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Equations are developed for calculating the density of aluminosilicate liquids as a function of composition and temperature. The mean molar volume at reference temperature Tr, is given by , where the summation is taken over all oxide components except A12O3, X stands for mole fraction, terms are constants derived independently from an analysis of volume-composition relations in alumina-free silicate liquids, and is the composition-dependent apparent partial molar volume of Al2O3. The thermal expansion coefficient of aluminosilicate liquids is given by , where terms are constants independent of temperature and composition, and is a composition-dependent term representing the effect of Al2O3 on the thermal expansion. Parameters necessary to calculate the volume of silicate liquids at any temperature T according to V(T) = Vrexp[α(T-Tr)], where Tr = 1400°C have been evaluated by least-square analysis of selected density measurements in aluminosilicate melts. Mean molar volumes of aluminosilicate liquids calculated according to the model equation conform to experimentally measured volumes with a root mean square difference of 0.28 and an average absolute difference of 0.90% for 248 experimental observations. The compositional dependence of is discussed in terms of several possible interpretations of the structural role of Al3+ in aluminosilicate melts. 相似文献
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Ralph Kretz 《Geochimica et cosmochimica acta》1982,46(3):411-421
Differences in the chemical composition of metamorphic and igneous pyroxene minerals may be attributed to a transfer reaction, which determines the Ca content of the minerals, and an exchange reaction, which determines the relative Mg:Fe2+ ratios. Natural data for associated Ca pyroxene (Cpx) and orthopyroxene (Opx) or pigeonite are combined with experimental data for Fe-free pyroxenes, to produce the following equations for the Cpx slope of the solvus surface: , and the following equation for the temperature-dependence of the Mg-Fe distribution coefficient: , where T is absolute temperature, X is , [Ca] is in Cpx, and KD is the distribution coefficient, defined as .The transfer and exchange equations form useful temperature indicators, and when applied to 9 sets of well-studied rocks, yield pairs of temperatures that are in good agreement. For example, temperatures obtained for the Bushveld Complex are 1020°C (solvus equation) and 980°C (exchange equation), based on 7 specimens. The uncertainty in these numbers, due to precision and accuracy errors, is estimated to be ±60°. 相似文献
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J.R Holloway 《Geochimica et cosmochimica acta》1973,37(3):651-666
The stability of the amphibole pargasite [NaCa2Mg4Al(Al2Si6))O22(OH)2] in the melting range has been determined at total pressures (P) of 1.2 to 8 kbar. The activity of H2O was controlled independently of P by using mixtures of H2O + CO2 in the fluid phase. The mole fraction of H2O in the fluid () ranged from 1.0 to 0.2.At P < 4 kbar the stability temperature (T) of pargasite decreases with decreasing at constant P. Above P ? 4 kbar stability T increases as is decreased below one, passes through a T maximum and then decreases with a further decrease in . This behavior is due to a decrease in the H2O content of the silicate liquid as decreases. The magnitude of the T maximum increases from about 10°C (relative to the stability T for ) at P = 5 kbar to about 30°C at P = 8 kbar, and the position of the maximum shifts from at P = 5 kbar to at P = 8 kbar.The H2O content of liquid coexisting with pargasite has been estimated as a function of at 5 and 8 kbar P, and can be used to estimate the H2O content of magmas. Because pargasite is stable at low values of at high P and T, hornblende can be an important phase in igneous processes even at relatively low H2O fugacities. 相似文献
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Bruce S. Hemingway Richard A. Robie James A. Kittrick 《Geochimica et cosmochimica acta》1978,42(10):1533-1543
Solution calorimetric measurements compared with solubility determinations from the literature for the same samples of gibbsite have provided a direct thermochemical cycle through which the Gibbs free energy of formation of [Al(OH)4 aq?] can be determined. The Gibbs free energy of formation of [Al(OH)4 aq?] at 298.15 K is ?1305 ± 1 kJ/mol. These heat-of-solution results show no significant difference in the thermodynamic properties of gibbsite particles in the range from 50 to 0.05 μm.The Gibbs free energies of formation at 298.15 K and 1 bar pressure of diaspore, boehmite and bayerite are ?9210 ± 5.0, ?918.4 ± 2.1 and ?1153 ± 2 kJ/mol based upon the Gibbs free energy of [A1(OH)4 aq?] calculated in this paper and the acceptance of ?1582.2 ± 1.3 and ?1154.9 ± 1.2 kJ/mol for the Gibbs free energy of formation of corundum and gibbsite, respectively.Values for the Gibbs free energy formation of [Al(OH)2 aq+] and [AlO2 aq?] were also calculated as ?914.2 ± 2.1 and ?830.9 ± 2.1 kJ/mol, respectively. The use of [AlC2 aq?] as a chemical species is discouraged.A revised Gibbs free energy of formation for [H4SiO4aq0] was recalculated from calorimetric data yielding a value of ?1307.5 ± 1.7 kJ/mol which is in good agreement with the results obtained from several solubility studies.Smoothed values for the thermodynamic functions CP0, (, , ST0 - S00, kaolinite are listed at integral temperatures between 298.15 and 800 K. The heat capacity of kaolinite at temperatures between 250 and 800 K may be calculated from the following equation: CP0 = 1430.26 ? 0.78850 T + 3.0340 × 10?4T2 ?1.85158 × 10?4T2.The thermodynamic properties of most of the geologically important Al-bearing phases have been referenced to the same reference state for Al, namely gibbsite. 相似文献
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Roger A. Burke James M. Brooks William M. Sackett 《Geochimica et cosmochimica acta》1981,45(5):627-634
Light hydrocarbon (C1-C3) concentrations in the water from four Red Sea brine basins (Atlantis II, Suakin, Nereus and Valdivia Deeps) and in sediment pore waters from two of these areas (Atlantis II and Suakin Deeps) are reported. The hydrocarbon gases in the Suakin Deep brine (T = ~ 25°C, , ) are apparently of biogenic origin as evidenced by ) ratios of ~ 1000. Methane concentrations (6–8 μl/l) in Suakin Deep sediments are nearly equal to those in the brine, suggesting sedimentary interstitial waters may be the source of the brine and associated methane.The Atlantis II Deep has two brine layers with significantly different light hydrocarbon concentrations indicating separate sources. The upper brine (T = ~ 50°C, , CH4 = ~ 155 μl/l) gas seems to be of biogenic origin [], whereas the lower brine (T = ~ 61°C, , CH4 = ~ 120μl/l) gas is apparently of thermogenic origin []. The thermogenic gas resulting from thermal cracking of organic matter in the sedimentary column apparently migrates into the basin with the brine, whereas the biogenic gas is produced in situ or at the seawater-brine interface. Methane concentrations in Atlantis II interstitial waters underlying the lower brine are about one half brine concentrations; this difference possibly reflects the known temporal variations of hydrothermal activity in the basin. 相似文献
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Frank J Millero 《Geochimica et cosmochimica acta》1982,46(1):11-22
The effect of presure on the solubility of minerals in water and seawater can be estimated from In where the volume (ΔV) and compressibility (ΔK) changes at atmospheric pressure (P = 0) are given by Values of the partial molal volume () and compressibilty () in water and seawater have been tabulated for some ions from 0 to 50°C. The compressibility change is quite large (~10 × 10?3 cm3 bar?1 mol?1) for the solubility of most minerals. This large compressibility change accounts for the large differences observed between values of ΔV obtained from linear plots of In Ksp versus P and molal volume data (Macdonald and North, 1974; North, 1974). Calculated values of for the solubility of CaCO3, SrSO4 and CaF2 in water were found to be in good agreement with direct measurements (Macdonald and North, 1974). Similar calculations for the solubility of minerals in seawater are also in good agreement with direct measurements (Ingle, 1975) providing that the surface of the solid phase is not appreciably altered. 相似文献
8.
N Guilhaumou P Dhamelincourt J-C Touray J Touret 《Geochimica et cosmochimica acta》1981,45(5):657-673
Optical and analytical studies were performed on 400 N2 + CO2 gas bearing inclusions in dolomites and quartz from Triassic outcrops in northern Tunisia. Other fluids present include brines (NaCl and KCl bearing inclusions) and rare liquid hydrocarbons. At the time of trapping, such fluids were heterogeneous gas + brine mixtures. In hydrocarbon free inclusions the mole ratio was determined using two different non-destructive and punctual techniques: Raman microprobe analysis, and optical estimation of the volume ratios of the different phases selected at low temperatures. In the observed range of compositions, the two methods agree reasonably well.The N2 + CO2 inclusions are divided into three classes of composition: (a) : Liquid nitrogen is always visible at very low temperature and homogenisation occurs in the range ?151°C to ? 147°C (nitrogen critical temperature) dry ice (solid CO2) sublimates between ?75°C and ?60°C; (b) : liquid nitrogen is visible at very low temperature but dry ice melts on heating; liquid and gas CO2 homogenise to liquid phase between ?51°C to ?22°C; (c) : liquid nitrogen is not visible even at very low temperature (?195°C) and liquid and gas CO2 homogenise to liquid phase between ?22°C and ?15°C. The observed phases changes are used to propose a preliminary phase diagram for the system CO2-N2 at low temperatures.Assuming additivity of partial pressures, isochores for the CO2-N2 inclusions have been computed. The intersection of these isochores with those for brine inclusions in the same samples may give the P and T of trapping of the fluids. 相似文献
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Calculations based on approximately 350 new measurements (CaT-PCO2) of the solubilities of calcite, aragonite and vaterite in CO2-H2O solutions between 0 and 90°C indicate the following values for the log of the equilibrium constants KC, KA, and KV respectively, for the reaction CaCO3(s) = Ca2+ + CO2?3: where T is in oK. At 25°C the logarithms of the equilibrium constants are ?8.480 ± 0.020, ?8.336 ± 0.020 and ?7.913 ± 0.020 for calcite, aragonite and vaterite, respectively.The equilibrium constants are internally consistent with an aqueous model that includes the CaHCO+3 and CaCO03 ion pairs, revised analytical expressions for CO2-H2O equilibria, and extended Debye-Hückel individual ion activity coefficients. Using this aqueous model, the equilibrium constant of aragonite shows no PCO2-dependence if the CaHCO+3 association constant is between 0 and 90°C, corresponding to the value logKCahco+3 = 1.11 ± 0.07 at 25°C. The CaCO03 association constant was measured potentiometrically to be between 5 and 80°C, yielding logKCaCO03 = 3.22 ± 0.14 at 25°C.The CO2-H2O equilibria have been critically evaluated and new empirical expressions for the temperature dependence of KH, K1 and K2 are , and logK2 = ?107.8871 ? 0.03252849T + 5151.79/T + 38.92561 logT ? 563713.9/T2 which may be used to at least 250°C. These expressions hold for 1 atm. total pressure between 0 and 100°C and follow the vapor pressure curve of water at higher temperatures.Extensive measurements of the pH of Ca-HCO3 solutions at 25°C and 0.956 atm PCO2 using different compositions of the reference electrode filling solution show that measured differences in pH are closely approximated by differences in liquid-junction potential as calculated by the Henderson equation. Liquid-junction corrected pH measurements agree with the calculated pH within 0.003-0.011 pH.Earlier arguments suggesting that the CaHCO+3 ion pair should not be included in the CaCO3-CO2-H2O aqueous model were based on less accurate calcite solubility data. The CaHCO+3 ion pair must be included in the aqueous model to account for the observed PCO2-dependence of aragonite solubility between 317 ppm CO2 and 100% CO2.Previous literature on the solubility of CaCO3 polymorphs have been critically evaluated using the aqueous model and the results are compared. 相似文献
11.
Thermal analysis of the halite liquidus in the system NaCl-H2O has been conducted for NaCl mole fractions (XNaCl) greater than 0.25 (i.e., > 50 wt. % NaCl) at pressures between 0.3 and 4.1 kb and temperatures greater than 450°C. The position of the liquidus was located by differential thermal analysis (DTA) of cooling scans only, as heating scans did not produce definitive DTA peaks. The dP/dT slope of the liquidus is positive and steep at high pressures, but at high XNaCl, and pressures below 0.5 kb it appears to reverse slope and intersects the three-phase curve (liquid-halite-vapour) at a shallow angle. However, due to the complex nature of the DTA signal when P <- 0.5 kb, there is considerable doubt about exactly what event has been recorded in the experiments conducted at these low pressures.The solubility of halite can be expressed as a function of the mole-fractional-based activity of NaCl in the liquid phase (L) in temperature (T, °K) and pressure (P, bars) In Our liquidus data (based on 10 compositions) above 500 bars for these brines were combined with this equation to generate activity coefficients of NaCl which were fit within their experimental uncertainties to the following one parameter Margules equation In . Concentrated solutions of NaCl show negative deviations from ideality which rapidly increase in magnitude with decreasing XNaCl. 相似文献
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John Geover 《Geochimica et cosmochimica acta》1974,38(10):1527-1548
For a phase at equilibrium in which two cation species are partitioned ideally between two sub-lattice sites, the excess functions of mixing (free energy, enthalpy and entropy) are directly related to the bulk composition of the phase and ΔGE°(T, P), the standard-state intra- crystalline exchange free energy. If the phase is not at equilibrium internally, an additional ordering parameter is necessary to fix the excess free energy of mixing, GmixEX, unambiguously. Conversely, for any fixed GmixEX there exists an infinity of possible intracrystalline cation dis- tributions, only one of which is the equilibrium distribution for the specified temperature and pressure. As ideal intraphase cation ordering becomes more pronounced, GmixEX decreases. In response, the total free energy of mixing for the phase decreases progressively for non-end member compositions, approaching, at the limits of ordering, values appropriate for stabilizing compounds of intermediate composition.The model-dependent activity coefficient for component A in the phase, γAT, can be calculated for any bulk composition, XAT, either from GmixEX directly or from more basic equations involving the interrelation of chemical potentials at equilibrium. A general form for γAT is ln , where Xjκ denotes the mole fraction of species j in site κ. The first term on the right-hand side of this equation is the contribution to γAT from ideal intracrystalline partitioning, and is common to the several theories lately presented to model intraphase cation partitioning. It can be shown rigorously that this term contributes to a negative deviation from ideality for the bulk phase. The second term is the contribution to the macroscopic activity coefficient from non-ideal intraphase partitioning, and is related to an enthalpy of mixing, HmixN in excess of that resulting from ideal inter-site cation ordering. While the expression represented by Y can take several functional forms, the additional enthalpy can be evaluated explicitly for specific non-ideal partitioning models from the relation .In those cases, GmixEX can also be determined exactly. 相似文献
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A differential rate equation for silica-water reactions from 0–300°C has been derived based on stoichiometry and activities of the reactants in the reaction SiO2(s) + 2H2O(l) = H4SiO4(aq) where () = (the relative interfacial area between the solid and aqueous phases/the relative mass of water in the system), and k+ and k? are the rate constants for, respectively, dissolution and precipitation. The rate constant for precipitation of all silica phases is and Eact for this reaction is 49.8 kJ mol?1. Corresponding equilibrium constants for this reaction with quartz, cristobalite, or amorphous silica were expressed as . Using , k was expressed as and a corresponding activation energy calculated:
a | b | c | Eact(kJ mol -1) | |
Quarts | 1.174 | -2.028 x 103 | -4158 | 67.4–76.6 |
α-Cristobalite | -0.739 | 0 | -3586 | 68.7 |
β-Cristobalite | -0.936 | 0 | -3392 | 65.0 |
Amorphous silica | -0.369 | -7.890 x 10-4 | 3438 | 60.9–64.9 |