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1.
Hydrolysis constants of dimethyltin(IV) cation, in different salt solutions (CaCl2: 0.15 I 0.90; MgCl2: 0.30 I 0.60; NaCl-–NaClO4, NaCl-–NaNO3 mixtures: I = 3; NaCl-–Na2SO4 mixtures: I = 1 mol dm-3) were determined by potentiometric ([H+]-glass electrode) measurements. These data, together with previous data (De Stefano et al., 1996b) were interpreted in terms of DHT (Debye–Hückel type) and Pitzer equations. The mixed electrolyte solution results also allowed us to obtain and parameters for the Pitzer equation. Calorimetric measurements were made at different ionic strengths in order to find the temperature dependence of hydrolysis constants and of the relative interaction parameters. The body of results allows us to determine the speciation of natural waters in a wide range of ionic strengths and temperatures.  相似文献   

2.
Synthesis experiments in the system MgAl2O4–MgFe2O4 [MgAl2–xFexO4 (0 x 2)] were carried out using a PbF2 flux. The crystalline products synthesized in the compositional range of 0.6 <x 1.2 consisted of two spinel phases, whereas those synthesized in the compositional ranges of 0.0 x 0.6 and 1.2 < x 2.0 crystallized as single spinel phases. Structure refinements of the spinel single crystals, which grew in the ranges of 0.0 x 0.6 and 1.2 < x 2.0, show that the degree of randomness of cation distribution between A and B sites increases as x approaches the two-phase region. This means that the degree of the size mismatch among Mg2+, Fe3+ and Al3+occupying each equivalent mixing site increases as x approaches the two-phase region. Consequently, if the coexistence of two spinels observed in the intermediate compositions reveals the existence of a miscibility gap at low temperatures, this increase in the degree of the size mismatch among the three cations is suggested as a factor of energetic destabilization to form the miscibility gap.  相似文献   

3.
The acid/base properties of the hematite/water interface and surfacecomplexation with gold has been studied by potentiometric titrations in thefour component system H+ – FeOH –AuCl 4 - – Cl-. Equilibrium measurementswere performed in NaCl media at 298.2 K. In the evaluation of equilibriummodel from experimental data the constant capacitance model was applied. Theacid/base properties were investigated in 0.1 M NaCl in the range 2.6 pH 7.4. The resulting intrinsic constants for protonation anddeprotonation of hydroxyl groups at the surface were log 1,1,0,0(int) s = 7.10 ± 0.06 andlog -1,1,0,0(int) s = - 7.80 ±0.06. The density of proton active surface sites was 2.85nm-2 and the specific capacitance 2.5 C V-1 m-2. In the investigation of surface complexation of gold, thepotentiometric titrations were performed in the range 2.0 pH 10.2.Titration data was supplemented with analysis of Au in the aqueous phase byatomic absorbance spectrometry. The equilibrium model proposed consists ofthe following monodentate surface complexes: FeOHAuCl3(log 0,1,1,-1 s = 1.45 ± 0.03),FeOHAuCl2OH (log -1,1,1,-2 s = -3.89 ± 0.02), FeOHAu(OH)3 (log -3,1,1,-4 s = -21.94 ± 0.05). Aslightly better fit could be obtained by assuming formation of a bidentatecomplex with the composition(FeO)2Au(OH)H2O. However, based onstructural arguments this complex was rejected.  相似文献   

4.
Comparison between two types of multifractal modeling   总被引：1，自引：0，他引：1  
The interrelationships between two previously developed multifractal models are discussed. These are the Evertsz-Mandelbrot model developed on the basis of the multifractal spectrum f(), and the Schertzer-Lovejoy model based on the codimension function C() where and represent Hölder exponent and field order, respectively. It is shown how these two models are interrelated: they are identical for values of within the range D–(0)D–min. where D is the Euclidean dimension. For D–maxD–(0), however, f() remains a continuous function of whereas C() assumes constant value. In this respect, the fractal spectrum f() can provide more information about the multifractal measure than the codimension function C(). The properties of the two models are illustrated by application to the binomial multiplicative cascade model.  相似文献   

5.
Divariant oxide plus metal assemblages potentially make useful redox sensors for use in hydrothermal and other high pressure experiments. Here we report the calibration of the (Ni, Mn)O/Ni redox sensor in which the Ni/NiO (NNO) oxygen buffer is displaced to lower oxygen chemical potentials (O2), by the solid solution of MnO in the oxide phase. This assemblage was chosen because: (1) it covers a useful range of O2; (2) the system can be calibrated very accurately. Values of O2 defined by the (Ni, Mn)O/Ni assemblage were determined electrochemically, from 900 to 1300 K, using calcia-stabilized zirconia solid electrolytes. The oxide compositions (8 in total, ranging from 0.1X NiO0.8) were analysed afterwards by electron microprobe, and were checked for internal consistency by measuring the lattice parameters (a0), using powder XRD. The accuracies of the measurements, both assessed theoretically and established empirically, are (1): ±80J/mol in O2, ±0.0002 Å in a0 and ±0.002 to 0.005 in X NiO. Activity-composition relations were fitted to the Redlich-Kister formalism. There is a slight asymmetry (corresponding to a subregular model) across the solution with A 0 G =9577(±45) J/mol, and A 1 G =–477(±80) J/mol. The experimental data were also used to derive the parameters Vex, Hex and Sex. There is no obvious relationship between excess volumes and enthalpies of mixing, nor between excess volumes and excess entropies. The experimental data from this study have been used to formulate the (Ni, Mn)O/Ni redox sensor expression: O2 = 2(NNO) + 2RTlnX NiO + 2(1 – X NiO)2[11483 – 1.697T] – 477(4X NiO – 1)(900 < T(K) < 1300) where O2(NNO)=–478967+248.514T–9.7961 T In T, from O'Neill and Pownceby(1993a).  相似文献   

6.
It is valuable in earthquake prediction to determine the occurrence probability of major earthquakes by making use of data obtained from precursory phenomena up to the time of the evaluation. In this study, the time evolution of the state determined by earthquakes and precursory phenomena was modelled using Markov chains. Various probabilities suitable for earthquake prediction were derived from the transition probability of the Markov chain with a chosen length of memory time. As an example, earthquake sequence records for northern China, which covered a period of about two thousand years, were examined and the results were also obtained from modern scientific observations of the radon anomaly which covered a period of about 10 years.Assuming moderate-sized earthquakes of two magnitude ranges 4 3/4 M 5 3/4, 6 M 6 3/4 as precursors to large earthquakes of a magnitude range, 7 M 8 1/2, transition probabilities were calculated for a time interval from 2 to 40 yr. The results showed that the precursory time of moderate-sized earthquakes is mainly distributed in a time span of around several years and that the earthquake occurrence probability is considerably large when the precursory earthquakes occur successively. Furthermore, it was shown that a larger moderate-sized earthquake (4 3/4 M 5 3/4) is a more effective precursor than an entire moderate-sized earthquake (4 3/4 M 6 3/4).Second, a multiple precursor case was tried by means of simulation based on the radon anomaly data obtained during a limited observation period. Simultaneous occurrence of two precursors makes the earthquake occurrence probability increase by 1.5–2.0 for a reasonable choice of a mean recurrence interval of the radon anomaly compared with the case where only a moderate-sized earthquake was treated as the precursor. However, the probability is much the same if the average recurrence interval of the radon anomaly is the same through time, including the preparatory period before the earthquake.  相似文献   

7.
Summary The Dumont Sill is an Archaean komatiitic intrusion, whichDuke (1986) subdivided into a mafic (MZ) and ultramafic zone (UMZ). The UMZ comprises an upper (UPZ) and a lower peridotite subzone (LPZ) consisting of olivine + chromite cumulates and a dunite subzone (DZ) between them, consisting of olivine ± sulfide cumulates.Three sulfide-rich layers in the DZ are delineated by anomalously high Ni, Cu, S and Se concentrations (Ni 0.95 wt %, Cu 0.07 wt.%, S 1.0 wt.%, Se 2.7 ppm). They also contain elevated contents of noble metals (Au 31.5 ppb, Pd 210 ppb, Pt 180 ppb, Ir 8.4 ppb, Os 6 ppb). Unmineralized samples contain 3–8 ppb Pd, 1–20 ppb Pt, 0.2–3.6 ppb Au, 0.5–6 ppb Ir, and 1–6 ppb Os.Samples belonging to the LPZ and UPZ and lying above and beneath the mineralized horizons have rather high Ir contents, generally between 2.9 to 4.4 ppb. In contrast, Ir contents of sulfide-free samples from the DZ and UPZ which lie immediately above the mineralized zones have significantly lower Ir concentrations, ranging from 0.1 to 1.5 ppb. This zone of Ir depletion coincides with a zone of Ni-depleted olivine and sulfide which crystallized just above sulfide-rich horizons in the DZ (Duke, 1986). It is suggested that Ir and Ni depletion in cumulates which lie between or above sulfide-rich zones are due to the lower Ir and Ni contents in olivine which crystallized from a silicate magma from which a sulfide liquid had already been segregated. Alternatively, if metal alloys control the distribution of Ir and Os in the DZ, the Ir depletion in the cumulates above the ore' horizons implies that crystallization of the metal phase ceased. This would be the case if, due to the segregation of sulfides, the Ir concentration in the silicate liquid falls below the solubility limit of the metal phase.The sulfide mineralization probably formed by fractional segregation of a sulfide/ oxide liquid, as the PGE concentrations in the sulfide liquid and PGE/Se, or PGE/S ratios tend to decrease from the bottom to the top in the mineralized zones.Duke (1986) proposed that sulfide saturation was caused by mixing of primitive komatiite magma with fractionated interstitial liquid, which was squeezed out of the cumulate pile. Sulfide segregation at the floor of the magma chamber is likely to have been a very localized event implying low R-factors. The small PGE-enrichment in the sulfide horizons of the Dumont Sill and the narrow zones of Ir-depletion just above the sulfide zones are consistent with the proposed process.
Die Verteilung von Platingruppen-Elementen im Dumont Sill, Quebec und ihre Bedeutung für die Bildung von Ni-Sulfid MIneralisationen
Zusammenfassung Der Dumont Sill ist eine komatiitische Intrusion, die von Duke (1986) in eine mafische (MZ) und eine ultramafische (UMZ) Zone untergliedert wurde. Die UMZ setzt sich aus einer oberen (UPZ) und einer unteren (LPZ) peridotitischen Subzone, die aus Olivinund Chromft-Kumulaten besteht, und einer dunitischen Subzone (DZ), zwischen diese beiden eingeschaltet, zusammen. Letztere besteht aus Olivin- und Sulfid-Kumulaten.Drei sulfidreiche Lagen innerhalb der DZ sind durch anomal hohe Gehalte an Ni, Cu, S und Se (Ni 0.95 Gew. %, Cu 0.07 Gew. %, S 1.0 Gew. %, Se 2.7 ppm) charakterisiert. Erhöhte Gehalte an Edelmetallen (Au 31.5 ppb, Pd 210 ppb, Pt 180 ppb, Ir 8.4 ppb, Os 6 ppb) sind ebenfalls an diese Lagen gebunden. Unvererzte Proben enthalten < 3–8 ppb Pd, 1–20 ppb Pt, 0.2–3.6 ppb Au, 0.5–6 ppb Ir und 1–6 ppb Os.Proben aus der LPZ und UPZ und solche aus dem Hangenden und Liegenden der Mineralisationshorizonte zeigen relativ hohe Ir-Gehalte; im allgemeinen zwischen 2.9 und 4.4 ppb. Im Gegensatz dazu sind die Ir-Gehalte sulfidfreier Proben unmittelbar über vererzten Lagen deutlich erniedrigt; sie variieren zwischen 0.1–1.5 ppb. Diese an Ir verarmte Zone entspricht einer Zone nickelarmer Olivine und Sulfide, die unmittelbar oberhalb der sulfidreichen Horizonte in der DZ kristallisierten (Duke, 1986). Es wird vermutet, daß die Ir- und Ni-Abreicherung in den Kumulaten, die oberhalb und zwischen den sulfid-reichen Zonen liegen, mit den niedrigeren Ir- und Ni-Gehalten der Olivinen zusammenhängt. Die Olivine kristallisierten aus einem Silikatmagma, von dem sich bereits eine Sulfidschmelze abgeschieden hatte.Soferne metallische Verbindungen die Ir- und Os-Verteilung in der DZ kontrollieren, würde die Ir-Abreicherung in den Kumulaten oberhalb des Erzhorizontes auf ein Ende der Kristallisation einer metallischen Phase hinweisen. Dieser Fall könnte eintreten, sobald durch die Ausscheidung von Sulfiden, die Ir-Konzentration in der silikatischen Schmelze unter die Löslichkeitsgrenze der Metallphase fällt.Die Sulfidvererzung bildete sich wahrscheinlich infolge von fraktionierter kristallisation einer Sulfid/Oxidschmelze, da die PGE Konzentrationen der Sulfidschmelze, und das PGE/S Verhältnis vom Liegenden zum Hangenden hin in den mineralisierten Horizonten abnehmen. Duke (1986) schlug ein Modell vor, in dem die Sulfid-Sättigung der silikatischen Schmelze durch eine Vermischung eines komatiitischen Magmas mit einer fraktionierten, interstitialen, aus den Kumulaten ausgequetschten Schmelze erklärt wird. Die Sulfidausfällung an der Basis der Magmenkammer scheint ein lokal recht begrenztes Phänomen gewesen zu sein, die niedrige R-Faktoren bedingt. Die geringfügige PGE-Anreicherung in den Sulfidlagen des Dumont Sills und die schmale Zone der Ir-Abreicherung unmittelbar oberhalb dieser sulfidischen Zone stehen mit diesen vorgeschlagenen Prozessen im Einklang.

With 6 Figures  相似文献   

8.
Résumé L'étude chimique comparée, à la microsonde électronique, d'owyheeite de treize gisements différents a révélé des fluctuations sensibles des teneurs en éléments majeurs, en liaison avec la nature des sulfosels associés, ainsi que la présence occasionnelle de différents éléments mineurs: Cu et As (très fréquents), Sn et Bi (moins fréquents), Tl et Se (exceptionnels). Compte tenu du mode de substitution de ces éléments mineurs, la projection des analyses dans le système Pb2S2–Ag2S–Sb2S3 délimite un champ restreint de solution solide dont l'allongement s'accorde avec la substitution 2 Pb2+Ag++Sb3+. Ce champ de solution solide englobe la composition de la variété téremkovite, mais exclue la formule donnée initialement parShannon. La formule Pb10–2x Sb11+x Ag3+x S28 (–0,13x+0,20) rend compte des termes à la résolution de la Ag/Sb maximal; l'obtention d'une formule plus générale reste subordonée à la résolution de la structure cristalline. Aucun élément mineur ne peut jouer à lui seul le rôle de stabilisateur de la structure, mais ce même rôle peut être joué complémentairement par différents éléments, tels que Cu et Sn. Les clichés de microdiffraction électronique montrent des phénomènes de sur-structure plus ou moins prononcés, en liaison avec la concentration en (Ag+Cu), ou avec le degré de finesse du maclage complexe spécifique de l'owyheeite.
Crystal chemistry of owyheeite: New data
Summary Comparative electron microprobe study of owyheeite from thirteen ore deposits shows significant variations in the concentration of major elements. These can be correlated with the chemical composition of the associated sulfosalts. Sometimes, some minor elements may be present: Cu and As (very frequent), Sn and Bi (less frequent), Tl and Se (exceptional). Considering certain substitution rules for minor elements, the analyses plotted in the Pb2S2–Ag2S–Sb2S3 system show a limited solid-solution field, the elongation of which follows the substitution 2 Pb2+Ag++Sb3+. This solid-solution field includes the composition of the variety teremkovite, but excludes the initial formula for owyheeite proposed byShannon. The formula Pb10–2x Sb11+x Ag3+x S28 (–0.13x+0.20) describes compositional variation of members with the highest Ag/Sb ratio; a more general formula would require the determination of the crystal structure. No individual minor element appears to be responsible for stabilizing owyheeite. The stabilization may be due to a combined effect of two elements, such as Cu and Sn. Electron diffraction patterns show superstructure reflections which are related to the (Ag+Cu) concentration, as well as to the scale of the complex twinning characteristic of owyheeite.

Avec 3 Figures  相似文献   

9.
Iron- and vanadium-bearing kyanites have been synthesized at 900 and 1100° C/20 kb in a piston-cylinder apparatus using Mn2O3/Mn3O4- and MnO/Mn-mixtures, respectively, as oxygen buffers. Solid solubility on the pseudobinary section Al2SiO5-Fe2SiO5(-V2SiO5) of the system Al2O3-Fe2O3(V2O3)-SiO2 extends up to 6.5 mole% (14mole %) of the theoretical end member FeSiO5(V2SiO5) at 900°C/20 kb. For bulk compositions with higher Fe2SiO5 (V2SiO5) contents the corundum type phases M2O3(M = Fe3+, V3+) are found to coexist with the Fe3+(V3+)-saturated kyanite solid solution plus quartz. The extent of solid solubility on the join Al2SiO5-Fe2SiO5 at 1 100°C was not found to be significantly higher than at 900° C. Microprobe analyses of iron bearing kyanites gave no significant indication of ternary solid solubility in these mixed crystals. Lattice constants a 0, b 0, c 0, and V0 of the kyanite solid solutions increase with increasing Fe2SiO5- and V2SiO5-contents proportionally to the ionic radii of Fe3+ and V3+, respectively, the triclinic angles ,, remain constant. Iron kyanites are light yellowish-green, vanadium kyanites are light green. Iron kyanites, (Al1.87 Fe 0.13 3+ )SiO5, were obtained as crystals up to 700 m in length.  相似文献   

10.
The unit-cell and atomic parameters of perdeuterated brushite have been extracted from Rietveld analysis of neutron powder diffraction data within the temperature range 4.2 to 470 K. The thermal expansion of brushite is anisotropic, with the largest expansion along the b axis due principally to the effect of the O(1)···D(4) and O(3)···D(2) hydrogen bonds. Expansion along the c axis, influenced by the Ow1···D(5) interwater hydrogen bond, is also large. The high temperature limits for the expansion coefficients for the unit-cell edges a, b and c are 9.7(5) × 10–6, 3.82(9) × 10–5 and 5.54(5) × 10–5 K–1, respectively, and for the cell volume it is 9.7(1) × 10–5 K–1. The angle displays oscillatory variation, and empirical data analysis results in = 1.28(3) × 10–6sin(0.0105 T) K–1, within this temperature range. The evolution of the thermal expansion tensor of brushite has been calculated between 50 T 400 K. At 300 K the magnitudes of the principal axes are 11 = 50(6) × 10–6 K–1, 22 = 26.7(7) × 10–6 K–1 and 33 = 7.0(5) × 10–6 K–1. The intermediate axis, 22, is parallel to b, and using IRE convention for the tensor orthonormal basis, the axes 11 and 33 have directions equal to (–0.228, 0, –0.974) and (–0.974, 0, 0.228) respectively. Under the conditions of these experiments, the onset of dehydration occurred at temperatures above 400 K. Bond valence analysis combined with assessments of the thermal evolution of the bonding within brushite suggests that dehydration is precipitated through instabilities in the chemical environment of the second water molecule.  相似文献   

11.
In-situ synchrotron X-ray diffraction experiments were conducted using the SPEED-1500 multi-anvil press of SPring-8 on stishovite SiO2 and pressure-volume-temperature data were collected at up to 22.5 GPa and 1,073 K, which corresponds to the pressure conditions of the base of the mantle transition zone. The analysis of room-temperature data yielded V0=46.56(1) Å3, KT 0=296(5) GPa and K T =4.2(4), and these properties were consistent with the subsequent thermal equation of state (EOS) analyses. A fit of the present data to high-temperature Birch-Murnaghan EOS yielded (KT /T) P =–0.046(5) GPa K–1 and = a + bT with values of a =1.26(11)×10–5 K–1 and b =1.29(17)×10–8 K–2. A fit to the thermal pressure EOS gives 0=1.62(9)×10–5 K–1, ( K T / T) V =–0.027(4) GPa K–1 and (2P /T 2) V =27(5)×10–7 GPa K–2. The lattice dynamical approach by Mie-Grüneisen-Debye EOS yielded 0=1.33(6), q =6.1(8) and 0=1160(120) K. The strong volume dependence of the thermal pressure of stishovite was revealed by the analysis of present data, which was not detectable by the previous high-temperature data at lower pressures, and this yields ( K T / T) V 0 and q 1. The analyses for the fictive volume for a and c axes show that relative stiffness of c axis to a axis is similar both on compression and thermal expansion. Present EOS enables the accurate estimate of density of SiO2 in the deep mantle conditions.  相似文献   

12.
The Araripe Plateau in northeastern Brazil has an area of about 8,000 km2, confined by 39°05E and 40°55E, and 7°10S and 7°50S. Due to high permeability of soils, a surface drainage system is practically inexistent. Water is stored in excavations with clayey soil, the barreiros. Monthly samples were taken for 18O measurements, from September 1999 to August 2000, from four barreiros, three dug wells and five drilled wells. Results show that (1) groundwaters in the eastern part of the plateau are derived from present-day rainfall (18O–3.2), whereas groundwaters in the western portion are isotopically different (18O–5.0); (2) barreiros are strongly marked seasonally by elevated 18O during the dry period due to elevated evaporation; (3) a dug well at a distance of 30 m from a barreiro exhibits 18O similar to that of the reservoir, indicating a strong interaction between groundwater and surface water; and (4) a tubular well of 242-m depth, located in a fault, exhibits strong seasonal changes in 18O and electrical conductivity, revealing downward leakage between aquifers.  相似文献   

13.
The first laser-induced 40Ar-39Ar incremental-heating mineral age data for the Timok Massif of the Banatitic Magmatic and Metallogenetic Belt (BMMB) demonstrate that the main mineralization stage at the giant Majdanpek Cu–Au(–Mo) porphyry deposit took place at 83.6–84.0±0.6 Ma (2), coinciding with the later, 83±1–89.0±0.6 Ma, stages of the first cycle of andesitic volcanism. The earliest-Campanian age for hydrothermal activity precludes an association with the later history of the BMMB, and discounts the metallogenetic role of Laramide plutonism for the dated deposits.Editorial handling: A. Cheilletz  相似文献   

14.
Zusmmenfassung Die Ergebnisse der Schwefelisotopenanalysen von sechs Sulfid- und vier Sulfatmineralproben von Bleiberg/Kreuth (Österreich) variieren von –6,9 bis –25,9 34S in den Sulfiden und von +14,8 bis +18,9 34S in den Sulfaten. Die große Variationsbreite der Schwefelisotopen und die Bevorzugung des leichten Schwefels deutet vermutlich auf bakterielle Prozesse der Sulfidfällung. Die Sulfatschwefel fallen in den Bereich der Schwefelisotopenzusammensetzung des mesozoischen (postskytischen) Meerwassers.
Determination of the sulfur isotopic composition in some sulfide and sulfate minerals of the lead zinc deposit, Bleiberg/Kreuth, Carinthia
Summary Results of sulfur isotope analyses on 6 sulfides and 4 sulfates from Bleiberg/Kreuth (Austria) range from –6.9 to –25.9 34S (in sulfides) and from +14.8 to +18.9 34S (in sulfates). A large range of sulfide sulfur isotope fractionation with appreciable light sulfur probably indicates a bacterial sulfur source in sulfide precipiation. The sulfate sulfur plots in the range of Mesozoic (post-Skytian) seawater sulfur isotopic composition.
  相似文献   

15.
DC and AC electrical conductivities were measured on samples of two different crystals of the mineral aegirine (NaFeSi2O6) parallel () and perpendicular () to the [001] direction of the clinopyroxene structure between 200 and 600 K. Impedance spectroscopy was applied (20 Hz–1 MHz) and the bulk DC conductivity DC was determined by extrapolating AC data to zero frequency. In both directions, the log DC – 1/T curves bend slightly. In the high- and low-temperature limits, differential activation energies were derived for measurements [001] of EA 0.45 and 0.35 eV, respectively, and the numbers [001] are very similar. The value of DC [001] with DC(300 K) 2.0 × 10–6 –1cm–1 is by a factor of 2–10 above that measured [001], depending on temperature, which means anisotropic charge transport. Below 350 K, the AC conductivity () (/2=frequency) is enhanced relative to DC for both directions with an increasing difference for rising frequencies on lowering the temperature. An approximate power law for () is noted at higher frequencies and low temperatures with () s, which is frequently observed on amorphous and disordered semiconductors. Scaling of () data is possible with reference to DC, which results in a quasi-universal curve for different temperatures. An attempt was made to discuss DC and AC results in the light of theoretical models of hopping charge transport and of a possible Fe2+ Fe3+ electron hopping mechanism. The thermopower (Seebeck effect) in the temperature range 360 K < T <770 K is negative in both directions. There is a linear – 1/T relationship above 400 K with activation energy E 0.030 eV [001] and 0.070 eV [001]. 57Fe Mössbauer spectroscopy was applied to detect Fe2+ in addition to the dominating concentration of Fe3+.  相似文献   

16.
The Mount Lofty Ranges comprises interlayered marbles, metapsammites, and metapelites that underwent regional metamorphism during the Delamarian Orogeny at 470–515 Ma. Peak metamorphic conditions increased from lowermost biotite grade (350–400°C) to migmatite grade (700°C) over 50–55 km parallel to the lithological strike of the rocks. With increasing metamorphic grade, 18O values of normal metapelites decrease from 14–16 to as low as 9.0, while 18O values of calcite in normal marbles decrease from 22–24 to as low as 13.2 These isotopic changes are far greater than can be accounted for by devolatilisation, implying widespread fluid-rock interaction. Contact metamorphism appears not to have affected the terrain, suggesting that fluid flow occurred during regional metamorphism. Down-temperature fluid flow from synmetamorphic granite plutons (18O=8.4–8.6) that occur at the highest metamorphic grades is unlikely to explain the resetting of oxygen isotopes because: (a) there is a paucity of skarns at granite-metasediment contacts; (b) the marbles generally do not contain low-XCO2 mineral assemblages; (c) there is insufficient granite to provide the required volumes of water; (d) the marbles and metapelites retain a several permil difference in 18O values, even at high metamorphic grades. The oxygen isotope resetting may be accounted for by along-strike up-temperature fluid flow during regional metamorphism with time-integrated fluid fluxes of up to 5x109 moles/m2 (105 m3/m2). If fluid flow occurred over 105–106 years, estimated intrinsic permeabilities are 10-20 to 10-16m2. Variations in 18O at individual outcrops suggest that time-integrated fluid fluxes and intrinsic permeabilities may locally have varied by at least an order of magnitude. A general increase in XCO2 values of marble assemblages with metamorphic grade is also consistent with the up-temperature fluid-flow model. Fluids in the metapelites may have been derived from these rocks by devolatilisation at low metamorphic grades; however, fluids in the marbles were probably derived in part from the surrounding siliceous rocks. The marble-metapelite boundaries preserve steep gradients in both 18O and XCO2 values, suggesting that across-strike fluid fluxes were much lower than those parallel to strike. Up-temperature fluid flow may also have formed orthoamphibole rocks and caused melting of the metapelites at high grades.This paper is a contribution to IGCP Project 304 Lower Crustal Processes  相似文献   

17.
Sulfur isotope ratios have been determined in 27 selected volcanic rocks from Iceland together with their whole rock chemistry. The 34S of analyzed basalts ranges from –2.0 to +0.4 with an average value of –0.8 Tholeiitic and alkaline rocks exhibit little difference in 34S values but the intermediate and acid rocks analyzed have higher 34S values up to +4.2 It is suggested that the overall variation in sulfur isotope composition of the basalts is caused by degassing. The small range of the 34S values and its similarity to other oceanic and continental basalts, suggest that the depleted mantle is homogeneous in its sulfur isotope composition. The 34S of the depleted mantle is estimated to be within the range for undegassed oceanic basalts, –0.5 to +1.0  相似文献   

18.
Temperatures of the formation of mud-volcanic waters are determined based on concentrations of some temperature-dependent components (Na–Li, Mg–Li). Estimates obtained for the Taman and Kakhetia regions are similar and range from 45 to 170°, which correspond to depths of 1–4.5 km. The calculated temperatures correlate with the chemical (Li, Rb, Cs, Sr, Ba, B, I, and HCO3) composition of water and 13 (2) and 13 (CH4) values in spontaneous gases. The isotope values indicate that mechanisms of the formation of 13-rich gases, i.e., gases with high 13 values (up to +16.0 in 2 and –23.4 in CH4) in mud-volcanic systems of Taman and Kakhetia are governed by fluid-generation temperatures rather than the supply of abyssal gases. The 11 value was determined for the first time in mud-volcanic products of the Caucasus region. This value ranges from +22.5 to +39.4 in the volcanic water of Georgia, from –1.2 to +7.4 in the clayey pulp of Georgia, and from –7.6 to +13.2 in the clayey pulp of Taman. It is shown that the 11 value in clay correlates with the fluid-generation temperature and 11 correlates with 13 in carbon-bearing gases. These correlations probably testify to the formation of different phases of mud-volcanic emanations in a single geochemical system and suggest the crucial role of temperature in the development of isotope-geochemical features.  相似文献   

19.
Kanonaite, with compositions plotting on the join Mn3+AlSiO5–Fe3+AlSiO5, was discovered in a late quartz vein of the Le Coreux metamorphic manganese deposit. A typical structural formula is (Mn3+3.69Fe3+0.36)Al3.95Si4.00O20, representing maximum solid solution within the system Al2SiO5–Mn2SiO5–Fe2SiO5. Refractive indices are =1.777; =1.855. The end-member compositions form the outermost, latest products in zoned crystals ranging to less manganiferous kanonaite. A crystal structure determination of a Mn-rich kanonaite confirms that about 96% of all the Mn3+ present is located in the strongly Jahn-Teller-distorted octahedron of the andalusite-type structure. Combining all relevant mineral-chemical and petrological data available on the deposit, a speculative model is presented in which kanonaite crystals with successively higher Mn3+ contents form during decreasing temperatures in the course of the anticlockwise PTt path of extensional metamorphism. Kaolinite occurring in zones within composite kanonaite porphyroblasts of adjacent phyllites is regarded here as by-product of a continuous retrograde breakdown reaction of less manganiferous kanonaite. In places, kanonaite was peripherally replaced by muscovite and Mn- and Fe-oxides.Editorial responsibility: J. HoefsDedicated to the late Dr. H.S. Yoder, Jr.  相似文献   

20.
Water samples were collected from the Truckee River-Pyramid Lake system, the Walker River-Walker Lake system, and the Carson River, all located in eastern California and western Nevada, U.S.A., at three different times (i.e., summer 1991, spring 1992, and autumn 1992) over a two year period. The concentrations of As, Na, Cl, PO4, and pH were measured in these river samples and the associated terminal lakes. Arsenic values ranged from below 13 nmol/kg near Truckee, California to 160 nmol/kg at Nixon, Nevada in the Truckee River, from 40 nmol/kg in the headwaters of both West and East Walker Rivers to 270 nmol/kg below Weber Reservoir on the main branch of the Walker River, and from <27 nmol/kg to 234 nmol/kg for the lower Carson River system. Arsenic concentrations in Steamboat Creek (0.91 mol/kg–1.80 mol/kg) in the Truckee River catchment are above the U.S. EPA drinking water maximum contaminant level of 0.67 mol/kg, as are the As concentrations in both Pyramid Lake (1.33 mol/kg–1.57 mol/kg ) and Walker Lake (13.7 mol/kg–18.7 mol/kg). Sources of As for all three rivers include weathering of As-rich rocks and/or regolith and input of high-As geothermal spring waters, both processes primarily, although not exclusively, adding As to the headwater regions of these rivers. Steamboat Hot Springs (29 mol/kg As 54.5 mol/kg), for example, is identified as a source of As to the Truckee River via Steamboat Creek. The high As concentrations in Pyramid and Walker Lakes are likely due to (1) desorption of arsenate from aquatic particulate matter in these high pH waters (9.0 pH 9.5), (2) limited biologic uptake of arsenate, and (3) evaporative concentration of the lake waters. Evaluation of molar PO4}/As ratios of river waters and geothermal spring waters (e.g., Steamboat Hot Springs), indicates that phosphate is substantially enriched in Steamboat Creek as well as the mid to lower reaches of the Walker and Carson Rivers. These regions of each river are dominated by agricultural interests and, additionally, in the case of Steamboat Creek, residential areas and golf courses. Our data strongly imply that phosphate-rich agricultural return flow has likely added P to these streams and, consequently, increased their respective P:As ratios.  相似文献   

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