2O Content Research Articles

Transition from shoshonitic to adakitic magmatism in the eastern Pontides, NE Turkey: Implications for slab window melting

The formation of the eastern Pontides orogenic belt has been widely assigned to a northward subduction of the Neotethyan oceanic slab during the late Mesozoic–Cenozoic. Here we provide an alternate model based on new geological, geochemical and isotopic data. The magmatic activity in the far south of the belt started in the early Campanian with shoshonitic trachyandesites and associated pyroclastics. This sequence is covered by the late Campanian–early Maastrichtian reefal limestones and another stage of high-K volcanism represented by analcimized leucite-rich ultrapotassic rocks of the Maastrichtian–early Paleocene (?) ages. The shoshonitic and ultrapotassic rocks, with K 2O contents ranging from 0.26 to 6.95 wt.%, display broadly similar rare earth and multi-element distribution patterns. Both rock types are enriched in LILE and LREE and depleted in HFSE (Nb, Ta and Ti), suggesting a subduction-enriched mantle source for the magma generation. Subsequently, during the late Paleocene, a stage of acidic magmatism (SiO 2 of 53.25–73.61 wt.%) that shows adakitic geochemical characteristics including high Sr/Y (46–416) and La/Yb (11–51) and low Y (2.6–12.2 ppm), is documented characterized by melting of a mafic source such as the MORB crust with garnet in the residue. The adakitic magmatism began at ~ 56 Ma and migrated toward the north through time, culminating with porphyritic andesites (~ 47 Ma) that were emplaced in the Gumushane–Bayburt line and its vicinity. North of this line, coeval magmas show typical calc-alkaline nature and continued to develop toward further north until the middle to late Eocene. Based on the spatial and temporal variations in the magmas generated in the eastern Pontides orogenic belt, we propose a new geodynamic model to explain the tectonomagmatic evolution of these rocks and correlate the adakitic magmatism to ridge subduction and slab window process within a south-dipping subduction zone. Our model is in contrast to the previous proposals which envisage partial melting or delamination of thickened lower continental crust due to the collision in the south during the Paleocene–Eocene.

The early Jurassic mafic–ultramafic intrusion and A-type granite from northeastern Guangdong, SE China: Age, origin, and tectonic significance

The early Yanshanian geology of Southeastern (SE) China is characterized by widespread igneous rocks consisting predominantly of granites and rhyolites, and subordinate mafic intrusive and volcanic rocks. However, the onset time, petrogenesis, and tectonic implications of the early Jurassic magmatism in SE China remain highly controversial. We report here zircon U–Pb ages, geochemistry, and Nd–Sr isotopic data for the Fe–Ti–V oxide-bearing Xianlan mafic–ultramafic intrusion and the Wengong granitic pluton in northeast Guangdong. SHRIMP and Cameca SIMS U–Pb zircon ages indicate that the Xialan gabbros and the Wengong granites were emplaced at 194 ± 1 Ma and 192 ± 1 Ma, respectively. Although the field observations show that the granitic pluton intruded the mafic–ultramafic intrusion, the dating results suggest that they were formed almost contemporaneously. The ore-barren gabbros of the Xialan intrusion are commonly high in Fe 2O 3, CaO and Al 2O 3 contents, with variable SiO 2, TiO 2, and MgO contents. In contrast, the Fe–Ti–V-bearing gabbros have higher Fe 2O 3, TiO 2 (3.5–5.4%) and V contents. These gabbros with high ε Nd(T) values (+ 1.7 to + 6.2) and low initial I Sr values (0.704 to 0.706), are characterized by LREE-enriched and “convex upwards” incompatible trace-element patterns with slightly negative Nb–Ta anomalies. The parental magma for the gabbros exhibits affinity with a high-Ti subalkaline basaltic magma generated by melting of a depleted OIB-like mantle source. We suggest that the gabbros originated by fractional crystallization of the parental magma plus varying degrees of crustal contamination. The Wengong granites have high SiO 2 and (Na 2O + K 2O) contents, are LREE-enriched and show relatively flat-HREE patterns and significantly negative Eu, Nb, Sr, P and Ti anomalies in the primitive mantle-normalized spidergrams. These granitic rocks display geochemical characteristics of A 2-type granites including high FeO T/MgO ratios (7.6–14.7), elevated high-field-strength element (HFSE) contents, and high Ga/Al ratios (2.75–3.49). The Wengong granites exhibit variably initial ε Nd(T) values ranging from − 2.8 to + 1.2, whereas the initial I Sr values show large uncertainties due to relatively high Rb/Sr ratios. The parental magma for these rocks exhibits affinity with a mildly alkaline magma, which was probably generated by partial melting of the regional Paleoproterozoic amphibolites and thereafter mixed with various amounts of the early Jurassic basaltic magmas. The granites were then formed by extensive crystal fractionation of the mildly alkaline magma. The Xialan mafic–ultramafic intrusion and the Wengong granitic pluton were formed in an anorogenic extensional environment. It is therefore suggested that ca. 194 Ma is an important onset timing of widespread anorogenic magmatism in SE China. We interpret the early Jurassic mafic–ultramafic intrusion and A-type granites to represent an anorogenic magmatism in response to an onset of asthenospheric mantle upwelling due to the break-up of a subducted flat-slab beneath the SE China continent.

The effect of tetrahedral Al 3+ on the partitioning of water between clinopyroxene and silicate melt

This experimental study examines the influence of tetrahedrally coordinated Al 3+ ( IVAl 3+) on the partitioning of H + between high-Ca clinopyroxene and silicate melt. Experiments were carried out at 1.5 GPa and 1275 to 1350 °C on a natural high-alumina basalt and a compositionally similar synthetic basalt that is nominally alumina free. The results extend the compositional range of clinopyroxene for which partitioning has been determined experimentally to both higher and lower IVAl 3+, thereby clarifying its role in maintaining charge neutrality during H + incorporation. Clinopyroxene-melt partition coefficients for H + ( D H 2 O Cpx − Melt ) determined for the high-alumina basalt are among largest ever reported ( D H 2 O Cpx − Melt = 0.0228 to 0.0477), while those determined for the nominally alumina-free starting composition are the smallest ( D H 2 O Cpx − Melt = 0.00445 to 0.0071). Our results confirm that H + is incorporated into clinopyroxene through two independent mechanisms: (1) the creation of metal vacancies and coupled hydroxyl defects and (2) a coupled substitution involving IVAl 3+ that creates isolated hydroxyl defects. The relative importance of each of these incorporation mechanisms was quantified by formulating D H 2 O Cpx − Melt as the sum of a metal vacancy-related partition coefficient ( D H 2 O V Me ) and an Al-coupled substitution-related partition coefficient ( D H 2 O Al ) and fitting the resulting expression to all available experimental data. The contribution of D H 2 O V Me to D H 2 O Cpx − Melt is relatively constant at 0.006 ± 0.002, but is sensitive to pressure, temperature, H 2O fugacity and pyroxene composition. The contribution of D H 2 O Al varies from ∼ 0 to 0.038 and is strongly dependent on phase composition, but insensitive to pressure and temperature. Two parameterizations of D H 2 O Cpx − Melt that account for the potential effects of temperature, pressure and phase composition were calibrated using our data and experimentally determined partition coefficients from the literature. The first parameterization considers only compositional effects and can be used to estimate D H 2 O Cpx − Melt in cases where pressure and/or temperature are unknown. This equation was used to demonstrate that the pre-eruptive H 2O contents of arc lavas calculated on the basis of H + in clinopyroxene phenocrysts are systematically higher than those inferred from olivine-hosted melt inclusions, so that the former provide a record that is closer to primary (undegassed) values. The second parameterization considers the effects of pressure and temperature in addition to phase composition and provides a moderately better fit to the experimental data. This equation was used to re-evaluate the influence of H 2O on the depth at which peridotite partial melting begins beneath oceanic spreading centers. Our calculations indicate that partial melting begins at depths that are shallower than suggested by previous estimates. For a potential temperature of 1350 °C, peridotite containing 50, 100, 150, and 200 ppm H 2O dissolved in nominally anhydrous minerals begins melting at depths of 75, 79, 83, and 87 km, respectively.

Spectroscopic analysis (FTIR, Raman) of water in mafic and intermediate glasses and glass inclusions

Micro-Raman spectroscopy, even though a very promising technique, is not still routinely applied to analyse H 2O in silicate glasses. The accuracy of Raman water determinations critically depends on the capability to predict and take into account both the matrix effects (bulk glass composition) and the analytical conditions on band intensities. On the other hand, micro-Fourier transform infrared spectroscopy is commonly used to measure the hydrous absorbing species (e.g., hydroxyl OH − and molecular H 2O) in natural glasses, but requires critical assumptions for the study of crystal-hosted glasses. Here, we quantify for the first time the matrix effect of Raman external calibration procedures for the quantification of the total H 2O content (H 2O T = OH − + H 2O m) in natural silicate glasses. The procedures are based on the calibration of either the absolute (external calibration) or scaled (parameterisation) intensity of the 3550 cm −1 band. A total of 67 mafic (basanite, basalt) and intermediate (andesite) glasses hosted in olivines, having between 0.2 and 4.8 wt% of H 2O, was analysed. Our new dataset demonstrates, for given water content, the height (intensity) of Raman H 2O T band depends on glass density, reflectance and water environment. Hence this matrix effect must be considered in the quantification of H 2O by Raman spectroscopy irrespective of the procedure, whereas the parameterisation mainly helps to predict and verify the self-consistency of the Raman results. In addition, to validate the capability of the micro-Raman to accurately determine the H 2O content of multicomponent aluminosilicate glasses, a subset of 23 glasses was analysed by both micro-Raman and micro-FTIR spectroscopy using the band at 3550 cm −1. We provide new FTIR absorptivity coefficients ( ε 3550) for basalt (62.80 ± 0.8 L mol −1 cm −1) and basanite (43.96 ± 0.6 L mol −1 cm −1). These values, together with an exhaustive review of literature data, confirm the non-linear decline of the FTIR absorptivity coefficient ( ε 3550) as the glass depolymerisation increases. We demonstrate the good agreement between micro-FTIR and micro-Raman determination of H 2O in silicate glasses when the matrix effects are properly considered.

Mantle Melting as a Function of Water Content beneath the Mariana Arc

Subduction zone magmas are characterized by high concentrations of pre-eruptive H_2O, presumably as a result of an H_2Oflux originating from the dehydrating, subducting slab. The extent of mantle melting increases as a function of increasing water content beneath back-arc basins and is predicted to increase in a similar manner beneath arc volcanoes. Here, we present new data for olivine-hosted, basaltic melt inclusions from the Mariana arc that reveal pre-eruptive H_2O contents of ~1•5-6•0 wt %, which are up to three times higher than concentrations reported for the Mariana Trough back-arc basin. Major element systematics of arc and back-arc basin basalts indicate that the back-arc basin melting regime does not simply mix with wet, arc-derived melts to produce the observed range of back-arc magmatic H_2O concentrations. Simple melting models reveal that the trend of increasing extents of melting with increasing H_2O concentrations of the mantle source identified in the Mariana Trough generally extends beneath the Mariana volcanic front to higher mantle water contents and higher extents of melting. In detail, however, each Mariana volcano may define a distinct relationship between extent of melting and the H_2O content of the mantle source. We develop a revised parameterization of hydrous melting, incorporating terms for variable pressure and mantle fertility, to describe the distinct relationships shown by each arc volcano. This model is used in combination with thermobarometry constraints to show that hydrous melts equilibrate at greater depths (34-87 km) and temperatures (>1300°C) beneath the Mariana arc than beneath the back-arc basin (21-37 km), although both magma types can form from a mantle of similar potential temperature (~1350°C).The difference lies in where the melts form and equilibrate. Arc melts are dominated by those that equilibrate within the hot core of the mantle wedge, whereas back-arc melts are dominated by those that equilibrate within the shallow zone of decompression melting beneath the spreading center. Despite higher absolute melting temperatures (>1300°C), Mariana arc melts reflect lower melt productivity as a result of wet melting conditions and a more refractory mantle source.

Investigation on elemental mercury oxidation mechanism by non-thermal plasma treatment

Converting elemental mercury into divalent compound is one of the most important steps for mercury abatement from coal fired flue gas. The oxidation of elemental mercury was investigated in this paper using dielectric barrier discharge (DBD) non-thermal plasma (NTP) technology at room temperature. Effects of different flue gas components like oxygen, moisture, HCl, NO and SO 2 were investigated. Results indicate that active radicals including O, O 3 and OH all contribute to the oxidation of elemental mercury. Under the conditions of 5% O 2 in the simulated flue gas, about 90.2% of Hg 0 was observed to be oxidized at 3.68 kV discharge voltage. The increase of discharge voltage, O 2 level and H 2O content can all improve the oxidation rate, individually. With O 2 and H 2O both existed, there is an optimal moisture level for the mercury oxidation during the NTP treatment. In this test, the observed optimal moisture level was around 0.74% by volume. Hydrogen chloride can promote the oxidation of mercury due to chlorine atoms produced in the plasma process. Both NO and SO 2 have inhibitory effects on mercury oxidation, which can be attributed to their competitive consumption of O 3 and O.

The effect of solvent ratio and water on the growth of C 60 nanowhiskers

The growth of C 60 nanowhiskers (C 60NWs) prepared by a modified liquid–liquid interfacial precipitation method is investigated, focusing on the effect of solvent ratio and water content in the C 60–toluene–isopropyl alcohol (IPA) solution system. The precipitation of C 60NWs was markedly influenced by the solvent ratio of toluene to IPA, and the C 60NWs were found to grow longer above a critical diameter ( D c), which depends on the solvent ratio. The addition of a small amount of H 2O to the C 60–toluene–IPA solution promoted the growth of C 60NWs. This catalytic effect of water on the growth of C 60NWs was confirmed also by the experiment using heavy water (D 2O) and by the decrease of growth activation energy of C 60NWs with increase of H 2O content in the C 60–toluene–IPA solution.

Effect of oxygen fugacity on the H 2O storage capacity of forsterite in the carbon-saturated systems

High pressure experiments have been performed in the systems Mg 2SiO 4–C–O–H and Mg 2SiO 4–K 2CO 3–C at 6.3 GPa and 1200 to 1600 °C using a split-sphere multi-anvil apparatus. In the Mg 2SiO 4–C–O–H system the composition of fluid was modeled by adding different amounts of water and stearic acid. The fO 2 was controlled by the Mo–MoO 2 or Fe–FeO oxygen buffers. Several experiments in the Mg 2SiO 4–C–O–H system and all experiments in the Mg 2SiO 4–K 2CO 3–C system have been conducted without buffering the fO 2. Forsterite in the system Mg 2SiO 4–K 2CO 3–C does not reveal OH absorption bands in the IR spectra, while forsterite coexisting with carbon-bearing fluid and silicate melt at log fO 2 from FMQ-2 to FMQ-5 (from 2 to 5 log units below fayalite-magnetite-quartz oxygen buffer) contains 800–1850 wt. ppm H 2O. The maximum concentrations were detected at 1400 °C and FMQ-3.5. We observed an increase in the solidus temperature in the system Mg 2SiO 4–C–O–H from 1200 to above 1600 °C with log fO 2 decreasing from FMQ-2 to FMQ-5. The increase of the solidus temperature and the broadening of the stability field of the H 2O–H 2–CH 4 subsolidus fluid phase at 1400–1600 °C explain the high H 2O storage capacity of forsterite relative to that crystallized from carbon-free, oxidized, hydrous, silicic melt. At temperatures above 1400 °C liquidus forsterite precipitated along with diamond from oxidized (FMQ-1) carbonate–silicate melt and from silicate melt dissolving the moderately reduced C–O–H fluid (from FMQ-2 to FMQ-3.5). Formation of diamond was not detected under ultra-reduced conditions (FMQ-5) at 1200–1600 °C. Olivine co-precipitating with diamond from dry carbonate–silicate or hydrous–silicic fluid/melt can provide information on the H 2O contents and speciation of the diamond-forming media in the mantle. The conditions for minimum post-crystallization alteration of olivine and its hydrogen content are discussed.

The influence of Al 2O 3 on the H 2O content in periclase and ferropericlase at 25 GPa

In this paper I present results of IR spectroscopic measurements of water solubility in Al-bearing periclase and ferropericlase (Mg# = 88) synthesized at 25 GPa and 1400–2000 °C. The IR spectra of their crystals show narrow absorption peaks at 3299, 3308, and 3474 cm −1. The calculated H 2O contents are 11–25 ppm in periclase (Al 2O 3 = 0.9–1.2 wt.%) and 14–79 ppm in ferropericlase (Al 2O 3 = 0.9–2.9 wt.%). Ferropericlase contains more H 2O and Al 2O 3 than periclase at 1800–2000 °C. I suggest that addition of Al 2O 3 does not influence the solubility of water in ferropericlase but can favor the additional incorporation of Fe 2O 3 into the structure. The incorporation of Fe 3+ into ferropericlase increases water solubility as a result of iron reduction to Fe 2+. It is shown that water has limited solubility in ferropericlase from mantle peridotite; therefore, ferropericlase cannot be considered an important hydrogen-bearing mineral in the lower mantle.

Electrical conductivity anisotropy of dry and hydrous olivine at 8 GPa

The effects of dissolved H 2O on the electrical conductivity and its anisotropy in olivine (Fo 90) at 8 GPa were investigated by complex impedance spectroscopy. At nominally anhydrous conditions, conduction along [1 0 0] and [0 0 1] is slightly higher than along [0 1 0] in contrast to observations made at lower pressures in earlier studies. Increasing H 2O content increases conductivities but activation energies are lower and H 2O concentration dependent. The use of polarized FTIR spectroscopy to determine H 2O concentrations reveals a weaker than expected effect that water has on olivine conductivity and distinguishes our results from earlier studies based on analyses using non-polarized infrared spectroscopy. We show that at H 2O concentrations of a few hundred wt ppm or less, that the dominant conduction mechanism at mantle temperatures continues via small polarons, such as that observed for anhydrous olivine. Our results also suggest that at depths greater than 200 km, the presence of H 2O may not be necessary to explain regions in the upper mantle where both electrical and seismic anisotropy are observed. This can be explained by differences in the pressure dependence of the activation energy for conduction along each of the three crystallographic axes. However, while electrical anisotropy of anhydrous olivine remains weak at 8 GPa, it is nevertheless enhanced by elevated concentrations (>several hundred wt ppm) of dissolved H 2O. At these conditions dominated by proton hopping, conductivity along [0 1 0] is highest, approximately an order of magnitude greater than along [1 0 0]. Additionally, at 1000 wt ppm and 1500 °C, an isotropic conductivity derived from the data is about 1 order of magnitude higher than that for nominally anhydrous olivine. Thus, in regions of the mantle characterized by anomalously high conductivities and both electrical and seismic anisotropy, significant amounts of dissolved hydrogen can be expected.

Effect of Al 2O 3 and K 2O content on structure, properties and devitrification of glasses in the Li 2O–SiO 2 system

The effect of Al 2O 3 and K 2O content on structure, sintering and devitrification behaviour of glasses in the Li 2O–SiO 2 system along with the properties of the resultant glass–ceramics (GCs) was investigated. Glasses containing Al 2O 3 and K 2O and featuring SiO 2/Li 2O molar ratios (3.13–4.88) far beyond that of lithium disilicate (Li 2Si 2O 5) stoichiometry were produced by conventional melt-quenching technique along with a bicomponent glass with a composition 23Li 2O–77SiO 2 (mol.%) (L 23S 77). The GCs were produced through two different methods: (a) nucleation and crystallization of monolithic bulk glass, (b) sintering and crystallization of glass powder compacts. Scanning electron microscopy (SEM) examination of as cast non-annealed monolithic glasses revealed precipitation of nanosize droplet phase in glassy matrices suggesting the occurrence of phase separation in all investigated compositions. The extent of segregation, as judged from the mean droplet diameter and the packing density of droplet phase, decreased with increasing Al 2O 3 and K 2O content in the glasses. The crystallization of glasses richer in Al 2O 3 and K 2O was dominated by surface nucleation leading to crystallization of lithium metasilicate (Li 2SiO 3) within the temperature range of 550–900 °C. On the other hand, the glass with lowest amount of Al 2O 3 and K 2O and glass L 23S 77 were prone to volume nucleation and crystallization, resulting in formation of Li 2Si 2O 5 within the temperature interval of 650–800 °C. Sintering and crystallization behaviour of glass powders was followed by hot stage microscopy (HSM) and differential thermal analysis (DTA), respectively. GCs from composition L 23S 77 demonstrated high fragility along with low flexural strength and density. The addition of Al 2O 3 and K 2O to Li 2O–SiO 2 system resulted in improved densification and mechanical strength.

Thermoluminescence of B 2O 3–Li 2O glass system doped with MgO

Lithium borate (LiB) glasses in the system (100− x)B 2O 3– xLi 2O with x=20, 30, 40, 50, 60 and 70 mol% were prepared. The glasses were doped with different concentrations of the order of 10 −1, 10 −2, 10 −3, 10 −4 and 10 −5 of MgO and their thermoluminescent (TL) response was investigated. The irradiations were performed using γ rays from a 60Co source in the dose range from 0.1 to 25 kGy. The material displayed good sensitivity for γ-rays and intensity of TL signals is dependent on γ-ray dose and Li 2O content. For each dose level and investigated temperature range (50–350 °C), exactly single isolated glow peak appears in the temperature range of 165–205 °C depending on both Li 2O concentrations and time of exposure. The shape of the glow peak has altered significantly with increase in the gamma ray dose or Li 2O concentrations. The glass composition with x=50 mol% doped with 10 −3 mol% of MgO presented the best TL response. The results of the present study indicated that the recorded single and isolated high temperature peak is a good candidate for TL dosimetric investigations. This indicates that 50 B 2O 3–50Li 2O-doped with 10 −3 mol% of MgO is possibly used as materials for radiation dosimetry in the dose range of 0.1–20 kGy.

Corrosion of reduced activation ferritic martensitic steel JLF-1 in purified Flinak at static and flowing conditions

Flinak (LiF–KF–NaF) has the potential to be a tritium breeder candidate for a self-cooled fusion blanket or a secondary heat-transfer fluid of the blanket system. Corrosion of the structural material in Flinak is one of its issues. A corrosion test for Reduced Activation Ferritic Martensitic (RAFM) steel, JLF-1 (Fe–9Cr–2W–0.1C), was performed at 600 °C using both purified and non-purified Flinak. The Flinak was purified by the electro-refining process, where Ni and H 2O content in the Flinak were decreased. The test was performed at static conditions and flowing conditions induced by an impeller. The results of the test in non-purified Flinak showed local corrosion on the steel surface at the grain, packet, block and lath boundaries. The corrosion of JLF-1 in purified Flinak was much less than that in the non-purified Flinak. The corrosion in these boundaries was not severe, though pitting corrosion by the local electro-circuit was partly detected. This is due to local impurity condensation either in the Flinak or on the surface. The corrosion loss in flowing condition was small, the same as that in the static conditions. The number of pitting corrosions on the surface for flowing conditions was less than that in the static test. The occurrence of pitting corrosion was controlled by the mixture and Flinak flow, in which the local impurity condensation was removed.

Pre-explosive conduit conditions of the 1997 Vulcanian explosions at Soufrière Hills Volcano, Montserrat: I. Pressure and vesicularity distributions

An authoritative case of Vulcanian eruptive dynamics is the series of 88 explosions that occurred between August and October 1997 at Soufrière Hills volcano on Montserrat Island. The state of the magmatic column just before a Vulcanian explosion is still poorly understood, but conditions the eruptive style. This study establishes such a pre-explosive stratigraphy by 1) documenting the textures covering the range of the 1997 products, 2) quantitative analysis of H 2O content in interstitial glass measured by Karl–Fischer Titration, and 3) combining these data with a simple model linking pre- and post-explosive vesicularities. The model shows that syn-explosive degassing affects greatly the way porosity evolves by decompression during an explosion. The stratigraphy reconstruction shows a three-part vertical layering of the conduit prior to explosion with overall denser values than those previously suggested. A dense and strongly degassed plug caps the column. It is underlain by a shallow transition zone featuring complex mingling between vesicular and dense magma up to 10 MPa. At higher pressure, up to 80 MPa, lies a more homogeneous zone of relatively dense (10–20 vol.%) magma, which was emplaced under partly open-system degassing. This conduit stratigraphy gives the vision of a strongly heterogeneous magma column immediately prior to its disruption. Our analysis suggests that fragmenting such a composite magma cannot happen in a single coherent pulse, but rather as stages. The transition zone contains heterogeneous amounts of exsolved gas that could explain the pulsatory nature of the Vulcanian jets at the beginning of the explosions. This contrasts with the nearly constant vesicularities of the deeper part of the pre-explosive magma column, which are propitious to a general, short-lived disruption.

The phase transformation and crystallization kinetics of (1 − x)Li 2O– xNa 2O–Al 2O 3–4SiO 2 glasses

The phase transformation and crystallization kinetics of (1 − x)Li 2O– xNa 2O–Al 2O 3–4SiO 2 glasses have been studied by using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction (ED) analysis. The crystallization temperature at the exothermic peak increases from 1171 to 1212 K when the Na 2O content increases from 0 to 0.6 mol. The crystalline phase is composed of spodumene crystallization when the Na 2O content increases from 0 to 0.6 mol. The activation energy of spodumene crystallization decreases from 444.0 ± 22.2 to 284.0 ± 10.8 kJ mol −1 when the Na 2O content increases from 0 to 0.4 mol. Moreover, the activation energy increases from 284.0 ± 10.8 to 446.0 ± 23.2 kJ mol −1 when the Na 2O content increases from 0.4 to 0.6 mol. The crystallization parameters m and n approach 2, indicating that the surface nucleation and two-dimensional growth are dominant in (1 − x)Li 2O– xNa 2O–Al 2O 3–4SiO 2 glasses.

Structure of H 2O-saturated peralkaline aluminosilicate melt and coexisting aluminosilicate-saturated aqueous fluid determined in-situ to 800 °C and ∼800 MPa

The structure of H 2O-saturated silicate melts and of silicate-saturated aqueous solutions, as well as that of supercritical silicate-rich aqueous liquids, has been characterized in-situ while the sample was at high temperature (to 800 °C) and pressure (up to 796 MPa). Structural information was obtained with confocal microRaman and with FTIR spectroscopy. Two Al-bearing glasses compositionally along the join Na 2O•4SiO 2–Na 2O•4(NaAl)O 2–H 2O (5 and 10 mol% Al 2O 3, denoted NA5 and NA10) were used as starting materials. Fluids and melts were examined along pressure-temperature trajectories of isochores of H 2O at nominal densities (from PVT properties of pure H 2O) of 0.85 g/cm 3 (NA10 experiments) and 0.86 g/cm 3 (NA5 experiments) with the aluminosilicate + H 2O sample contained in an externally-heated, Ir-gasketed hydrothermal diamond anvil cell. Molecular H 2O (H 2O°) and OH groups that form bonds with cations exist in all three phases. The OH/H 2O° ratio is positively correlated with temperature and pressure (and, therefore, fugacity of H 2O, f H2O) with (OH/H 2O°) melt > (OH/H 2O°) fluid at all pressures and temperatures. Structural units of Q 3, Q 2, Q 1, and Q 0 type occur together in fluids, in melts, and, when outside the two-phase melt + fluid boundary, in single-phase liquids. The abundance of Q 0 and Q 1 increases and Q 2 and Q 3 decrease with f H2O. Therefore, the NBO/ T (nonbridging oxygen per tetrahedrally coordination cations), of melt is a positive function of f H2O. The NBO/ T of silicate in coexisting aqueous fluid, although greater than in melt, is less sensitive to f H2O. The melt structural data are used to describe relationships between activity of H 2O and melting phase relations of silicate systems at high pressure and temperature. The data were also combined with available partial molar configurational heat capacity of Q n -species in melts to illustrate how these quantities can be employed to estimate relationships between heat capacity of melts and their H 2O content.

Study on molding semi-coke used for flue-gas desulphurization

This paper investigated the preparation process of molding semi-coke and its application in flue-gas desulphurization. Factors affecting the desulphurization capability of molding semi-coke were studied, including gas temperature, space velocity, O 2 content and H 2O content in flue-gas. Results show that the molding semi-coke would have a better activity if calcined under nitrogen atmosphere with steam and 2% oxygen at 700 °C for 2 h. The optimal operating conditions are as follows: temperature 60–80 °C, space velocity 600 h −1, oxygen content 5% and H 2O content 8%.

H 2O- and temperature-zoning in magma chambers: The example of the Tufo Giallo della Via Tiberina eruptions (Sabatini Volcanic District, central Italy)

Textural and chemical variations of juvenile clasts are widely observed in pyroclastic deposits. In particular, the co-existence of whitish, pumiceous, and dark grey, scoriaceous, juvenile clasts has been observed in many eruptive units of well-known volcanoes (i.e., Somma–Vesuvius, Vulsini, Colli Albani, Stromboli). Here we report the example of the Tufo Giallo della Via Tiberina (TGVT) pyroclastic succession, which comprises two eruptive units emplaced at ca. 561 and 548 ka, during the early explosive activity of the Sabatini Volcanic District (SVD; Roman Province, central Italy). TGVT deposits, as well as underlying pyroclastic products (FAD, ca. 582 ka), are characterized by coexisting whitish pumice and black–grey scoria clasts showing common phonolitic composition but different textural features: white pumice is highly vesicular, vitrophyric, and contains scarce, > 50 µm-sized, feldspar and clinopyroxene crystals, while black–grey scoria is poorly vesicular, highly crystallized, and contains diffuse leucite phenocrysts. The latter records crystallization under H 2O-undersaturated conditions, as opposed to the vitrophyric texture of white pumice indicating higher temperature and H 2O concentration. On these grounds, a thermally and H 2O-zoned pre-eruptive system has been modelled for the phonolitic magma chambers feeding the early SVD events, in which white pumice and black–grey scoria represent the inner and peripheral portions of the reservoirs, respectively. Extensive leucite + clinopyroxene crystallization in the H 2O-undersaturated, peripheral portions of the reservoirs, resulted in water flux toward the inner zones, where the higher temperature and increasing H 2O content acted to delay crystallization in the white pumice-feeder magma. The withdrawal of white pumice at the eruption onset produced decompression of the peripheral magma, triggering black–grey scoria eruption during the late phases of explosive events.

Crystallization behavior of (1 − x)Li 2O· xNa 2O·Al 2O 3·4SiO 2 glasses

The crystallization behavior of the (1 − x)Li 2O· xNa 2O·Al 2O 3·4SiO 2 glasses has been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED) and energy dispersive spectroscopy (EDS). The crystalline phase was composed of β-spodumene. The isothermal crystallization kinetics of β-spodumene from the (1 − x)Li 2O· xNa 2O·Al 2O 3·4SiO 2 glasses has also been studied by a quantitative X-ray diffraction method. The activation energy of β-spodumene formation decreases from 359.2 to 317.8 kJ/mol when the Na 2O content increases from 0 to 0.4 mol and it increases from 317.8 to 376.9 kJ/mol when the Na 2O content increases from 0.4 to 0.6 mol. The surface nucleation and plate-like growth were dominant in the crystallization of the (1 − x)Li 2O· xNa 2O·Al 2O 3·4SiO 2 glasses.

The regular shape of stratovolcanoes: A DEM-based morphometrical approach

We studied the shape of the most regular-shaped stratovolcanoes of the world to mathematically define the form of the ideal stratovolcano. Based on the Shuttle Radar Topographic Mission data we selected 19 of the most circular and symmetrical volcanoes, which incidentally all belong to subduction-related arcs surrounding the Pacific. The selection of volcanoes benefitted from the introduction of a new definition of circularity which is more robust than previous definitions, being independent of the erosional dissection of the cone. Our study on the shape of stratovolcanoes was based on the analysis of the radial elevation profiles of each volcano. The lower half section of the volcanoes is always well fitted by a logarithmic curve, while the upper half section is not, and falls into two groups: it is fitted either by a line (“C-type”, conical upper part) or by a parabolic arc (“P-type”, parabolic/concave upper part). A quantitative discrimination between these groups is obtained by fitting their upper slope with a linear function: C-type volcanoes show small, whereas P-type volcanoes show significant negative angular coefficient. The proposed threshold between the two groups is − 50 × 10 − 4 °/m. Chemical composition of eruptive products indicates higher SiO 2 and/or higher H 2O content for C-type volcanoes, which could imply a higher incidence of mildly explosive (e.g. strombolian) eruptions. We propose that this higher explosivity is responsible for forming the constant uppermost slopes by the deposition of ballistic tephra and its subsequent stabilisation at a constant angle. By contrast, P-type volcanoes are characterized by a smaller SiO 2 and H 2O content, which can be responsible for a higher incidence of effusive events and/or a lower incidence of upper flank-forming (i.e. mild) explosive eruptions. Therefore, the concave upper flanks of these volcanoes may be shaped typically by lava flows. Based on this hypothesis, we propose that the morphometric analysis of the elevation profile of stratovolcanoes can provide insights into their dominant eruptive style.