共查询到20条相似文献,搜索用时 390 毫秒
1.
The dependence of water concentration in synthetic (Mg, Fe2+)-cordierite on the composition of the solid solution was examined in experiments that lasted for 10 days at = 200–230 MPa,
t = 600–700°C, and oxygen fugacity corresponding to the Fe-FeO buffer. Mass spectrometric data indicate that the dependence
of water concentration in cordierite on its Fe mole fraction Fe2+/(Fe2+ + Mg) has maxima at compositions with F = 0.2–0.3. IR diffuse reflectance spectroscopic data and data on the structural setting
of H2O molecules in the structural channels of alkali-free (Mg, Fe2+)-cordierite indicate that the H-H vector of some H2O molecules (H2O-II) is perpendicular to [001] of the crystal. The dependence of the magnetic properties of synthetic (Mg, Fe2+)-cordierite was studied by static magnetization technique at 5–300 K in an external magnetic field up to 20 kOe in strength. 相似文献
2.
We present H2O analyses of MgSiO3 pyroxene crystals quenched from hydrous conditions in the presence of olivine or wadsleyite at 8–13.4 GPa and 1,100–1,400°C.
Raman spectroscopy shows that all pyroxenes have low clinoenstatite structure, which we infer to indicate that the crystals
were high clinoenstatite (C2/c) during conditions of synthesis. H2O analyses were performed by secondary ion mass spectrometry and confirmed by unpolarized Fourier transform infrared spectroscopy
on randomly oriented crystals. Measured H2O concentrations increase with pressure and range from 0.08 wt.% H2O at 8 GPa and 1,300°C up to 0.67 wt.% at 13.4 GPa and 1,300°C. At fixed pressure, H2O storage capacity diminishes with increasing temperature and the magnitude of this effect increases with pressure. This trend,
which we attribute to diminishing activity of H2O in coexisting fluids as the proportion of dissolved silicate increases, is opposite to that observed previously at low pressure.
We observe clinoenstatite 1.4 GPa below the pressure stability of clinoenstatite under nominally dry conditions. This stabilization
of clinoenstatite relative to orthoenstatite under hydrous conditions is likely owing to preferential substitution of H2O into the high clinoenstatite polymorph. At 8–11 GPa and 1,200–1,400°C, observed H2O partitioning between olivine and clinoenstatite gives values of D
ol/CEn between 0.65 and 0.87. At 13 GPa and 1,300°C, partitioning between wadsleyite and clinoenstatite, D
wd/CEn, gives a value of 2.8 ± 0.4. 相似文献
3.
4.
Oxygen isotope exchange rate between dissolved sulfate and water was experimentally determined at 100, 200 and 300°C. The isotope exchange rate is strongly dependent on temperature and pH of the solution. Combining the temperature and pH dependence of the reaction rate, the exchange reaction was estimated to be first-order with respect to sulfate. The logarithm of apparent rate constant of exchange reaction at a given temperature is a function of the pH calculated at the experimental temperatures. From the pH dependence of the apparent rate constant, it was deduced that the isotope exchange reaction between dissolved sulfate and water proceeds through collision between H2SO04 and H2O at low pH, and between HSO?4 and H2O at intermediate pH. The isotope exchange rate obtained indicates that oxygen isotope geothermometry utilizing the studied isotope exchange is suitable for temperature estimation of geothermal reservoirs. The extrapolated half-life of this reaction to oceanic temperature is about 109 years, implying that exchange between oceanic sulfate and water cannot control the oxygen isotope ratio of oceanic sulfates. 相似文献
5.
Annette K. Kleppe Andrew P. Jephcoat Joseph R. Smyth 《Physics and Chemistry of Minerals》2006,32(10):700-709
Raman spectra of monoclinic Fo90 hydrous wadsleyite with 2.4 wt% H2O have been measured in a diamond-anvil cell with helium as a pressure-transmitting medium to 58.4 GPa at room temperature. The most intense, characteristic wadsleyite modes, the Si–O–Si symmetric stretch at 721 cm−1 and the symmetric stretch of the SiO3 unit at 918 cm−1, shift continuously to 58.4 GPa showing no evidence of a first order change in the crystal structure despite compression well beyond the stability field of wadsleyite in terms of pressure. The pressure dependence of these two modes is nearly identical for Fo90 hydrous and Fo100 anhydrous wadsleyite. A striking feature in the high-pressure Raman spectra of Fo90 hydrous wadsleyite is the appearance of new Raman modes above 9 GPa in the mid-frequency range (300–650 cm−1 at 1-bar and shifted to 500–850 cm−1 at 58.4 GPa) accompanied by a significant growth in their intensities under further compression. In the OH stretching frequency range Fo90 hydrous wadsleyite exhibits a larger number of modes than the Mg end-member phase. The higher number of modes may be due to either additional protonation sites or simply that we observe a different subset of all possible OH modes for each sample. The high-pressure behaviour of the OH stretching modes of Fo90 and Fo100 hydrous wadsleyite is consistent: OH stretching modes with frequencies <3,530 cm−1 decrease with increasing pressure whereas the higher-frequency OH modes show a close to constant pressure dependence to at least 13.2 GPa. The approximately constant pressure dependence of the OH modes above 3,530 cm−1 is consistent with protons being located at the O1···O edges around M3. 相似文献
6.
Konstantin D. Litasov Anton Shatskiy Eiji Ohtani Tomoo Katsura 《Physics and Chemistry of Minerals》2011,38(1):75-84
The H2O content of wadsleyite were measured in a wide pressure (13–20 GPa) and temperature range (1,200–1,900°C) using FTIR method.
We confirmed significant decrease of the H2O content of wadsleyite with increasing temperature and reported first systematic data for temperature interval of 1,400–1,900°C.
Wadsleyite contains 0.37–0.55 wt% H2O at 1,600°C, which may be close to its water storage capacity along average mantle geotherm in the transition zone. Accordingly,
water storage capacity of the average mantle in the transition zone may be estimated as 0.2–0.3 wt% H2O. The H2O contents of wadsleyite at 1,800–1,900°C are 0.22–0.39 wt%, indicating that it can store significant amount of water even
under the hot mantle environments. Temperature dependence of the H2O content of wadsleyite can be described by exponential equation
C\textH2 \textO = 6 3 7.0 7 \texte - 0.00 4 8T , C_{{{\text{H}}_{2} {\text{O}}}} = 6 3 7.0 7 {\text{e}}^{ - 0.00 4 8T} , where T is in °C. This equation is valid for temperature range 1,200–2,100°C with the coefficient of determination R
2 = 0.954. Temperature dependence of H2O partition coefficient between wadsleyite and forsterite (D
wd/fo) is complex. According to our data apparent Dwd/fo decreases with increasing temperature from D
wd/fo = 4–5 at 1,200°C, reaches a minimum of D
wd/fo = 2.0 at 1,400–1,500°C, and then again increases to D
wd/fo = 4–6 at 1,700–1,900°C. 相似文献
7.
A mid‐ocean ridge basalt (MORB)‐type eclogite from the Moldanubian domain in the Bohemian Massif retains evidence of its prograde path in the form of inclusions of hornblende, plagioclase, clinopyroxene, titanite, ilmenite and rutile preserved in zoned garnet. Prograde zoning involves a flat grossular core followed by a grossular spike and decrease at the rim, whereas Fe/(Fe + Mg) is also flat in the core and then decreases at the rim. In a pseudosection for H2O‐saturated conditions, garnet with such a zoning grows along an isothermal burial path at c. 750 °C from 10 kbar in the assemblage plagioclase‐hornblende‐diopsidic clinopyroxene‐quartz, then in hornblende‐diopsidic clinopyroxene‐quartz, and ends its growth at 17–18 kbar. From this point, there is no pseudosection‐based information on further increase in pressure or temperature. Then, with garnet‐clinopyroxene thermometry, the focus is on the dependence on, and the uncertainties stemming from the unknown Fe3+ content in clinopyroxene. Assuming no Fe3+ in the clinopyroxene gives a serious and unwarranted upward bias to calculated temperatures. A Fe3+‐contributed uncertainty of ±40 °C combined with a calibration and other uncertainties gives a peak temperature of 760 ± 90 °C at 18 kbar, consistent with no further heating following burial to eclogite facies conditions. Further pseudosection modelling suggests that decompression to c. 12 kbar occurred essentially isothermally from the metamorphic peak under H2O‐undersaturated conditions (c. 1.3 mol.% H2O) that allowed the preservation of the majority of garnet with symplectitic as well as relict clinopyroxene. The modelling also shows that a MORB‐type eclogite decompressed to c. 8 kbar ends as an amphibolite if it is H2O saturated, but if it is H2O‐undersaturated it contains assemblages with orthopyroxene. Increasing H2O undersaturation causes an earlier transition to SiO2 undersaturation on decompression, leading to the appearance of spinel‐bearing assemblages. Granulite facies‐looking overprints of eclogites may develop at amphibolite facies conditions. 相似文献
8.
D. L. Kohlstedt H. Keppler D. C. Rubie 《Contributions to Mineralogy and Petrology》1996,123(4):345-357
The solubility of hydroxyl in the α, β and γ phases of (Mg,Fe)2SiO4 was investigated by hydrothermally annealing single crystals of San Carlos olivine. Experiments were performed at a temperature
of 1000° or 1100 °C under a confining pressure of 2.5 to 19.5 GPa in a multianvil apparatus with the oxygen fugacity buffered
by the Ni:NiO solid-state reaction. Hydroxyl solubilities were determined from infrared spectra obtained of polished thin
sections in crack-free regions ≤100 μm in diameter. In the α-stability field, hydroxyl solubility increases systematically
with increasing confining pressure, reaching a value of ∼20,000 H/106Si (1200 wt ppm H2O) at the α-β phase boundary near 13 GPa and 1100 °C. In the β field, the hydroxyl content is ∼400,000 H/106Si (24,000 wt ppm H2O) at 14–15 GPa and 1100 °C. In the γ field, the solubility is ∼450,000 H/106Si (27,000 wt ppm H2O) at 19.5 GPa and 1100 °C. The observed dependence of hydroxyl solubility with increasing confining pressure in the α phase
reflects an increase in water fugacity with increasing pressure moderated by a molar volume term associated with the incorporation
of hydroxyl ions into the olivine structure. Combined with published results on the dependence of hydroxyl solubility on water
fugacity, the present results for the α phase can be summarized by the relation C
OH
= A(T)f nH2Oexp(−PΔV/RT), where A(T) = 1.1 H/106Si/MPa at 1100 °C, n = 1, and ΔV = 10.6×10–6 m3/mol. These data demonstrate that the entire present-day water content of the upper mantle could be incorporated in the mineral
olivine alone; therefore, a free hydrous fluid phase cannot be stable in those regions of the upper mantle with a normal concentration
of hydrogen. Free hydrous fluids are restricted to special tectonic environments, such as the mantle wedge above a subduction
zone.
Received: 10 February 1995 / Accepted: 23 October 1995 相似文献
9.
Raman spectra of the three Al2SiO5 polymorphs; andalusite, sillimanite and kyanite were recorded as a function of pressure at room temperature. All the Raman active bands which could be observed from the high-pressure cell showed a linear pressure dependence for each of the three Al2SiO5 polymorphs and no phase changes were observed over the pressure ranges used in this study. In andalusite and to a lesser extent in sillimanite, vibrations which could be correlated with internal motions of the SiO4 tetrahedra were generally well separated from the lattice modes and showed a greater pressure dependence than that observed for other modes. The distinct pressure dependence of the internal SiO4 modes is less evident in kyanite, probably due to the lack of continuous tetrahedral chains and the fact that the rigid SiO4 tetrahedra now form an integral part of the structural network. At ambient pressure, kyanite also exhibits two fluorescence bands at 705 and 706.2 nm which are due to small amounts of Cr3+ in the kyanite crystals. These fluorescence bands showed a non-linear frequency shift as pressure was increased. 相似文献
10.
Bjorn Mysen 《Geochimica et cosmochimica acta》2010,74(14):4123-170
The structure of H2O-saturated silicate melts and of silicate-saturated aqueous solutions, as well as that of supercritical silicate-rich aqueous liquids, has been characterized in-situ while the sample was at high temperature (to 800 °C) and pressure (up to 796 MPa). Structural information was obtained with confocal microRaman and with FTIR spectroscopy. Two Al-bearing glasses compositionally along the join Na2O•4SiO2-Na2O•4(NaAl)O2-H2O (5 and 10 mol% Al2O3, denoted NA5 and NA10) were used as starting materials. Fluids and melts were examined along pressure-temperature trajectories of isochores of H2O at nominal densities (from PVT properties of pure H2O) of 0.85 g/cm3 (NA10 experiments) and 0.86 g/cm3 (NA5 experiments) with the aluminosilicate + H2O sample contained in an externally-heated, Ir-gasketed hydrothermal diamond anvil cell.Molecular H2O (H2O°) and OH groups that form bonds with cations exist in all three phases. The OH/H2O° ratio is positively correlated with temperature and pressure (and, therefore, fugacity of H2O, fH2O) with (OH/H2O°)melt > (OH/H2O°)fluid at all pressures and temperatures. Structural units of Q3, Q2, Q1, and Q0 type occur together in fluids, in melts, and, when outside the two-phase melt + fluid boundary, in single-phase liquids. The abundance of Q0 and Q1 increases and Q2 and Q3 decrease with fH2O. Therefore, the NBO/T (nonbridging oxygen per tetrahedrally coordination cations), of melt is a positive function of fH2O. The NBO/T of silicate in coexisting aqueous fluid, although greater than in melt, is less sensitive to fH2O.The melt structural data are used to describe relationships between activity of H2O and melting phase relations of silicate systems at high pressure and temperature. The data were also combined with available partial molar configurational heat capacity of Qn-species in melts to illustrate how these quantities can be employed to estimate relationships between heat capacity of melts and their H2O content. 相似文献
11.
Adam C. Simon Thomas Pettke Philip M. Piccoli 《Geochimica et cosmochimica acta》2004,68(23):4905-4914
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
12.
A. K. Kleppe A. P. Jephcoat H. Olijnyk A. E. Slesinger S. C. Kohn B. J. Wood 《Physics and Chemistry of Minerals》2001,28(4):232-241
Raman spectra of hydrous β-Mg2SiO4 (1.65 wt% H2O) have been measured in a diamond-anvil cell with helium as a pressure-transmitting medium at room temperature to 50 GPa.
We observe three OH-stretching modes, a doublet with components at 3329 and 3373 cm−1, which decrease linearly with pressure, and a single mode at 3586 cm−1, which remains nearly constant up to 24 GPa before decreasing at higher pressures. Assessment of the mode frequencies and
their pressure dependence, together with previous results from X-ray and IR data, are consistent with protonation of the O1
site in agreement with previous studies. Strict assignment of Raman activity awaits detailed structural models. The nature
of the protonation in wadsleyite may require more specific experimental probes for full solution of the hydrogen-site problem.
Received: 18 July 2000 / Accepted: 22 November 2000 相似文献
13.
An experimental study of the solubility of Pt and Pd sulfides and Au metal in aqueous bisulfide solutions was conducted at temperatures from 200° to 350 °C and at saturated vapor pressure. A 500-mL Bridgemantype pressure vessel constructed of titanium, and equipped with a motor-driven magnetic stirrer was employed. The pH and the oxidation state were buffered by the coexistence of H2S/HS–/SO
inf4
sup2–
. The pH at temperature was calculated to be in the range 5.91–9.43, and S was 0.3–2.2 m. Under the experimental conditions, the measured solubility of gold is about two to three orders of magnitude greater than that of either platinum and palladium, and the measured solubility of platinum is, in general, approximately equal to that of palladium, in molal units. The solubilities are found to be in the range: platinum 4–800 ppb, palladium 1–400 ppb, and gold 2–300 ppm. The solubility data can be modeled adequately using the following reactions: Au+H2S+HH–=Au(HS)
2
–
+1/2H2 (K14); PtS+HS–+H+=Pt (HS)
2
0
(K15); PdS+HS–+H+=Pd (HS)
2
0
(K16); PtS2+H2=Pt (HS)
2
0
(K21).With equilibrium constants determined as follows (errors represent two standard deviations): Preliminary measurements of the solubilities of metallic Pt, Pd and Au as hydroxide complexes were also conducted using a second titanium pressure vessel, at temperatures of 200° to 350 °C and vapor saturation pressure, with pH and the oxidation state controlled or buffered by adding known amounts of NaOH and H2 gas. The concentration of NaOH was in the range 0.01–1.3 m, and the partial pressure of H2 at 200 °C was 62–275 bars, initially. Under the temperature and pressure conditions of these experiments, the solubility of platinum in 1 m NaOH solution is less than 100 ppb, that of palladium is less than 10 ppb and that of gold is less than 0.2 ppm; and in 0.01 m NaOH solutions, both Pt and Pd solubilities are less than 1 ppb. These data indicate that the contributions of hydroxide complexes to the total solubilities in the bisulfide runs, where the pH was in the range of 5.9–9.4, are negligible. The concentrations of both Pt and Pd as bisulfide complexes in the Salton Sea geothermal system predicted using the stability constants determined in this work agree very well with those values measured by McKibben et al. (1990). This calculation strongly suggests that the PGE are transported in moderately reducing, near neutral hydrothermal fluids as bisulfide complexes, as is gold. However, the much lower maximum solubility of the PGE relative to gold severely constrains models of re genesis, and may explain the relative rarity of hydrothermal PGE deposits compared to the relative abundance of hydrothermal Au deposits. 相似文献
14.
Olivier Vidal Thomas Theye Christian Chopin 《Contributions to Mineralogy and Petrology》1994,118(3):256-270
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
15.
The incorporation of H into olivine is influenced by a significant number of thermodynamic variables (pressure, temperature, oxygen fugacity, etc.). Given the strong influence that H has on the solidus temperature and rheological behavior of mantle peridotite, it is necessary to determine its solubility in olivine over the range of conditions found in the upper mantle. This study presents results from hydration experiments carried out to determine the effects of pressure, temperature, and the fugacities of H2O and O2 on H solubility in San Carlos olivine at upper mantle conditions. Experiments were carried out at 1–2 GPa and 1,200 °C using a piston-cylinder device. The fugacity of O2 was controlled at the Fe0–FeO, FeO–Fe3O4, or Ni0–NiO buffer. Variable duration experiments indicate that equilibration is achieved within 6 h. Hydrogen contents of the experimental products were measured by secondary ion mass spectrometry, and relative changes to the point defect populations were investigated using Fourier transform infrared spectroscopy. Results from our experiments demonstrate that H solubility in San Carlos olivine is sensitive to pressure, the activity of SiO2, and the fugacities of H2O and O2. Of these variables, the fugacity of H2O has the strongest influence. The solubility of H in olivine increases with increasing SiO2 activity, indicating incorporation into vacancies on octahedral lattice sites. The forsterite content of the olivine has no discernible effect on H solubility between 88.17 and 91.41, and there is no correlation between the concentrations of Ti and H. Further, in all but one of our experimentally hydrated olivines, the concentration of Ti is too low for H to be incorporated dominantly as a Ti-clinohumite-like defect. Our experimentally hydrated olivines are characterized by strong infrared absorption peaks at wavenumbers of 3,330, 3,356, 3,525, and 3,572 cm?1. The heights of peaks at 3,330 and 3,356 cm?1 correlate positively with O2 fugacity, while those at 3,525 and 3,572 cm?1 correlate with H2O fugacity. 相似文献
16.
Water diffusion is one of the most important characteristics of many processes dealt with in magmatic geochemistry, petrology,
and volcanology. We have experimentally examined water diffusion in Fe-free andesite and basalt melts (stoichiometric mixtures
of the minerals albite + diopside + wollastonite) at 3 and 100 MPa, 1300×C, up to approximately 4 wt % water in the melts,
and a total (lithostatic) pressure of 100 MPa on a high gas pressure apparatus equipped with a unique internal device. The
experiments were conducted simultaneously with the use of two different methods: diffusion hydration and couples. Water solubility
in the melts and water concentrations along the diffusion profiles (C
H
2
O) were determined by quantitative IR microspectroscopy, using the Beer-Lambert law. A structural chemical model is proposed
for calculating and predicting the concentration dependence of the molar absorption coefficient of the hydroxyl group and
water molecules in andesite and basalt glasses. The diffusion coefficients of water (D
H
2
O) are derived by the mathematical analysis of concentration profiles and the analytical solution of the second Fick diffusion
law. Preliminary results indicated D
H
2
O is roughly one order of magnitude higher in basaltic melts than in andesitic ones (at the same temperatures and P
H
2
O) and significantly (exponentially) increases with increasing water concentrations in andesitic and basaltic melts. The newly
obtained experimental data are proved to be fully consistent with the results obtained on the D
H
2
O dependence on C
H
2
O in melts of acid rocks (rhyolite and obsidian). The derived quantitative dependence between D
H
2
O and melt viscosity is used to develope principles of a new method for predicting and calculating the temperature, concentration,
and pressure dependences of D
H
2
O in magmatic melts of the of acid-basic series (up to 3 wt % C
H
2
O) at crustal T, P parameters. 相似文献
17.
The rate of chrysotile dissolution over five days was studied in constant-pH, batch suspensions at 25°C. After the first day, release of Mg occurred at a constant rate and exhibited a fractional dependence on pH, [H+]0.24. Interpreted in terms of a site-binding model for adsorption of protons on the surface, this fractional dependence implies that the rate is limited by a chemical reaction involving less than one adsorbed proton per Mg released into solution. The actual magnitude of the rate (10?15.7 mol cm?2 s?1 at pH 8) supports this interpretation. The inorganics NO3?, Cl?, HCO3? and SO4- and the organics catechol and oxalate affected the rate of Mg release only during the initial 12 to 24 hours of each experiment. Silica release was linear from the outset of each experiment, but showed no definite pH dependence. 相似文献
18.
The melting reaction: albite(solid)+ H2O(fluid) =albite-H2O(melt) has been determined in the presence of H2O–NaCl fluids at 5 and 9.2 kbar, and results compared with those obtained in presence of H2O–CO2 fluids. To a good approximation, albite melts congruently at 9 kbar, indicating that the melting temperature at constant
pressure is principally determined by water activity. At 5 kbar, the temperature (T)- mole fraction (X
(H2O) ) melting relations in the two systems are almost coincident. By contrast, H2O–NaCl mixing at 9 kbar is quite non-ideal; albite melts ∼70 °C higher in H2O–NaCl brines than in H2O–CO2 fluids for X
(H2O) =0.8 and ∼100 °C higher for X
(H2O) =0.5. The melting temperature of albite in H2O–NaCl fluids of X
(H2O)=0.8 is ∼100 °C higher than in pure water. The P–T curves for albite melting at constant H2O–NaCl show a temperature minimum at about 5 kbar. Water activities in H2O–NaCl fluids calculated from these results, from new experimental data on the dehydration of brucite in presence of H2O–NaCl fluid at 9 kbar, and from previously published experimental data, indicate a large decrease with increasing fluid pressure
at pressures up to 10 kbar. Aqueous brines with dissolved chloride salt contents comparable to those of real crustal fluids
provide a mechanism for reducing water activities, buffering and limiting crustal melting, and generating anhydrous mineral
assemblages during deep crustal metamorphism in the granulite facies and in subduction-related metamorphism. Low water activity
in high pressure-temperature metamorphic mineral assemblages is not necessarily a criterion of fluid absence or melting, but
may be due to the presence of low a
(H2O) brines.
Received: 17 March 1995/Accepted: 9 April 1996 相似文献
19.
The structure of H2O-saturated silicate melts, coexisting silicate-saturated aqueous solutions, and supercritical silicate liquids in the system Na2O·4SiO2–H2O has been characterized with the sample at high temperature and pressure in a hydrothermal diamond anvil cell (HDAC). Structural information was obtained with confocal microRaman and with FTIR microscopy. Fluids and melts were examined along pressure-temperature trajectories defined by the isochores of H2O at nominal densities, ρfluid, (from EOS of pure H2O) of 0.90 and 0.78 g/cm3. With ρfluid = 0.78 g/cm3, water-saturated melt and silicate-saturated aqueous fluid coexist to the highest temperature (800 °C) and pressure (677 MPa), whereas with ρfluid = 0.90 g/cm3, a homogeneous single-phase liquid phase exists through the temperature and pressure range (25–800 °C, 0.1–1033 MPa). Less than 5 vol% quartz precipitates near 650 °C in both experimental series, thus driving Na/Si-ratios of melt + fluid phase assemblages to higher values than that of the Na2O·4SiO2 starting material.Molecular H2O (H2O°) and structurally bonded OH groups were observed in coexisting melts and fluids as well as in supercritical liquids. Their OH/(H2O)-ratio is positively correlated with temperature. The OH/(H2O)° in melts is greater than in coexisting fluids. Structural units of Q3, Q2, Q1, and Q0 type are observed in all phases under all conditions. An expression of the form, 12Q3 + 13H2O2Q2 + 6Q1 + 4Q0, describes the equilibrium among those structural units. This equilibrium shifts to the right with increasing pressure and temperature with a ΔH of the reaction near 425 kJ/mol. 相似文献
20.
Calculation of multicomponent chemical equilibria and reaction processes in systems involving minerals,gases and an aqueous phase 总被引:1,自引:0,他引:1
Mark H Reed 《Geochimica et cosmochimica acta》1982,46(4):513-528
The compositional characteristics of many geochemical systems which involve the interaction of natural aqueous solutions with minerals and gases are conveniently described using the following thermodynamic components: Cl?, SO4=, HS?, CO3=, H+, Na+, K+, Ca++, Mg++, Fe++, Zn++, Cu+, Al+++, SiO2 and H2O. A set of mass balance and mass action equations equal in number to the number of components plus the number of saturated minerals (and gases) is defined for a specified temperature, pressure and bulk composition. The mass balance equations include terms for minerals, gases and the molalities of aqueous complexes and dissociated species. This set of non-linear equations can be solved with the aid of a computer using'a Newton-Raphson technique. The calculation takes account of aqueous ion complexing, oxidation-reduction equilibria, activity coefficients, non-unit water activity and solid solutions. The use of H+, SO4=, HS? and H2O as components allows straightforward treatment of processes involving oxidation-reduction, evaporation, boiling and changes of total aqueous H+ due to hydrolysis, mineral reaction or temperature change. One product of this approach is a technique for calculating pH at high temperature from measurement of pH at room temperature.By linking a series of discrete overall heterogeneous equilibrium calculations in which incremental changes of bulk composition, temperature or pressure are made, dynamic geochemical processes can be modeled. Example calculations for two such processes are given. These are the heating of seawater from 25° to 300°C and the isothermal irreversible reaction of rhyolite with an aqueous solution at 250°C. 相似文献