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1.
Studies of the pedogenic iron oxyhydroxides in suites of latest Holocene to middle Pleistocene soils formed on fluvial deposits of the transverse ranges, southern California, indicate that the content and composition of iron oxyhydroxide change in a systematic manner. Analysis of total secondary free iron oxides (dithionite extractable, Fe2O3d) and ferrihydrite (oxalate extractable, Fe2O3o) shows that (1) a single-logarithmic model (Y = a + b log X) or double logarithmic model (log Y = a + b log X), where Y is the total mass of pedogenic Fe oxides (g/cm2-soil column) and X is soil age, describes the rate of increase in Fe2O3d with time; (2) the Fe2O3d content correlates linearly with soil reddening and clay content; (3) the ratio, which indicates the degree of Fe oxide crystallinity, is moderately high to very high (0.22–0.58) in middle Holocene to latest Pleistocene soils and progressively decreases to less than 0.10 in older soils; (4) the value of the ratio also appears to be infuenced by climate; and (5) temporal changes in Fe oxide content and mineralogy are accompanied by related, systematic changes in clay mineralogy and organic matter content. These relationships are attributed to a soil environment that must initially favor ferrihydrite precipitation and/or organic matter-Fe complexation. Subsequent transformation to hematite causes increasingly intense reddening and a concomitant decrease in the ratio. The results demonstrate that iron oxide analysis is useful for numerical age studies of noncalcic soils and shows potential as an indicator of paleoclimates. 相似文献
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Mechanisms and kinetics of aqueous oxidation-reduction and dissolved O2 interaction in the presence of augite, biotite and hornblende were studied in oxic and anoxic solutions at pH 1–9 at 25°C. Oxidation of surface iron on the minerals coincided with both surface release of Fe+2 and by reduction of Fe+3 in solution. Reaction with iron silicates consumed dissolved oxygen at a rate that increased with decreasing pH. Both Fe+3 and O2 consumption were shown to be controlled by coupled electron-cation transfer reactions of the form; and where M is a cation of charge +z. The spontaneous reduction of aqueous Fe+3in the presence of precipitated Fe(OH)3bracketed the surface oxidation standard half cell between +0.33 and +0.52 volts. Concurrent hydrolysis reactions involving cation release from the iron silicates were suppressed by the above reactions. Calculated oxidation depths in the minerals varied between 12 and 80Å and were apparently controlled by rates of solid-state cation diffusion. 相似文献
4.
Microprobe analyses on a xenocrystic suite of salites, aegirine-augites, aegirines, titan-aegirines and acmites from a lower Tertiary ash layer in northern Denmark are presented. The sodic pyroxenes show an unusual titan-enrichment and up to 42 mol.% of the component , is estimated. Optical absorption measurements show no evidence for Ti3+. The titan-aegirines were formed during late to post-magmatic crystallization in a system with a high Ti4+/Fe2+ ratio and were followed by acmite showing enrichment in jadeite. Comparison with experimentally investigated titan-aegirine indicates crystallization far below the Mn2O3Mn3O4f02 buffer. 相似文献
5.
The relative reactivities of pulverized samples (100–200 mesh) of 3 marcasite and 7 pyrite specimens from various sources were determined at 25°C and pH 2.0 in ferric chloride solutions with initial ferric iron concentrations of 10?3 molal. The rate of the reaction: was determined by calculating the rate of reduction of aqueous ferric ion from measured oxidation-reduction potentials. The reaction follows the rate law: where mFe3+ is the molal concentration of uncomplexed ferric iron, k is the rate constant and is the surface area of reacting solid to mass of solution ratio. The measured rate constants, k, range from 1.0 × 10?4 to 2.7 × 10?4 sec?1 ± 5%, with lower-temperature/early diagenetic pyrite having the smallest rate constants, marcasite intermediate, and pyrite of higher-temperature hydrothermal and metamorphic origin having the greatest rate constants. Geologically, these small relative differences between the rate constants are not significant, so the fundamental reactivities of marcasite and pyrite are not appreciably different.The activation energy of the reaction for a hydrothermal pyrite in the temperature interval of 25 to 50°C is 92 kJ mol?1. This relatively high activation energy indicates that a surface reaction controls the rate over this temperature range. The BET-measured specific surface area for lower-temperature/early diagenetic pyrite is an order of magnitude greater than that for pyrite of higher-temperature origin. Consequently, since the lower-temperature types have a much greater ratio, they appear to be more reactive per unit mass than the higher temperature types. 相似文献
6.
Stephen E Haggerty 《Geochimica et cosmochimica acta》1973,37(4):857-867
Electron microprobe analyses of the spinel mineral group, ilmenite and rutile have been carried out on part of the Luna 20 soil sample. The spinel group shows an almost continuous trend from MgAl8O4 to FeCr2O4 and a discontinuous trend from FeCr2O4 to Fe2TiO4. Well defined non-linear relationships exist within the spinel group for Fe-Mg substitution, for divalent () versus trivalent (), and for divalent versus . For Cr-Al substitution the relationship is linear and is negative for Mg-rich spinel and positive for Fe-Ti rich spinel. In general a combination of aluminous-rich chromite and ulvöspinel in the Luna 16 samples, combined with the chromian-pleonaste in Apollo 14 define comparable major compositional trends to those observed in Luna 20. Ilmenite is present in trace amounts. It is exsolved from pleonaste and pyroxene, is present in subsolidusreduced ulvöspinel and has undergone reequilibration to produce oriented intergrowths of chromite + rutile. Primary ilmenite is among the most magnesian-rieh (6 wt.% MgO) yet found in the lunar samples. The high MgO, inferred high Cr2O3 concentrations and the iron content of rutile (2.5 wt.% FeO) suggest crystallization at high temperatures and pressures for some components of the Luna 20 soil. 相似文献
7.
Walter Riesen Heinz Gamsjäger Paul W. Schindler 《Geochimica et cosmochimica acta》1977,41(9):1193-1200
The carbonato and hydrogencarbonato complexes of Mg2+ were investigated at 25 and 50° in solutions of the constant ClO4? molality (3 M) consisting preponderantly of NaClO4. The experimental data could be explained assuming the following equilibria: Mg2+ + CO2B + H2O ag MgHCO+3 + H+, , Mg2+ + 2 CO2g + 2 H2Oag Mg(HCO3)02 ± 2 H+, , ?15.37 ± 0.39 (50°), Mg2+ + CO2g + H2Oag MgCO03 + 2 H+, ,?15.23 ± 0.02 (50°), with the assumption γMgCO30 = γMg(HCO3)02, ΔG0(I = 0) for the reaction MgCO03 + CO2g + H2O = Mg(HCO3)02 was estimated to be ?3.91 ± 0.86 and 0.6 ± 2.4 kJ/mol at 25 and 50°C, respectively. The abundance of carbonate linked Mg(II) species in fresh water systems is discussed. 相似文献
8.
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
9.
Charles D Byers David W Muenow Michael O Garcia 《Geochimica et cosmochimica acta》1983,47(9):1551-1558
Glasses from submarine lavas recovered by the ALVIN submersible from the Galapagos Spreading Center (GSC) near 86°W have been analyzed by electron microprobe for major elements and by high-temperature mass spectrometry for volatiles. The samples studied range in composition from basalt to andesite and are more evolved than typical MORBs. Previous studies indicate that they are related to normal MORB by extensive crystal fractionation in small, isolated magma chambers. The H2O, Cl and F contents of these lavas are substantially higher than any previously reported for MORBs. H2O, Cl and F abundances increase linearly with P2O5 content, which is used as an indicator of the extent of crystal fractionation. The ratios measured in the andesite glasses progressively decrease with increasing P2O5 content and are probably related to fractionation of Fe-Tioxides. Reduced carbon gas species, principally CH4 and CO, were discovered in these glasses. The presence of reduced carbon species in GSC glasses may be indicative of a more reduced oxidation state of the upper mantle than is commonly assumed. 相似文献
10.
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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The solubility of rutile has been determined in a series of compositions in the K2O-Al2O3-SiO2 system ( + Al2O3) = 0.38–0.90), and the CaO-Al2O3-SiO2 system (). Isothermal results in the KAS system at 1325°C, 1400°C, and 1475°C show rutile solubility to be a strong function of the ratio. For example, at 1475°C the amount of TiO2 required for rutile saturation varies from 9.5 wt% () to 11.5 wt% () to 41.2 wt% (). In the CAS system at 1475°C, rutile solubility is not a strong function of . The amount of TiO2 required for saturation varies from 14 wt% () to 16.2 wt% ().The solubility changes in KAS melts are interpreted to be due to the formation of strong complexes between Ti and K+ in excess of that needed to charge balance Al3+. The suggested stoichiometry of this complex is K2Ti2O5 or K2Ti3O7. In CAS melts, the data suggest that Ca2+ in excess of A13+ is not as effective at complexing with Ti as is K+. The greater solubility of rutile in CAS melts when is less than 0.54 compared to KAS melts of equal ratio results primarily from competition between Ti and Al for complexing cations (Ca vs. K).TiKβ x-ray emission spectra of KAS glasses () with 7 mole% added TiO2, rutile, and Ba2TiO4, demonstrate that the average Ti-O bond length in these glasses is equal to that of rutile rather than Ba2TiO4, implying that Ti in these compositions is 6-fold rather than 4-fold coordinated. Re-examination of published spectroscopic data in light of these results and the solubility data, suggests that the 6-fold coordination polyhedron of Ti is highly distorted, with at least one Ti-O bond grossly undersatisfied in terms of Pauling's rules. 相似文献
13.
Dieke Postma 《Geochimica et cosmochimica acta》1985,49(4):1023-1033
Redox reactions between Fe2+ in solution and Mn-oxides are proposed as a mechanism for concentration of Mn in sediments both during weathering and diagenesis in marine sediments, e.g. the formation of Mn-nodules.If such a mechanism is to be effective, then reaction rates between Fe2+ and Mn-oxides should be fast. The kinetics and stoichiometry of the reaction between dissolved Fe2+ and synthetically prepared birnessite (Mn7O13·5H2O) were studied experimentally in the pH range 3–6.Results show a stoichiometry which at pH < 4 conforms to a simple reaction between Fe2+ and birnessite, releasing Mn2+ and Fe3+ to the solution. At pH > 4 FeOOH is precipitated and excess Fe2+ consumption compared to the theoretical stoichiometry is observed. The excess Fe2+ consumption is not due to a formation of a quantitative MnOOH layer but rather to adsorption.Reaction kinetics are very fast at pH < 4 and change at pH 4 to a slower mechanism. At pH > 4 the reaction is fast initially until 17% of the bimessite has dissolved and changes then to a slower stage. The later stage can be described by the equation: where J is the overall rate of Mn2+ release, m0 and m the mass of birnessite at time t = 0 and t > 0, β = 6.76?0.94 pH and γ has values of 0.76 at pH 5 and 0.39 at pH 6. The rate constant k is 7.2·10?7 moles s?1 g?1 (moles/1)?0.31 at pH 5 and 9.6·10?8 moles s?1 g?1 (moles/1)0.06 at pH 6.Diffusion calculations show that the rate is controlled by surface reaction and it is tentatively proposed that the availability of vacancies in octahedral [MnO6]sheets of the birnessite surface could be rate controlling. It is concluded that reactions between Fe(II) and birnessite, and probably other Mn-oxides, are fast enough to be important in natural environments at the earth surface. 相似文献
14.
Serpentinization of cumulate ultramafic rocks from the North Arm Mountain massif of the Bay of Islands ophiolite 总被引：1，自引：0，他引：1
Partially serpentinized dunites and wehrlites comprise the bulk of the cumulate ultramafic unit at the North Arm Mountain massif of the Bay of Islands ophiolite complex, Newfoundland. In a suite of 59 dunites and werhlites from the base of the unit, the serpentinized portions consist of lizardite + chrysotile + brucite + (accessory) magnetite. The ratio of . Petrographic observations show that most serpentinization occurred at the expense of olivine; only limited amounts of clinopyroxene were serpentized. An estimated volume increase of 32% accompanied serpentinization of the peridotites. Reconstructions of the primary modal proportions of wehrlites (made taking this volume increase into account) contain an average of 6% more clinopyroxene and 6% less olivine than do modal reconstructions that ignore the volume increase. Mass balance calculations provide no clear evidence for appreciable metasomatism of Al2O3, CaO, FeO, MgO, or SiO2 during Serpentinization. The presence of brucite, the evidence that most serpentinization occurred at the expense of olivine, and the lack of appreciable metasomatism, suggest that the primary reaction that controlled serpentinization of the peridotites is: . olivine added serpentine brucite 相似文献
15.
To simulate trapping of meteoritic noble gases by solids, 18 samples of Fe3O4 were synthesized in a noble gas atmosphere at 350–720 K by the reactions: 3Fe + 4H2O → Fe3O4 + 4H2 (Ne, Ar, Kr, Xe) 3Fe + 4CO → Fe3O3 + 4C + carbides (Xe only) Phases were separated by selective solvents (HgCl2, HCl). Noble gas contents were analyzed by mass spectrometry, or, in runs where 36 d Xe127 tracer was used, by γ-counting. Surface areas, as measured by the BET method, ranged from 1 to 400 m2/g. Isotopic fractionations were below the detection limit of 0.5%/m.u.Sorption of Xe on Fe3O4 and C obeys Henry's Law between and atm, but shows only a slight temperature dependence between 650 and 720 K (). The mean distribution coefficient KXe is cc STP/g atm for Fe3O4 and only a factor of greater for C; such similarity for two cogenetic phases was predicted by Lewis et al. (1977). Stepped heating and etching experiments show that 20–50% of the total Xe is physically adsorbed and about 20% is trapped in the solid. The rest is chemisorbed with . The desorption or exchange half-time for the last two components is >102 yr at room temperature.Etching experiments showed a possible analogy to “Phase ” in meteorites. A typical carbon + carbide sample, when etched with HNO3, lost 47% of its Xe but only 0.9% of its mass, corresponding to a ~0.6 Å layer. Though this etchable, surficial gas component was more thermolabile than (release below 1000°C, compared to 1200–1600°C), another experiment shows that the proportion of chemisorbed Xe increases upon moderate heating (1 hr at 450°C). Apparently adsorbed gases can become “fixed” to the crystal, by processes not involving volume diffusion (recrystallization, chemical reaction, migration to traps, etc.). Such mechanisms may have acted in the solar nebula, to strengthen the binding of adsorbed gases.Adsorbed atmospheric noble gases are present in all samples, and dominate whenever the noble gas partial pressure in the atmosphere is greater than that in the synthesis. Many of the results of Lancet and Anders (1973) seem to have been dominated by such an atmospheric component; others are suspect for other reasons, whereas still others seem reliable. When the doubtful samples of Lancet and Anders are eliminated or corrected, the fractionation pattern—as in our samples—no longer peaks at Ar, but rises monotonically from Ne to Xe. No clear evidence remains for the strong temperature dependence claimed by these authors. 相似文献
16.
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
17.
Frank J Millero 《Geochimica et cosmochimica acta》1985,49(2):547-553
The effect of ionic interactions of the major components of natural waters on the oxidation of Cu(I) and Fe(II) has been examined. The various ion pairs of these metals have been shown to have different rates of oxidation. For Fe(II), the chloride and sulfate ion pairs are not easily oxidized. The measured decrease in the rate constant at a fixed pH in chloride and sulfate solutions agrees very well with the values predicted. The effect of pH (6 to 8) on the oxidation of Fe(II) in water and seawater have been shown to follow the rate equation where k1 and k2 are the pseudo first order rate constants, β1 and β2 are the hydrolysis constants for Fe(OH)+ and Fe(OH)0. The value of αFE is the fraction of free Fe2+. The value of k1 (2.0 ±0.5 min?1) in water and seawater are similar within experimental error. The value of k2 (1.2 × 105 min?1) in seawater is 28% of its value in water in reasonable agreement with predictions using an ion pairing model.For the oxidation of Cu(I) a rate equation of the form was found where k0 (14.1 sec?1) and k1 (3.9 sec?1) are the pseudo first order rate constants for the oxidation of Cu+ and CuCl0, β1 is the formation constant for CuCl0 and αCu is the fraction of free Cu+. Thus, unlike the results for Fe(II), Cu(I) chloride complexes have measurable rates of oxidation. 相似文献
18.
E.J. Reardon 《Chemical Geology》1976,18(4):309-325
Potentiometric measurements in dilute sodium borate solutions with added alkali earth chlordie salts yield the following expressions for the dissociation constants of alkali earth borate ion pairs from 10 to 50°C:where T is in °K. Enthalpies for the dissociation reactions at 25°C are less than 1 kcal./mole for all the alkali earth borate ion pairs.Values for pK(NaH2BO3°) from 5 to 55°C computed from the experimental data of Owen and King are in good agreement with those determined potentiometrically. The average value from both methods is 0.22 ± 0.1 at 25°C.Application to seawater of computed pK's for MgH2BO3+, CaH2BO3+ and NaH2BO30 yields an apparent dissociation constant for boric acid of 8.73 vs. 8.70 measured by Lyman, 8.68 by Buch and 8.73 by Byrne and Kester. 相似文献
19.
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
20.
Charles D Byers David M Christie David W Muenow John M Sinton 《Geochimica et cosmochimica acta》1984,48(11):2239-2245
Volatiles and major elements in abyssal glasses ranging in composition from basalt, ferrobasalt, andesite to rhyodacite from the Galapagos Spreading Center (GSC) near 95°W were analyzed using electron microprobe and high temperature mass spectrometry. Total volatile content ranged from 0.32 wt.% to 2.74 wt.%. Volatile abundances of MORB glasses from the 95.5°W propagating rift are similar to those from the adjacent normal rift (avg. 0.34 wt.%) and lower than those of N-type MORB from the Mid-Atlantic Ridge (avg. 0.49 wt.%). Although both propagating and non-propagating rift glasses contain trace amounts of methane (<0.01 wt.%) and carbon monoxide (0.04 wt.%), significantly higher 100 ratios are observed for the primitive propagating rift glasses. Water contents of the most primitive GSC glasses are ~0.09 wt.% suggesting a water content for the mantle source of ~0.02 wt.% which indicates that source masses with very low water content can be involved in the generation of MORB.In fractionated ferrobasalt, andesite and rhyodacite glasses from the 95.5°W propagating rift, increasing abundances of H2O, Cl and F indicate highly incompatible behavior, whereas CO2 and reduced carbon species appear to decrease in abundance with increasing differentiation. Ferric-ferrous ratios increase from basalt to andesite and reduce to near zero in the rhyodacite. These values are not distinguishable from those previously reported for similar fractionated glasses from the Galapagos 85°W propagating rift, despite the apparent suppression of oxide precipitation in the 85°W suite. 相似文献