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1.
The solubility of water in coexisting enstatite and forsterite was investigated by simultaneously synthesizing the two phases in a series of high pressure and temperature piston cylinder experiments. Experiments were performed at 1.0 and 2.0 GPa at temperatures between 1,100 and 1,420°C. Integrated OH absorbances were determined using polarized infrared spectroscopy on orientated single crystals of each phase. Phase water contents were estimated using the calibration of Libowitzky and Rossman (Am Mineral 82:1111–1115, 1997). Enstatite crystals, synthesized in equilibrium with forsterite and an aqueous phase at 1,350°C and 2.0 GPa, contain 114 ppm H2O. This is reduced to 59 ppm at 1,100°C, under otherwise identical conditions, suggesting a strong temperature dependence. At 1,350°C and 1.0 GPa water solubility in enstatite is 89 ppm, significantly lower than that at 2.0 GPa. In contrast water solubility in forsterite is essentially constant, being in the range 36–41 ppm for all conditions studied. These data give partition coefficients in the range 2.28–3.31 for all experiments at 1,350°C and 1.34 for one experiment at 1,100°C. The incorporation of Al2O3 in enstatite modifies the OH stretching spectrum in a systematic way, and slightly increases the water solubility.  相似文献   

2.
We define and calibrate a new model of molar volume as a function of pressure, temperature, ordering state, and composition for spinels in the supersystem (Mg, Fe2+)(Al, Cr, Fe3+)2O4 ? (Mg, Fe2+)2TiO4. We use 832 X-ray and neutron diffraction measurements performed on spinels at ambient and in situ high-P, T conditions to calibrate end-member equations of state and an excess volume model for this system. The effect on molar volume of cation ordering over the octahedral and tetrahedral sites is captured with linear dependence on Mg2+, Al3+, and Fe3+ site occupancy terms. We allow standard-state volumes and coefficients of thermal expansion of the end members to vary within their uncertainties during extraction of the mixing properties, in order to achieve the best fit. Published equations of state of the various spinel end members are analyzed to obtain optimal values of the bulk modulus and its pressure derivative, for each explicit end member. For any spinel composition in the supersystem, the model molar volume is obtained by adding excess volume and cation order-dependent terms to a linear combination of the five end-member volumes, estimated at pressure and temperature using the high-T Vinet equation of state. The preferred model has a total of 9 excess volume and order-dependent parameters and fits nearly all experiments to within 0.02 J/bar/mol, or better than 0.5 % in volume. The model is compared to the current MELTS spinel model with a demonstration of the impact of the model difference on the estimated spinel-garnet lherzolite transition pressure.  相似文献   

3.
本文采用合成溶胶凝胶中间体的技术方法,降低了硅酸盐熔体的熔化温度,并在１７５０～１８５０℃和２．０～４．０ＧＰａ条件下合面出９个ＳｉＯ２－Ａｌ２Ｏ３－Ｎａ２Ｏ（Ｋ２Ｏ）系列淬火硅权盐熔体,淬火熔体中Ｎａ（Ｋ）／Ａ１≤１属过铝质硅酸盐熔体,其激光拉曼微探针（ＬＲＭ）研究表明,随压力增大,Ｔ－Ｏｎｂ在高频区（９００～１２００ｃｍ＾－１）的对称和反对称伸缩振动频率明显减小,过铝质熔体中存在六配位铝,且随  相似文献   

4.
The thermal stability of sideronatrite, ideally Na2Fe3+(SO4)2(OH)·3(H2O), and its decomposition products were investigated by combining thermogravimetric and differential thermal analysis, in situ high-temperature X-ray powder diffraction (HT-XRPD) and Fourier transform infrared spectroscopy (HT-FTIR). The data show that for increasing temperature there are four main dehydration/transformation steps in sideronatrite: (a) between 30 and 40 °C sideronatrite transforms into metasideronatrite after the loss of two water molecules; both XRD and FTIR suggest that this transformation occurs via minor adjustments in the building block. (b) between 120 and 300 °C metasideronatrite transforms into metasideronatrite II, a still poorly characterized phase with possible orthorhombic symmetry, consequently to the loss of an additional water molecule; X-ray diffraction data suggest that metasideronatrite disappears from the assemblage above 175 °C. (c) between 315 and 415 °C metasideronatrite II transforms into the anhydrous Na3Fe(SO4)3 compound. This step occurs via the loss of hydroxyl groups that involves the breakdown of the [Fe3+(SO4)2(OH)] ∞ 2? chains and the formation of an intermediate transient amorphous phase precursor of Na3Fe(SO4)3. (d) for T > 500 °C, the Na3Fe(SO4)3 compound is replaced by the Na-sulfate thenardite, Na2SO4, plus Fe-oxides, according to the Na3Fe3+(SO4)3 → 3/2 Na2(SO4) + 1/2 Fe2O3 + SOx reaction products. The Na–Fe sulfate disappears around 540 °C. For higher temperatures, the Na-sulfates decomposes and only hematite survives in the final product. The understanding of the thermal behavior of minerals such as sideronatrite and related sulfates is important both from an environmental point of view, due to the presence of these phases in evaporitic deposits, soils and sediments including extraterrestrial occurrences, and from the technological point of view, due to the use of these materials in many industrial applications.  相似文献   

5.
Experiments on water solubility in forsterite in the systems Mg2SiO4–K2Mg(CO3)2–H2O and Mg2SiO4–H2O–C were conducted at 7.5–14.0 GPa and 1200–1600 °C. The resulting crystals contain 448 to 1480 ppm water, which is 40–70% less than in the forsterite–water system under the same conditions. This can be attributed to lower water activity in the carbonate-bearing melt. The water content of forsterite was found to vary systematically with temperature and pressure. For instance, at 14 GPa in the system forsterite–carbonate–H2O the H2O content of forsterite drops from 1140 ppm at 1200 °C to 450 ppm at 1600 °C, and at 8 GPa it remains constant or increases from 550 to 870 ppm at 1300–1600 °C. Preliminary data for D-H-bearing forsterite are reported. Considerable differences were found between IR spectra of D-H- and H-bearing forsterite. The results suggest that CO2 can significantly affect the width of the olivine-wadsleyite transition, i.e., the 410-km seismic discontinuity, which is a function of the water content of olivine and wadsleyite.  相似文献   

6.
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7.
Liquid–liquid immiscibility has crucial influences on geological processes, such as magma degassing and formation of ore deposits. Sulfate, as an important component, associates with many kinds of deposits. Two types of immiscibility, including (i) fluid–melt immiscibility between an aqueous solution and a sulfate melt, and (ii) fluid–fluid immiscibility between two aqueous fluids with different sulfate concentrations, have been identified for sulfate–water systems. In this study, we investigated the immiscibility behaviors of a sulfate- and quartz-saturated Na2SO4–SiO2–H2O system at elevated temperature, to explore the phase relationships involving both types of immiscibility. The fluid–melt immiscibility appeared first when the Na2SO4–SiO2–H2O sample was heated to ~270°C, and then fluid–fluid immiscibility emerged while the sample was further heated to ~450°C. At this stage, the coexistence of one water-saturated sulfate melt and two aqueous fluids with distinct sulfate concentrations was observed. The three immiscible phases remain stable over a wide pressure–temperature range, and the appearance temperature of the fluid–fluid immiscibility increases with the increased pressure. Considering that sulfate components occur extensively in carbonatite-related deposits, the fluid–fluid immiscibility can result in significant sulfate fractionation and provides implications for understanding the formation of carbonatite-related rare earth deposits.  相似文献   

8.
The pseudo-binary system Mg3Al2Si3O12–Na2MgSi5O12 modelling the sodium-bearing garnet solid solutions has been studied at 7 and 8.5 GPa and 1,500–1,950°C. The Na-bearing garnet is a liquidus phase of the system up to 60 mol% Na2MgSi5O12 (NaGrt). At higher content of NaGrt in the system, enstatite (up to ∼80 mol%) and then coesite are observed as liquidus phases. Our experiments provided evidence for a stable sodium incorporation in garnet (0.3–0.6 wt% Na2O) and its control by temperature and pressure. The highest sodium contents were obtained in experiments at P = 8.5 GPa. Near the liquidus (T = 1,840°C), the equilibrium concentration of Na2O in garnet is 0.7–0.8 wt% (∼6 mol% Na2MgSi5O12). With the temperature decrease, Na concentration in Grt increases, and the maximal Na2MgSi5O12 content of ∼12 mol% (1.52 wt% Na2O) is gained at the solidus of the system (T = 1,760°С). The data obtained show that most of natural diamonds, with inclusions of Na-bearing garnets usually containing <0.4 wt% Na2O, could be formed from sodium-rich melts at pressures lower than 7 GPa. Majoritic garnets with higher sodium concentrations (>1 wt% Na2O) may crystallize at a pressure range of 7.0–8.5 GPa. However the upper pressure limit for the formation of naturally occurring Na-bearing garnets is restricted by the eclogite/garnetite bulk composition.  相似文献   

9.
Samples with eclogitic composition in the system CaO–FeO–Fe2O3–MgO–Al2O3–SiO2 were produced from various kinds of starting materials held in graphite-lined Pt capsules at a pressure of 2.5–3.0 GPa and temperatures of 800–1,300 °C using a piston-cylinder or Belt apparatus. Garnets and clinopyroxenes were characterized by analytical transmission electron microscopy and electron probe micro-analysis (EPMA). Fe3+/ΣFe ratios determined by electron energy-loss spectroscopy (EELS) decrease in clinopyroxene from 22.2 ± 3.4 % at 800 °C to 13.3 ± 5.4 % at 1,300 °C, while in garnet, they vary between 10.8 ± 1.5 and 15.4 ± 4.7 %, respectively. Temperature estimates according to Krogh (Contrib Mineral Petrol 99:44–48, 1988) reproduce the experimental temperature to ±60 °C without systematic deviations if total iron is used in the calculation. If only the Fe2+ content is used, which was obtained by combining EPMA and EELS results, the experimental temperature is underestimated by 33 °C on average at 800–1,200 °C and overestimated by 77 °C on average at 1,300 °C. These systematic deviations can be explained by the temperature-dependent ratio of Fe2+/ΣFe in garnet divided by that in clinopyroxene. Since the difference between the calculated and experimental temperature is relatively small, a Fe2+-based recalibration of the thermometer appears not to be necessary for the investigated system in the range of pressure, temperature and composition covered by the experiments of this study.  相似文献   

10.
To elaborate physicochemical models for the origin of crystalline rocks, experimental studies of the field of high-alumina assemblages of the system CaO–MgO–Al2O3–SiO2 were carried out at 10–30 kbar and 1250–1535 °C. We have determined the phase relations between the melt (L) and An, Sp, Cpx, Cor, and Ga, the slope of the rays of the monovariant reactions An + Sp = Cpx + Cor + (Ga) and L = Cpx +Ga + Cor + Sp, the position of the nonvariant point (An, Sp, Cpx, Cor, Ga, L), and the compositions of phases participating in these reactions. Based on a topological analysis of the studied segment of the system CaO–MgO–Al2O3–SiO2, we have substantiated that “eclogitization” must follow the reaction Opx + An + Sp = Cpx + Ga. A fundamental continuous series of eutectic monovariant equilibria was observed: L = Cpx + Opx + Fo + An, L = Cpx + Opx + An + Sp, L = Cpx (+ Ga) + An + Sp, and L = Cpx + Cor (+ Ga) + An. A change in the melt composition in this series of eutectic reactions depending on pressure must reflect the most likely magma genesis trend in nature. Comparision of the composition fields in which the above series of reactions is observed with the composition fields of the rocks of magmatic formations showed that this series is most similar to the alkali-earth series of rocks. The mineralogical compositions of cumulates and phenocrysts found in the effusive and dike varieties of these rocks correspond to unique sets of subsolidus phase associations and individual subsolidus phases crystallizing in this fundamental eutectic series.  相似文献   

11.
Powell  R 梁方通 《世界地质》1992,11(1):216-226
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12.
正1 Introduction China has very abundant liquid mineral resources.Especially,the brine resources in the west of Sichuan Basin are pushed into the first place in China,whose K and B contents are unusually high.These rare liquid mineral resources have very good exploitation prospect(Lin,2001;2006).Generally speaking,phase equilibrium  相似文献   

13.
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14.
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15.
坯样中SiO2与Al2O3对电瓷制品机械强度的影响   总被引：3，自引：0，他引：3  
机械强度是电瓷制品的主要性能之一,与坯料中Ａｌ２Ｏ３与ＳｉＯ２质量分数有密切关系,本次试验结果表明,随着坯料中Ａｌ２Ｏ３质量分散的增加,ＳｉＯ２质量分数的减少,电瓷制品的抗折强度,抗冲击强度也相应提高,本文对其产生机理进行了较详细的讨论。f  相似文献   

16.
The equilibrium in which hydrous Fe-cordierite breaks down to almandine, sillimanite, quartz, and water was previously experimentally determined by Richardson (1968) and Holdaway and Lee (1977) using QMF buffer and by Weisbrod (1973) using QIF buffer. All these studies yielded similar results — a negative dP/dT slope for the equilibrium curve. However, based on theoretical arguments, Martignole and Sisi (1981), and based on Fe-Mg partitioning experiments on coexisting cordierite and garnet in equilibrium with sillimanite and quartz, Aranovich and Podlesskii (1983) suggested that this equilibrium curve has a positive dP/dT slope and its position depends on the water content of the equilibrium cordierite. We have redetermined this equilibrium using a much improved tecnique of detecting reaction direction, and cordierite starting material that contained virtually no hercynite. Hercynite was present as a contaminant in the cordierites of previous experimental studies and possibly reacted with quartz during the experimental runs to expand the apparent stability field of Fe-cordierite. We synthesized Fe-cordierite from reagent grade oxides at 710°C and 2 kbar (using QMF buffer) with two intermediate stages of grinding and mixing. The cordierite has a unit cell volume of 1574.60 Å3 (molar volume=23.706 J/bar) and no Fe3+ as indicated by X-ray diffraction and room temperature Mössbauer studies respectively. Reaction direction was concluded by noting20% change of the ratios of intensities of two key X-ray diffraction peaks of cordierite and almandine. Our results show that the four-phase equilibrium curve passes through the points 2.1 kbar, 650°C and 2.5 kbar, 750°C. This disagrees with all previous experimental studies. H2O in the Fe-cordierite, equilibrated at 2.2 kbar and 700°C and determined by H-extraction line in the stable isotope laboratory, is 1.13 wt% (n=0.41 moles). H2O content of pure Mg-cordierite equilibrated under identical conditions and determined by thermogravimentric conditions and determined by thermogravimetric analysis is 1.22 wt% (n=0.40). Similar determinations on Fe-cordierite and Mg-cordierite equilibrated at 2.0 kbar and 650°C show 1.27 wt% (n=0.46) and 1.47 wt% (n=0.48) of H2O respectively. Thus, H2O content appears to be independent of Fe/Mg ratio in cordierite, a conclusion which supports previous experimental determinations. The experimentally determined equilibrium curve represents conditions of PH2O=Ptotal. From this we calculated the anhydrous curve representing equilibrium under conditions of X H2O V =0.0. A family of calculated equilibrium curves of constant n H2O Cord cut the experimentally determined curve at a very small angle indicating a slight variation in n H2O Cord in cordierite in equilibrium with almandine, sillimanite, and quartz under the conditions of constant X H2O V . Ancther set of calculated equilibrium curves, each representing constant a H2O V demonstrate that the slopes of the curves vary with X H2O V , and are all positive in the full range of 0.0X H2O V 1.0.  相似文献   

17.
Experiments ranging from 2 to 3 GPa and 800 to 1300 °C and at 0.15 GPa and 770 °C were performed to investigate the stability and mutual solubility of the K2ZrSi3O9 (wadeite) and K2TiSi3O9 cyclosilicates under upper mantle conditions. The K2ZrSi3O9–K2TiSi3O9 join exhibits complete miscibility in the P–T interval investigated. With increasing degree of melting the solid solution becomes progressively enriched in Zr, indicating that K2ZrSi3O9 is the more refractory end member. At 2 GPa, in the more complex K2ZrSi3O9–K2TiSi3O9–K2Mg6Al2Si6O20(OH)4 system, the presence of phlogopite clearly limits the extent of solid solution of the cyclosilicate to more Zr-rich compositions [Zr/(Zr + Ti) > 0.85], comparable to wadeite found in nature, with TiO2 partitioning strongly into the coexisting mica and/or liquid. However, at 1200 °C, with increasing pressure from 2 to 3 GPa, the partitioning behaviour of TiO2 changes in favour of the cyclosilicate, with Zr/(Zr + Ti) of the K2(Zr,Ti)Si3O9 phase decreasing from ∼0.9 to ∼0.6. The variation in the Ti content of the coexisting phlogopite is related to its degree of melting to forsterite and liquid, following the major substitution VITi+VI□=2VIMg. Received: 26 January 1999 / Accepted: 10 January 2000  相似文献   

18.
The incorporation of hydrogen in enstatite in a hydrous system containing various amounts of NaCl was investigated at 25 kbar. The hydrogen content in enstatite shows a clear negative correlation to the NaCl-concentration in the system. The most favourable explanation is the reduction of water fugacity due to dilution. Other reasons for the limited hydrogen incorporation at high NaCl levels, such as a significant influence of Na+ on the defect chemistry or an exchange between OH- and Cl−in enstatite, appear much less important. A partition coefficient D Na En/Fluid = 0.0013 could be determined, demonstrating that Na is less incompatible in enstatite than H. The new results support the idea that dissolved components have to be considered when the total hydrogen storage capacity in nominally anhydrous minerals is estimated, especially in geological settings with high levels of halogens, such as subduction zones.  相似文献   

19.
The thermoelastic parameters of synthetic Mn3Al2Si3O12 spessartine garnet were examined in situ at high pressure up to 13 GPa and high temperature up to 1,100 K, by synchrotron radiation energy dispersive X-ray diffraction within a DIA-type multi-anvil press apparatus. The analysis of room temperature data yielded K 0 = 172 ± 4 GPa and K 0 ′  = 5.0 ± 0.9 when V 0,300 is fixed to 1,564.96 Å3. Fitting of P–V–T data by means of the high-temperature third-order Birch–Murnaghan EoS gives the thermoelastic parameters: K 0 = 171 ± 4 GPa, K 0 ′  = 5.3 ± 0.8, (?K 0,T /?T) P  = ?0.049 ± 0.007 GPa K?1, a 0 = 1.59 ± 0.33 × 10?5 K?1 and b 0 = 2.91 ± 0.69 × 10?8 K?2 (e.g., α 0,300 = 2.46 ± 0.54 × 10?5 K?1). Comparison with thermoelastic properties of other garnet end-members indicated that the compression mechanism of spessartine might be the same as almandine and pyrope but differs from that of grossular. On the other hand, at high temperature, spessartine softens substantially faster than pyrope and grossular. Such softening, which is also reported for almandine, emphasize the importance of the cation in the dodecahedral site on the thermoelastic properties of aluminosilicate garnet.  相似文献   

20.
The phase state of fluid in the system H3BO3–NaF–SiO2–H2O was studied at 350–800 °C and 1–2 kbar by the method of synthetic fluid inclusions. The increase in the solubility of quartz and the high reciprocal solubility of H3BO3 and NaF in water fluid at high temperatures are due to the formation of complexes containing B, F, Si, and Na. At 800 °C and 2 kbar, both liquid and gas immiscible phases (viscous silicate-water-salt liquid and three water fluids with different contents of B and F) are dispersed within each other. The Raman spectra of aqueous solutions and viscous liquid show not only a peak of [B(OH)3]0 but also peaks of complexes [B(OH)4]–, polyborates [B4O5(OH)4]2–, [B3O3(OH)4]–, and [B5O6(OH)4]–, and/or fluoroborates [B3F6O3]3–, [BF2(OH)2]–, [BF3(OH)]–, and [BF4]–. The high viscosity of nonfreezing fluid is due to the polymerization of complexes of polyborates and fluorine-substituted polyborates containing Si and Na. Solutions in fluid inclusions belong to P–Q type complicated by a metastable or stable immiscibility region. Metastable fluid equilibria transform into stable ones owing to the formation of new complexes at 800 ºC and 2 kbar as a result of the interaction of quartz with B-F-containing fluid. At high concentrations of F and B in natural fluids, complexes containing B, F, Si, and alkaline metals and silicate-water-salt dispersed phases might be produced and concentrate many elements, including ore-forming ones. Their transformation into vitreous masses or viscous liquids (gels, jellies) during cooling and the subsequent crystallization of these products at low temperatures (300–400 °C) should lead to the release of fluid enriched in the above elements.  相似文献   

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