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Silicate Melts (silicate + melt)
Selected AbstractsCrystallization of Highly Supercooled Silicate MeltsADVANCED ENGINEERING MATERIALS, Issue 12 2006M. Roskosz Crystallization of liquids in the system CaO-MgO-Al2O3 -SiO2 at one atmosphere has been studied at temperatures between the glass transition (Tg) and the solidus. To determine the textures, compositions and unit-cell parameters of the crystalline phases, the authors have characterized the experimental charges over a wide range of length scales by scanning and transmission electron microscopy, electron microprobe analyses, X-ray diffraction, and Raman spectroscopy. With increasing temperature, crystals tend to reach the equilibrium composition, but the relative importance of thermodynamic and kinetic factors is a single function of T - Tg, regardless of liquid composition. This feature is of considerable practical interest as it provides the possibility, not only to predict, but also to control the composition of the crystallizing phases. [source] Melt,wall rock interaction in the mantle shown by silicate melt inclusions in peridotite xenoliths from the central Pannonian Basin (western Hungary)ISLAND ARC, Issue 2 2009Csaba Szabó Abstract In this paper we present a detailed textural and geochemical study of two equigranular textured amphibole-bearing spinel lherzolite xenoliths from Szigliget, Bakony,Balaton Highland Volcanic Field (BBHVF, western Hungary) containing abundant primary silicate melt inclusions (SMIs) in clinopyroxene rims and secondary SMIs in orthopyroxene (and rarely spinel) along healed fractures. The SMIs are dominantly composed of silicate glass and CO2 -rich bubbles. Clinopyroxene and orthopyroxene are zoned in both studied xenoliths, especially with respect to Fe, Mg, Na, and Al contents. Cores of clinopyroxenes in both xenoliths show trace element distribution close to primitive mantle. Rims of clinopyroxenes are enriched in Th, U, light rare earth elements (LREEs) and medium REEs (MREEs). Amphiboles in the Szg08 xenolith exhibit elevated Rb, Ba, Nb, Ta, LREE, and MREE contents. The composition of silicate glass in the SMIs covers a wide range from the basaltic trachyandesite and andesite to phonolitic compositions. The glasses are particularly rich in P2O5. Both primary and secondary SMIs are strongly enriched in incompatible trace elements (mostly U, Th, La, Zr) and display a slight negative Hf anomaly. The development of zoned pyroxenes, as well as the entrapment of primary SMIs in the clinopyroxene rims, happened after partial melting and subsequent crystallization of clinopyroxenes, most probably due to an interaction between hot volatile-bearing evolved melt and mantle wall-rocks. This silicate melt filled microfractures in orthopyroxenes (and rarely spinels) resulting in secondary SMIs. [source] Calculated phase equilibria in K2O-FeO-MgO-Al2O3 -SiO2 -H2O for silica-undersaturated sapphirine-bearing mineral assemblagesJOURNAL OF METAMORPHIC GEOLOGY, Issue 4 2005D. E. KELSEY Abstract Silica-undersaturated, sapphirine-bearing granulites occur in a large number of localities worldwide. Such rocks have historically been under-utilized for estimating P,T evolution histories because of limited experimental work, and a consequent poor understanding of the topology and P,T location of silica-undersaturated mineral equilibria. Here, a calculated P,T projection for sapphirine-bearing, silica-undersaturated metapelitic rock compositions is constructed using THERMOCALC for the FeO-MgO-Al2O3 -SiO2 (FMAS) and KFMASH (+K2O + H2O) chemical systems, allowing quantitative analysis of silica-undersaturated mineral assemblages. This study builds on that for KFMASH sapphirine + quartz equilibria [Kelsey et al. (2004) Journal of Metamorphic Geology, vol. 22, pp. 559,578]. FMAS equilibria are significantly displaced in P,T space from silicate melt-bearing KFMASH equilibria. The large number of univariant silica-undersaturated KFMASH equilibria result in a P,T projection that is topologically more complex than could be established on the basis of experiments and/or natural assemblages. Coexisting sapphirine and silicate melt (with or without corundum) occur down to c. 900 °C in KFMASH, some 100 °C lower than in silica-saturated compositions, and from pressures of c.,1 to ,12 kbar. Mineral compositions and composition ranges for the calculated phases are consistent with natural examples. Bulk silica has a significant effect on the stability of sapphirine-bearing assemblages at a given P,T, resulting in a wide variety of possible granulite facies assemblages in silica-undersaturated metapelites. Calculated pseudosections are able to reproduce many naturally occurring silica-undersaturated assemblages, either within a single assemblage field or as the product of a P,T trajectory crossing several fields. With an understanding of the importance of bulk composition on sapphirine stability and textural development, silica-undersaturated assemblages may be utilized in a quantitative manner in the detailed metamorphic investigation of high-grade terranes. [source] Calculation of partial melting equilibria in the system Na2O,CaO,K2O,FeO,MgO,Al2O3,SiO2,H2O (NCKFMASH)JOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2001R. W. White Abstract A thermodynamic model for haplogranitic melts in the system Na2O,CaO,K2O,Al2O3,SiO2,H2O (NCKASH) is extended by the addition of FeO and MgO, with the data for the additional end-members of the liquid incorporated in the Holland & Powell (1998) internally consistent thermodynamic dataset. The resulting dataset, with the software thermocalc, is then used to calculate melting relationships for metapelitic rock compositions. The main forms for this are P,T and T,X pseudosections calculated for particular rock compositions and composition ranges. The relationships in these full-system pseudosections are controlled by the low-variance equilibria in subsystems of NCKFMASH. In particular, the solidus relationships are controlled by the solidus relationships in NKASH, and the ferromagnesian mineral relationships are controlled by those in KFMASH. However, calculations in NCKFMASH allow the relationships between the common metapelitic minerals and silicate melt to be determined. In particular, the production of silicate melt and melt loss from such rocks allow observations to be made about the processes involved in producing granulite facies rocks, particularly relating to open-system behaviour of rocks under high-grade conditions. [source] Aqueous fluids at elevated pressure and temperatureGEOFLUIDS (ELECTRONIC), Issue 1-2 2010A. LIEBSCHER Abstract The general major component composition of aqueous fluids at elevated pressure and temperature conditions can be represented by H2O, different non-polar gases like CO2 and different dissolved metal halides like NaCl or CaCl2. At high pressure, the mutual solubility of H2O and silicate melts increases and also silicates may form essential components of aqueous fluids. Given the huge range of P,T,x regimes in crust and mantle, aqueous fluids at elevated pressure and temperature are highly variable in composition and exhibit specific physicochemical properties. This paper reviews principal phase relations in one- and two-component fluid systems, phase relations and properties of binary and ternary fluid systems, properties of pure H2O at elevated P,T conditions, and aqueous fluids in H2O,silicate systems at high pressure and temperature. At metamorphic conditions, even the physicochemical properties of pure water substantially differ from those at ambient conditions. Under typical mid- to lower-crustal metamorphic conditions, the density of pure H2O is , the ion product Kw = 10,7.5 to approximately 10,12.5, the dielectric constant , = 8,25, and the viscosity , = 0.0001,0.0002 Pa sec compared to , Kw = 10,14, , = 78 and , = 0.001 Pa sec at ambient conditions. Adding dissolved metal halides and non-polar gases to H2O significantly enlarges the pressure,temperature range, where different aqueous fluids may co-exist and leads to potential two-phase fluid conditions under must mid- to lower-crustal P,T conditions. As a result of the increased mutual solubility between aqueous fluids and silicate melts at high pressure, the differences between fluid and melt vanishes and the distinction between fluid and melt becomes obsolete. Both are completely miscible at pressures above the respective critical curve giving rise to so-called supercritical fluids. These supercritical fluids combine comparably low viscosity with high solute contents and are very effective metasomatising agents within the mantle wedge above subduction zones. [source] Quantitative Raman spectroscopy: speciation of cesium silicate glassesJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2009Wim J. Malfait Abstract The silicate speciation forms an important aspect of the structure of silicate melts, a subject of interest to both the earth- and materials science communities. In this study, the Qn speciation of binary cesium silicate glasses was studied by Raman spectroscopy. A method to extract the equilibrium constant from a set of Raman spectra is presented, and the least-squares optimization algorithm is given (in Supporting Information). Log(K), the equilibrium constant of the speciation reaction, 2Q3 = Q4 + Q2, equals ,2.72 ± 0.11 at the glass transition. This extends the previously established correlation between log(K) and the inverse of the ionic radius of the network modifier to cesium. Copyright © 2009 John Wiley & Sons, Ltd. [source] Binary Phase Diagram of the Manganese Oxide,Iron Oxide SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009Jarrod V. Crum The phase equilibrium of the MnOx,FeOy binary system was measured within a temperature range of 750°,1590°C in air to examine inconsistencies found in literature, i.e., discrepancies related to the boundary between the spinel and hausmannite+spinel phase fields. Several studies are available in the literature that describe this boundary however the results and methods by which they were studied vary namely in terms of the atmosphere (air versus reducing) used and heat treatment/analysis methods. In addition, samples in the discrepancy region of the diagram revert to the hausmannite phase spontaneously upon cooling due to a displacive transformation. In order to accurately measure the phase boundaries, the following measurement methods were used: isothermal heat treatments followed by rapid quenching (in air or water), dilatometry, differential thermal analysis with thermogravimetric analysis, as well as room temperature and hot-stage X-ray diffraction (XRD). Phase assemblage(s) in each specimen were determined by XRD. Data were compared with literature and a new, self consistent phase diagram was developed. The results are reported along with background information and a comparison with previously reported data. This study will support development of a model for thermodynamic equilibria in complex, multioxide silicate melts. [source] A Limited Review of Water Diffusivity and Solubility in Glasses and MeltsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2008James E. Shelby A limited review of the literature dealing with water solubility and diffusion in oxide glasses and melts is presented, with an emphasis on simple and commercial compositions and on work during the past decade. Several methods for determination of water solubilities and diffusivities are discussed. Experimental results are presented for silicate, borate, and germanate glasses and melts. Water diffusivities always increase with increasing temperature and modifier oxide content in these melts. Variations in water solubility and diffusivity with alkali and alkaline earth identity for otherwise identical compositions are small, while variations with the identity of the glass-forming oxide are large. Water solubility increases with increasing modifier oxide content in alkali silicate melts, but decreases with increasing modifier oxide content in alkali borate and germanate melts. [source] Application of MELTS to kinetic evaporation models of FeO-bearing silicate meltsMETEORITICS & PLANETARY SCIENCE, Issue 1 2004Article first published online: 26 JAN 2010 No abstract is available for this article. [source] Magmatic inclusions and felsic clasts in the Dar al Gani 319 polymict ureiliteMETEORITICS & PLANETARY SCIENCE, Issue 4 2001Yukio IKEDA Type I ureilite clasts (olivine-pigeonite assemblages with carbon), as well as other lithic and mineral clasts in this meteorite, are described in Ikeda et al.(2000). The magmatic inclusions in the type II ureilite clasts consist mainly of magnesian augite and glass. They metastably crystallized euhedral pyroxenes, resulting in feldspar component-enriched glass. On the other hand, the magmatic inclusions in the large plagioclase clast consist mainly of pyroxene and plagioclase, with a mesostasis. They crystallized with a composition along the cotectic line between the pyroxene and plagioclase liquidus fields. DaG 319 also contains felsic lithic clasts that represent various types of igneous lithologies. These are the rare components not found in the common monomict ureilites. Porphyritic felsic clasts, the main type, contain phenocrysts of plagioclase and pyroxene, and their groundmass consists mainly of plagioclase, pyroxene, and minor phosphate, ilmenite, chromite, and/or glass. Crystallization of these porphyritic clasts took place along the cotectic line between the pyroxene and plagioclase fields. Pilotaxitic felsic clasts crystallized plagioclase laths and minor interstitial pyroxene under metastable conditions, and the mesostasis is extremely enriched in plagioclase component in spite of the ubiquitous crystallization of plagioclase laths in the clasts. We suggest that there are two crystallization trends, pyroxene-metal and pyroxene-plagioclase trends, for the magmatic inclusions and felsic lithic clasts in DaG 319. The pyroxene-metal crystallization trend corresponds to the magmatic inclusions in the type II ureilite clasts and the pilotaxitic felsic clasts, where crystallization took place under reducing and metastable conditions, suppressing precipitation of plagioclase. The pyroxene-plagioclase crystallization trend corresponds to the magmatic inclusions in the isolated plagioclase clast and the porphyritic felsic clasts. This trend developed under oxidizing conditions in magma chambers within the ureilite parent body. The felsic clasts may have formed mainly from albite component-rich silicate melts produced by fractional partial melting of chondritic precursors. The common monomict ureilites, type I ureilites, may have formed by the fractional partial melting of alkali-bearing chondritic precursors. However, type II ureilites may have formed as cumulates from a basaltic melt. [source] Ferrous silicate spherules with euhedral iron-nickel metal grains from CH carbonaceous chondrites: Evidence for supercooling and condensation under oxidizing conditionsMETEORITICS & PLANETARY SCIENCE, Issue 6 2000A. N. KROT The silicate portions of the spherules are highly depleted in refractory lithophile elements (CaO, Al2O3, and TiO2 <0.04 wt%) and enriched in FeO, MnO, Cr2O3, and Na2O relative to the dominant, volatile-poor, magnesian chondrules from CH chondrites. The Fe/(Fe + Mg) ratio in the silicate portions of the spherules is positively correlated with Fe concentration in metal grains, which suggests that this correlation is not due to oxidation, reduction, or both of iron (FeOsil , Femet) during melting of metal-silicate solid precursors. Rather, we suggest that this is a condensation signature of the precursors formed under oxidizing conditions. Each metal grain is compositionally uniform, but there are significant intergrain compositional variations: about 8,18 wt% Ni, <0.09 wt% Cr, and a sub-solar Co/Ni ratio. The precursor materials of these spherules were thus characterized by extreme elemental fractionations, which have not been observed in chondritic materials before. Particularly striking is the fractionation of Ni and Co in the rounded-to-euhedral metal grains, which has resulted in a Co/Ni ratio significantly below solar. The liquidus temperatures of the euhedral Fe, Ni metal grains are lower than those of the coexisting ferrous silicates, and we infer that the former crystallized in supercooled silicate melts. The metal grains are compositionally metastable; they are not decomposed into taenite and kamacite, which suggests fast postcrystallization cooling at temperatures below 970 K and lack of subsequent prolonged thermal metamorphism at temperatures above 400,500 K. [source] | |||||||||||||