Description: Hydrothermal experiments were conducted at ca. 1 to 7000 bars and 700 to 1250 °C in 121 rhyolitic to basaltic systems to determine Cl solubility in silicate melts, i.e., the maximum Cl concentration in melts that are saturated in a hydrosaline liquid with or without an aqueous or aqueous-carbonic vapor. The Cl concentration of melts increases with the Cl contents of the fluid unless the melt coexists with vapor plus hydrosaline liquid at fixed pressure and temperature; this phase assemblage buffers the Cl content of each phase with increasing Cl in the system. The Cl content of fluid(s)-saturated melts is independent of the CO 2 concentration of the saline liquid ± vapor with up to 21 wt% CO 2 in the fluid(s). The experiments show that Cl dissolution in aluminosilicate melts increases with temperature and pressure. Chlorine solubility is also a function of melt composition; it increases with the molar ([Al 1/2 +Ca 1/2 +Mg 1/2 +Na]/Si) of the melt. These experimental data have been integrated with results involving 41 other experiments ( Webster and De Vivo 2002 ) to develop a broadly expanded model that supports calculation of Cl solubility in 163 aluminosilicate melts. This empirical model applies to Cl dissolution in melts of most silicate magmas at depths as great as 25 km. It determines the exsolution of hydrosaline liquid, with or without a coexisting vapor, as magmas ascend from depth, cool, crystallize, and differentiate from mafic to felsic compositions. In combination with H 2 O solubility models, our model supports determination of H 2 O-Cl solubility relations for most aluminosilicate magmas and is useful for barometric estimations based on silicate melt inclusions containing low CO 2 and moderate to high-Cl concentrations. The model is applied to the phase relations of fluids in volatile-enriched magmas of Augustine volcano, Alaska. The Cl and H 2 O concentrations of melt inclusions from 14, basaltic to dacitic eruptive units are compared with modeled solubilities of Cl and H 2 O in Augustine melts. The majority of these eruptions involved magmas that first exsolved aqueous to aqueous-carbonic vapors when the melts were dacitic in composition (i.e., before the residual melts in these magmas had evolved to felsic compositions) and well prior to the eruptions. Hydrosaline liquid with or without a vapor phase exsolved from other, more-felsic fractions of Augustine melts at low, near-surface pressures of several tens of bars.

Description: This paper describes the design and the performance of the timing detector developed by the TOTEM Collaboration for the Roman Pots (RPs) to measure the Time-Of-Flight (TOF) of the protons produced in central diffractive interactions at the LHC . The measurement of the TOF of the protons allows the determination of the longitudinal position of the proton interaction vertex and its association with one of the vertices reconstructed by the CMS detectors. The TOF detector is based on single crystal Chemical Vapor Deposition (scCVD) diamond plates and is designed to measure the protons TOF with about 50 ps time precision. This upgrade to the TOTEM apparatus will be used in the LHC run 2 and will tag the central diffractive events up to an interaction pileup of about 1. A dedicated fast and low noise electronics for the signal amplification has been developed. The digitization of the diamond signal is performed by sampling the waveform. After introducin...

Description: The solubility of H2O-CO2 fluids in a synthetic analogue of a phono-tephritic lava composition from Alban Hills (Central Italy) was experimentally determined from 50 to 500 MPa and 1200 and 1250°C. H2O and CO2 contents in experimental glasses were determined by bulk analytical methods and FTIR spectroscopy. For the quantification of volatile concentrations by IR spectroscopy we have calibrated the absorption coefficients of water-related and carbon-related bands for phono-tephritic compositions. The determined absorption coefficients are 0.62 ± 0.06 L mol-1cm-1 for the band at ~4500 cm-1 (OH groups) and 1.02 ± 0.03 L mol-1cm-1 for the band at ~5200 cm-1 (H2O molecules). The coefficient for the fundamental OH stretching vibration at 3550 cm-1 is 63.9 ± 5.4 L mol-1cm-1. CO2 is bound in the phono-tephritic glass as CO32- exclusively; its concentration was quantified by the peak height of the doublet near the 1500 cm-1 band with the calibrated absorption coefficient of 308 ± 110 L mol-1cm-1. 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. H2O solubility in the ultrapotassic melts (7.52 wt% K2O) 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°C, the CO2 capacity of the phono-tephritic melt is about 0.82 wt%. The high CO2 capacity is probably related to the high K2O content of the melt. At both 200 and 500 MPa, the H2O solubility shows a non linear dependence on XfH2O in the whole XfH2O range. The variation of CO2 solubility with XfCO2 displays a pronounced convex shape in particular at 500 MPa, implying that dissolved H2O promotes the solubility of CO2. Our experimental data on CO2 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 CO2 from limestone into the magma. However, although the CO2 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 〈 1 wt% at the P-T conditions of the magma chamber below Alban Hills.

Description: Published

Description: 105–120

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

Description: JCR Journal

Description: reserved

Description: Plagioclase crystal size distribution (CSD) has been investigated in a quartz-diorite body, in the leucosome of migmatites and in the melanosome of un-melted contact metamorphic rocks from Gennargentu Complex (Sardinia, Italy). During the crystallization of the dioritic magma, a variety of competing kinetic processes determine the evolution of the igneous microstructure, but the relative contribution of each process remains elusive. Our approach was aimed to study the plagioclase crystallization from a liquid (quartz-diorites and migmatite leucosomes), comparing it to a crystallization at subsolidus conditions. CSD indicates that plagioclase in the quartz-diorite nucleated and grew in a cooling system at a constant cooling rate, producing straight-line CSD in a diagram of ln of population density vs. size range. The plagioclase crystallization continued until the latent heat was available and the temperature was high enough to allow the plagioclase growing. This can occur only when a crystal is held at temperature close to its liquidus for a long period of time. Under these conditions, the plagioclase nucleation rate is zero, but growth rate is high for crystal larger than the critical size. This does not necessarily mean that the temperature was held constant, just that the undercooling remained small (Ostwald ripening process). The aggregated small crystals, due to their high surface energy per unit volume, to minimise energy in the system dissolved and“fed” the growth of larger crystals. This process occurs because small grains have a higher surface energy per unit volume than do larger grains. The crystallization temperature (~900 °C, 100 MPa) allows the formation of plagioclase as liquidus phase. From CSD measurements we calculated the different cooling ages for the different sample types

Description: Published

Description: 401-418

Description: 4V. Vulcani e ambiente

Description: N/A or not JCR

Description: restricted

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 viscosity of shoshonitic melts from Vulcanello Peninsula (Vulcano Island, Italy) is experimentally determined at temperatures between 733 K and 1673 K. The water content of the melts varies from 0.03 to 4.75 wt% H2O. The micropenetration technique is employed at ambient pressure in the high viscosity range (109-1012 Pa·s). Falling sphere(s) experiments are performed at 500 and 2000 MPa in the low viscosity range (100.5-103 Pa·s). Results show a decrease of about 2 orders of magnitude in viscosity if ~ 3 wt% of water is added to the dry melt at 1300 K. At high temperature the viscosity of Vulcanello melts is intermediate between that of andesitic and basaltic melts. In contrast, at low temperatures (≤1050 K), the shoshonitic melt is characterized by a lower viscosity with respect to the two previous melts. Based on our new data set, a calculation model is proposed to predict the viscosity of the shoshonitic melts as a function of temperature and water content. The viscosity data are used to constrain the ascent velocity of shoshonitic magmas from Vulcanello within dikes. Using petrological data (temperature and crystal content of the magma) and volcanological information (geometrical parameters of the eruptive fissure and depth of magma storage), we estimate the time scale for the ascent of magma from the main reservoir to the surface. Results show time scales in the order of hours to few days. We conclude that the rapid ascent of poorly evolved melts from Moho depths should be taken into account for the hazard assessment of Vulcano Island.

Description: Published

Description: 89-102

Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce

Description: JCR Journal

Description: open

Description: Viscosities of shoshonitic and latitic melts, relevant to the Campi Flegrei caldera magmas, have been experimentally determined at atmospheric pressure and 0.5 GPa, temperatures between 840 K and 1870 K, and H2O contents from 0.02 to 3.30 wt%. The concentric cylinder technique was employed at atmospheric pressure to determine viscosity of nominally anhydrous melts in the viscosity range of 101.5 - 103 Pa·s. The micropenetration technique was used to determine the viscosity of hydrous and anhydrous melts at atmospheric pressure in the high viscosity range (1010 Pa·s). Falling sphere experiments were performed at 0.5 GPa in the low viscosity range (from 100.35 to 102.79 Pa·s) in order to obtain viscosity data of anhydrous and hydrous melts. The combination of data obtained from the three different techniques adopted permits a general description of viscosity as a function of temperature and water content using the following modified VFT equation: where η is the viscosity in Pa·s, T the temperature in K, w the H2O content in wt%, and a, b, c, d, e, g are the VFT parameters. This model reproduces the experimental data (95 measurements) with a 1σ standard deviation of 0.19 and 0.22 log units for shoshonite and latite, respectively. The proposed model has been applied also to a more evolved composition (trachyte) from the same area in order to create a general model applicable to the whole compositional range of Campi Flegrei products. Moreover, speed data have been used to constrain the ascent velocity of latitic, shoshonitic, and trachytic melts within dikes. Using petrological data and volcanological information (geometrical parameters of the eruptive fissure and depth of magma storage), we estimate a time scale for the ascent of melt from 9 km to 4 km depth (where deep and shallow reservoirs, respectively, are located) in the order of few minutes. Such a rapid ascent should be taken into account for the hazard assessment in the Campi Flegrei area.

Description: Published

Description: 50-59

Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce

Description: JCR Journal

Description: open

Description: The viscosity of an iron-bearing melt with composition similar to Unzen andesite was determined experimentally in the high (109-1010.5 Pa·s) and low (5-1000 Pa·s) viscosity range using a parallel plate viscometer and the falling sphere method, respectively. Falling sphere experiments were carried out in an internally heated argon pressure vessel and in a piston cylinder apparatus at 1323 to 1573 K and 200 to 2000 MPa. Creep experiments were performed in the temperature range of 747 - 845 K at 300 MPa. The water content of the melt varies from nominally dry to 6.2 wt% H2O. The Fe2+/Fetot ratio was determined for each sample in the quenched glass using a colorimetric method. Pressure has minor influence on the viscosity compared with the effect of temperature, water content (main compositional parameter controlling the viscosity) or with the Fe2+/Fetot ratio (especially important at low water content of the melt). Based on our new viscosity data and literature data with measured Fe2+/Fetot ratio we propose a new empirical equation to estimate the viscosity η (in Pa·s) of andesitic melts as a function of temperature T (in K), water content w (in wt%) and Fe2+/Fetot ratio. The derived relationship reproduces the experimental data (87 in total) in the viscosity range from 100.5 to 1013 Pa·s with a 1σ standard deviation of 0.17 log units. However, application of this calculation model is limited to Fe2+/Fetot〉0.3 and to temperatures above Tg. Moreover, in the high viscosity range the variation of viscosity with water content is constrained only by few experimental data and needs verification by additional measurements. The viscosity data are used to interpret mixing processes in the Unzen magma chamber prior to 1991-1995 eruption. We demonstrate that the viscosities of the rhyolite and andesite melts from the two end-member magmas are nearly identical prior and during mixing, enabling efficient magma mixing.

Description: Published

Description: 208-217

Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce

Description: JCR Journal

Description: open

Description: The 5th April 2003 paroxysmal event was the strongest explosion that has occurred at Stromboli in the last 50 years. This event lasted only few minutes and was characterised by two violent explosions, followed by gas and pyroclast emission. In order to constrain models of the dynamics of the paroxystic event the viscosity of anhydrous and hydrous Stromboli high potassium (HK)-basaltic melts have been measured. Viscosity has been investigated in the low viscosity range with the falling sphere method at superliquidus temperatures (1423 to 1673 K) and 0.5 GPa and in the high viscosity range with micropenetration near the glass transition temperature (723 to 1035 K) at atmospheric pressure. Falling sphere experiments were performed in a piston cylinder apparatus with melts whose water content varies from nominally anhydrous (0.02 wt.% H2O) to 4.16 wt.% H2O. The combination of high- and low-viscosity data permits a general description of the viscosity as a function of temperature and water contentusing a modified Tamman–Vogel–Fulcher equation. Using these new viscosity data, an estimation of the flow regime and magma velocity is performed. Our data suggest that the ascent of magma from the 7–8 km deep reservoir to a shallower reservoir located at about 3 km of depth, may occur within minutes. Moreover, we infer a turbulent flow regime. Finally, our estimates of the ascent velocity agree qualitatively with results from petrological studies (e.g. [Bertagnini, A., Métrich, N., Landi, P., Rosi, M., 2003. Stromboli volcano (Aeolian Archipelago, Italy): an openwindowon the deep-feeding system of a steady state basaltic volcano. Journal of Geophysical Research 108, 2336–2350.]), which indicate a turbulent flow regime and rapid ascent velocities such to inhibit volatile-loss-induced crystallization.We conclude that hazard evaluation at Stromboli Island should incorporate the likelihood of very rapid ascent of less-evolved melts from depth.

Description: Published

Description: 278-285

Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce

Description: JCR Journal

Description: reserved

Description: been experimentally quantified via cooling-induced solidification approach. GFA is measured by the critical cooling rate Rc, the rate at which a melt solidifies ≤2 area% of crystals. Cooling rates of 9000, 1800, 180, 60, 7 and 1 °C/h have been run between 1300 °C (super-liquidus region) and 800 °C (quenching temperature), at air fO2 and ambient P for six silicate melts with compositions ranging from basalt (B) to rhyolite (R) (i.e., B100, B80R20, B60R40, B40R60, B20R80 and R100) and water contents comprised between 53 (B100) and 384 (B20R80) ppm. The ranges of cooling rates and chemical compositions used in this study are the broadest ever investigated in the Earth sciences. The phase proportions (area%) were determined by image analysis on about 500 back-scattered electron images collected over different magnifications. Phases are glass, clinopyroxene (cpx), spinel (sp) and plagioclase (plg). Sp is ubiquitous with abundance of few area% and nucleates earlier than silicate crystals. Cpx solidifies in all runs except in R100 and its abundance follows asymmetric broad Gaussian-like trends (with tails towards low rates) as a function of cooling rate. Moving from B100 to B40R60 these trends conserve their shape but shift progressively to lower cooling rates and mineral abundances. Plg crystallises only at low cooling rates and in SiO2-poor compositions. Run-products with low amounts of crystals (≤5 area%) clearly show that cpx preferentially nucleates on surfaces of sp, whereas a significant crystallisation of cpx (N5 area%) is observed with decreasing cooling rate and with changing composition from B100 to B20R80. The crystallisation of silicate crystals is related to the chemical diffusivity of components in the melt. Also the initial crystallisation of plg occurs preferentially on cpx. In general, the amount of crystals decreases as the cooling rate increases; however, in some cases, the amount of crystals remains constant or even decreases for B80R20 with decreasing cooling rate. Rc values change over 5 orders of magnitude being b1, 7, 620, 3020, 8020 and 9000 °C/h for R100, B20R80, B40R60, B60R40 and B80R20 and B100, respectively. The variation of Rc can be modelled through NBO/T (nonbridging oxygen per tetrahedron) parameter by the following equation: Rc=a / {1+e−[(NBO/T − b)/c]},where a, b and c are fitting parameters equal to 9214, 0.297 and 0.040, respectively. Similarly to other glass-forming liquids (network, metallic and molecular systems), Rc for natural sub-alkaline silicate melts is inversely related to the reduced glass transition parameter Trg (Trg=Tg / Tm) and can be quantified with the equation Rc= a × Trg−b, where a and b are 1.19 × 10−4 and 28.7, respectively. These results may be used to retrieve the solidification conditions of aphyric, degassed and oxidised lavas; in addition, our data provide general constrains on the crystallisation kinetics of natural crystal-bearing silicate melts erupted on Earth (e.g. lavas with phenocrysts). The relationship between crystal content and cooling rate suggests that the solidification path induced by degassing can be also complex and nonlinear. The growth of crystalswith size up to 1 mm from a nearly anhydrous superheated silicate melt indicates that variable cooling conditions of lavas have to be accounted to discriminate amongminerals formed before, during and after eruptions.Moreover, our results can be used to design glass-ceramics from naturally available easy to find, low-cost starting materials.

Description: Published

Description: 25-44

Description: 4V. Vulcani e ambiente

Description: JCR Journal

Description: restricted