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Phase Relations (phase + relation)
Selected AbstractsPhase Relations Between ,-Tricalcium Phosphate and Hydroxyapatite with Manganese(II): Structural and Spectroscopic PropertiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2006Isaac Mayer Abstract The preparation of Mn-containing ,-tricalcium phosphate (,-TCP) samples was achieved in two ways: a) transformation of precipitated Mn-containing calcium hydroxyapatite (HA) to ,-TCP by heating at 1100 °C, and b) preparation by solid-state reaction of a mixture of CaCO3, (NH4)2HPO4, and Mn(NO3)2 at 1100 °C. Powder X-ray diffraction (XRD) analyses of the samples, obtained by both methods, show well-defined patterns with structural data of the rhombohedral R3c, ,-TCP phase. The calculated lattice constants are smaller than those known for ,-Ca3(PO4)2 because of substitution of Ca2+ by Mn2+. EPR spectroscopy indeed reveals that manganese is divalent in the samples. Apparently, the Ca(5) site in the ,-TCP structure is occupied by Mn2+. The distribution of Mn2+ between the ,-TCP and the HA phase in the case of preparation (b) was studied by EPR spectroscopy, and a pronounced preference for the former lattice was found. Micron- and submicron-sized crystals with visible faces were observed by TEM in the case of ,-TCP prepared by solid-state reaction, and large micron-sized, droplike-shaped crystals, sensitive to beam radiation, were found in the case of samples prepared by heating HA at elevated temperatures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Phase Relations in the Na0.5Bi0.5TiO3,Li3xLa(2/3),x,(1/3),2xTiO3 SystemINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2 2009Matja, Spreitzer The phase relations and the mechanism of solid-state synthesis for the Na0.5Bi0.5TiO3,Li3xLa(2/3),x,(1/3),2xTiO3 system were investigated using X-ray powder diffraction, scanning electron microscopy, and thermal analysis. The study revealed that the extent of the homogeneity range,which is related to the A-site substitution between (Na0.5Bi0.5)2+ and (Li3xLa(2/3),x,(1/3),2x)2+ pseudo cations of a perovskite structure,depends strongly on the ordering of the (Li3xLa(2/3),x,(1/3),2x)2+ species. The solid-state reaction of the compounds in the homogeneity range is completed only after multiple high-temperature firings. However, the system is also subjected to a slow thermal decomposition; this is particularly so for the compounds with a high × value and an increased Li3xLa(2/3),x,(1/3),2xTiO3 concentration. [source] Phase Relations in the Pyrochlore-Rich Part of the Bi2O3,TiO2,Nd2O3 SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009pela Kunej In this study we used solid-state synthesis to determine the phase relations in the pyrochlore-rich part of the Bi2O3,TiO2,Nd2O3 system at 1100°C. The samples were analyzed using X-ray powder diffraction and scanning electron microscopy with energy- and wavelength-dispersive spectroscopy. A single-phase pyrochlore ceramic was obtained with the addition of 4.5 mol% of Nd2O3. We determined the solubility limits for the three solid solutions: (i) the pyrochlore solid solution Bi(1.6,1.08x)NdxTi2O(6.4+0.3x), where 0.25 Phase Relations and Thermal Expansion Studies in the Ceria,Yttria SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2004Sandeep V. Chavan The synthesis, characterization, and bulk and lattice thermal expansions of a series of compounds with general composition Ce1,xYxO2,x/2 (0.0 ,x, 1.0) are reported. The XRD pattern of each product was refined to learn the solid solubility limit and the homogeneity range. The solid solubility limit of YO1.5 in CeO2 lattice, under the conditions of slow cooling from 1400°C, is represented as Ce0.55Y0.45O1.775 (i.e., 45 mol% of YO1.5). The subsequent compositions were biphase. There was no solubility of CeO2 into the lattice of YO1.5. The bulk thermal expansion measurements from ambient to 1123 K, as investigated using a dilatometer, revealed that the ,l (293,1123 K) values, within the homogeneity range, decreased on increased Y3+ content. A similar trend was observed for average lattice thermal expansion coefficient, ,a (293,1473 K), as investigated using high-temperature XRD. No ordered phases were obtained in this system under the used conditions. These studies on Ce1,xYxO2,x/2 (0.0 ,x, 1.0) system can be used to simulate the phase relation and thermal expansion behavior of Pu1,xYxO2,x/2 (0.0 ,x, 1.0), because CeO2 is widely used as a surrogate material for PuO2. [source] Preliminary Observations on Phase Relations in the "V2O3,FeO" and V2O3,TiO2 Systems from 1400°C to 1600°C in Reducing AtmospheresJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2000Theresa Coetsee Phase relations within the "V2O3,FeO" and V2O3,TiO2 oxide systems were determined using the quench technique. Experimental conditions were as follows: partial oxygen pressures of 3.02 × 10,10, 2.99 × 10,9, and 2.31 × 10,8 atm at 1400°, 1500°, and 1600°C, respectively. Analysis techniques that were used to determine the phase relations within the reacted samples included X-ray diffractometry, electron probe microanalysis (energy-dispersive spectroscopy and wavelength-dispersive spectroscopy), and optical microscopy. The solid-solution phases M2O3, M3O5, and higher Magneli phases (MnO2n,1, where M = V, Ti) were identified in the V2O3,TiO2 system. In the "V2O3,FeO" system, the solid-solution phases M2O3 and M3O4 (where M = V, Ti), as well as liquid, were identified. [source] ChemInform Abstract: Subsolidus Phase Relations in the System ZnO,B2O3,V2O5.CHEMINFORM, Issue 26 2009Zhibing Zhan Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Phase Relations of the Ag,Ga,N System.CHEMINFORM, Issue 20 2007Y. Zhang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] On the Phase Relations in the ZrO2,YO1.5,AlO1.5 SystemCHEMINFORM, Issue 41 2006S. Lakiza Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Phase Relations in the Y2O3,BaO,B2O3 System.CHEMINFORM, Issue 10 2005X. Z. Li Abstract For Abstract see ChemInform Abstract in Full Text. [source] Phase Relations in the Ti3Sn,D System.CHEMINFORM, Issue 12 2004M. Vennstroem Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Phase Relations in the System Y2O3,CaO,B2O3.CHEMINFORM, Issue 47 2001Y. Zhang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Thermal Decomposition of TeSeO4 and Te3SeO8 , Phase Relations in the Ternary System TeO2/SeO2/Bi2SeO5.CHEMINFORM, Issue 44 2001P. Schmidt Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Phase relations in the Ba,Sr,Co,Fe,O system at 1273,K in airJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2009Zhèn Yáng Selected compositions of the Ba,Sr,Co,Fe,O system were synthesized from powders by the solid-state reaction method. Samples were equilibrated at 1273,K for 36,000,s in air. The resulting powders were characterized by X-ray diffraction (XRD) at room temperature and by high-temperature in situ XRD. The phases present in the BaxSr1,xCoyFe1,yO3,, system are outlined for 1273,K in air. For most of the quaternary compositions, the cubic perovskite is formed, except for the compositions with x = 1 (excluding y = 0.4), y = 1 and x, y = 0.8, where the phases mainly show hexagonal distortions, and x, y = 0, for which a predominant cubic phase is mixed with other phases. [source] Spinel,cordierite symplectites replacing andalusite: evidence for melt-assisted diapirism in the Bushveld Complex, South AfricaJOURNAL OF METAMORPHIC GEOLOGY, Issue 6 2004T. Johnson Abstract Spinel,cordierite symplectites partially replacing andalusite occur in metapelitic rocks within the cores of several country rock diapirs that have ascended into the upper levels of layered mafic/ultramafic rocks in the Bushveld Complex. We investigate the petrogenesis of these symplectites in one of these diapirs, the Phepane dome. Petrographic evidence indicates that at conditions immediately below the solidus the rocks were characterized by a cordierite-, biotite- and K-feldspar-rich matrix and 5,10 mm long andalusite porphyroblasts surrounded by biotite-rich fringes. Phase relations in the MnNCKFMASHT model system constrain the near-solidus prograde path to around 3 kbar and imply that andalusite persisted metastably into the sillimanite + melt field, where the fringing relationship between biotite and andalusite provided spatially restricted equilibrium domains with silica-deficient effective bulk compositions that focused suprasolidus reaction. MnNCKFMASHT pseudosections that model these compositional domains suggest that volatile phase-absent melting reactions consuming andalusite and biotite initially produced a moat of cordierite surrounding andalusite; reaction progressed until all quartz was consumed. Spinel is predicted to grow with cordierite at around 720 °C. Formation of the aluminous solid products was strongly controlled by the receding edge of andalusite grains, with symplectites forming at the andalusite-cordierite moat interface. Decompression due to melt-assisted diapiric rise of the floor rocks into the overlying mafic/ultramafic rocks occurred close to the thermal peak. Re-crossing of the solidus at P = 1.5,2 kbar, T > 700 °C resulted in preservation of the symplectites. Two features of the silica-deficient domains inhibited resorption of spinel. First, the cordierite moat armoured the symplectites from reaction with crystallizing melt in the outer part of the pseudomorphs. Second, an up- T step in the solidus at low- P, which may be in excess of 100 °C higher than the quartz-saturated solidus, resulted in high- T crystallization of melt on decompression. Even in metapelitic rocks where melt is retained, preservation of spinel is favoured by decompression. [source] Preliminary Observations on Phase Relations in the "V2O3,FeO" and V2O3,TiO2 Systems from 1400°C to 1600°C in Reducing AtmospheresJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2000Theresa Coetsee Phase relations within the "V2O3,FeO" and V2O3,TiO2 oxide systems were determined using the quench technique. Experimental conditions were as follows: partial oxygen pressures of 3.02 × 10,10, 2.99 × 10,9, and 2.31 × 10,8 atm at 1400°, 1500°, and 1600°C, respectively. Analysis techniques that were used to determine the phase relations within the reacted samples included X-ray diffractometry, electron probe microanalysis (energy-dispersive spectroscopy and wavelength-dispersive spectroscopy), and optical microscopy. The solid-solution phases M2O3, M3O5, and higher Magneli phases (MnO2n,1, where M = V, Ti) were identified in the V2O3,TiO2 system. In the "V2O3,FeO" system, the solid-solution phases M2O3 and M3O4 (where M = V, Ti), as well as liquid, were identified. [source] Phase Relations and Thermal Expansion Studies in the Ceria,Yttria SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2004Sandeep V. Chavan The synthesis, characterization, and bulk and lattice thermal expansions of a series of compounds with general composition Ce1,xYxO2,x/2 (0.0 ,x, 1.0) are reported. The XRD pattern of each product was refined to learn the solid solubility limit and the homogeneity range. The solid solubility limit of YO1.5 in CeO2 lattice, under the conditions of slow cooling from 1400°C, is represented as Ce0.55Y0.45O1.775 (i.e., 45 mol% of YO1.5). The subsequent compositions were biphase. There was no solubility of CeO2 into the lattice of YO1.5. The bulk thermal expansion measurements from ambient to 1123 K, as investigated using a dilatometer, revealed that the ,l (293,1123 K) values, within the homogeneity range, decreased on increased Y3+ content. A similar trend was observed for average lattice thermal expansion coefficient, ,a (293,1473 K), as investigated using high-temperature XRD. No ordered phases were obtained in this system under the used conditions. These studies on Ce1,xYxO2,x/2 (0.0 ,x, 1.0) system can be used to simulate the phase relation and thermal expansion behavior of Pu1,xYxO2,x/2 (0.0 ,x, 1.0), because CeO2 is widely used as a surrogate material for PuO2. [source] Coherent control of plasmon,phonon oscillations in a semiconductor using two ultrashort optical pulsesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2003M. I. Bakunov Abstract We show that a pair of ultrashort optical pulses with an arbitrary phase relation can be used to control the amplitude of the plasmon,phonon oscillations in the depletion layer of a polar semiconductor. The coherent control of the plasmon,phonon oscillations is always accompanied by the excitation of uniform motion of electrons and holes. [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] Br/Cl signature of hydrothermal fluids: liquid,vapour fractionation of bromine revisitedGEOFLUIDS (ELECTRONIC), Issue 2 2006A. LIEBSCHER Abstract Br/Cl ratios of hydrothermal fluids are widely used as geochemical tracers in marine hydrothermal systems to prove fluid phase separation processes. However, previous results of the liquid,vapour fractionation of bromine are ambiguous. Here we report new experimental results of the liquid,vapour fractionation of bromine in the system H2O,NaCl,NaBr at 380,450°C and 22.9,41.7 MPa. Our data indicate that bromine is generally more enriched than chlorine in the liquid phase. Calculated exchange coefficients KD(Br-Cl)liquid-vapour for the reaction Brvapour + Clliquid = Brliquid + Clvapour are between 0.94 ± 0.08 and 1.66 ± 0.14 within the investigated P,T range. They correlate positively with DClliquid-vapour and suggest increasing bromine,chlorine fractionation with increasing opening of the liquid,vapour solvus, i.e. increasing distance to the critical curve in the H2O,NaCl system. An empirical fit of the form KD(Br-Cl)liquid-vapour = a*ln[b*(DClliquid-vapour,1) + e1/a] yields a = 0.349 and b = 1.697. Based on this empirical fit and the well-constrained phase relations in the H2O,NaCl system we calculated the effect of fluid phase separation on the Br/Cl signature of a hydrothermal fluid with initial seawater composition for closed and open adiabatic ascents along the 4.5 and 4.8 J g,1 K,1 isentropes. The calculations indicate that fluid phase separation can significantly alter the Br/Cl ratio in hydrothermal fluids. The predicted Br/Cl evolutions are in accord with the Br/Cl signatures in low-salinity vent fluids from the 9 to 10°N East Pacific Rise. [source] Polyphase evolution and reaction sequence of compositional domains in metabasalt: a model based on local chemical equilibrium and metamorphic differentiationGEOLOGICAL JOURNAL, Issue 3-4 2000T. M. Toóth Abstract Eclogitic garnet amphibolite samples from the Southern Steep Belt of the Central Alps show evidence of several stages of metamorphic evolution and exhumation. A method for unravelling this evolution is presented and applied to these samples. It involves a combination of detailed petrographic analysis and microchemical characterization with quantitative models of the thermodynamically stable phase relations for specific compositional domains of each sample. Preserved mineral relics and textural evidence are compared to model predictions to identify the important irreversible reactions. The interpretation of the exhumation history is thus based on the consistency of a wide spectrum of observations with predicted phase diagrams, leading to robust reconstruction of a pressure,temperature (P,T) path even where the mineralogical relics in samples are insufficient, due to retrogression, to warrant application of multi-equilibrium thermobarometric techniques. The formation of compositionally different domains in the metabasalt samples studied is attributed to prograde growth of porphyroblasts (e.g. garnet, plagioclase, zoisite) in the matrix, implying substantial metamorphic differentiation at the scale of a few millimetres. Chemical interaction among different domains during the subsequent P,T evolution is shown to have been very limited. This led to different reaction sequences during exhumation, in which relics preserved in different domains reflect a range of continually changing P,T conditions. For samples from a single outcrop, we deduce a Barrovian prograde path to eclogite facies (23,±,3,kbar, 750,±,50°C), followed by (rapid) decompression to 8,±,1,kbar and 675,±,25°C, and a final heating phase at similar pressures reaching 750,±,40°C. This evolution is attributed to the Alpine cycle involving subduction,collision and slab breakoff,extrusion of tectonic fragments that make up the Southern Steep Belt of the Central Alps. Copyright © 2000 John Wiley & Sons, Ltd. [source] Diffusion through time-dependent mediaGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2000M. Holschneider Summary In this theoretical paper we show how to solve a time-dependent diffusion equation by means of a perturbation series. This technique is applied to the case of diffusion of a liquid through a time-dependent porous matrix. We compute to first order the phase and amplitude relations between the small deformation of the transporting matrix and the corresponding variation of the saturation at the surface. In particular we show that, for a large frequency range, there is a constant phase shift of ,/2 between the matrix and the surface saturation variations. Since the conductivity is to first approximation proportional to the saturation at the surface, this might explain the observed phase relations observed in an experiment in a cave near Abaratsubo (Japan). [source] Comparison of spontaneous and septally driven hippocampal theta field and theta-related cellular activityHIPPOCAMPUS, Issue 1 2004Darren Scarlett Abstract Experiments were carried out for the purpose of comparing the electrophysiological properties of spontaneously occurring hippocampal theta field activity with those of theta-like field activity elicited by 5-Hz and 7-Hz electrical stimulation of the medial septum in urethane-anesthetized rats. Experiment 1 compared the amplitude and phase depth profiles for the three conditions of spontaneously occurring theta, theta elicited by 5-Hz medial septal stimulation, and theta elicited by 7-Hz medial septal stimulation. The results supported the conclusion that septally elicited theta field activity exhibited characteristics similar to those of spontaneously occurring theta field activity. Experiment 2 compared the discharge properties of hippocampal theta-related cellular discharges during spontaneous and septally elicited theta field activity. In contrast to the results of Experiment 1, the findings of Experiment 2 supported the conclusion that electrical stimulation of medial septal nuclei did not produce typical responses of hippocampal theta-related cellular activity. During spontaneously occurring field conditions, HPC theta-ON cells increased their discharge rates during spontaneous theta field activity, relative to LIA, and theta-OFF cells decreased (often to zero) their discharge rates during theta field activity relative to LIA. During septally elicited theta-like activity, phasic and tonic theta-ON cells decreased their discharge rates (some were totally inhibited), and most tonic theta-OFF cells increased their discharge rates (although two were totally inhibited). In addition, the discharges (albeit reduced) of the majority of both phasic and tonic theta-ON cells during septal driving became entrained to the stimulation pulses and thus exhibited rhythmicity and strong phase relations with the field activity. Furthermore, both cell types discharged near the positive peak of the septally elicited theta field activity during 5-Hz stimulation and near the negative peak during 7-Hz stimulation. The discharges of most tonic theta-OFF cells also became entrained to the stimulation pulses and exhibited similar phase relations to theta-ON cells during the 5-Hz and 7-Hz driving frequencies. Thus, based on cellular evidence, electrical stimulation of the medial septum activates the hippocampal neural circuitry involved in the generation of theta field activity in a nonphysiological manner. The findings of the present paper provide an explanation for why electrical stimulation of the medial septum in freely moving rats elicits a theta-like field activity that is dissociated from the normal behavioral correlates, in contrast to those elicited by stimulation of the posterior nucleus of the hypothalamus (Bland and Oddie. 2001. Behav Brain Res 127:119,136). © 2003 Wiley-Liss, Inc. [source] Influence of ferric iron on the stability of mineral assemblagesJOURNAL OF METAMORPHIC GEOLOGY, Issue 6 2010J. F. A. DIENER Abstract Ferric iron is present in all metamorphic rocks and has the ability to significantly affect their phase relations. However, the influence of ferric iron has commonly been ignored, or at least not been considered quantitatively, mainly because its abundance in rocks and minerals is not determined by routine analytical techniques. Mineral equilibria calculations that explicitly account for ferric iron can be used to examine its effect on the phase relations in rocks and, in principle, allow the estimation of the oxidation state of rocks. This is illustrated with calculated pseudosections in NCKFMASHTO for mafic and pelitic rock compositions. In addition, it is shown that ferric iron has the capacity to significantly increase the stability of the corundum + quartz assemblage, making it possible for this assemblage to exist at crustal P,T conditions in oxidized rocks of appropriate composition. [source] Three metamorphic events recorded in a single garnet: Integrated phase modelling, in situ LA-ICPMS and SIMS geochronology from the Moine Supergroup, NW ScotlandJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2010K. A. CUTTS Abstract In situ LA-ICP-MS monazite geochronology from a garnet-bearing diatexite within the Moine Supergroup (Glenfinnan Group) NW Scotland records three temporally distinct metamorphic events within a single garnet porphyroblast. The initial growth of garnet occurred in the interval c. 825,780 Ma, as recorded by monazite inclusions located in the garnet core. Modelled P,T conditions based on the preserved garnet core composition indicate an initially comparatively high geothermal gradient regime and peak conditions of ,650 °C and 7 kbar. Monazite within a compositionally distinct second shell of garnet has an age of 724 ± 6 Ma. This is indistinguishable from a SIMS age of 725 ± 4 Ma obtained from metamorphic zircon in the sample, which is interpreted to record the timing of migmatization. This second stage of garnet growth occurred on a P,T path from ,6 kbar and 650 °C rising to ,9 kbar and 700 °C, with the peak conditions associated with partial melting. A third garnet zone which forms the rim contains monazite with an age of 464 ± 3 Ma. Monazite in the surrounding matrix has an age of 462 ± 2 Ma. This corresponds well with a U,Pb SIMS zircon age of 463 ± 4 Ma obtained from a deformed pegmatite that was emplaced during widespread folding and reworking of the migmatite fabric. The P,T conditions associated with the final phase of garnet growth were ,7 kbar and 650 °C. The monazite ages coupled with the phase relations modelled from this multistage garnet indicate that it records two Neoproterozoic tectonothermal events as well as the widespread Ordovician Grampian event associated with Caledonian orogenesis. Thus, this single garnet records much of the Neoproterozoic to Ordovician thermal history in NW Scotland, and highlights the long history of porphyroblast growth that can be revealed by in situ isotopic dating and associated P,T modelling. This approach has the potential to reveal much of the thermal architecture of Neoproterozoic events within the Moine Supergroup, despite intense Caledonian reworking, if suitable textural and mineralogical relationships can be indentified elsewhere. [source] Metamorphic phase relations in orthopyroxene-bearing granitoids: implication for high-pressure metamorphism and prograde melting in the continental crustJOURNAL OF METAMORPHIC GEOLOGY, Issue 4 2009S. K. BHOWMIK Abstract In this work, the factors controlling the formation and preservation of high-pressure mineral assemblages in the metamorphosed orthopyroxene-bearing metagranitoids of the Sandmata Complex, Aravalli-Delhi Mobile Belt (ADMB), northwestern India have been modelled. The rocks range in composition from farsundite through quartz mangerite to opdalite, and with varying K2O, Ca/(Ca + Na)rock and FeOtot + MgO contents. A two stage metamorphic evolution has been recorded in these rocks. An early hydration event stabilized biotite with or without epidote at the expense of magmatic orthopyroxene and plagioclase. Subsequent high-pressure granulite facies metamorphism (,15 kbar, ,800 °C) of these hydrated rocks produced two rock types with contrasting mineralogy and textures. In the non-migmatitic metagranitoids, spectacular garnet ± K-feldspar ± quartz corona was formed around reacting biotite, plagioclase, quartz and/or pyroxene. In contrast, biotite ± epidote melting produced migmatites, containing porphyroblastic garnet incongruent solids and leucosomes. Applying NCKFMASHTO T,M(H2O) and P,T pseudosection modelling techniques, it is demonstrated that the differential response of these magmatic rocks to high-pressure metamorphism is primarily controlled by the scale of initial hydration. Rocks, which were pervasively hydrated, produced garnetiferous migmatites, while for limited hydration, the same metamorphism formed sub-solidus garnet-bearing coronae. Based on the sequence of mineral assemblage evolution and the mineral compositional zoning features in the two metagranitoids, a clockwise metamorphic P,T path is constrained for the high-pressure metamorphic event. The finding has major implications in formulating geodynamic model of crustal amalgamation in the ADMB. [source] Partial melting of metagreywacke: a calculated mineral equilibria studyJOURNAL OF METAMORPHIC GEOLOGY, Issue 8 2008T. E. JOHNSON Abstract Greywacke occurs in most regionally metamorphosed orogenic terranes, with depositional ages from Archean to recent. It is commonly the dominant siliciclastic rock type, many times more abundant than pelite. Using calculated pseudosections in the Na2O,CaO,K2O,FeO,MgO,Al2O3,SiO2,H2O,TiO2,O system, the partial melting of metagreywacke is investigated using several natural protolith compositions that reflect the main observed compositional variations. At conditions appropriate for regional metamorphism at mid-crustal depths (6,8 kbar), high- T subsolidus assemblages are dominated by quartz, plagioclase and biotite with minor garnet, orthoamphibole, sillimanite, muscovite and/or K-feldspar (±Fe,Ti oxides). Modelled solidus temperatures are dependent on bulk composition and vary from 640 to 690 °C. Assuming minimal melting at the H2O-saturated solidus, initial prograde anatexis at temperatures up to ,800 °C is characterized by very low melt productivity. Significant melt production in commonly occurring (intermediate) metagreywacke compositions is controlled by the breakdown of biotite and production of orthopyroxene (±K-feldspar) across multivariant fields until biotite is exhausted at 850,900 °C. Assuming some melt is retained in the source, then at temperatures beyond that of biotite stability, melt production occurs via the consumption of plagioclase, quartz and any remaining K-feldspar as the melt becomes progressively more Ca-rich and H2O-undersaturated. Melt productivity with increasing temperature across the melting interval in metagreywacke is generally gradational when compared to metapelite, which is characterized by more step-like melt production. Comparison of the calculated phase relations with experimental data shows good consistency once the latter are considered in terms of the variance of the equilibria involved. Calculations on the presumed protolith compositions of residual granulite facies metagreywacke from the Archean Ashuanipi subprovince (Quebec) show good agreement with observed phase relations. The degree of melt production and subsequent melt loss is consistent with the previously inferred petrogenesis based on geochemical mass balance. The results show that, for temperatures above 850 °C, metagreywacke is sufficiently fertile to produce large volumes of melt, the separation from source and ascent of which may result in large-scale crustal differentiation if metagreywacke is abundant. [source] Prograde metamorphic sequence of REE minerals in pelitic rocks of the Central Alps: implications for allanite,monazite,xenotime phase relations from 250 to 610 °CJOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2008E. JANOTS Abstract The distribution of REE minerals in metasedimentary rocks was investigated to gain insight into the stability of allanite, monazite and xenotime in metapelites. Samples were collected in the central Swiss Alps, along a well-established metamorphic field gradient that record conditions from very low grade metamorphism (250 °C) to the lower amphibolite facies (,600 °C). In the Alpine metapelites investigated, mass balance calculations show that LREE are mainly transferred between monazite and allanite during the course of prograde metamorphism. At very low grade metamorphism, detrital monazite grains (mostly Variscan in age) have two distinct populations in terms of LREE and MREE compositions. Newly formed monazite crystallized during low-grade metamorphism (<440 °C); these are enriched in La, but depleted in Th and Y, compared with inherited grains. Upon the appearance of chloritoid (,440,450 °C, thermometry based on chlorite,choritoid and carbonaceous material), monazite is consumed, and MREE and LREE are taken up preferentially in two distinct zones of allanite distinguishable by EMPA and X-ray mapping. Prior to garnet growth, allanite acquires two growth zones of clinozoisite: a first one rich in HREE + Y and a second one containing low REE contents. Following garnet growth, close to the chloritoid,out zone boundary (,556,580 °C, based on phase equilibrium calculations), allanite and its rims are partially to totally replaced by monazite and xenotime, both associated with plagioclase (± biotite ± staurolite ± kyanite ± quartz). In these samples, epidote relics are located in the matrix or as inclusions in garnet, and these preserve their characteristic chemical and textural growth zoning, indicating that they did not experience re-equilibration following their prograde formation. Hence, the partial breakdown of allanite to monazite offers the attractive possibility to obtain in situ ages, representing two distinct crystallization stages. In addition, the complex REE + Y and Th zoning pattern of allanite and monazite are essential monitors of crystallization conditions at relatively low metamorphic grade. [source] Deformation, mass transfer and mineral reactions in an eclogite facies shear zone in a polymetamorphic metapelite (Monte Rosa nappe, western Alps)JOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2004L. M. Keller Abstract This study analyses the mineralogical and chemical transformations associated with an Alpine shear zone in polymetamorphic metapelites from the Monte Rosa nappe in the upper Val Loranco (N-Italy). In the shear zone, the pre-Alpine assemblage plagioclase + biotite + kyanite is replaced by the assemblage garnet + phengite + paragonite at eclogite facies conditions of about 650 °C at 12.5 kbar. Outside the shear zone, only minute progress of the same metamorphic reaction was attained during the Alpine metamorphic overprint and the pre-Alpine mineral assemblage is largely preserved. Textures of incomplete reaction, such as garnet rims at former grain contacts between pre-existing plagioclase and biotite, are preserved in the country rocks of the shear zone. Reaction textures and phase relations indicate that the Alpine metamorphic overprint occurred under largely anhydrous conditions in low strain domains. In contrast, the mineralogical changes and phase equilibrium diagrams indicate water saturation within the Alpine shear zones. Shear zone formation occurred at approximately constant volume but was associated with substantial gains in silica and losses in aluminium and potassium. Changes in mineral modes associated with chemical alteration and progressive deformation indicate that plagioclase, biotite and kyanite were not only consumed in the course of the garnet-and phengite-producing reactions, but were also dissolved ,congruently' during shear zone formation. A large fraction of the silica liberated by plagioclase, biotite and kyanite dissolution was immediately re-precipitated to form quartz, but the dissolved aluminium- and potassium-bearing species appear to have been stable in solution and were removed via the pore fluid. The reaction causes the localization of deformation by producing fine-grained white mica, which forms a mechanically weak aggregate. [source] Eclogites from the south Tianshan, NW China: petrological characteristic and calculated mineral equilibria in the Na2O,CaO,FeO,MgO,Al2O3,SiO2,H2O systemJOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2003C. J. Wei Abstract Eclogites from the south Tianshan, NW China are grouped into two types: glaucophane and hornblende eclogites, composed, respectively, of garnet + omphacite + glaucophane + paragonite + epidote + quartz and garnet + omphacite + hornblende (sensu lato) + paragonite + epidote + quartz, plus accessory rutile and ilmenite. These eclogites are diverse both in mineral composition and texture not only between the two types but also among the different selected samples within the glaucophane eclogite. Using thermocalc 3.1 and recent models of activity,composition relation for minerals, a P,T projection and a series of P,T pseudosections for specific samples of eclogite have been calculated in the system Na2O,CaO,FeO,MgO,Al2O3,SiO2,H2O (NCFMASH) with quartz and water taken to be in excess. On the basis of these phase diagrams, the phase relations and P,T conditions are well delineated. The three selected samples of glaucophane eclogite AK05, AK11 and AK17 are estimated to have peak P,T conditions, respectively, of 540,550 °C at c. 16 kbar, c. 560 °C at 15,17 kbar and c. 580 °C at 15,19 kbar, and two samples of hornblende eclogite AK10 and AK30 of 610,630 °C and 17,18 kbar. Together with H2O-content contours in the related P,T pseudosections and textural relations, both types of eclogite are inferred to show clockwise P,T paths, with the hornblende eclogite being transformed from the glaucophane eclogite assemblage dominantly through increasing temperature. [source] Occurrence of calcite in Sanbagawa pelitic schists: implications for the formation of garnet, rutile, oligoclase, biotite and hornblendeJOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2002A. Goto Abstract The frequency of occurrence of minerals in 1876 samples of Sanbagawa pelitic schist in central Shikoku is summarized on the basis of microscopic observation accompanied, in part, by use of an electron microprobe. All samples contain quartz, plagioclase, phengite, chlorite and graphite. More than 90% of samples contain clinozoisite, titanite and apatite. Garnet is present in 95% of samples from the garnet zone, and biotite is present in 64% of samples from the albite-biotite zone. Calcite is found in about 40% of samples of the pelitic schist collected from outcrop, but occurs in 95% of the pelitic schist from drill cores. Calcite was apparently ubiquitous in the pelitic schist during the Sanbagawa metamorphism, but must have been dissolved recently by the action of surface or ground water. The mineral assemblages of the Sanbagawa pelitic schist have to be analyzed in the system with excess calcite, quartz, albite (or oligoclase), clinozoisite, graphite and fluid that is composed mainly of H2O, CO2 and CH4. In the presence of calcite, reactions that produce garnet, rutile, oligoclase, biotite and hornblende, some of which define isograds of the metamorphic belt, should be written as mixed volatile equilibria that tend to take place at lower temperature than the dehydration reactions that have been proposed. The presence of calcite in pelitic schist suggests that fluid composition is a variable as important in determining mineral assemblages as pressure and temperature. Thus Ca-bearing phases must be taken into account to analyze the phase relations of calcite-bearing pelitic schist, even if CaO content of Sanbagawa pelitic schist is low. As calcite is a common phase, the mineral assemblages of the biotite zone pelitic schist may contravene the mineralogical phase rule and warrant further study. [source]
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