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1.
A new microscope vacuum heating stage and gas analyzer has been developed for measurement of H2O, CO2, SO2, and noncondensable gas (H2, CO, N2, Ar, CH4, etc.) evolved from samples, particularly natural glass, at temperatures up to 1280°C. The gas evolved upon heating to 1280δC is collected in a liquid nitrogen cold trap. Gas components are identified by the characteristic vapor pressure and temperature ranges over which solid and vapor are in equilibrium during sublimation of individual components. The masses of CO2, SO2, and H2O derived from samples and blanks are calculated using the ideal gas law, the molecular weights of the components, and the gauge constant (i.e. the ratio of the number of moles of a gas to its partial pressure in the constant volume). Results obtained by repeated determinations of H2O, CO2, and SO2 evolved from a submarine basaltic glass from Kilauea volcano, Hawaii, (average sample mass = 3 × 10?3 g) gave probable errors for the determinations of H2O (0.23%), CO2 (0.025%), and S (0.071%) equal to 4, 10, and 8% respectively, of the concentrations. Determinations of H2O in smaller samples of H2O-poor basaltic pumice show a linear proportionality (0.063%) between the measured H2O and the sample mass over the range 0.1 × 10?6 to 1.7 × 10?6 g H2O. Comparisons of H2O determinations by this technique with those obtained by Penfield, gas chromatic, microcoulometric, and vacuum fusion techniques used elsewhere show reasonably good agreement. Determinations of SO2 by this technique agree reasonably well X-ray fluorescence and electron microprobe determinations of sulfur. Determinations of CO2 by the present technique are reproducible but cannot be compared directly to measurements made in other labs because of differences in samples analyzed. The principle advantages of this analytical technique are the very small sample required, the simultaneous determination of H2O, CO2, SO2 and noncondensable gas, the avoidance of calibration procedures dependent on chemical standards, and the visual observations that can be made during sample outgassing.  相似文献   

2.
Comparison of theoretical and analytical equilibrium constants based on the reactions CH4 + 2H2O = CO2 + 4H2, 2NH3 = N2 + 3H2 and iron(II)-aluminium-silicate + 2H2S = FeS2 + H2 + aluminium-silicate, shows that the composition of fluids discharged from geothermal areas in New Zealand (Wairakei, Kawerau, Broadlands) reflects close to complete attainment of chemical equilibrium within the system H2O, CO2, H2S, NH3, H2, N2 and CH4. Under conditions prevailing in explored geothermal systems in New Zealand, the minerals graphite (elemental carbon), anhydrite, pyrrhotite, magnetite do not appear to take part in the overall equilibrium system. The three physical parameters required to evaluate geothermal gas reactions are temperature, pressure and vapor-liquid ratios within the gas equilibration zone.  相似文献   

3.
According to the compositions of the underground brine resources in the west of Sichuan Basin, solubilities of the ternary systems NaBr–Na2SO4–H2O and KBr–K2SO4–H2O were investigated by isothermal method at 348 K. The equilibrium solid phases, solubilities of salts, and densities of the solutions were determined. On the basis of the experimental data, the phase diagrams and the density-composition diagrams were plotted. In the two ternary systems, the phase diagrams consist of two univariant curves, one invariant point and two crystallization fields. Neither solid solution nor double salts were found. The equilibrium solid phases in the ternary system NaBr–Na2SO4–H2O are NaBr and Na2SO4, and those in the ternary system KBr–K2SO4–H2O are KBr and K2SO4. Using the solubilities data of the two ternary subsystems at 348 K, mixing ion-interaction parameters of Pitzer’s equation θxxx, Ψxxx and Ψxxx were fitted by multiple linear regression method. Based on the chemical model of Pitzer’s electrolyte solution theory, the solubilities of phase equilibria in the two ternary systems NaBr–Na2SO4–H2O and KBr–K2SO4–H2O were calculated with corresponding parameters. The calculation diagrams were plotted. The results showed that the calculated values have a good agreement with experimental data.  相似文献   

4.
Theory is derived from the work of Urey (Urey H. C. [1947] The thermodynamic properties of isotopic substances. J. Chem. Soc. 562-581) to calculate equilibrium constants commonly used in geochemical equilibrium and reaction-transport models for reactions of individual isotopic species. Urey showed that equilibrium constants of isotope exchange reactions for molecules that contain two or more atoms of the same element in equivalent positions are related to isotope fractionation factors by α = (Kex)1/n, where n is the number of atoms exchanged. This relation is extended to include species containing multiple isotopes, for example 13C16O18O and 1H2H18O. The equilibrium constants of the isotope exchange reactions can be expressed as ratios of individual isotope equilibrium constants for geochemical reactions. Knowledge of the equilibrium constant for the dominant isotopic species can then be used to calculate the individual isotope equilibrium constants.Individual isotope equilibrium constants are calculated for the reaction CO2g = CO2aq for all species that can be formed from 12C, 13C, 16O, and 18O; for the reaction between 12C18O2aq and 1H218Ol; and among the various 1H, 2H, 16O, and 18O species of H2O. This is a subset of a larger number of equilibrium constants calculated elsewhere (Thorstenson D. C. and Parkhurst D. L. [2002] Calculation of individual isotope equilibrium constants for implementation in geochemical models. Water-Resources Investigation Report 02-4172. U.S. Geological Survey). Activity coefficients, activity-concentration conventions for the isotopic variants of H2O in the solvent 1H216Ol, and salt effects on isotope fractionation have been included in the derivations. The effects of nonideality are small because of the chemical similarity of different isotopic species of the same molecule or ion. The temperature dependence of the individual isotope equilibrium constants can be calculated from the temperature dependence of the fractionation factors.The derivations can be extended to calculation of individual isotope equilibrium constants for ion pairs and equilibrium constants for isotopic species of other chemical elements. The individual isotope approach calculates the same phase isotopic compositions as existing methods, but also provides concentrations of individual species, which are needed in calculations of mass-dependent effects in transport processes. The equilibrium constants derived in this paper are used to calculate the example of gas-water equilibrium for CO2 in an acidic aqueous solution.  相似文献   

5.
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6.
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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7.
Erickson and Helz (2000) established that molybdate, MoO4−2, is quickly and completely transformed to thiomolybdate, MoS4−2, by reaction with sulfide. They monitored the equilibria and kinetics of this process by measuring the UV-visible spectra of solutions containing the different oxythiomolybdate species. There is interest in the analogous reactions for the ReO4− species but little experimental data. We have therefore calculated quantum-chemically the equilibrium constants in solution for the sulfidation reactions of both MoO4−2 and ReO4−, as well as recalculating their UV-visible charge-transfer spectra. Calculations using configuration interaction singles and time-dependent hybrid Hartree-Fock density functional methods give good absolute values and trends in UV-vis energies for both series. For MoO4−2 the calculated equilibrium constants for the various sulfidation steps match reasonably well against the experimental values (within two log K units). For the ReO4− sulfidation reaction the first two steps are considerably less favorable than for MoO4−2, suggesting that the “geochemical switch” of Erickson and Helz, a rapid transformation of oxyanion to thioanion highly dependent on sulfide concentration, will be less effective in the Re case. However, both our calculations and experiment indicate that ReO4− and ReS4− are both easier to reduce than their Mo analogs, so that reduction of these Re(VII) species will be the preferred mechanism for their removal from seawater. A previous suggestion that the neutral species MoO4H2 is actually the hydrated octahedral Mo(OH)6 species is found to be incorrect, but the MoO3(OH2)3 species, a highly distorted six-coordinate complex, is almost competitive in energy with MoO4H2 plus two H2O.  相似文献   

8.
EH pH diagrams have been calculated using the PHREEQC programme in order to establish the predominance fields of Mn, Fe, Co, Ni, Cu and As in bottom waters from the Angola Basin. Predominance fields are presented separately for both aquatic species and solid mineral phases in order to simplify interpretation of the data. The diagrams show significant differences from standard EH pH diagrams for these elements calculated for freshwater at 25 °C and 1 bar which assume an element concentration of 10-6 M. In particular, our diagrams show that Mn2+ and NiCO 3 0 are the predominant aquatic species for Mn and Ni in bottom seawater and FeOOH, Fe2O3, Fe3O4, CoFe2O4, CuFe2O4, CuFeO2, and Ba3 (AsO4)2 the predominant solid phases for Fe, Co, Cu and As, respectively. Mn and Ni are therefore undersaturated and Fe, Co, Cu and As supersaturated in bottom seawater from the Angola Basin. Neither rhodochrosite (MnCO3) nor siderite (FeCO3) can form in this marine environment in equilibrium with seawater. A mixed Mn-Ca carbonate is therefore formed within the pore waters of reducing sediments. The high Ni/Cu ratios in cobalt-rich manganese crusts formed adjacent to the oxygen minimum zone may be explained by the change from Cu2+ to CuCl 3 2- as the dominant aquatic species of Cu in seawater at an EH of +0.48 V.  相似文献   

9.
Nickel plays a central role as an enzyme co-factor in the metabolism of methanogenic Archaea. Methanogens can fractionate Ni isotopes during assimilation, opening the possibility of using the stable isotopic composition of Ni as a biomarker. However, other sources of Ni isotopic variations need to be evaluated before one can establish Ni isotopes as an unambiguous tracer of methanogenesis in the rock record. Equilibrium exchange of Ni between the different species present in the ocean is a potential source of isotopic fractionation. Through controlled laboratory experiments and theoretical calculations, we quantify equilibrium Ni isotope fractionation between different species relevant to the modern and ancient ocean: Ni(H2O)62+, Ni(H2O)182+, NiOH(H2O)5+, Ni(OH)2(H2O)4, NiCl(H2O)5+, cis-NiCl2(H2O)4, trans-NiCl2(H2O)4, NiHS(H2O)5+, Ni(HS)2(H2O)4, NiSO4(H2O)4, NiHCO3(H2O)4+, NiCO3(H2O)4, and organic ligands (crown ether and oxalic acid). The magnitude of ligand-controlled Ni isotopic fractionation, approximately 1.25‰/amu (2.5‰ for the 60Ni/58Ni ratio), is similar to that previously measured in cultures of methanogenic Archaea.  相似文献   

10.
During the metamorphism of siliceous carbonates, decomposition of tremolite yields diopside, enstatite, quartz and H2O according to the following reaction: 1 tremolite 2 diopside + 3 enstatite + 1 quartz + 1 H2O.For the application to natural processes, it is of special interest to evaluate the equilibrium temperature of this reaction, as a function of the CO2-content of the H2O-CO2 fluid phase for several total pressures. These values were calculated for the total pressures of 1000 and 2000 bars, usingBoyd's experimentally determined univariant equilibrium data [Fig. 1 (Boyd, 1954 and 1959)]. Curves (a) and (b) of Fig. 3 give the results in a temperature-X CO 2-diagram.The decomposition curves of tremolite intersect the equilibrium curves of other reactions which also take place during metamorphism of siliceous carbonates. If the total pressure can be estimated, these points of intersection together with the appropriate field observations will give information on the temperature and composition of the fluid phase during metamorphism.  相似文献   

11.
The fractionation of the isotopes of Mo between different geological environments has recently been determined to high accuracy using mass spectrometry (Barling et al., 2001). Fractionation is observed between Mo in seawater, where it exists primarily in the form of the Mo(VI) anion molybdate, MoO4−2, and in oxic sediments, where the Mo is isotopically lighter than in sea water by ∼1.8‰ (in terms of the 97Mo, 95Mo isotope pair). EXAFS evidence exists for a five- or six-coordinate Mo environment in the Fe,Mn oxyhydroxides of ferromanganese nodules (Kuhn et al., 2003). In sediment regimes which are anoxic and sulfidic (sometimes referred to as euxinic), where the Mo(VI) is expected to exist as a sulfide, no fractionation is observed compared to seawater. This is presumably because of the stoichiometric conversion of the Mo from MoO4−2 to MoS4−2 (Erickson and Helz, 2000) and then to other sulfides. If the conversion is stoichiometrically complete, mass balance requires the same isotopic distribution in reactant and product. This is a result of the very high equilibrium constant for this reaction. Thus, to understand isotopic fractionation processes both the equilibrium constants for the isotopic fractionation reactions and the equilbrium constants for transformation of one chemical compound to another must be considered.We here present quantum mechanical calculations of the isotopic fractionation equilibrium constants for the isotopes 92Mo and 100Mo between MoO4−2, MoO3(OH)−, MoO2(OH)2, MoO3, MoO3(OH2)3, MoS4−2 and a number of other oxidic and sulfidic complexes of Mo. The fractionation equilibrium constants are calculated directly from the computed vibrational, rotational and translational contributions to the free energy in the gas-phase using quantum methods. Calculated vibrational frequencies and ratios of frequencies for different isotopomers are first obtained using a number of different quantum methods and compared with available experimental data to establish the most reliable methodology.We have also calculated free energy changes in aqueous solution for a range of reactions of MoO4−2 and MoO2(OH)2 with H2O and H2S. We present evidence for the instability of the monomeric octahedral species Mo(OH)6 commonly assumed to exist in acid solution and suggest highly distorted six-coordinate MoO3(OH2)3 or three-coordinate MoO3 as better representations of the species present. We have also calculated visible-UV absorption spectra to support our interpretation of the speciation. MoO3 is calculated to be isotopically lighter than MoO4−2 by 1.6‰, consistent with the experimentally observed difference between sea water and oxic sediments. We explain the isotopic lightness of oxic sediments as arising from an intermediate step in which a three coordinate MoO3 species is formed in aqueous solution, and subsequently attaches to the surface of a Fe,Mn oxyhydroxide mineral.  相似文献   

12.
Molecular based equations of state (EOS) are attractive because they can take into account the energetic contribution of the main types of molecular interactions. This study models vapor-liquid equilibrium (VLE) and PVTx properties of the H2O-CO2 binary system using a Lennard-Jones (LJ) referenced SAFT (Statistical Associating Fluid Theory) EOS. The improved SAFT-LJ EOS is defined in terms of the residual molar Helmholtz energy, which is a sum of four terms representing the contributions from LJ segment-segment interactions, chain-forming among the LJ segments, short-range associations and long-range multi-polar interactions. CO2 is modeled as a linear chain molecule with a constant quadrupole moment, and H2O is modeled as a spherical molecule with four association sites and a dipole moment. The multi-polar contribution to Helmholtz energy, including the dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole contribution for H2O-CO2 system, is calculated using the theory of Gubbins and Twu (1978). Six parameters for pure H2O and four parameters for pure CO2 are needed in our model. The Van der Waals one-fluid mixing rule is used to calculate the Lennard-Jones energy parameter and volume parameter for the mixture. Two or three binary parameters are needed for CO2-H2O mixtures, which are evaluated from phase equilibrium data of the binary system. Comparison with the experimental data shows that our model represents the PVT properties of CO2 better than other SAFT EOS without a quadrupole contribution. For the CO2-H2O system, our model agrees well with the vapor-liquid equilibrium data from 323-623 K. The average relative deviation for CO2 solubility (expressed in mole fraction) in water is within 6%. Our model can also predict the PVTx properties of CO2-H2O mixtures up to 1073 K and 3000 bar. The good performance of this model indicates that: (1) taking account of the multi-polar contribution explicitly improves the agreement of calculated properties with experimental data at high temperatures and high pressures, (2) the molecular-based EOS with just a few parameters fit to data in the sub-critical region can predict the thermodynamic properties of fluids over a wide range of P-T conditions.  相似文献   

13.
Quaternary volcanism in the Mt. Shasta region has produced primitive magmas [Mg/(Mg+Fe*)>0.7, MgO>8 wt% and Ni>150 ppm] ranging in composition from high-alumina basalt to andesite and these record variable extents ofmelting in their mantle source. Trace and major element chemical variations, petrologic evidence and the results of phase equilibrium studies are consistent with variations in H2O content in the mantle source as the primary control on the differences in extent of melting. High-SiO2, high-MgO (SiO2=52% and MgO=11 wt%) basaltic andesites resemble hydrous melts (H2O=3 to 5 wt%) in equilibrium with a depleted harzburgite residue. These magmas represent depletion of the mantle source by 20 to 30 wt% melting. High-SiO2, high-MgO (SiO2=58% and MgO=9 wt%) andesites are produced by higher degrees of melting and contain evidence for higher H2O contents (H2O=6 wt%). High-alumina basalts (SiO2=48.5% and Al2O3=17 wt%) represent nearly anhydrous low degree partial melts (from 6 to 10% depletion) of a mantle source that has been only slightly enriched by a fluid component derived from the subducted slab. The temperatures and pressures of last equilibration with upper mantle are 1200°C and 1300°C for the basaltic andesite and basaltic magmas, respectively. A model is developed that satisfies the petrologic temperature constraints and involves magma generation whereby a heterogeneous distribution of H2O in the mantle results in the production of a spectrum of mantle melts ranging from wet (calc-alkaline) to dry (tholeiitic).  相似文献   

14.
Dissolved oxygen (DO) and organic carbon (Corg) are among the highest- and lowest-potential reactants, respectively, of redox couples in natural waters. When DO and Corg are present in subsurface settings, other couples are drawn toward potentials imposed by them, generating a bimodal clustering of calculated redox potentials. Which cluster a couple is drawn toward is determined by whether the couple’s oxidant or reductant is more concentrated. Generally, reactants >10-6M are near equilibrium with their dominant complementary reactant and in a cluster, whereas reactants <10-6M are relatively slow to react and diverge from the clusters. These observations suggest that reactions of higher-potential oxidants with lower-potential reductants commonly proceed simultaneously, regardless of the presence of other potential reactants, with the rates of reaction being determined more by concentration than relative potentials. As DO or Corg decreases, the potential gap separating couples diminishes. In waters having quantifiable concentrations of higher potential oxidants O2 and NO3-, [H2] was not diagnostic of their presence. In the water we analyzed having no quantifiable O2 or NO3-, redox potential calculated with [H2] was similar to potentials calculated for SO42- reduction and methanogenesis. Composite reactions, NO3-→N2 and O2→H2O, are best characterized in multiple steps due to slow reaction of low-concentration intermediates. The [CO] data we report, among the first for groundwater, are high compared to water equilibrated with the atmosphere.  相似文献   

15.
A model is developed for the calculation of coupled phase and aqueous species equilibrium in the H2O-CO2-NaCl-CaCO3 system from 0 to 250 °C, 1 to 1000 bar with NaCl concentrations up to saturation of halite. The vapor-liquid-solid (calcite, halite) equilibrium together with the chemical equilibrium of H+, Na+, Ca2+, , Ca(OH)+, OH−, Cl−, , , CO2(aq) and CaCO3(aq) in the aqueous liquid phase as a function of temperature, pressure, NaCl concentrations, CO2(aq) concentrations can be calculated, with accuracy close to those of experiments in the stated T-P-m range, hence calcite solubility, CO2 gas solubility, alkalinity and pH values can be accurately calculated. The merit and advantage of this model is its predictability, the model was generally not constructed by fitting experimental data.One of the focuses of this study is to predict calcite solubility, with accuracy consistent with the works in previous experimental studies. The resulted model reproduces the following: (1) as temperature increases, the calcite solubility decreases. For example, when temperature increases from 273 to 373 K, calcite solubility decreases by about 50%; (2) with the increase of pressure, calcite solubility increases. For example, at 373 K changing pressure from 10 to 500 bar may increase calcite solubility by as much as 30%; (3) dissolved CO2 can increase calcite solubility substantially; (4) increasing concentration of NaCl up to 2 m will increase calcite solubility, but further increasing NaCl solubility beyond 2 m will decrease its solubility.The functionality of pH value, alkalinity, CO2 gas solubility, and the concentrations of many aqueous species with temperature, pressure and NaCl(aq) concentrations can be found from the application of this model. Online calculation is made available on www.geochem-model.org/models/h2o_co2_nacl_caco3/calc.php.  相似文献   

16.
Recent experimental studies have reported the existence of two new Sb sulfide species, Sb2S52− and Sb2S62−, in alkaline sulfidic solutions in equilibrium with stibnite, Sb2S3, and orthorhombic S. These species contain Sb(V), which has also recently been identified in similar solutions using EXAFS by other researchers. This represents a significant change from the consensus a decade ago that sulfidic solutions of Sb contained only Sb(III) species. I have calculated from first principles of quantum mechanics the energetics for the oxidation of the Sb(III) sulfide dimer Sb2S42− to the mixed Sb(III,V) dimer Sb2S52− and then to the all Sb(V) dimer, Sb2S62−. Gas-phase reaction energies have been evaluated using polarized valence double zeta effective core potential basis sets and Moller-Plesset second order treatments of electron correlation. All translational, rotational and vibrational contributions to the gas-phase reaction free energy have been calculated. Hydration energies have been obtained using the COSMO version of the self-consistent reaction field polarizable continuum method. Negative free energy changes are calculated for the oxidation of the dianion of the III,III dimer to the III,V dimer by both small polysulfides, like S4H−, and elemental S, modeled as S8. For the further oxidation of the III,V dimer to the V,V dimer the reaction free energies are calculated to be close to zero. The partially protonated Sb III,III dimer monoanion HSb2S4− can also be oxidized, but the reaction is not so favorable as for the dianion. Comparison of the calculated aqueous deprotonation energies of H2Sb2S4, H2Sb2S5 and H2Sb2S6 and their dianions with values calculated for various oxyacids indicates that the III,V and V,V dimers will have pKa2 values <5, so that their dianions will be the dominant species in alkaline solutions. These results are thus consistent with the recent identification of Sb2S52− and Sb2S62− species. I have also calculated the Raman spectra of Sb2S52− and Sb2S62− to assist in their identification. The calculated vibrational frequencies of the III,V and V,V dimers are characteristically higher than those of the III,III dimer I previously studied. The III,V dimer may contribute shoulders to the Raman spectrum.  相似文献   

17.
The melting of phlogopite-quartz and sanidine-quartz under vapor-absent conditions and in the presence of H2O-CO2 vapor have been determined from 5–20 kbar. In the lower crust (P=6–10 kbar), phlogopite + quartz melts incongruently to enstatite + liquid at temperatures as low as 710° C in the presence of H2O. When the activity of water is sufficiently reduced by addition of CO2, phlogopite + quartz undergoes a dehydration reaction to enstatite + sanidine + vapor, for example at 790±10° C, 5 kbar, with \(X_{H_2 O}^V\) =0.35. In the absence of vapor, phlogopite + quartz is stable up to a maximum temperature of 900° C in the crust; at higher temperatures this assemblage melts incongruently to enstatite + sanidine + liquid. The melting of sanidine-quartz in the presence of H2O-CO2 vapor shows marked topological differences from melting in the system albite-H2O-CO2, and as a result, apparent activity coefficients for water calculated from sanidine-quartz H2O-CO2 are less than those calculated from albite-H2O-CO2 by up to a factor of five. These data shed light on anatexis in the lower crust, but uncertainties related to ordering of Al and Si in natural and synthetic micas forestall a more rigorous analysis. Nevertheless, maximum temperatures for some granulite terranes can be established.  相似文献   

18.
We have examined the effect of pressure on the apparent equilibrium constant, K′, for magnetite solubility (Fe3O4mt + 6HClfluid + H2fluid = 3FeCl2fluid + 4H2Ofluid) and the relative iron-carrying capacities of magmatic vapor and brine by conducting experiments in a rhyolite melt-vapor-brine-magnetite system at 800°C, fO2 = NNO and pressures ranging from 100 to 145 MPa. Iron concentrations in synthetic vapor and brine fluid inclusions were quantified by using laser-ablation inductively-coupled-plasma-mass-spectrometry (LA-ICPMS). Hydrogen chloride (HCl) concentrations in magmatic vapor were inferred by potentiometric measurements of H+ in quenched run product fluids. These data yield calculated values for log K′, assuming aH2O = XH2O, of 1.7, 4.9, 6.2, 6.8 and 9.1 at 100, 110, 130, 140 and 145 MPa, respectively. The concentration of iron in magmatic vapor increases by an order of magnitude, whereas the concentration of iron in magmatic brine remains constant (within 1σ) with increasing pressure as the 800°C critical pressure is approached along the vapor-brine solvus. The concentrations of iron in vapor and brine fluid inclusions yield calculated partition coefficients (DFev/b) of 0.05, 0.14, 0.27 and 0.56 at 110, 130, 140 and 145 MPa, respectively. Our data reveal that pressure fluctuations may significantly affect the value of log K′. More importantly, the data demonstrate conclusively that a significant amount of iron can be transported by a low-density aqueous vapor in the magmatic-hydrothermal environment.  相似文献   

19.
The reaction chloritoid (ctd)=almandine (alm)+diaspore+H2O (CAD) has been reversed using Fe3+-free synthetic chloritoid and almandine, under fO2 conditions of the solid oxygen buffer Fe/FeO (CADWI), and using partially oxidized synthetic minerals under fO2 conditions of the solid oxygen buffer Ni/NiO (CADNNO). Experiments have been conducted between 550 and 700°C, 25 and 45 kbar. The equilibrium pressure and temperature conditions are strongly dependent on the fO2 conditions (CADNNO lies some-what 50°C higher than CADWI). This can be explained by a decrease in aH2O for experiments conducted on the Fe/FeO buffer, and a decrease in actd and aalm (through incorporation of ferric iron preferentially in chloritoid) for experiments conducted on the Ni/NiO buffer. The H2O activity has been calculated using the MRK equation of state, and the values obtained checked against the shift of the equilibrium diaspore=corundum+H2O bracketed on the Fe/FeO buffer and under unbuffered fO2 conditions. For fO2 buffered by the assemblage Fe/FeO, aH2O increases with pressure from about 0.85 at 600°C, 12 kbar to about 0.9 at 605°C, 25 kbar and 1 above 28 kbar. For fO2 buffered by the assemblage Ni/NiO, aH2O=1. The aH2O decrease from Ni/NiO to Fe/FeO is, however, too small to be entirely responsible for the temperature shift between CADNNO and CADWI. In consequence, the amount of ferric iron in almandine and chloritoid growing in the CADNNO experiments must be significant and change along the CADNNO, precluding calculation of the thermodynamic properties of chloritoid from this reaction. Our experimental data obtained on the Fe/FeO buffer are combined, using a thermodynamic analysis, with Ganguly's (1969) reversal of the reaction chloritoid=almandine+corundum +H2O (CAC) on the same oxygen buffer. Experimental brackets are mutually consistent and allow extraction of the thermodynamic parameters H o f,ctd and S octd. Our thermodynamic data are compared with others, generally calculated using Ganguly's bracketing of CACNNO. The agreement between the different data sets is relatively good at low pressure, but becomes rapidly very poor toward high pressure conditions. Using our thermodynamic data for chloritoid and KD=(Fe3+/Al)ctd/(Fe3+/Al)alm estimated from natural assemblages, we have calculated the composition of chloritoid and almandine growing from CADNNO and CACNNO. The Fe3+ content in chloritoid and almandine increases with pressure, from less than 0.038 per FeAl2SiO5(OH)2 formula unit at 10 kbar to at least 0.2 per formula unit above 30 kbar. This implies that chloritoid and almandine do contain Fe3+ in most natural assemblages. The reliability of our results compared to natural systems and thermodynamic data for Mg-chloritoid is tested by comparing the equilibrium conditions for the reaction chloritoid+quartz=garnet (gt)+kyanite+H2O (CQGK), calculated for intermediate Fe–Mg chloritoid and garnet compositions, from the system FASH and from the system MASH. For 0.65<(XFe)gt<0.8, CQKG calculated from FASH and MASH overlap for KD=(Mg/Fe)ctd/(Mg/Fe)gt=2. This is in good agreement with the KD values reported from chloritoid+garnet+quartz+kyanite natural assemblages.  相似文献   

20.
《Geochimica et cosmochimica acta》1999,63(13-14):2025-2041
A new method for computing complicated equilibria in hydrothermal mixed fluids, H2O-non-polar gas, is proposed. The computation algorithm is based on the electrostatic approach for the interaction between aqueous species and H2O. The approach uses the SUPCRT92 database and the HKF format and may be considered as an application of the revised HKF model for mixed H2O-non-polar gas fluids. Thermodynamic properties of dissolved gases at high temperatures and pressures are calculated using the Redlich-Kwong approach. Dielectric permittivity of the mixed solvent is estimated by the modified Kirkwood equation.The proposed approach is validated using available experimental data on the dissociation constants of H2O and NaCl and the solubility of both covalent and ion crystals (SiO2, AgCl, Ag2SO4, Ca(OH)2, CaCO3) in H2O-non-polar component (dioxane, Ar, CO2) mixtures. Predicted and experimental data are in close agreement over a wide range of P-T-xgas conditions (up to 500°C, 4 kbar and 0.25–0.3 mole fraction of non-polar gas). It is also shown how the computation method can be applied to estimate the Born parameters of aqueous species.The proposed approach enables not only examination of isolated reactions, but the study of equilibria of whole systems. Thus, it allows modelling of mixed natural fluids.  相似文献   

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