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1.
William E. Glassley 《Geochimica et cosmochimica acta》1983,47(3):597-616
Compositional differences between granulite facies rocks and equivalent amphibolite facies rocks and the observation of CO2-rich fluid inclusions in granulites, have led to the suggestion that CO2 must play a role in modifying the composition of deep continental crust. How CO2 effects this change has remained unclear. Using the thermodynamic properties of aqueous ions in a fluid of evolving ratio, it is possible to model the incongruent dissolution of feldspars under conditions appropriate for granulite facies metamorphism. The results demonstrate that dissolution will be strongly enhanced at high ratios, with ion solubilities being Na+ >K+ ? Ca++. This enhancement is compatible with the reported compositional contrasts between granulite and amphibolite facies rock, but requires large fluid volumes.To test the dissolution model, a detailed field and petrologic study was conducted in a well exposed granulite facies terrane in West Greenland. Strong correlation between fluid composition and bulk rock chemistry can be documented; CO2-rich regions contain rocks which consistently have low ratios, while H2O-rich regions consistently have high ratios. Magnetite rims on sulfide grains are ubiquitous in high regions and are absent in high regions, and they provide evidence that CO2 was introduced into the region. These correlations and observations are predictable from the properties of the dissolution process. These considerations, along with observations regarding graphite petrogenesis, provide strong arguments that the total fluid volume interacting with the rock during metamorphism was very large, in some cases equaling or exceeding total rock volume. Such large fluid volumes can lead to significant compositional modification of the crust, and will mask the original protolith chemistry. Such processes should lead to Ca- and Al-enriched, Na-, K-, S- and Si-depleted residues in the deep crust. 相似文献
2.
A new technique for the determination of intrinsic oxygen fugacities () of single and polyphase geological samples with solid ZrO2, oxygen-specific electrolytes is described. Essentially the procedure involves isolating the emf signal from the sample from that unavoidably imposed by the residual atmosphere inside the sample-bearing sensor. By varying the of the residual atmosphere, it is possible to determine a ‘plateau’ value of constant recorded from the sensor which represents a reversed intrinsic measurement for the sample alone, and where the extent of the plateau reflects the innate buffering capability of the sample. A measure of the precision and accuracy of the data obtained is the fact that identical values are obtained whether on a heating or cooling cycle of the sample + compatible atmosphere system.These techniques have been applied to measurements of the intrinsic of spinels from peridotites and megacryst assemblages from Australia, West Germany and the U.S.A. Oxidation states range from ~- 0.25 log10 units more oxidized to 1 log10 unit more reduced than the iron-wüstite (IW) buffer. The overall reduced nature of the spinels and the range of 's obtained are striking features of the data. One implication of the results is that the majority of mantle-derived magmas are initially highly reduced, and the relatively oxidized values observed at surface (~- 4–5 log10 orders more oxidized than IW) reflect late-stage alteration, perhaps by H2 loss (Sato, 1978). 相似文献
3.
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
4.
Stability constants of hydroxocomplexes of Al(III):Al(OH)2+ and A1(OH)4? have been measured in the 20–70°C temperature range by reactions involving only dissolved species. The stability constant of the first complex ion is studied by measuring pH of solutions of aluminium salts at several concentrations. of aluminate ion is deduced from equilibrium constants of the reaction between the trioxalato aluminium (III) complex ion and Al3+ in acid medium, and between the same complex ion and A1(OH)4? in alkaline medium. The K values and the associated ΔH are and ΔH1 = 11.8 Kcal; and ΔH4 = 42.45 Kcal. These last results are not in agreement with the values of recent tables for and of Al3+ and Al(OH)4?. We suggest a consistent set of data for dissolved and solid Al species and for some aluminosilicates. 相似文献
5.
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
6.
Experimental quartz solubilities in H2O (Anderson and Burnham, 1965, 1967) were used together with equations of state for quartz and aqueous species (Helgesonet al., 1978; Walther and Helgeson, 1977) to calculate the dielectric constant of H2O () at pressures and temperatures greater than those for which experimental measurements (Heger, 1969; Lukashovet al., 1975) are available ( and ). Estimates of computed in this way for 2 kb (which are the most reliable) range from 9.6 at 600°C to 5.6 at 800°C. These values are 0.5 and 0.8 units greater, respectively, than corresponding values estimated by Quist and Marshall (1965), but they differ by <0.3 units from extrapolated values computed from Pitzer's (1983) adaptation of the Kirkwood (1939) equation. The estimates of generated from quartz solubilities at 2 kb were fit with a power function of temperature, which was then used together with equations and data given by Helgeson and Kirkham (1974a,b, 1976) Helgesonet al. (1981), and Helgeson (1982b, 1984) to calculate Born functions, Debye Hückel parameters, and the thermodynamic properties of Na+, K+, Mg++, Ca++, and other aqueous species of geologic interest at temperatures to 900°C. 相似文献
7.
T.M Seward 《Geochimica et cosmochimica acta》1973,37(3):379-399
The solubility of gold in aqueous sulphide solutions has been determined from pH20°C ≈ 4 to pH20°C ≈ 9.5 in the presence of a pyrite-pyrrhotite redox buffer at temperatures from 160 to 300°C and 1000 bar pressure. Maximum solubilities were obtained in the neutral region of pH as, for example, with mNaHS = 0.15 m, pH20°C = 5.96, T = 309°C, P = 1000 bar where a gold solubility of 225 mg/kg was obtained. It was concluded that three thio gold complexes contributed to the solubility. The complex Au2(HS)2S2? predominated in alkaline solution, the Au(HS)2? complex occurred in the neutral pH region, and in the acid pH region, it was concluded with less certainty that the Au(HS)° complex was present. Formation constants calculated forAu2(HS)2S2? and Au (HS)2? emphasize their high stability. In the temperature range from 175 to 250°C, values of pβ for Au2(HS)2S2? vary from ?53.0 to 47.9 (±1.6) and from ?23.1 to ?19.5 ( ± 1.5) for Au(HS)2?. Equilibrium constante for the dissolution reactions, and 2Au° + H2S + 2H8? ? Au(HS)2? + H2 vary from pKm = +2.4 to +2.55 (±0.10) for Au2(HS)2S2? and from pKn = + 1.29 to + 1.19 (±0.10) for Au(HS)2? over the temperature range 175 to 250°C. Enthalpies of these dissolution reactions were calculated to be ΔHm° = ?5.2 ±2.0 kcal/mol and ΔHn° = +1.7 ±2.0 kcal/mol respectively. It was concluded that gold is probably transported in hydrothermal ore solutions as both thio and chloro complexes and may be deposited in response to changes in temperature, pressure, pH, oxidation potential of the system and total sulphur concentration. 相似文献
8.
Richard J. Williams 《Geochimica et cosmochimica acta》1974,38(9):1415-1433
The distribution coefficients of Eu and Sr for plagioclase-liquid and clinopyroxene-liquid pairs as a function of temperature and oxygen fugacity were experimentally investigated using an oceanic ridge basalt enriched with Eu and Sr as the starting material. Experiments were conducted between 1190° and 1140°C over a range of oxygen fugacities between 10?8 and 10?14 atm.The molar distribution coefficients are given by the equations: logPLSr = 7320/T ? 4.62logKCPXSr = 18020/T ? 13.10. Similarly, the weight fraction distribution coefficients are given by the equations: logDPLSr = 6570/T ? 4.30logDCPXSr = 18434/T ? 13.62.Although the mole fraction distribution coefficients have a smaller dependence on bulk composition than do the weight fraction distribution coefficients, they are not independent of bulk composition, thereby restricting the application of these experimental results to rocks similar to oceanic ridge basalts in bulk composition.Because the Sr distribution coefficients are independent of oxygen fugacity, they may be used as geothermometers. If the temperature can be determined independently — for example, with the Sr distribution coefficients, the Eu distribution coefficients may be used as oxygen geobarometers. Throughout the range of oxygen fugacities ascribed to terrestrial and lunar basalts, plagioclase concentrates Eu but clinopyroxene rejects Eu. 相似文献
9.
M. Ichikuni 《Chemical Geology》1979,27(3):207-214
The uptake of F by aragonite is attributed to the ion-exchange process, in which one CO32? ion in the structure is replaced by two F? ions. Under the equilibrium condition at 15° C and 1 atm., the partition of F between aragonite and aqueous solution is described by: were [F] denotes the F content of aragonite in mol/g, and aF and aCa are the aqueous activities of F? and Ca2+, respectively. The equation was successfully applied to estimating the F content of marine aragonite. 相似文献
10.
Frank J Millero 《Geochimica et cosmochimica acta》1981,45(11):2085-2089
The stoichiometric, , and apparent, K'HA, constants for the ionization of a number of weak acids (NH4+, HSO4?, HF, H2O, B(OH)3, H2CO3, HCO3?, H3PO4, H2PO4?, HPO42, H3AsO4 H2AsO4? and HAsO42?) in seawater at 25°C diluted with water have been fitted to equations of the form (Millero, 1979). In where In KHA is the thermodynamic constant in water, S is the salinity, A and B are adjustable parameters. The validity of this equation in estuarine waters has been examined by using an ion pairing model (Millero and Schreiber, 1981). The calculated values of and K'HA at S = 35%. are in good agreement with the measured values for all the systems examined. The equation used to extrapolate the measured values to pure water KHA predicted values that agreed with those determined by using the ion pairing model. The exception was the ionization of HPO42? due to the strong interactions of Ca2+ and Mg2+ with PO43?. The differences in the predicted values of in seawater diluted with pure water and average river water were very small for all the acids except HPO42? (the maximum ΔpK = 0.96 in average river water). The larger difference in the for HPO42? in river waters is due to the strong interactions of Ca2+ and PO43?. 相似文献
11.
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
12.
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 |