共查询到20条相似文献，搜索用时 671 毫秒
1.
We have analysed the kinetics of Argon and CO2 diffusion in simplified iron free rhyolitic to hawaiitic melts using the diffusion couple technique. The concentration distance profiles of Ar and CO2 were measured with electron microprobe analysis and Fourier Transform Infrared Spectroscopy, respectively. Error functions were fitted to the symmetrical concentration distance profiles to extract the diffusion coefficients.In the temperature range 1373 to 1773 K the activation energies for Ar diffusion range from 169 ± 20 to 257 ± 62 kJ mol−1. Ar diffusivity increases exponentially with the degree of depolymerisation. In contrast, the mobility of total CO2, that is identical to Ar mobility in rhyolitic melt, keeps constant with changing bulk composition from rhyolite to hawaiite. CO2 speciation at 1623 K and 500 MPa was modeled for the range of compositions studied using the diffusion data of Ar and total CO2 in combination with network former diffusion calculated from viscosity data. Within error this model is in excellent agreement with CO2 speciation data extrapolated from temperatures near the glass transition temperature for dacitic melt composition. This model shows that even in highly depolymerised hawaiitic and tholeiitic melts molecular CO2 is a stable species and contributes 70 to 80% to the total CO2 diffusion, respectively. 相似文献
2.
We determined total CO2 solubilities in andesite melts with a range of compositions. Melts were equilibrated with excess C-O(-H) fluid at 1 GPa and 1300°C then quenched to glasses. Samples were analyzed using an electron microprobe for major elements, ion microprobe for C-O-H volatiles, and Fourier transform infrared spectroscopy for molecular H2O, OH−, molecular CO2, and CO32−. CO2 solubility was determined in hydrous andesite glasses and we found that H2O content has a strong influence on C-O speciation and total CO2 solubility. In anhydrous andesite melts with ∼60 wt.% SiO2, total CO2 solubility is ∼0.3 wt.% at 1300°C and 1 GPa and total CO2 solubility increases by about 0.06 wt.% per wt.% of total H2O. As total H2O increases from ∼0 to ∼3.4 wt.%, molecular CO2 decreases (from 0.07 ± 0.01 wt.% to ∼0.01 wt.%) and CO32− increases (from 0.24 ± 0.04 wt.% to 0.57 ± 0.09 wt.%). Molecular CO2 increases as the calculated mole fraction of CO2 in the fluid increases, showing Henrian behavior. In contrast, CO32− decreases as the calculated mole fraction of CO2 in the fluid increases, indicating that CO32− solubility is strongly dependent on the availability of reactive oxygens in the melt. These findings have implications for CO2 degassing. If substantial H2O is present, total CO2 solubility is higher and CO2 will degas at relatively shallow levels compared to a drier melt. Total CO2 solubility was also examined in andesitic glasses with additional Ca, K, or Mg and low H2O contents (<1 wt.%). We found that total CO2 solubility is negatively correlated with (Si + Al) cation mole fraction and positively correlated with cations with large Gibbs free energy of decarbonation or high charge-to-radius ratios (e.g., Ca). Combining our andesite data with data from the literature, we find that molecular CO2 is more abundant in highly polymerized melts with high ionic porosities (>∼48.3%), and low nonbridging oxygen/tetrahedral oxygen (<∼0.3). Carbonate dominates most silicate melts and is most abundant in depolymerized melts with low ionic porosities, high nonbridging oxygen/tetrahedral oxygen (>∼0.3), and abundant cations with large Gibbs free energy of decarbonation or high charge-to-radius ratio. In natural silicate melt, the oxygens in the carbonate are likely associated with tetrahedral and network-modifying cations (including Ca, H, or H-bonds) or a combinations of those cations. 相似文献
3.
Ben D. Stanley Marc M. Hirschmann Anthony C. Withers 《Geochimica et cosmochimica acta》2011,75(20):5987-6003
To understand possible volcanogenic fluxes of CO2 to the Martian atmosphere, we investigated experimentally carbonate solubility in a synthetic melt based on the Adirondack-class Humphrey basalt at 1-2.5 GPa and 1400-1625 °C. Starting materials included both oxidized and reduced compositions, allowing a test of the effect of iron oxidation state on CO2 solubility. CO2 contents in experimental glasses were determined using Fourier transform infrared spectroscopy (FTIR) and Fe3+/FeT was measured by Mössbauer spectroscopy. The CO2 contents of glasses show no dependence on Fe3+/FeT and range from 0.34 to 2.12 wt.%. For Humphrey basalt, analysis of glasses with gravimetrically-determined CO2 contents allowed calibration of an integrated molar absorptivity of 81,500 ± 1500 L mol−1 cm−2 for the integrated area under the carbonate doublet at 1430 and 1520 cm−1. The experimentally determined CO2 solubilities allow calibration of the thermodynamic parameters governing dissolution of CO2 vapor as carbonate in silicate melt, KII, (Stolper and Holloway, 1988) as follows: , ΔV0 = 20.85 ± 0.91 cm3 mol−1, and ΔH0 = −17.96 ± 10.2 kJ mol−1. This relation, combined with the known thermodynamics of graphite oxidation, facilitates calculation of the CO2 dissolved in magmas derived from graphite-saturated Martian basalt source regions as a function of P, T, and fO2. For the source region for Humphrey, constrained by phase equilibria to be near 1350 °C and 1.2 GPa, the resulting CO2 contents are 51 ppm at the iron-wüstite buffer (IW), and 510 ppm at one order of magnitude above IW (IW + 1). However, solubilities are expected to be greater for depolymerized partial melts similar to primitive shergottite Yamato 980459 (Y 980459). This, combined with hotter source temperatures (1540 °C and 1.2 GPa) could allow hot plume-like magmas similar to Y 980459 to dissolve 240 ppm CO2 at IW and 0.24 wt.% of CO2 at IW + 1. For expected magmatic fluxes over the last 4.5 Ga of Martian history, magmas similar to Humphrey would only produce 0.03 and 0.26 bars from sources at IW and IW + 1, respectively. On the other hand, more primitive magmas like Y 980459 could plausibly produce 0.12 and 1.2 bars at IW and IW + 1, respectively. Thus, if typical Martian volcanic activity was reduced and the melting conditions cool, then degassing of CO2 to the atmosphere may not be sufficient to create greenhouse conditions required by observations of liquid surface water. However, if a significant fraction of Martian magmas derive from hot and primitive sources, as may have been true during the formation of Tharsis in the late Noachian, that are also slightly oxidized (IW + 1.2), then significant contribution of volcanogenic CO2 to an early Martian greenhouse is plausible. 相似文献
4.
To investigate the influence of temperature and composition on the diffusivities of dissolved carbon dioxide and argon in silicate melts, diffusion experiments were performed at magmatic pressure and temperature conditions in (a) albite melts with excess Na2O (0-8.6 wt%) and a constant Si/Al ratio of 3, and (b) albite70quartz30 to jadeite melts with decreasing SiO2 content and a constant Na/Al ratio of 1. We obtained diffusion coefficients at 500 MPa and 1323-1673 K. In the fully polymerized system Ab70Qz30 - Jd, the change in composition only has a weak effect on bulk CO2 diffusivity, but Ar diffusivity increases clearly with decreasing SiO2 content. In the system Ab + Na2O, bulk CO2 and Ar diffusivity increase significantly with gradual depolymerisation. The relatively small change in composition on molar basis in the depolymerized system leads to a significantly larger change in diffusivities compared to the fully polymerized Ab70Qz30-Jd join. Within error, activation energies for bulk CO2 and Ar diffusion in both systems are identical with decreasing silica content (Ab + Na2O: 159 ± 25 kJ mol−1 for bulk CO2 and 130 ± 8 kJ mol−1 for Ar; Ab70Qz30-Jd: 163 ± 16 kJ mol−1 for bulk CO2 and 148 ± 15 kJ mol−1 for Ar) even though this results in depolymerisation in one system and not the other.Although there is a variation in CO2 speciation with changing composition as observed in quenched glasses, it has previously established that this is not a true representation of the species present in the melt, with the ratio of molecular CO2 to carbonate decreasing during quenching. Thus, diffusion coefficients for the individual CO2 species cannot be directly derived by measuring molecular CO2 and CO32- concentration-distance profiles in the glasses. To obtain diffusivities of individual CO2 species, we have made two assumptions that (1) inert Ar can be used as a proxy for molecular CO2 diffusion characteristics as shown by our previous work and (2) the diffusivity of CO32− can be calculated assuming it is identical to network forming components (Si4+ and Al3+). This is derived from viscosity data (Eyring eqn.) and suggests that CO32− diffusion would be several orders of magnitude slower than molecular CO2 diffusion.The systematics of measured bulk CO2 diffusivity rates and comparison with the Ar proxy all suggest that the faster molecular CO2 species is much more dominant in melts than measurements on resulting quenched glasses would suggest. This study has confirmed an observation of surprisingly consistent bulk CO2 diffusivity across a range of natural compositions were Ar diffusivity significantly increases. This is consistent with an actual increase in molecular CO2 mobility (similar to Ar) that is combined with an increase in the proportion of the slower carbonate in the melt.These results demonstrate that the CO2 diffusion and speciation model provides an insight into the transport processes in the melt and is promising and an alternative tool to in situ speciation measurements at magmatic conditions, which at the moment are technically extremely difficult. We present the first high pressure high temperature in situ MIR spectra of a CO2 bearing albitic glass/melt suggesting that molecular CO2 is a stable species at high temperature, which is qualitatively consistent with the modelled CO2 speciation data. 相似文献
5.
G. Brey 《Contributions to Mineralogy and Petrology》1976,57(2):215-221
CO2 solubility has a slight negative temperature dependence in olivine melilitite at 30 kb with 9% CO2 dissolved at 1,450 °C, 8.5% at 1,550 °C and 8.3% at 1,650° C. CO2 is dissolved as the carbonate molecule (CO
3
2–
) only. Feldspar melts (albite-anorthite) dissolve much less CO2 at 30 kb (around 2%) with a slight increase with increasing anorthite content. A CO2 absorption peak in infrared spectra of albite-rich glasses diappears in favour of the CO
3
2–
peak with increasing anorthite content. It is inferred that CO2 was present as CO
3
2–
in albite-rich melts also, but reverts to CO2 during quenching because of bonding differences related to Ca2+ and Na+ in the melts. 相似文献
6.
The sodium solubility in silicate melts in the CaO-MgO-SiO2 (CMS) system at 1400 °C has been measured by using a closed thermochemical reactor designed to control alkali metal activity. In this reactor, Na(g) evaporation from a Na2O-xSiO2 melt imposes an alkali metal vapor pressure in equilibrium with the molten silicate samples. Because of equilibrium conditions in the reactor, the activity of sodium-metal oxide in the molten samples is the same as that of the source, i.e., aNa2O(sample) = aNa2O(source). This design also allows to determine the sodium oxide activity coefficient in the samples. Thirty-three different CMS compositions were studied. The results show that the amount of sodium entering from the gas phase (i.e., Na2O solubility) is strongly sensitive to silica content of the melt and, to a lesser extent, the relative amounts of CaO and MgO. Despite the large range of tested melt compositions (0 < CaO and MgO < 40; 40 < SiO2 < 100; in wt%), we found that Na2O solubility is conveniently modeled as a linear function of the optical basicity (Λ) calculated on a Na-free basis melt composition. In our experiments, γNa2O(sample) ranges from 7 × 10−7 to 5 × 10−6, indicating a strongly non-ideal behavior of Na2O solubility in the studied CMS melts (γNa2O(sample) ? 1). In addition to showing the effect of sodium on phase relationships in the CMS system, this Na2O solubility study brings valuable new constraints on how melt structure controls the solubility of Na in the CMS silicate melts. Our results suggest that Na2O addition causes depolymerization of the melt by preferential breaking of Si-O-Si bonds of the most polymerized tetrahedral sites, mainly Q4. 相似文献
7.
CO2 solubility was measured in a synthetic iron-free phonolite (haplo-phonolite) by equilibrating melt with excess CO2 fluid in a piston cylinder apparatus for a range of pressures (1.0- 2.5 GPa) and temperatures (1300 to 1550°C). The quenched glasses were then analysed using a bulk carbon analytical method (LECO). The measured solubilities are between 0.65 and 2.77 wt.% for the range of conditions studied and show a negative correlation with temperature as reported for most other silicate melt compositions.A range of carbonate species are present within the glass, as well as minor amounts of molecular CO2. FTIR and NMR analyses suggest that carbonate is present as both ‘network’ and ‘depolymerised’ units as shown for relatively highly polymerised compositions in the model of Brooker et al. (2001b). The bulk CO2 analyses were used to calibrate the IR extinction coefficient for the carbonate groups. However, the results show that the values obtained for the glasses vary with the melt equilibration conditions, presumably because the ratio of the different carbonate species changes as a complex function of run pressure, temperature and quench rate. Thus the use of IR may not be a reliable method for the quantification of dissolved CO2 concentrations in natural glasses of ‘intermediate’ composition. 相似文献
8.
Edet E. Isuk 《Lithos》1983,16(1):17-22
The effects of excess SiO2 and CO2 on the solubility of molybdenite in hydrous sodium disilicate melts were experimentally determined at 680 bars and 650°C. The molybdenite solubility decreases with increasing SiO2 and CO2. Under the experimental conditions, the MoS2 content of the vapor-saturated liquid decreases from 10 wt.% to 2.5 wt.% at SiO2 saturation. In the presence of CO2, the solubility decreases to 4.6 wt.% MoS2 and becomes negligible at high PCO2. These results are explained as deriving from the increased polymerization and hence decreased NBO/Si ratio of the melt with increasing SiO2 content and CO2, respectively. Sulfur dissolves principally as SO4?2 at the relatively high fo2 of the experiments. Consequently, the effect of sulfur is to lower the Mo solubility by effectively decreasing the NBO/Si ratio of the melt. Sulfur saturation is, therefore, likely to be a limiting factor in the Mo content of alkali silicate melts because of the chalcophile affinities of molybdenum. 相似文献
9.
Traditionally, the application of stable isotopes in Carbon Capture and Storage (CCS) projects has focused on δ13C values of CO2 to trace the migration of injected CO2 in the subsurface. More recently the use of δ18O values of both CO2 and reservoir fluids has been proposed as a method for quantifying in situ CO2 reservoir saturations due to O isotope exchange between CO2 and H2O and subsequent changes in δ18OH2O values in the presence of high concentrations of CO2. To verify that O isotope exchange between CO2 and H2O reaches equilibrium within days, and that δ18OH2O values indeed change predictably due to the presence of CO2, a laboratory study was conducted during which the isotope composition of H2O, CO2, and dissolved inorganic C (DIC) was determined at representative reservoir conditions (50 °C and up to 19 MPa) and varying CO2 pressures. Conditions typical for the Pembina Cardium CO2 Monitoring Pilot in Alberta (Canada) were chosen for the experiments. Results obtained showed that δ18O values of CO2 were on average 36.4 ± 2.2‰ (1σ, n = 15) higher than those of water at all pressures up to and including reservoir pressure (19 MPa), in excellent agreement with the theoretically predicted isotope enrichment factor of 35.5‰ for the experimental temperatures of 50 °C. By using 18O enriched water for the experiments it was demonstrated that changes in the δ18O values of water were predictably related to the fraction of O in the system sourced from CO2 in excellent agreement with theoretical predictions. Since the fraction of O sourced from CO2 is related to the total volumetric saturation of CO2 and water as a fraction of the total volume of the system, it is concluded that changes in δ18O values of reservoir fluids can be used to calculate reservoir saturations of CO2 in CCS settings given that the δ18O values of CO2 and water are sufficiently distinct. 相似文献
10.
Experimental determination of oxygen isotope fractionations between CO2 vapor and soda-melilite melt
We report results of experiments constraining oxygen isotope fractionations between CO2 vapor and Na-rich melilitic melt at 1 bar and 1250 and 1400°C. The fractionation factor constrained by bracketed experiments, 1000.lnαCO2-Na melilitic melt, is 2.65±0.25 ‰ (±2σ; n=92) at 1250°C and 2.16±0.16 ‰ (2σ; n=16) at 1400°C. These values are independent of Na content over the range investigated (7.5 to 13.0 wt. % Na2O). We combine these data with the known reduced partition function ratio of CO2 to obtain an equation describing the reduced partition function ratio of Na-rich melilite melt as a function of temperature. We also fit previously measured CO2-melt or -glass fractionations to obtain temperature-dependent reduced partition function ratios for all experimentally studied melts and glasses (including silica, rhyolite, albite, anorthite, Na-rich melilite, and basalt). The systematics of these data suggest that reduced partition function ratios of silicate melts can be approximated either by using the Garlick index (a measure of the polymerization of the melt) or by describing melts as mixtures of normative minerals or equivalent melt compositions. These systematics suggest oxygen isotope fractionation between basalt and olivine at 1300°C of approximately 0.4 to 0.5‰, consistent with most (but not all) basalt glass-olivine fractionations measured in terrestrial and lunar basalts. 相似文献
11.
The diffusion of water in dacitic and andesitic melts was investigated at temperatures of 1458 to 1858 K and pressures between 0.5 and 1.5 GPa using the diffusion couple technique. Pairs of nominally dry glasses and hydrous glasses containing between 1.5 and 6.3 wt.% dissolved H2O were heated for 60 to 480 s in a piston cylinder apparatus. Concentration profiles of hydrous species (OH groups and H2O molecules) and total water (CH2Ot = sum of OH and H2O) were measured along the cylindrical axis of the diffusion sample using IR microspectroscopy. Electron microprobe traverses show no significant change in relative proportions of anhydrous components along H2O profiles, indicating that our data can be treated as effective binary interdiffusion between H2O and the rest of the silicate melt. Bulk water diffusivity (DH2Ot) was derived from profiles of total water using a modified Boltzmann-Matano method as well as using fittings assuming a functional relationship between DH2Ot and CH2Ot. In dacitic melts DH2Ot is proportional to CH2Ot up to 6 wt.%. In andesitic melts the dependence of DH2Ot on CH2Ot is less pronounced. A pressure effect on water diffusivity could not be resolved for either dacitic or andesitic melt in the range 0.5 to 1.5 GPa. Combining our results with previous studies on water diffusion in rhyolite and basalt show that for a given water content DH2Ot increases monotonically with increasing melt depolymerization at temperatures >1500 K. Assuming an Arrhenian behavior in the whole compositional range, the following formulation was derived to estimate DH2Ot (m2/s) at 1 wt.% H2Ot in melts with rhyolitic to andesitic composition as a function of T (K), P (MPa) and S (wt.% SiO2):
12.
Colin G. Macpherson David R. Hilton Tibor J. Dunai 《Geochimica et cosmochimica acta》2005,69(24):5729-5746
New volatile data (CO2, H2O, He, Ne, and Ar) are presented for 24 submarine basaltic glasses from the Kolbeinsey Ridge, Tjörnes Fracture Zone and Mohns Ridge, North Atlantic. Low CO2 and He contents indicate that magmas were strongly outgassed with the extent of degassing increasing toward the south, as expected from shallower ridge depths. Ne and Ar are significantly more abundant in the southernmost glasses than predicted for degassed melt. The strong atmospheric isotopic signal associated with this excess Ne and Ar suggests syn- or posteruptive contamination by air. Degassing, by itself, cannot generate the large variations in δ13C values of dissolved CO2 or coupled CO2-Ar variations. This suggests that δ13C values were also affected by some other processes, most probably melt-crust interaction. Modelling indicates that degassing had a negligible influence on water owing to its higher solubility in basaltic melt than the other volatiles. Low H2O contents in the glasses reflect melting of a mantle source that is not water-rich relative to the source of N-MORB.Before eruption, Kolbeinsey Ridge melts contained ∼400 ppm CO2 with δ13C of −6‰, 0.1 to 0.35 wt.% H2O, 3He/4He ∼11 RA, and CO2/3He of ∼2 × 109. We model restored volatile characteristics and find homogeneous compositions in the source of Kolbeinsey Ridge magmas. Relative to the MORB-source, He and Ne are mildly fractionated while the 40Ar/36Ar may be low. The 3He/4He ratios in Tjörnes Fracture Zone glasses are slightly higher (13.6 RA) than on Kolbeinsey Ridge, suggesting a greater contribution of Icelandic mantle from the south, but the lack of 3He/4He variation along the Kolbeinsey Ridge is inconsistent with active dispersal of Icelandic mantle beyond the Tjörnes Fracture Zone. 相似文献
13.
The experiments were conducted in the open CO2 system to find out the equilibrium fractionation between the carbonate ion and CO2(g). The existence of isotopic equilibrium was checked using the two-direction approach by passing the CO2−N2 gases with different δ13C compositions (− 1.5‰ and − 23‰) through the carbonate solution with δ13C = − 4.2‰. The ΔCO3T2−−CO2(g) equilibrium fractionation is given as 6.03 ± 0.17‰ at 25 °C. Discussion is provided about the significance of carbonate complexing in determination of ΔCO3T2−−CO2(g) and ΔHCO3T−−CO2(g) fractionations. Finally, an isotope numerical model of flow and kinetics of hydration and dehydroxylation is built to predict the isotopic behaviour of the system with time. 相似文献
14.
We have performed a series of molecular dynamics simulations aimed at the evaluation of the solubility of CO2 in silicate melts of natural composition (from felsic to ultramafic). In making in contact within the simulation cell a supercritical CO2 phase with a silicate melt of a given composition, we have been able to evaluate (i) the solubility of CO2 in the P-T range 1473-2273 K and 20-150 kbar, (ii) the density change experienced by the CO2-bearing melt, (iii) the respective concentrations of CO2 and species in the melt, (iv) the lifetime and the diffusivity of these species and (v) the structure of the melt around the carbonate groups. The main results are the following:(1) The solubility of CO2 increases markedly with the pressure in the three investigated melts (a rhyolite, a mid-ocean ridge basalt and a kimberlite) from about ∼2 wt% CO2 at 20 kbar to ∼25 wt% at 100 kbar and 2273 K. The solubility is found to be weakly dependent on the melt composition (as far as the present compositions are concerned) and it is only at very high pressure (above ∼100 kbar) that a clear hierarchy between solubilities occurs (rhyolite < MORB < kimberlite). Furthermore at a given pressure the calculated solubility is negatively correlated with the temperature.(2) In CO2-saturated melts, the proportion of carbonate ions is positively correlated with the pressure at isothermal condition and is negatively correlated with the temperature at isobaric condition (and vice versa for molecular CO2). Furthermore, at fixed (P, T) conditions the proportion of carbonate ions is higher in CO2-undersaturated melts than in the CO2-saturated melt. Although the proportion of molecular CO2 decreases when the degree of depolymerization of the melt increases, it is still significant in CO2-saturated basic and ultrabasic compositions at high temperatures. This finding is at variance with experimental data on CO2-bearing glasses which show no evidence of molecular CO2 as soon as the degree of depolymerization of the melt is high (e.g. basalt). These conflicting results can be reconciled with each other by noticing that a simple low temperature extrapolation of the simulation data predicts that the proportion of molecular CO2 in basaltic melts might be negligible in the glass at room temperature.(3) The carbonate ions are found to be transient species in the liquid phase, with a lifetime increasing exponentially with the inverse of the temperature. Contrarily to a usual assumption, the diffusivity of carbonate ions into the liquid silicate is not vanishingly small with respect to that of CO2 molecules: in MORB they differ from each other by a factor of ∼6 at 1473 K and only a factor of ∼2 at 2273 K. Although the bulk diffusivity of CO2 is governed primarily by the diffusivity of CO2 molecules, the carbonate ions contribute significantly to the diffusivity of CO2 in depolymerized melts.(4) Concerning the structure of the CO2-bearing silicate melt, the carbonate ions are found to be preferentially associated with NBO’s of the melt, with an affinity for NBOs which exceeds that for BOs by almost one order of magnitude. This result explains why the concentration in carbonate ions is positively correlated with the degree of depolymerization of the melt and diminishes drastically in fully polymerized melts where the number of NBO’s is close to zero. Furthermore, the network modifier cations are not randomly distributed in the close vicinity of carbonate groups but exhibit a preferential ordering which depends at once on the nature of the cation and on the melt composition. However at the high temperatures investigated here, there is no evidence of long lived complexes between carbonate groups and metal cations. 相似文献
15.
Burkhard C. Schmidt François Holtz Michel Pichavant 《Contributions to Mineralogy and Petrology》1999,136(3):213-224
The water solubility in haplogranitic melts (normative composition Ab39Or32Qz29) coexisting with H2O-H2 fluids at 800 and 950 °C and 1, 2 and 3 kbar vapour pressure has been determined using IR spectroscopy. The experiments were
performed in internally heated pressure vessels and the hydrogen fugacity (f
H2) was controlled using the double capsule technique and oxygen buffer assemblages (WM and IW). Due to the limited lifetimes
of these oxygen buffers the water solubility was determined from diffusion profiles (concentration-distance profiles) measured
with IR spectroscopy in the quenched glasses. The reliability of the experimental strategy was demonstrated by comparing the
results of short- and long-duration experiments performed with pure H2O fluids. The water solubility in Ab39Or32Qz29 melts equilibrated with H2O-H2 fluids decreases progressively with decreasing f
H2O, as f
H2 (or X
H2) increases in the fluid phase. The effect of H2 on the evolution of the water solubility is similar to that of CO2 or another volatile with a low solubility in the melt and can be calculated in a first approximation with the Burnham water
solubility model. Recalculation of high temperature water speciation for AOQ melts coexisting with H2O-H2 fluids at 800 °C, 2 kbar suggests that the concentrations of molecular H2O are proportional to f
H2O (calculated using available mixing models), indicating Henrian behaviour for the solubility of molecular H2O in haplogranitic melts.
Received: 29 June 1998 / Accepted: 10 March 1999 相似文献
16.
The patterns of dissolved inorganic C (DIC) and aqueous CO2 in rivers and estuaries sampled during summer and winter in the Australian Victorian Alps were examined. Together with historical (1978–1990) geochemical data, this study provides, for the first time, a multi-annual coverage of the linkage between CO2 release via wetland evasion and CO2 consumption via combined carbonate and aluminosilicate weathering. δ13C values imply that carbonate weathering contributes ∼36% of the DIC in the rivers although carbonates comprise less than 5% of the study area. Baseflow/interflow flushing of respired C3 plant detritus accounts for ∼50% and atmospheric precipitation accounts for ∼14% of the DIC. The influence of in river respiration and photosynthesis on the DIC concentrations is negligible. River waters are supersaturated with CO2 and evade ∼27.7 × 106 mol/km2/a to ∼70.9 × 106 mol/km2/a CO2 to the atmosphere with the highest values in the low runoff rivers. This is slightly higher than the global average reflecting higher gas transfer velocities due to high wind speeds. Evaded CO2 is not balanced by CO2 consumption via combined carbonate and aluminosilicate weathering which implies that chemical weathering does not significantly neutralize respiration derived H2CO3. The results of this study have implications for global assessments of chemical weathering yields in river systems draining passive margin terrains as high respiration derived DIC concentrations are not directly connected to high carbonate and aluminosilicate weathering rates. 相似文献
17.
Carbon isotopic fractionation between CO2 vapour,silicate and carbonate melts: an experimental study to 30 kbar 总被引：5，自引：0，他引：5
David P. Mattey W. R. Taylor D. H. Green C. T. Pillinger 《Contributions to Mineralogy and Petrology》1990,104(4):492-505
The carbon isotopic fractionation between CO2 vapour and sodamelilite (NaCaAlSi2O7) melt over a range of pressures and temperatures has been investigated using solid-media piston-cylinder high pressure apparatus. Ag2C2O4 was the source of CO2 and experimental oxygen fugacity was buffered at hematite-magnetite by the double capsule technique. The abundance and isotopic composition of carbon dissolved in sodamelilite (SM) glass were determined by stepped heating and the 13C of coexisting vapour was determined directly by capsule piercing. CO2 solubility in SM displays a complex behavior with temperature. At pressures up to 10 kbars CO2 dissolves in SM to form carbonate ion complexes and the solubility data suggest slight negative temperature dependence. Above 20 kbars CO2 reacts with SM to form immiscible Na-rich silicate and Ca-rich carbonate melts and CO2 solubility in Na-enriched silicate melt rises with increasing temperature above the liquidus. Measured values for carbon isotopic fractionation between CO2 vapour and carbonate ions dissoived in sodamelilite melt at 1200°–1400° C and 5–30 kbars average 2.4±0.2, favouring13C enrichment in CO2 vapour. The results are maxima and are independent of pressure and temperature. Similar values of 2 are obtained for the carbon isotopic fractionation between CO2 vapour and carbonate melts at 1300°–1400° C and 20–30 kbars. 相似文献
18.
. Cl solubility in evolved alkaline melts was investigated at 860-930 °C and pressures of 25 to 250 MPa using natural trachytes and a synthetic phonolite equilibrated with subcritical fluids in the H2O-(Na,K)Cl system (i.e. silicate melt coexisted with water-rich aqueous fluid and a saline brine). Fluid phase characteristics were identified by examination of fluid inclusions present in the run product glasses and the fluid bulk composition was calculated by mass balance. The Cl contents of trachytic glasses coexisting with subcritical fluids increase linearly with decreasing pressure from 250 to 25 MPa and range from 0.37 to 0.90 wt%; Cl in the phonolitic glass ranges from 0.35 to 0.59 wt%. These values are approximately twice those found in metaluminous rhyolitic melts under similar conditions. Variations from peralkaline to peraluminous composition has little effect on Cl solubility in trachytes, whereas it is a more important factor in phonolites. More generally, melt structure, in particular non-bringing oxygen, appears to strongly influence Cl solubility in silicate melts. The negative correlation between pressure and melt Cl content is governed by the large negative partial volume of NaCl in the vapour phase. No change in Cl solubility is observed between 200 and 250 MPa. Comparison of our experimental results with Cl abundance in glass inclusion and matrix glass from Italian volcanoes can be used to identify those eruptive products preserved in the geologic record which may have been associated with large Cl emissions. 相似文献
19.
Robert L. Linnen Michel Pichavant Franois Holtz 《Geochimica et cosmochimica acta》1996,60(24):4965-4976
The diffusion profile method has been employed to measure tin diffusion coefficients and SnO2 solubility in water-saturated, peralkaline to peraluminous haplogranitic melts at 850°C, 2 kbar, and log ƒO2 conditions ranging from FMQ - 0.57 to FMQ + 3.49. At reduced conditions cassiterite is highly soluble and tin is present dominantly as a Sn2+ species, whereas at oxidized conditions SnO2 is much less soluble, and tin is present dominantly as a Sn4+ species. There is a strong melt composition control on SnO2 solubility; solubilities are at a minimum at the subaluminous composition, increase strongly with alkali content in peralkaline compositions and weakly with Al content in peraluminous compositions. In the case of the latter, this increase can only be distinguished at reduced conditions, e.g., at a log ƒO2 of FMQ - 0.57 cassiterite solubility increases from 2.78 to 4.11 wt% SnO2 for melt with Al/(Na + K)compositions (A.S.I.) of 1.0 and 1.2, respectively. At oxidized conditions SnO2 solubility is 500 ppm for both the A.S.I. 1.0 and 1.2 compositions. By comparison Sn02 solubilities in the most peralkaline composition investigated range from 3.94 wt% to -10 wt% Sn02, for the most oxidized to the most reduced conditions, respectively. Thermodynamic modelling of the data indicates that the Sn4+/ΣSn ratio in the melt is also at a minimum at the subaluminous composition, ranging from 0.4 at log ƒO2 of FMQ + 3.49 to 0.01 at FMQ - 0.57. Over the same log foZ range the Sn4+/ΣSn ratio for the A.S.I. 0.6 composition ranges from 0.98 to 0.4 and for the A.S.I. 1.25 composition, from 0.8 to 0.02.Tin diffusivity is dependent on both fO2 and melt composition. The effective binary diffusion coefficient of tin at reduced conditions is approximately 10−7.5 cm2/sec for the peraluminous compositions and 10−8.2 cm2/sec for the peralkaline compositions. At oxidized conditions these values decrease to approximately 10−8.2 and 10−9.0 cm2/sec, respectively. These are interpreted to reflect relatively fast diffusion where Sn2+ is the dominant valence and tin in this case behaves similar to a network modifier and relatively slow diffusion where Sn4+ is dominant and tin likely has a lower coordination number. Alternatively, the coordination of Sn2+ and Sn4+ is the same, but the bond strengths are different. At fixed fO2 the faster diffusivity in the peraluminous compositions reflects the lower Sn4+/Sn2+ ratio. The fact the Sn4+/Sn2+ ratio in melts varies greatly with ƒO2 at redox conditions near FMQ suggests that the partitioning behaviour of tin possibly changes during the evolution of an igneous suite in general and of a peraluminous granite suite in particular. 相似文献
20.
Infrared spectroscopy has been used to study the speciation of CO2 in glasses near the NaAlO2-SiO2 join quenched from melts held at high temperatures and pressures. Absorption bands resulting from the antisymmetric stretches of both molecular CO2 (2,352 cm–1) and CO
3
2–
(1,610 cm–1 and 1,375 cm–1) are observed in these glasses. The latter are attributed to distorted Na-carbonate ionic-complexes. Molar absorptivities of 945 liters/mole-cm for the molecular CO2 band, 200 liters/mole-cm for the 1,610 cm–1 band, and 235 liters/mole-cm for the 1,375 cm–1 band have been determined. These molar absorptivities allow the quantitative determination of species concentrations in the glasses with a precision on the order of several percent of the amount present. The accuracy of the method is estimated to be ±15–20% at present.The ratio of molecular CO2 to CO
3
2–
in sodium aluminosilicate glasses varies little for each silicate composition over the range of total dissolved CO2 content (0–2%), pressure (15–33 kbar) and temperature (1,400–1,560° C) that we have studied. This ratio is, however, a strong function of silicate composition, increasing both with decreasing Na2O content along the NaAlO2-SiO2 join and with decreasing Na2O content in peraluminous compositions off the join.Infrared spectroscopic measurements of species concentrations in glasses provide insights into the molecular level processes accompanying CO2 solution in melts and can be used to test and constrain thermodynamic models of CO2-bearing melts. CO2 speciation in silicate melts can be modelled by equilibria between molecular CO2, CO
3
2–
, and oxygen species in the melts. Consideration of the thermodynamics of such equilibria can account for the observed linear relationship between molecular CO2 and carbonate concentrations in glasses, the proposed linear relationship between total dissolved CO2 content and the activity of CO2 in melts, and observed variations in CO2 solubility in melts. 相似文献