification parameters on heating or cooling obtained by DSC investigations, also for chemically complex (natural) systems, extend the results from previous observations conducted on simple silicate systems. These outcomes are relevant for lavas or magmas that re-heat glass-bearing volcanic rocks, as well as for fabricating glass-ceramic materials with desirable texture and composition of phases starting from abundant and very cheap raw volcanic rocks.

Description: Published

Description: 21-30

Description: 3V. Proprietà dei magmi e dei prodotti vulcanici

Description: JCR Journal

Description: The Fucino lacustrine basin in central Italy is a large flat area mostly devoted to agriculture, with urbanization along the perimeter of the ancient lake. In 1915 a strong earthquake struck the area (Mw 7.0), producing large damages and geological effects, including surface faulting, ground failures and liquefaction. A channel excavated in the lacustrine sediments exposed ground failure, with dykes of fine-grained sediment that we interpret as the result of earthquake-induced liquefaction. We present the results of a multidisciplinary work aimed at characterizing in detail the geology of the buried stratigraphic succession, its susceptibility to liquefaction and the likely source of the fine-grained liquefied material. The succession down to 20 m deep is formed by fine-grained sediments younger than ~170–180 kyrs (mostly Late Pleistocene - Holocene), prevailingly silt or silt-clay mixtures. The geological field analysis indicates that the dykes are filled by prevailing silt, liquefied and transported by upward-directed flow of short duration, as for earthquake-induced liquefaction. Tilting and lateral spreading accompanied the process. The overall liquefaction potential derived from the “simplified methods” is high. Correlations of X-Ray Powder Diffraction mineralogy of samples from drilling cores with those from dykes allowed us to identify the most likely source layer filling dykes, corresponding to a silt layer at 7–8 m depths. This layer and the dykes lack illite and montmorillonite clay particles. These results contribute to improve studies of liquefactions in sediments that differ from typical liquefiable loose sands. They have also implications for microzonation studies. Most samples show grain-size curves that do not fit within the field of potentially liquefiable soils, suggesting that criteria based on grain-size can be poorly significant in seismic microzonation studies of recent (Late Pleistocene-Holocene) lacustrine, fine-grained successions.

Description: Published

Description: 105621

Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica

Description: JCR Journal

Description: Mid-ocean ridge basalts (MORBs) are the most abundant eruptive tholeiitic products on Earth. Many experiments have been performed to investigate the solidification of basalts but under limited thermal ranges of cooling (ΔTc) and cooling rates (ΔT/Δt). We analyze the experimental charges solidified from previous studies: the BIR1A basalt from USGS was solidified using ΔT/Δt of 1, 7, 60, 180, 1800 and 9000 °C/h, in the ΔTc between 1300 and 800 °C, at atmospheric conditions. The previous studies allowed determining the glass-forming ability (GFA) of sub-alkaline silicate liquids, but do not give information on their textures. Here, we quantify the evolution of sizes, shapes, number of crystals per area (#/A), CSDs and growth rates (Gs) of plg (plagioclase), cpx (clinopyroxene) and sp. (spinel). Textures were investigated by image analysis on thousands of crystals and are one of the most complete datasets ever obtained from laboratory studies: they reflect rapid, intermediate and sluggish cooled parts of MORB from liquidus to solidus. Faceted plg grows only at ΔT/Δt ≤ 60 °C/h, while cpx and sp. became dendritic at ΔT/Δt between 60 and 180 °C/h. As ΔT/Δt increase, crystal size ranges decrease from 1000 to 10 μm at 1 °C/h to 100–1 at 60 °C/h μm for plg, from 400 to 8 μm at 1 °C/h to 25–0.5 μm at 1800 °C/h μm for cpx, and from 90 to 6 μm at 1 °C/h to 6–0.5 at 1800 °C/h μm, for sp. The #/A increases with increasing ΔT/Δt, except for cpx between 60 and 180 °C/h. As ΔT/Δt increases, CSDs of plg, cpx and sp increase their slopes (m) and population densities per size (n0), reduce the size ranges and tend to be log-linear. At low ΔT/Δt, CSDs are composed of several log-linear segments, which slopes are related to different pulses of crystal nucleation, and subsequent growth by coarsening. The CSDs parameters (slope, m, and nucleation density per size, n0) linearly scale each other and both are highly correlated with ΔT/Δt. Maximum (Gmax) and average (GCSD) growth rates are computed respectively by averaged major axis (Lmax) of the five longest crystals and by the m of CSDs. Both the Gs are a function of experimental time (t) and increase with the increasing of ΔT/Δt, changing up to two orders of magnitude. The Gmax of cpx is correlated with m and n0 and can be used in natural MORB to retrieve either ΔT/Δt and Gmax. The plg and cpx crystals with sizes between 0.1 and 1 mm are abundant in the experimental charges obtained at low ΔT/Δt. In volcanic rocks, these crystal sizes are generally considered representative of intra-telluric conditions (phenocrysts and microphenocrysts). Our data demonstrate that crystals with mm-sizes may also grow in syn-topost- depositional conditions. The continuous evolution of textures in response to ΔT/Δt variations implies that kinetic effects can fully capture the solidification of MORBs. As a result, the widely accepted assumption that phenocrysts represent the products of evolution processes in volcanic conduits or magma reservoirs could be not valid for some basaltic lavas.

Description: Published

Description: 103165

Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici

Description: JCR Journal

Description: The in situ differential scanning calorimetry (DSC) technique has been applied to investigate the solidification paths of a basaltic liquid. The starting glass was heated up to 1300°C, kept at this superliquidus temperature for 2 h and cooled at rates (ΔT/Δt) of 7, 60, 180, 1000, and 1800°C/h, down to 800 and 600°C. Glass transition temperature (Tg), crystallization temperature (Tx_HR) and melting temperature (Tm) were measured by in situ DSC spectra on heating. Tx measured along the cooling paths (Tx_CR) shows exothermic peaks that change from a single symmetric shape (7 and 60°C/h) to multi-component patterns (180, 1000, and 1800°C/h). The recovered products characterized by field emission gun source of the scanning electron microscopy and electron probe micro-analyzer-wavelength dispersive spectrometers show a phase assemblage of spinel (sp), clinopyroxene (cpx), melilite (mel), plagioclase (plg), and glass. Moreover, crystal size distributions (CSDs) and growth rates (Gmax and GCSD) were also determined. The crystal content slightly increases from 7 to 1800°C/h. Faceted sp are present in all the run products with an amount always 〈2 area%. Cpx increases from 7 to 1800°C/h, changing its texture from almost faceted to dendritic between 60 and 180°C/h. The area% of mel follows an asymmetric Gaussian trend, while plg nucleates only at 7°C/h with a content 〈2 area%. The coupling of DSC and SEM outcomes indicate that sp nucleate first, followed by cpx and mel (and/or plg). The increment of ΔT/Δt causes an increase of the CSD slope (m) and crystal population density per size (n0), as well as a decrease of the crystal size, for both cpx and sp. The log-linear CSD segments with different slopes at 7 and 60°C/h suggest multiple nucleation events and crystal growth by coarsening. Gmax and GCSD for cpx and sp directly measured on the actual crystallization time by DSC spectra, both increase with the increasing of ΔT/Δt. The onset temperature of crystallization (Txi) decreases as ΔT/Δt increases, following an exponential trend that defines the uppermost portion of a time-transformation-temperature-like curve. This analytical model allows us to quantitatively model the kinetic crystallization paths of dry basalts.

Description: Published

Description: 337

Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici

Description: JCR Journal

Description: Asbestos may cause adverse effects, but relationship between mineralogy and texture of fibres versus toxicity is still lacking. Toxicological studies can be interpreted and compared only if quantitative features of fibres are determined. Here, riebeckitic ("crocidolite") amphibole fibres were analysed by XRPD, FTIR, SEM-EDS and EMP-WDS; only crystals with stochiometryA□BNa2C(Fe2+2.5Mg0.5)CFe3+2TSi8O22W(OH)2are present in the starting material used for the experiments. Fibres deposited from solutions of 0.1, 1, 10, 25, 50, 75 and 100mg/L were counted by image analysis using SEM images. At 0.1 and 1mg/L the fibres are well separated, whereas between 1 and 10mg/L they start to agglomerate. In-vitro tests performed on fibres deposited at the same mg/L concentrations show that the toxic potential follows a curvilinear increasing trend with a decreasing rate. Since the range of sizes of single fibres and their mineralogy are constant, this decreasing rate can be only attributed to the increasing amount of agglomerated fibres. Hence, single versus agglomerated fibre population is a factor that cannot be neglected in defining the final adverse effects of asbestos. The analytical protocol proposed here is valuable for any aero-dispersed dust, in polluted environments, as well as in the interpretation of experimental studies.

Description: Published

Description: 472-485

Description: 7A. Geofisica per il monitoraggio ambientale e geologia medica

Description: JCR Journal

Description: 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.

Description: Published

Description: 311-320

Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici

Description: JCR Journal

Description: 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.

Description: Published

Description: id 44

Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici

Description: JCR Journal

Description: Rock substrates beneath active volcanoes are frequently subjected to temperature changes caused by the input of new magma from the depth and/or the intrusion of magma bodies of variable thickness within the subvolcanic rocks. The primary effect of the influx of hot magma is the heating of surrounding host rocks with the consequent modification of their physical and chemical properties. To assess mobilization in subvolcanic thermal regimes, we have performed radon (220Rn) thermal experiments on a phonolitic lava exposed to temperatures in the range of 100-900°C. Results from these experiments indicate that transient Rn signals are not unequivocally related to substrate deformation caused by tectonic stresses, but rather to the temperature-dependent diffusion of radionuclides through the structural discontinuities of rocks which serve as preferential pathways for gas release. Intense heating/cooling cycles are accompanied by rapid expansion and contraction of minerals. Rapid thermal cycling produced both inter- and intra-crystal microfracturing, as well as the formation of macroscopic faults. The increased number of diffusion paths dramatically intensified Rn migration, leading to much higher emissions than temperature-dependent transient changes. This geochemical behaviour is analogous to positive anomalies recorded on active volcanoes where dyke injections produce thermal stress and deformation in the host rocks. An increased Rn signal far away from the location of a magmatic intrusion is also consistent with microfracturing of subsurface rocks over long distances via thermal stress propagation and the opening of new pathways.

Description: Published

Description: id 190782

Description: 4V. Processi pre-eruttivi

Description: JCR Journal

Description: A new target for worldwide geothermal exploration and exploitation is represented by the submarine hydrothermal activity. A geologically young (Upper Pliocene – Pleistocene) area in the Tyrrhenian sea, on the west shore of Italy, provides important heat sources from some seamounts. The heat flow data are characterized by positive anomalies comparable to those of onshore geothermal fields. A geothermal exploration program of the Marsili seamount, the largest volcanic edifice (~30 km in length) in Europe, suggests the presence of a geothermal activity testified by oxy- and hydroxide-deposits predominantly made up of Fe- and Mn-rich sediments, crusts and nodules. Several rock samples of Marsili volcanic activity were collected during dredging and coring projects. These rocks are lavas, pillows and dikes with a calc–alkaline affinity and ranging in composition from basalt to andesite to trachy-andesite. Some tephra layers were also sampled at the top of the volcano showing shoshonitic to latitic bulk compositions and variable amounts of crystals. Importantly, isotopic ratios of noble gases extracted from selected solid samples have provided novel constrains on the Marsili magmatism. In November 2007 and July 2011, water-column studies were carried out aboard of the R/V Urania and Astrea. Isotope analyses of the gases dissolved in water samples collected at the top the Marsili have evidenced that the He/4He isotope ratio, i.e. a clear indicator of hydrothermal input, is in excess with respect to the background and it is also associated with the anomalous behaviour of hydrothermal-derived gases (CO2, CO, CH4). Although some hydrothermal emissions are known to occur offshore the Aeolian subaerial volcanoes, results from our isotope analyses are the first to confirm the hydrothermal activity of Marsili. The highest 3He values were measured over the shallowest part of the seamount, where hydroxide deposits were found. The chemical composition of the dissolved gases clearly shows the presence of CO2 and CH4 over a wide water column depth range. The same anomalies were found in 2007 and 2011, depicting the presence of a persistent plume related to the deep hydrothermal activity of Marsili. A high heat flow (250 mW/m2) is measured at the uppermost portion of the volcano, reaching the maximum value (500 mW/m2) in the central parts. It coincides with gravity and magnetic anomalies, suggesting the presence of magmatic bodies intruding within shallow and thinned crustal levels. Although direct thermal measurements on the Marsili seamount are still lacking, our results give important constraints on the submarine volcanic and hydrothermal activity. Moreover, they support an ongoing project (carried out by Eurobuilding SpA company on the Italian Minister of Economic Development permission) aimed to drill the first offshore geothermal well at the top of the seamount that may potentially represent one of the most abundant energy resources worldwide; this mainly in response to the large amount and virtually infinite recharge of the circulating fluids. To conclude, it is worth noting that besides the scientific information concerning the geothermal activity, the technologies available at the present time will permit on-site geothermal exploitation and 68 production of electric energy (~1 GW) from a seamount located at ~100 km far from the Italian coasts.

Description: Unpublished

Description: La Jolla, California, USA

Description: 2.4. TTC - Laboratori di geochimica dei fluidi

Description: restricted

Description: This article has been accepted for publication in Geophysical Journal Internationa ©: The Authors 2017. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Uploaded in accordance with the publisher's self-archiving policy.

Description: Thermal gradients due to magma dynamics in active volcanic areas may affect the emanating power of the substrate and the background level of radon signal. This is particularly effective in subvolcanic substrates where intense hydrothermal alteration and/or weathering processes generally form hydrous minerals, such as zeolites able to store and release great amounts of H2O(up to ∼ 25 wt.%) at relative low temperatures. To better understand the role played by thermally induced devolatilization reactions on the radon signal, a new experimental setup has been developed for measuring in real time the radon emission from a zeolitized volcanic tuff. Progressive dehydration phenomena with increasing temperature produce radon emissions two orders of magnitude higher than those measured during rock deformation, microfracturing and failure. In this framework, mineral devolatilization reactions can contribute significantly to produce radon emissions spatially heterogeneous and non-stationary in time, resulting in a transient state dictated by temperature gradients and the carrier effects of subsurface gases. Results from these experiments can be extrapolated to the temporal and spatial scales of magmatic processes, where the ascent of small magma batches from depth causes volatile release due to dehydration phenomena that increase the radon signal from the degassing host rock material

Description: Published

Description: 558-571

Description: 3V. Proprietà dei magmi e dei prodotti vulcanici

Description: 6A. Geochimica per l'ambiente

Description: JCR Journal