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1.
Speciation of aqueous magnesium in the system MgO-SiO2-H2O-HCl in supercritical aqueous fluids has been investigated using standard rapid-quench hydrothermal techniques and a modification of the Ag + AgCl buffer method (Frantz and Eugster, 1973. Am. J. Sci.267, 268–286). A concentric double-capsule charge was utilized. The outer gold capsule contained the assemblage talc + quartz + Ag + AgCl + H2O-MgCl2 fluid; the inner platinum capsule, Ag + AgCl + H2O-HCl fluid. During the experiments, and thus equilibrated between the two capsules. After quenching, measurement of the chloride concentration in the fluid in the inner capsule and total magnesium in the fluid in the outer capsule defines the concentrations of HCl and Mg that coexist with talc + quartz in the outer capsule. Changes in the measured molality of HCl as a function of the total magnesium concentration at constant P and T were used to identify the predominant species of magnesium in the hydrothermal fluid. Experimental results showed that at 2000 bar, MgCl°2 is the predominant species above 550°C and Mg2+, below 400°C. Data at intermediate temperatures when combined with the dissociation constant for HCl were used to obtain the dissociation constant for MgCl°2. The results of these experiments were combined with results from experiments using Ag + AgCl in conjunction with the oxygen buffer, hematite-magnetite, to obtain the equilibrium constant for the reaction from which the difference in Gibbs free energy of MgCl°2 and HC1° was obtained as a function of temperature at 1000, 1500 and 2000 bar pressure, Solubility constants for brucite. forsterite, chrysotile, and talc were calculated. 相似文献
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本文介绍了热力学相图在浅成低温热液硫化物矿床中的应用,并以三江地区金顶铅锌矿床中的矿物含量为例进行定量分析。一方面在相同温度下,浓度与矿物(组合)之间存在对应关系,并且一些矿物(组合)对应特定的酸碱条件,例如在400K和105Pa条件下,黄铁矿与方铅矿的组合在碱性环境下稳定,而方铅矿与闪锌矿的组合在酸性环境中稳定,且酸性条件下当lg[Pb2+]≥-11.29时,才开始出现方铅矿;另一方面对比了298.15K和400K条件下矿物共生组合的及介质pH值的变化情况,并得到400K条件下形成矿物或矿物组合所需离子的浓度更高。 相似文献
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Speciation of aqueous calcium chloride and the solubility of wollastonite represented by the reaction wollastonite + 2HCl° → CaCl2° + quartz + H2O were experimentally investigated at 1 and 2 kbar in the range 425–600°C using rapid-quench hydrothermal techniques and a modified Ag + AgCl buffer technique (Frantz and Popp, 1979). Variation in the measured concentration in HCl° as a function of total dissolved calcium was used to identify associated aqueous CaCl2° as the predominant calcium species in the fluid at temperatures above 500°C at 2 kbar. The data were used to calculate the equilibrium constant for the above reaction as a function of temperature and pressure, from which the difference in Gibbs free energy of formation between CaCl2° and HCl° at 1 and 2 kbar, 450°–600°C was calculated. Solubility constants for minerals in the system MgO-CaO-SiO2-H2O-HCl-CO2 were calculated using the data from this study and from Frantz and Popp (1979). Calculated mineral solubilities were used to calculate the solution compositions and solid alteration products resulting from interactions of a Ca-Mg silicate mineral (diopside) with hydrothermal solutions containing a range of different total chloride concentrations. High total chloride (2.0 m) in the solution results in Si-Mg enrichment in the solids and Ca enrichment in the fluid, whereas low total chloride (0.008 m) results in Mg enrichment in the solids and Ca-Si enrichment in the fluid. 相似文献
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An equation of state (EOS) based on thermodynamic perturbation theory is presented for the NaCl-H2O-CH4 system. This equation consistently reproduces PvTX properties and phase equilibria with an accuracy close to that of data in the temperature, pressure and concentration ranges from 648 K to 873 K, 0 to 2500 bar and up to 2.37 mol % NaCl. Good agreement with recent ternary immiscibility data from 673 K to 873 K suggests that the EOS may provide accurate predictions for NaCl concentrations as high as 40 mol %. We could not find any experimental data above 873 K that can be used to validate the predictions of the EOS inside the ternary. However, parameters for the mixed ternary system were established from parameters evaluated for pure and binary systems and accurate combination rules. Therefore, predictions in the ternary should be reliable to the high temperatures and pressures where the EOS for the lower order systems are valid (about 1300 K and 5000 bar). Using the same combining approach, an EOS for the quaternary NaCl-H2O-CO2-CH4 is constructed on the basis of parameters from our earlier model for the NaCl-H2O-CO2 system and the present NaCl-H2O-CH4 model. This suggests that predictions of the quaternary EOS are reliable also to about 1300 K and 5000 bar. 相似文献
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Bruce G. Aitken 《Geochimica et cosmochimica acta》1983,47(3):351-362
At a total pressure of 5 kb, calcic, Cl-free scapolite (Me83) is stable relative to plagioclase-bearing assemblages at , . With decreasing temperature, scapolite breaks down to plagioclase + calcite. Scapolite is replaced by plagioclase + grossular + cancrinite + CO2 in the presence of H2O-rich fluids. The stable coexistence of scapolite and calcite, an assemblage typical of most natural occurrences of calcic scapolite, is limited by the reaction: scapolite + calcite → grossular + cancrinite + CO2, which occurs at 750°C, XCO2 = 0.46; 700°C, XCO2 = 0.33; 650°C, XCO2 = 0.18, for the chosen bulk composition.Generalization of the experimental results to encompass the complete range of fully carbonated scapolite compositions indicates that mizzonite (Me75) has the largest T-XCO2 stability field. For scapolite more calcic than mizzonite, stable growth is restricted to conditions of increasingly higher temperature and XCO2.The experimental results are consistent with various petrologic features of scapolite-bearing rocks, particularly scapolite-clinopyroxene granulites, and indicate that such rocks were formed in the presence of CO2-rich fluids. 相似文献
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Chemical equilibrium between sodium-aluminum silicate minerals and chloride bearing fluid has been experimentally determined in the range 500–700°C at 1 kbar, using rapid-quench hydrothermal methods and two modifications of the Ag + AgCl acid buffer technique. The temperature dependence of the thermodynamic equilibrium constant (K) for the reaction Albite Andalusite Qtz. can be described by the following equation: log k = ?4.437 + 5205.6/T(K) The data from this study are consistent with experimental results reported by Montoya and Hemley (1975) for lower temperature equilibria defined by the assemblages albite + paragonite + quartz + fluid and paragonite + andalusite + quartz + fluid. Values of the equilibrium constants for the above reactions were used to estimate the difference in Gibbs free energy of formation between NaClo and HClo in the range 400–700°C and 1–2 kbar. Similar calculations using data from phase equilibrium studies reported in the literature were made to determine the difference in Gibbs free energy of formation between KClo and HClo. These data permit modelling of the chemical interaction between muscovite + kspar + paragonite + albite + quartz assemblages and chloride-bearing hydrothermal fluids. 相似文献
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The solubility of hematite in chloride-bearing hydrothermal fluids was determined in the temperature range 400–600°C and at 1000 and 2000 bars using double-capsule, rapid-quench hydrothermal techniques and a modification of the Ag + AgCl buffer method (Frantz and Popp, 1979). The changes in the molalities of associated hydrogen chloride () as a function of the molality of total iron in the fluid at constant temperature and pressure were used to identify the predominant species of iron in the hydrothermal fluid. The molality of associated HCl varied from 0.01 to 0.15. Associated FeCl20 was found to be the most abundant species in equilibrium with hematite. Determination of Cl/Fe in the fluid in equilibrium with hematite yields values approximately equal to 2.0 suggesting that ferrous iron is the dominant oxidation state.The equilibrium constant for the reaction Fe2O3 + 4HCl0 + H2 = 2FeCl20 + 3H2O was calculated and used to estimate the difference in Gibbs free energy between FeCl20 and HCl0 in the temperature range 400–600°C at 1000 and 2000 bars pressure. 相似文献
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Nabil Z Boctor 《Geochimica et cosmochimica acta》1985,49(2):565-575
The solubility of rhodonite, represented by the reaction MnSiO3 (rhodonite) + 2HCl0 = MnCl20 + SiO2 (quartz) + H2O, was investigated experimentally in the temperature range 400°–700°C at 1 and 2 kbar by rapid-quench hydrothermal techniques and the Ag-AgCl buffer methods. Variations in the molalities of associated hydrogen chloride (mHCl0) as a function of the molalities of total Mn indicate that Mn in the fluid in equilibrium with the assemblage rhodonite + quartz is predominantly associated as MnCl20. The Mn:Cl in the fluid ?2, indicating that Mn+2 is the dominant oxidation state.The solubility data were used to calculate the equilibrium constant of the above reaction as a function of temperature, pressure, and the difference in Gibbs free energy of formation between MnCl20 and HCl0. The equilibrium constants of solubility for Mn minerals for which thermochemical data are available were also calculated. Calculated mineral solubilities were used in conjunction with the data of Frantz et al. (1981) to calculate the composition of supercritical fluids in equilibrium with Mn-bearing phases and assemblages. At 400°C and 1000 bars, supercritical fluids in equilibrium with olivines of compositions similar to those present in MORB tend to be enriched in Mn, despite the low mole fraction of tephroite in the olivine. Supercritical fluids in equilibrium with the assemblage quartz-hematite-rhodonite at 500° and 400°C and 1000 bars show high concentrations of Mn relative to Fe. Manganese concentrations in the fluids increase with decrease in the mole fraction of H, whereas Fe concentrations decrease. The data indicate that H fugacity plays a significant role in the separation of Mn from Fe in chloride-bearing hydrothermal fluids at supercritical temperatures. 相似文献
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The system CaMgSi2O6CaAl2SiO6CaFeAlSiO6 has been studied in air at 1 atm. The phase assemblage at subsolidus temperatures in the CaMgSi2O6-rich portion is Cpx + An + Mel and that in the CaMgSi2O6-poor portion Cpx + An + Mel + Sp. At subsolidus temperatures the sigle-phase field of clinopyroxene increases with an increase in the CaFeAlSiO6 component of the system. The Al2O3 content of clinopyroxene, however, continues to increase beyond the single-phase field and attains at least 16.04 wt.% Al2O3 with 3.9 wt.% Fe2O3. The stability field of fassaite in the system over a range of pressures and oxygen fugacities has been estimated from data in the literature as well as the present data. The CaFeAlSiO6 content of fassaite is dependent on oxygen fugacity, but is not influenced by pressure. The stability field is strongly influenced by oxygen fugacity at low and high pressure, and decreases with decreasing oxygen fugacity. Clinopyroxenes in both volcanic and metamorphic rocks from various localities, when plotted on the CaMgSi2O6CaAl2SiO6CaFeAlSiO6 triangle, show that there is no compositional gap between diopside and fassaitic pyroxene in metamorphic rocks, and that the fassaitic pyroxene in alkalic rocks becomes richer in both CaAl2SiO6 and CaFeAlSiO5 components as crystallization proceeds. These results agree with those obtained in the experimental study. 相似文献
14.
Dionysis I. Foustoukos Jennifer L. Houghton Stefan M. Sievert 《Geochimica et cosmochimica acta》2011,75(6):1594-1607
Hydrothermal experiments were conducted to evaluate the kinetics of H2(aq) oxidation in the homogeneous H2-O2-H2O system at conditions reflecting subsurface/near-seafloor hydrothermal environments (55-250 °C and 242-497 bar). The kinetics of the water-forming reaction that controls the fundamental equilibrium between dissolved H2(aq) and O2(aq), are expected to impose significant constraints on the redox gradients that develop when mixing occurs between oxygenated seawater and high-temperature anoxic vent fluid at near-seafloor conditions. Experimental data indicate that, indeed, the kinetics of H2(aq)-O2(aq) equilibrium become slower with decreasing temperature, allowing excess H2(aq) to remain in solution. Sluggish reaction rates of H2(aq) oxidation suggest that active microbial populations in near-seafloor and subsurface environments could potentially utilize both H2(aq) and O2(aq), even at temperatures lower than 40 °C due to H2(aq) persistence in the seawater/vent fluid mixtures. For these H2-O2 disequilibrium conditions, redox gradients along the seawater/hydrothermal fluid mixing interface are not sharp and microbially-mediated H2(aq) oxidation coupled with a lack of other electron acceptors (e.g. nitrate) could provide an important energy source available at low-temperature diffuse flow vent sites.More importantly, when H2(aq)-O2(aq) disequilibrium conditions apply, formation of metastable hydrogen peroxide is observed. The yield of H2O2(aq) synthesis appears to be enhanced under conditions of elevated H2(aq)/O2(aq) molar ratios that correspond to abundant H2(aq) concentrations. Formation of metastable H2O2 is expected to affect the distribution of dissolved organic carbon (DOC) owing to the existence of an additional strong oxidizing agent. Oxidation of magnetite and/or Fe++ by hydrogen peroxide could also induce formation of metastable hydroxyl radicals (•OH) through Fenton-type reactions, further broadening the implications of hydrogen peroxide in hydrothermal environments. 相似文献
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Anders Lindh 《Lithos》1972,5(4):325-343
Phase relations in the system FeO---Fe2O3---TiO2, at temperatures ranging between 300°C and 700°C, have been investigated experimentally with special refference to the reaction Fe3O4 + TiO2 = Fe2O3 + FeTiO3. Pressure was varied between 500 and 2000 bars but its effect was negligible. Magnetite and rutile are the stable assemblage at temperatures above 550 dgC, and hematite and ilmenite are stable for lower temperatures. The equilibrium oxygen fugacity is estimated to be 10−17.5 bars at equilibrium temperature. It is suggested that intermediate hematite-ilmenite solid solutions are inhomogeneous, consisting of ‘domains’ of hematite and ilmenite. The ‘domains’ are too small to be resolved by X-ray diffraction techniques. The top of the solvus curve in the hematite-ilmenite solution corresponds to a temperature of 660°C. Regular solution theory is not applicable to the solid solution. 相似文献
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低硅埃达克岩(low-SiO2adakites,LSA,SiO2<60%)和高硅埃达克岩(high-SiO2adakites,HSA,SiO2>60%)的术语是Martin等(2005)提出来的。本文不赞同上述分类,因为,他们的低硅埃达克岩是赞岐岩而不是埃达克岩。赞岐岩是幔源的,埃达克岩是壳源的,虽然埃达克岩可以与地幔混合形成高镁的埃达克岩,但仍然是壳源的。不应当把壳源的岩浆和幔源的岩浆混淆起来。 相似文献
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《Geochimica et cosmochimica acta》1986,50(7):1475-1484
The heat capacity of a natural monticellite (Ca1.00Mg.09Fe.91Mn.01Si0.99O3.99) measured between 9.6 and 343 K using intermittent-heating, adiabatic calorimetry yields Cp0(298) and S2980 of 123.64 ± 0.18 and 109.44 ± 0.16 J · mol−1K−1 respectively. Extrapolation of this entropy value to end-member monticellite results in an S0298 = 108.1 ± 0.2 J · mol−1K−1. High-temperature heat-capacity data were measured between 340–1000 K with a differential scanning calorimeter. The high-temperature data were combined with the 290–350 K adiabatic values, extrapolated to 1700 K, and integrated to yield the following entropy equation for end-member monticellite (298–1700 K): ST0(J · mol−1K−1) = S2980 + 164.79 In T + 15.337 · 10−3T + 22.791 · 105T−2 − 968.94. Phase equilibria in the CaO-MgO-SiO2 system were calculated from 973 to 1673 K and 0 to 12 kbar with these new data combined with existing data for akermanite (Ak), diopside (Di), forsterite (Fo), merwinite (Me) and wollastonite (Wo). The location of the calculated reactions involving the phases Mo and Fo is affected by their mutual solid solution. A best fit of the thermodynamically generated curves to all experiments is made when the S0298 of Me is 250.2 J · mol−1 K−1 less than the measured value of 253.2 J · mol−1 K−1.A best fit to the reversals for the solid-solid and decarbonation reactions in the CaO-MgO-SiO2-CO2 system was obtained with the ΔG0298 (kJ · mole−1) for the phases Ak(−3667), Di(−3025), Fo(−2051), Me(−4317) and Mo(−2133). The two invariant points − Wo and −Fo for the solid-solid reactions are located at 1008 ± 5 K and 6.3 ± 0.1 kbar, and 1361 ± 10 K and 10.2 ± 0.2 kbar respectively. The location of the thermodynamically generated curves is in excellent agreement with most experimental data on decarbonation equilibria involving these phases. 相似文献
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The solubility of crystalline Mg(OH)2(cr) was determined by measuring the equilibrium H+ concentration in water, 0.01-2.7 m MgCl2, 0.1-5.6 m NaCl, and in mixtures of 0.5 and 5.0 m NaCl containing 0.01-0.05 m MgCl2. In MgCl2 solutions above 2 molal, magnesium hydroxide converted into hydrated magnesium oxychloride. The solid-liquid equilibrium of Mg2(OH)3Cl·4H2O(cr) was studied in 2.1-5.2 m MgCl2. Using known ion interaction Pitzer coefficients for the system Mg-Na-H-OH-Cl-H2O (25°C), the following equilibrium constants at I = 0 are calculated:
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Claude T. Herzberg 《Geochimica et cosmochimica acta》1978,42(7):945-957
One petrogenetic grid for plagioclase-, spinel- and garnet-lherzolite analogues in the system CaO-MgO-Al2O3-SiO2 is presented from 1 bar to 30 kbar and 400 to 1500°C. Another grid for olivine-gabbro, spinel-gabbro and garnet-pyroxenite analogues in the same system is presented from 1 bar to 25 kbar and 500 to 1500°C. Both grids show the distribution of the mineral assemblages and the variations in the composition of clinopyroxene with temperature and pressure. They were developed by applying simple thermodynamic mixing models of clinopyroxene to experimentally determined clino-pyroxene compositions.Calcium tschermak's pyroxene (CaAl2SiO6) in complex CaMgSi2O6-CaAl2SiO6-Mg2Si2O6 clinopyroxenes is best represented by a local charge balance mixing model where Enthalpy and entropy changes of subsolidus reactions involving variations in the CaAl2SiO6 and Mg2Si2O6 content of clinopyroxene are interdependent due to nonideal mixing of these two end-members. CaAl2SiO6 can strongly reduce the mutual solubility of clinopyroxene and orthopyroxene at moderate pressures and high temperatures. Failure to take this into account can result in temperature underestimates (up to 150°C) of spinel-lherzolites, garnet-pyroxenites, low pressure garnet-lherzolites, spinel-gabbros, and high pressure plagioclase-lherzolites and olivine-gabbros. However, at temperatures and pressures where the Al2O3 content of clinopyroxene is low (e.g. garnet-lherzolite nodules in kimberlite), the mutual solubility is adequantely represented by experimental results in the system CaO-MgO-SiO2. 相似文献