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1.
Equations are developed for calculating the density of aluminosilicate liquids as a function of composition and temperature. The mean molar volume at reference temperature Tr, is given by , where the summation is taken over all oxide components except A1 2O 3, X stands for mole fraction, terms are constants derived independently from an analysis of volume-composition relations in alumina-free silicate liquids, and is the composition-dependent apparent partial molar volume of Al 2O 3. The thermal expansion coefficient of aluminosilicate liquids is given by , where terms are constants independent of temperature and composition, and is a composition-dependent term representing the effect of Al 2O 3 on the thermal expansion. Parameters necessary to calculate the volume of silicate liquids at any temperature T according to V( T) = Vrexp[ α( T- Tr)], where Tr = 1400° C have been evaluated by least-square analysis of selected density measurements in aluminosilicate melts. Mean molar volumes of aluminosilicate liquids calculated according to the model equation conform to experimentally measured volumes with a root mean square difference of 0.28 and an average absolute difference of 0.90% for 248 experimental observations. The compositional dependence of is discussed in terms of several possible interpretations of the structural role of Al 3+ in aluminosilicate melts. 相似文献
3.
The stability of the amphibole pargasite [NaCa 2Mg 4Al(Al 2Si 6))O 22(OH) 2] in the melting range has been determined at total pressures ( P) of 1.2 to 8 kbar. The activity of H 2O was controlled independently of P by using mixtures of H 2O + CO 2 in the fluid phase. The mole fraction of H 2O in the fluid ( ) ranged from 1.0 to 0.2.At P < 4 kbar the stability temperature ( T) of pargasite decreases with decreasing at constant P. Above P ? 4 kbar stability T increases as is decreased below one, passes through a T maximum and then decreases with a further decrease in . This behavior is due to a decrease in the H 2O content of the silicate liquid as decreases. The magnitude of the T maximum increases from about 10°C (relative to the stability T for ) at P = 5 kbar to about 30°C at P = 8 kbar, and the position of the maximum shifts from at P = 5 kbar to at P = 8 kbar.The H 2O content of liquid coexisting with pargasite has been estimated as a function of at 5 and 8 kbar P, and can be used to estimate the H 2O content of magmas. Because pargasite is stable at low values of at high P and T, hornblende can be an important phase in igneous processes even at relatively low H 2O fugacities. 相似文献
4.
It is proposed that the ‘M value’ of an igneous rock should be 100Mg/(Mg + ΣFe) and that the ‘Mg value’ should be 100Mg/(Mg + Fe 2+). A plea is made to standardize any necessary corrections for Fe 2O 3 so that for basic rocks. 相似文献
6.
Mechanisms and kinetics of aqueous oxidation-reduction and dissolved O 2 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 O 2 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
7.
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 MgAl 8O 4 to FeCr 2O 4 and a discontinuous trend from FeCr 2O 4 to Fe 2TiO 4. 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 Cr 2O 3 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
8.
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:Fe 2+ 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
9.
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 H 2O, Cl and F contents of these lavas are substantially higher than any previously reported for MORBs. H 2O, Cl and F abundances increase linearly with P 2O 5 content, which is used as an indicator of the extent of crystal fractionation. The ratios measured in the andesite glasses progressively decrease with increasing P 2O 5 content and are probably related to fractionation of Fe-Tioxides. Reduced carbon gas species, principally CH 4 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.
K and Rb distributions between aqueous alkali chloride vapour phase (0.7 molar) and coexisting phlogopites and sanidines have been investigated in the range 500 to 800°C at 2000 kg/cm 2 total pressure.Complete solid solution of RbMg 3AlSi 3O 10(OH) 2 in KMg 3AlSi 3O 10(OH) 2 exists at and above 700°C. At 500°C a possible miscibility gap between approximately 0.2 and 0.6 mole fraction of the Rb end-member is indicated.Only limited solid solution of Rb AlSi 3O 8 in KAlSi 3O 8 has been found at all temperatures investigated.Distribution coefficients, expressed as in solid/(Rb/K) in vapour, are appreciably temperature-dependent but at each temperature are independent of composition for low Rb end-member mole fractions in the solids. The determined values and their approximate Rb end-member mole fraction ( ) ranges of constancy are summarized as follows: (°C) | (°C)T | | | | | | 500 | | 0–0.2 | | 0–0.07 | | 700 | | 0–0.2 | | 0–0.1 | | 800 | | 0–0.2 | | 0–0.1 | 相似文献
11.
CaCO 3Ca(OH) 2CaS serves as a model system for sulfide solubility in carbonatite magmas. Experiments at 1 kbar delineate fields for primary crystallization of CaCO 3, Ca(OH) 2 and CaS. The three fields meet at a ternary eutectic at 652°C with liquid composition (wt%): CaCO3 = 46.1%, Ca( OH) 2 = 51.9%, CaS = 2.0%. Two crystallization sequences are possible for liquids that precipitate calcite, depending upon whether the liquid is on the low-CaS side, or the high-CaS side of the line connecting CaCO 3 to the eutectic liquid. Low-CaS liquids precipitate no sulfide until the eutectic temperature is reached leading to sulfide enrichment. The higher-CaS liquids precipitate some sulfide above the eutectic temperature, but the sulfide content of the melt is not greatly depleted as the eutectic temperature is approached. Theoretical considerations indicate that sulfide solubility in carbonate melts will be directly proportional to and inversely proportional to ; it also is likely to be directly proportional to melt basicity, defined here by . A strong similarity exists in the processes which control sulfide solubility in carbonate and in silicate melts. By analogy with silicates, ferrous iron, which was absent in our experiments, may also exert an important influence on sulfide solubility in natural carbonatite magmas. 相似文献
12.
In shale, mudstone and siltstone samples (154) a positive relationship exists between the ratio and the quartz content. As the grain size of the sediment increases, so titanium oxides (rutile and anatase are present) increase in importance relative to the silicates, due to sorting. In sandstones the ratio reflects the maturity, but the degree of sorting must be taken into account. The ratio of TiO 2 substituting in the clay minerals to the Al 2O 3 content is not greater than 0.025 based on the whole rock analyses. This is borne out by values close to 0.010 obtained following the method of Raman and Jackson ( Amer. Mineral. 50, 1086–1094, 1965). The addition of volcanic material to the normal sediment may either increase or decrease the whole rock ratio depending on the ash composition. Volcanic contributions may thus be recognized and several examples are given from the British Carboniferous. 相似文献
13.
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
14.
The enthalpies of solution of a suite of 19 high-structural state synthetic plagioclases were measured in a Pb 2B 2O 5 melt at 970 K. The samples were crystallized from analyzed glasses at 1200°C and 20 kbar pressure in a piston-cylinder apparatus. A number of runs were also made on Amelia albite and Amelia albite synthetically disordered at 1050–1080°C and one bar for one month and at 1200°C and 20 kbar for 10 hr. The component oxides of anorthite, CaO, Al 2O 3 and SiO 2, were remeasured.The ΔH of disorder of albite inferred in the present study from albite crystallized from glass is 3.23 kcal, which agrees with the 3.4 found by Holm and Kleppa (1968). It is not certain whether this value includes the ΔH of a reversible displacive transition to monoclinic symmetry, as suggested by Helgeson et al. (1978) for the Holm-Kleppa results. The enthalpy of solution value for albite accepted for the solid solution series is based on the heat-treated Amelia albite and is 2.86 kcal less than for untreated Amelia albite.The enthalpy of formation from the oxides at 970 K of synthetic anorthite is ?24.06 ± 0.31 kcal, significantly higher than the ?23.16 kcal found by Charlu et al. (1978), and in good agreement with the value of ?23.89 ± 0.82 given by Robie et al. (1979), based on acid calorimetry.The excess enthalpy of mixing in high plagioclase can be represented by the expression, valid at 970 K: ΔHex(±0.16 kcal) = 6.7461 XabX2An + 2.0247 XAnX2Ab where XAb and XAn are, respectively, the mole fractions of NaAlSi 3O 8 and CaAl 2Si 2O 8. This ΔH ex, together with the mixing entropy of Kerrick and Darken's (1975) Al-avoidance model, reproduces almost perfectly the free energy of mixing found by Orville (1972) in aqueous cation-exchange experiments at 700°C. It is likely that Al-avoidance is the significant stabilizing factor in the high plagioclase series, at least for XAn≥ 0.3. At high temperatures the plagioclases have nearly the free energies of ideal one-site solid solutions. The Al-avoidance model leads to the following Gibbs energy of mixing for the high plagioclase series: . The entropy and enthalpy of mixing should be very nearly independent of temperature because of the unlikelihood of excess heat capacity in the albite-anorthite join. 相似文献
16.
When quenched metastable wüstite (Fe .924O and Fe .947O) is held at 300°C at pressures up to 200 kbar in a diamond anvil cell, a mixture of magnetite, metallic iron and wüstite is found. We interpret this to indicate that magnetite plus metallic iron constitute the stable phase assemblage at pressures and temperatures below this boundary is stoichiometric FeO ( ) at pressures below 110 kbar at 300°C. However, just below the boundary in the pressure range 110 kbar to 200 kbar at 300°C, the residuál wüstite is non-stoichiometric ( ). Data collected at pressures and temperatures above the boundary indicate that non-stoichiometric wüstite (Fe xO) plus metallic iron constitute the stable phase assemblage and that the value of x in Fe xO increases as pressure is increased isothermally to 100 kbar and then decreases as pressure is increased above 100 kbar. 相似文献
17.
The olivine-ilmenite thermometer of Andersen and Lindsley (1979) was based on an incorrect formulation for the excess free energy of an asymmetric ternary solution. A valid formulation is derived and used to revise the parameters of the olivine-ilmenite thermometer. For olivine and ilmenite that have equilibrated above 700°C, temperature can be calculated from: with . The revised model gives Wil·gkG = 5767?3.09 T + 0.011 P and ΔGexch = 7301 ? 8.9 T ? 0.047 P ( T in K, P in bars). Applications include Apollo 17 breccias and kimberlites. 相似文献
18.
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 Ti 3+. The titan-aegirines were formed during late to post-magmatic crystallization in a system with a high Ti 4+/Fe 2+ ratio and were followed by acmite showing enrichment in jadeite. Comparison with experimentally investigated titan-aegirine indicates crystallization far below the Mn 2O 3Mn 3O 4f 02 buffer. 相似文献
19.
For a phase at equilibrium in which two cation species are partitioned ideally between two sub-lattice sites, the excess functions of mixing (free energy, enthalpy and entropy) are directly related to the bulk composition of the phase and ΔGE°( T, P), the standard-state intra- crystalline exchange free energy. If the phase is not at equilibrium internally, an additional ordering parameter is necessary to fix the excess free energy of mixing, GmixEX, unambiguously. Conversely, for any fixed GmixEX there exists an infinity of possible intracrystalline cation dis- tributions, only one of which is the equilibrium distribution for the specified temperature and pressure. As ideal intraphase cation ordering becomes more pronounced, GmixEX decreases. In response, the total free energy of mixing for the phase decreases progressively for non-end member compositions, approaching, at the limits of ordering, values appropriate for stabilizing compounds of intermediate composition.The model-dependent activity coefficient for component A in the phase, γ AT, can be calculated for any bulk composition, XAT, either from GmixEX directly or from more basic equations involving the interrelation of chemical potentials at equilibrium. A general form for γ AT is ln , where Xjκ denotes the mole fraction of species j in site κ. The first term on the right-hand side of this equation is the contribution to γ AT from ideal intracrystalline partitioning, and is common to the several theories lately presented to model intraphase cation partitioning. It can be shown rigorously that this term contributes to a negative deviation from ideality for the bulk phase. The second term is the contribution to the macroscopic activity coefficient from non-ideal intraphase partitioning, and is related to an enthalpy of mixing, HmixN in excess of that resulting from ideal inter-site cation ordering. While the expression represented by Y can take several functional forms, the additional enthalpy can be evaluated explicitly for specific non-ideal partitioning models from the relation .In those cases, GmixEX can also be determined exactly. 相似文献
20.
The F contents of a number of Apollo 14 and 15 samples range from less than a ppm for anorthosite rock fragments to ~165 ppm for some soils and breccias. Apollo 15 soils tend to have lower F contents (50–70 ppm) than soils from other sites. In most cases samples were run simultaneously with W-1 in which F was determined to be 216 (±11) ppm.The ratio is 0·032 ± 0·005 in soils and rocks. A correlation exists in soils between F, P 2O 5, and that fraction of the Cl which is insoluble in hot water. The ratio in soils and rocks, though different, requires that the phosphate phase involved be fluorapatite; this is consistent with mineralogical observations. F, like Cl, is correlated with KREEP elements at all sites for which data are available. 相似文献
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