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1.
Experimental data on the etching of diamond crystals in basaltic melt at 1130°C with variable oxygen fugacity in the environment are considered. The oxygen fugacity was set with the HM and NNO buffers. The study was carried out on a 0.6–0.8 mm fraction (powder) of natural diamond crystals. It has been established that, at the same temperature, the rate of diamond etching (oxidation) in silicate melt depends on the oxygen fugacity in the environment. The etching rate decreases with decline in the oxygen fugacity from the case where the melt comes into contact with atmospheric air to the conditions controlled by the HM and NNO buffers. Under the conditions of the HM and NNO buffers, oxidation was accompanied by surface graphitization of diamond crystals. 相似文献
2.
An experimental study has been carried out to determine the partition coefficients of tungsten between aqueous fluids and
granitic melts at 800 °C and 1.5 kb with natural granite as the starting material. The effects of the solutions on the partition
coefficients of tungsten show a sequence of P > CO
3
2−
> B > H 2O. The effects are limited (generally K
D
< 0.3) and the tungsten shows a preferential trend toward the melt over the aqueous fluid. The value of K
D
increases with increasing concentration of phosphorus; the K
D
increases first and then reduces with the concentration of CO
3
2−
when temperature decreases, the K
D
between the solution of CO
3
2−
and the silicate melt increases, and that between the solution of B 4O
7
2−
and the silicate melt decreases. The partition coefficients of phosphorus and sodium between fluids and silicate melts have
been calculated from the concentrations of the elements in the melts. The K
D
value for phosphorus is 0.38 and that for sodium is 0.56. Evidence shows that the elements tend to become richer and richer
in the melts. 相似文献
3.
The igneous rocks of the Katzenbuckel, Southwest Germany, represent a unique and unusual alkaline to peralkaline association within the European Volcanic Province. The magmatic activity can be subdivided into two main phases. Phase I comprises the main rock bodies of phonolite and nepheline syenite, which were later intruded by different peralkaline dyke rocks (tinguaites and alkali feldspar syenite dykes) of phase II. The dyke assemblage was accompanied by magnetite and apatite veins and was followed by a late-stage pneumatolytic activity causing autometasomatic alterations. As is typical for alkaline to peralkaline igneous rocks, early mafic minerals of phase I rocks comprise olivine, augite and Fe–Ti oxides, which are substituted in the course of fractionation by Na-amphibole and Na-pyroxene. For the early magmatic stage, calculated temperatures range between 880 and 780 °C with low silica activities (0.4 to 0.6) but high relative oxygen fugacities between 0.5 and 1.9 log units above the FMQ buffer. Even higher oxygen fugacities (above the HM buffer) are indicated for the autometasomatic alteration, which occurred at temperatures between 585 and 780 °C and resulted in the formation of pseudobrookite and hematite. The unusually high oxygen fugacities (even during the early magmatic stage) are recorded by the major element compositions of the mafic minerals (forsterite content in olivine between 68 and 78 mol%, up to 6.2 wt.% ZrO2 and 8.5 wt.% TiO2 in clinopyroxene), the unusual mineral assemblages (pseudobrookite, freudenbergite) and by the enrichment of Fe3+ in the felsic minerals (up to 2.8 wt.% Fe2O3 in alkali feldspar and up to 2.6 wt.% Fe2O3 in nepheline). These observations point to a metasomatically enriched and highly oxidized lithospheric mantle as a major source for the Katzenbuckel melts. 相似文献
4.
The partitioning of copper and molybdenum between silicate melts and aqueous fluids has been determined at 750°C, and 1.4 Kb. The experiments were conducted in a inch ID, rapid quench, cold seal pressure vessel. The aqueous and glass phase run products were analyzed by atomic absorption spectrophotometry and ion microprobe, respectively. The vapor/melt partition coefficient for copper, , defined as the ratio of the concentrations of copper in the vapor to copper in the melt was found to be at NNO up to at least 4.5 moles of chlorine per kg of solution. The partition coefficient for molybdenum is equal to 2.5 ± 1.6 at NNO and QFM; its value is independent of the fluorine concentration of the melt up to at least 1.7 wt. percent fluorine, and of the chlorine concentration up to at least 4.5 moles of chlorine per kg of solution. Copper is probably present in the univalent state in both the silicate melt and in the associated aqueous phase at NNO; the most important aqueous complex of copper is probably CuCl 0. Molybdenum is probably present in the aqueous phase as one or more molybdate species. 相似文献
5.
Summary Several experimentally-based, empirical calibrations of the fO 2 of natural silicate melts at atmospheric pressure as a function of melt composition, melt Fe 2+/Fe 3+, and crystallization temperature have been developed (e.g. Sack et al., 1980; Kilinc et al., 1983; Kress and Carmichael, 1988; Borisov and Shapkin, 1990). Cr-Al spinel is a liquidus phase of primitive mantle-derived melts, and is commonly found as inclusions in near-liquidus phenocrysts (mainly olivine). The established atmospheric pressure correlation between Fe 2+/Fe 3+ values in spinel and coexisting melts over a broad range of basaltic compositions ( Maurel and Maurel, 1982) can be used to calculate the Fe 2+/Fe 3+ value of a melt if the composition of the equilibrium spinel is known. Compositions and crystallization temperatures of primitive melts can be determined by experimental studies of melt inclusions trapped by early-formed refractory phenocrysts. Thus, the association of spinel and melt inclusions in early liquidus phenocrysts can be used to estimate fO 2 conditions at the time of their crystallization.In this paper, we present a calibration of this method and discuss its applications. We conclude that combination of the equations of Maurel and Maurel (1982) and Borisov and Shapkin (1990) can be used to calculate fO 2 with an accuracy of ±0.71og units, when liquidus spinels have TiO 2 <2.5 wt% and Cr 2O 3 > 13 wt.%, and melt compositions are in the range from basaltic to picritic with H 2O contents <6 wt.%.Using this technique we find NNO fO 2 values of –0.8 to –1.4 for MORB dredged at the VEMA Fracture Zone in the Atlantic, and 0 to + 1 for Tongan high-Ca boninites.
Die Berechnung von Fe2+/Fe3+ und der Sauerstoff-Fugazitäten für primitive Mantelschmelzen: Kalibration einer empirischen Methode Zusammenfassung Empirische, auf Experimenten basierende, Kalibrationen zur Berechnung von fO2 natürlicher Silikatschmelzen bei atmosphärischem Druck in Abhängigkeit von der Schmelzzusammensetzung, des Fe2+/Fe3+ Verhältnisses und der Kristallisationstemperatur wurden z.B. vonSack et al. (1980),Kilinc et al. (1983),Kress undCarmichael (1988) undBorisov undShapkin (1980) entwickelt. Cr-Al-Spinell ist eine Liquidusphase primitiver Mantelschmelzen und kommt üblicherweise als Einschluß in near-liquidus Phänokristallen (hauptsächlich in Olivin) vor. Die Korrelation des Atmosphärendruckes zwischen Fe2+/Fe3+ in Spinell und koexistierender Schmelze kann dazu verwendet werden, das Verhältnis von Fe2+/Fe3+ der Schmelze für einen weiten Bereich basaltischer Zusammensetzungen zu berechnen, wenn die Zusammensetzung des im Gleichgewicht gebildeten Spinells bekannt ist (Maurel undMaurel, 1982). Die Zusammensetzungen und Kristallisationstemperaturen primitiver Schmelzen können durch experimentelle Studien von Schmelzeinschlüssen, die in früh gebildeten refraktären Phänokristallen eingeschlossen wurden, ermittelt werden. Daher lassen sich Spinelle und assoziierte Schmelzeinschlüsse in frühen Liquidus-Phänokristallen dazu benützen, die fO2-Bedingungen während der Kristallisation abzuschätzen.In dieser Arbeit präsentieren wir eine neue Kalibration dieser Methode und diskutieren ihre Anwendungen. Wir schlußfolgern, daß unter Kombination der verwendeten Gleichungen vonMaurel undMaurel (1982) sowie vonBorisov undShapkin (1990) fO2 mit einer Genauigkeit von ±0.7 log Einheiten berechnet werden kann, soferne die Liquidus-Spinelle < 2.5 Gew.% TiO2 und > 13 Gew.% Cr2O3 haben und die Schmelzzusammensetzungen von basaltisch bis pikritisch, mit maximal 6 Gew.% H2O, reichen.Unter Verwendung dieser Technik wurden die NNO fO2 Werte für die von der VEMA Fracture Zone im Atlantik stammenden MORB Proben mit 0.8 bis - 1.4, die der der High-Ca Boninite von Tonga mit 0 bis + 1 bestimmt.
With 7 Figures 相似文献
6.
Interpretation of Re-Os isotopic systematics applied to mantle and mantle-derived rocks is currently hindered by the poorly understood behaviour of Re and Os during partial melting. Of particular interest is the incompatibility of Re and how it partitions between melt and the different mantle phases. Here, we study the partitioning behaviour of Re between the common upper mantle minerals (garnet, spinel, clinopyroxene, orthopyroxene, and olivine) and silicate melt under temperature (1275-1450 °C) and pressure (1.5-3.2 GPa) conditions relevant for basaltic magma genesis, over a range of oxygen fugacity (?O 2) large enough (QFM+5.6 to QFM−2.9) to demonstrate the effects of changing the oxidation state of Re from 4+ to 6+. Rhenium crystal/silicate-melt partition coefficients vary by 4-5 orders of magnitude, from moderately compatible to highly incompatible, for pyroxenes, garnet, and spinel as the oxidation state of Re changes from 4+ to 6+, but Re in either oxidation state is incompatible in olivine. Because the changeover from the one Re oxidation state to the other occurs over the range of ?O 2s pertinent to partial melting in the Earth’s mantle, bulk Re crystal/silicate-melt partition coefficients during mantle melting are also expected to vary significantly according to the oxidation state of the system. For instance, assuming QFM−0.7 and QFM+1.6 as average ?O 2 for mid-ocean ridge (MORBs) and island arc (IABs) basalts, respectively, a difference of at least one order of magnitude for bulk Re partition coefficients is expected (excluding any influence from a sulphide phase). Hence, Re is probably much more incompatible during the genesis of IABs compared to MORBs. Our results also demonstrate that Re 4+ has a partitioning behaviour similar to Ti 4+ rather than Yb, and is accordingly not a sensitive indicator of garnet in the source. The lower concentrations of Re observed in ocean island basalts (OIBs) compared to MORBs are therefore not a result of being generated deeper in the mantle where garnet is stable, leaving the hypothesis of late-stage loss of Re from OIB lavas by degassing as the most plausible explanation. 相似文献
7.
The speciation of sulfur as a function of oxygen fugacity was calculated in glasses of basaltic composition saturated experimentally with either sulfide or sulfate phases. The experiments were conducted on mixtures of synthetic and natural materials equilibrated at 1300 °C and 1 GPa in a piston-cylinder apparatus. Sulfur speciation was calculated by measuring the peak shift of the sulfur Kα radiation relative to a sulfide standard, whereas oxygen fugacity was calculated from the composition of olivine and spinel present in the assemblages. The results are consistent with sulfur being present as sulfite (S 4+) in addition to sulfate (S 6+) in oxidized melts. Therefore, sulfur speciation derived from SKα peak shifts should be seen as ”sulfate mole fraction equivalents“ (X(S 6+) eq.). Using the data available, an empiric function:
8.
Experiments were performed in the three-phase system high-silica rhyolite melt + low-salinity aqueous vapor + hydrosaline
brine, to investigate the exchange equilibria for hydrogen, potassium, and sodium in magmatic-hydrothermal systems at 800
°C and 100 MPa, and 850 °C and 50 MPa. The K
aqm/melt
H,Na and K
aqm/melt
H,K for hydrogen-sodium exchange between a vapor + brine mixture and a silicate melt are inversely proportional to the total
chloride concentration (ΣCl) in the vapor + brine mixture indicating that HCl/NaCl and HCl/KCl are higher in the low-salinity
aqueous vapor relative to high-salinity brine. The equilibrium constants for vapor/melt and brine/melt exchange were extracted
from regressions of K
a
q
m
/
m
e
l
t
H
,
N
a
and K
a
q
m
/
m
e
l
t
H
,
K
versus the proportion of aqueous vapor relative to brine in the aqueous mixture (F aqv) at P and T, expressed as a function of ΣCl. No significant pressure effect on the empirically determined exchange constants was observed
for the range of pressures investigated. Model equilibrium constants are: K
aqv/melt
H,Na(vapor/melt)=26(±1.3) at 100 MPa (800 °C), and 19( ± 7.0) at 50 MPa (850 °C); K
aqv/melt
H,K=14(±1.1) at 100 MPa (800 °C), and 24(±12) at 50 MPa (850 °C); K
aqb/melt
H,b(brine/melt)= 1.6(±0.7) at 100 MPa (800 °C), and 3.9(±2.3) at 50 MPa (850 °C); and K
aqb/melt
H,K=2.7(±1.2) at 100 MPa (800 °C) and 3.8(±2.3) at 50 MPa (850 °C). Values for K
aqv/melt
H,K and K
aqb/melt
H,K were used to calculate KCl/HCl in the aqueous vapor and brine as a function of melt aluminum saturation index (ASI: molar
Al 2O 3/(K 2O+Na 2O+CaO) and pressure. The model log KCl/HCl values show that a change in melt ASI from peraluminous (ASI = 1.04) to moderately
metaluminous (ASI = 1.01) shifts the cooling pathway (in temperature-log KCl/HCl space) of the aqueous vapor toward the andalusite+muscovite+K-feldspar
reaction point.
Received: 22 August 1996 / Accepted: 5 February 1997 相似文献
9.
The influence of oxygen fugacity ( fO 2) and temperature on the valence and structural state of iron was experimentally studied in glasses quenched from natural aluminosilicate melts of granite and pantellerite compositions exposed to various T- fO 2 conditions (1100–1420°C and 10 ?12–10 ?0.68 bar) at a total pressure of 1 atm. The quenched glasses were investigated by Mössbauer spectroscopy. It was shown that the effect of oxygen fugacity on the redox state of iron at 1320–1420°C can be described by the equation log(Fe 3+/Fe 2+) = k log( fO 2) + q, where k and q are constants depending on melt composition and temperature. The Fe 3+/Fe 2+ ratio decreases with decreasing fO 2 ( T = const) and increasing temperature ( fO 2 = const). The structural state of Fe 3+ depends on the degree of iron oxidation. With increasing Fe 3+/Fe 2+ ≥ 1, the dominant coordination of Fe 3+ changes from octahedral to tetrahedral. Ferrous iron ions occur in octahedral (and/or five-coordinated) sites independent of Fe 3+/Fe 2+. 相似文献
10.
Chromite was equilibrated with two natural basic liquids and one natural ultrabasic liquid at temperatures and oxygen fugacities appropriate to geological conditions. The experiments were designed to document changes in mineral and glass compositions between the iron-wüstite and nickel-nickel oxide buffers, with special emphasis on conditions along quartz-fayalite-magnetite. The Cr contents of the melts at chromite saturation increase strongly with increasing temperature and with decreasing oxygen fugacity.A relationship is described which accounts for the compositional dependence of the partitioning of Cr between spinels and silicate melts by considering the exchange of FeCr 2O 4 component between the crystalline and melt phases. Interpretation of the data in terms of this exchange suggests that Cr 3+ in metaluminous melts occurs in octahedrally coordinated sites, and that it does not depend on charge-balancing by monovalent cations. In this model, Cr 3+ is proposed to behave like network-modifying Al 3+ and Fe 3+, i.e., the excess aluminum and ferric iron which do not participate in tetrahedrally coordinated matrix or network-forming complexes.The results can also be applied to the problem of the formation of massive chromitites of great lateral extent in basic layered intrusions. The data are consistent with a model in which the crystallization of chromite is initiated through magma mixing, in combination with the rapid heat loss associated with periodic influxes of magma into a chamber. An alternative model, in which chromite crystallization is initiated by repeated fluctuations in oxygen fugacity, is possible only if the magma fO2 is not controlled by an oxygen buffer such as QFM. 相似文献
11.
Previous models of water solubility in silicate melts generally assume essentially complete reaction of water molecules to hydroxyl groups. In this paper a new model is proposed that is based on the hypothesis that the observed concentrations of molecular water and hydroxyl groups in hydrous silicate glasses reflect those of the melts from which they were quenched. The new model relates the proportions of molecular water and hydroxyl groups in melts via the following reaction describing the homogeneous equilibrium between melt species: H 2O molecular (melt) + oxygen (melt) = 2OH (melt). An equilibrium constant has been formulated for this reaction and species are assumed to mix ideally. Given an equilibrium constant for this reaction of 0.1–0.3, the proposed model can account for variations in the concentrations of molecular water and hydroxyl groups in melts as functions of the total dissolved water content that are similar to those observed in glasses. The solubility of molecular water in melt is described by the following reaction: H 2O (vapor) = H 2O molecular (melt).These reactions describing the homogeneous and heterogeneous equilibria of hydrous silicate melts can account for the following observations: the linearity between fH2O and the square of the mole fraction of dissolved water at low total water contents and deviations from linearity at high total water contents; the difference between the partial molar volume of water in melts at low total water contents and at high total water contents; the similarity between water contents of vapor-saturated melts of significantly different compositions at high pressures versus the dependence on melt composition of water solubility in silicate melts at low pressures; and the variations of viscosity, electrical conductivity, the diffusivity of “water,” the diffusivity of cesium, and phase relationships with the total dissolved water contents of melts.This model is thus consistent with available observations on hydrous melt systems and available data on the species concentrations of hydrous glasses and is easily tested, since measurements of the concentrations of molecular water and hydroxyl groups in silicate glasses quenched from melts equilibrated over a range of conditions and total dissolved water contents are readily obtainable. 相似文献
13.
The oxygen fugacity(f O2) may affect the ionic conductivity of olivine under upper mantle conditions because Mg vacancies can be produced in the crystal structure by the oxidization of iron from Fe 2+ to Fe3+. Here we investigated olivine ionic conductivity at 4 GPa, as a function of temperature, crystallographic orientation, and oxygen fugacity, corresponding to the topmost asthenospheric conditions. The results demonstrate that the ionic conductivity is insensitive to f O2 under relatively reduced conditions(f O2 below Re-ReO 2 buffer), whereas it has a clear f O2-dependence under relatively oxidized conditions(f O2 around the magnetite-hematite buffer). The ionic conduction in olivine may contribute significantly to the conductivity anomaly in the topmost asthenosphere especially at relatively oxidized conditions. 相似文献
14.
The magmatic oxygen fugacity ( fO 2) of a thirty foot wide feldspathic peridotite dyke has been determined using the experimental method of Fudali (1965). Determinations were made on samples from both the marginal and central portions of the dyke and a difference of approximately one order of magnitude in fO 2 was observed. This difference is attributed to the increase in the H 2O content of the liquid as crystallization proceeded and to diffusion of hydrogen out of the dyke. It is concluded that the dyke was emplaced with an fO 2 between 10 –8 and 10 –9 atmospheres. Data on the absorbtion of Fe by the silver/palladium sample containers during the experiments are given in an appendix. 相似文献
16.
Partitioning of Ca, Mn, Mg, and Fe 2+ between olivine and melt has been used to examine the influence of energetically nonequivalent nonbridging oxygen in silicate melts. Partitioning experiments were conducted at ambient pressure in air and 1400°C with melts in equilibrium with forsterite-rich olivine (Fo >95 mol%). The main compositional variables of the melts were NBO/T and Na/(Na+Ca). In all melts, the main structural units were of Q 4, Q 3, and Q 2 type with nonbridging oxygen, therefore, in the Q 3 and Q 2 units.For melts with high Q 3/Q 2-abundance ratio (corresponding to NBO/T near 1), increasing Na/(Na+Ca) [and Na/(Na+Ca+Mn+Mg+Fe 2+)] results in a systematic decrease of the partition coefficients, K Caol/melt, K Mnol/melt, K Mgol/melt, and K Fe2+ol/melt, because of ordering of the network-modifying Ca, Mn, Mg, and Fe 2+ among nonbridging oxygen in Q 3 and Q 2 structural units. This decrease is more pronounced the smaller the ionic radius of the cation. With decreasing Q 3/Q 2 abundance ratio (less-polymerized melts) this effect becomes less pronounced.Activity-composition relations among network-modifying cations in silicate melts are, therefore, governed by availability of energetically nonequivalent nonbridging oxygen in individual Q n-species in the melt. As a result, any composition change that enhances abundance of highly depolymerized Q n-species will cause partition coefficients to decrease. 相似文献
17.
The viscoelastic behavior of silicate melts has been measured for a range of compositions (NaAlSi 3O 8, NaCaAlSi 2O 7, CaMgSi 2O 6, Li 2Si 4O 9, Na 2Si 4O 9, K 2Si 4O 9, Na 2Si 3O 7, K 2Si 3O 7 and Na 2Si 2O 5) using the fiber elongation method. A1l compositions exhibit Newtonian behavior at low strain-rates, but non-Newtonian behavior at higher strain-rates, with strain-rate increasing faster than the applied stress. The decrease in shear viscosity observed at the high strain-rates ranges from 0.3 to 1.6 log 10 units (Pa s). The relaxation strain-rates, relax, of these melts have been estimated from the low strain-rate, Newtonian, shear viscosity, using the Maxwell relationship; relax= –1=( s/G ) –1. For all compositions investigated, the onset of non-Newtonian rheology is observed at strain-rates 2.5+0.5 orders of magnitude less than the calculated relaxation strain-rate. This difference between the non-Newtonian onset and the relaxation strain-rate is larger than that predicted by the single relaxation time Maxwell model. Normalization of the experimental strain-rates to the relaxation strain-rate predicted from the Maxwell relation, eliminates the composition. and temperature-dependence of the onset of non-Newtonian behavior. The distribution of relaxation in the viscoelastic region appears to be unrelated to melt chemistry. This conclusion is consistent with the torsional, frequency domain study of Mills (1974) which illustrated a composition-invariance of the distribution of the imaginary component of the shear modulus in melts on the Na 2O-SiO 2 join. The present, time domain study of viscoelasticity contrasts with frequency domain studies in terms of the absolute strains employed. The present study employs relatively large total strains (up to 2). This compares with typical strains of 10 –8 in ultrasonic (frequency domain) studies. The stresses used to achieve the strain-rates required to observe viscoelastic behavior in this study approach the tensile strength of the fibers with the result that some of our experiments were terminated by fiber breakage. Although the breakage is unrelated to the observation of non-Newtonian viscosity, their close proximity in this and earlier studies suggests that brittle failure of igneous melts, may, in general, be preceded by a period of non-Newtonian rheology. 相似文献
19.
地幔氧逸度是反映地幔氧化还原程度的参量,由温度、压力、岩石化学成分、矿物结构等共同作用控制.目前对上地幔氧逸度的研究主要针对镁橄榄石-磁铁矿-石英体系、含角闪石的橄榄岩体系和玄武岩(熔体)体系,通过实验岩石学方法进行.地幔氧逸度在垂直深度上随深度增加而减小受到普遍认可.天然样品和理论研究认为,岩石圈地幔底部的软流圈氧逸... 相似文献
20.
Several observations of non-Newtonian viscosity of silicate liquids at high stress or strain rates have been published in recent years. However, this phenomenon is not well understood yet. In this paper attention is drawn to the fact that steady state logarithmic values of reduced viscosities of silicate liquids under high stress show a linear dependence on the squared value of the applied stress. This relationship suggests that the elastic work done by the stress on the liquid is related to the observed viscosity decreases. It is shown that the development of non-Newtonian viscosity in silicate melts under high stress can be explained with the Adam and Gibbs (1965) theory, if one accepts that this elastic work generates configurational entropy. 相似文献
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