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1.
The oxygen fugacity (
) of a C-O-H fluid in equilibrium with graphite has been determined in the range 10–30 kbar by equilibrating solid
-buffer assemblages in graphite capsules containing C-O-H fluid. By using different buffers (FexO-Fe3O4, Ni-NiO, Co-CoO, Mo-MoO2), the
of the graphite-saturated fluid is bracketed within a narrow range. This technique produces a calibration for the
imposed on a sample contained within a graphite capsule. To achieve a thermodynamically-invariant system at fixed P and T,
the
was imposed on the system with an external buffer and the double-capsule technique. The experiments were performed in solid-media,
high pressure apparatus with 19 mm tale-pyrex assemblies. A series of experiments at 10, 15, 20, 25, and 30 kbar, 800–1600°
C, with
imposed by the Fe2O3-Fe3O4-H2O equilibrium were conducted. The experimental results have been fitted to the following equation:
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相似文献
2.
J. W. Jones 《Contributions to Mineralogy and Petrology》1972,37(4):291-306
In the Rogers Pass area of British Columbia the almandine garnet isograd results from a reaction of the form: 5.31 ferroan-dolomite+8.75 paragonite+4.80 pyrrhotite+3.57 albite+16.83 quartz+1.97 O2=1.00 garnet+16.44 andesine+1.53 chlorite+2.40 S2+1.90 H2O+10.62 CO2. The coefficients of this reaction are quite sensitive to the Mn content of ferroan-dolomite.Experimental data applied to mineral compositions present at the isograd, permits calculation of two intersecting P, T equilibrium curves. P=29088–39.583 T is obtained for the sub-system paragonite-margarite (solid-solution), plagioclase, quartz, ferroan-dolomite, and P=28.247 T–14126 is obtained for the sub-system epidote, quartz, garnet, plagioclase. These equations yield P=3898 bars and T=638° K (365° C). These values are consistent with the FeS content of sphalerite in the assemblage pyrite, pyrrhotite, sphalerite and with other estimates for the area.At these values of P and T the composition of the fluid phase in equilibrium with graphite in the system C-O-H-S during the formation of garnet is estimated as:
bars,
bars,
bars,
bars,
bars,
bars,
bars,
bars,
, bars,
bars. 相似文献
3.
Jeffrey A. Grambling 《Contributions to Mineralogy and Petrology》1986,94(2):149-164
Two metamorphic isograds cut across graphitic schist near Pecos Baldy, New Mexico. The southern isograd marks the first coexistence of staurolite with biotite, whereas the northern isograd marks the first coexistence of andalusite with biotite. The isograds do not record changes in temperature or pressure. Instead, they record a regional gradient in the composition of the metamorphic fluid phase. Ortega Quartzite, which contains primary hematite, lies immediately north of the graphitic schist. Mineral compositions within the schist change gradually toward the quartzite, reflecting gradients in
and
. The chemical potential gradients, locally as high as 72 cal/m in
and 9 cal/m in
, controlled the positions of the two mapped isograds. The staurolite-biotite isograd records where
fell below 0.80, at
near 10–23 bars; the andalusite-biotite isograd records where
fell below 0.25, at
near 10–22 bars. Dehydration and oxidation were coupled by graphite-fluid equilibrium.The chemical potential gradients apparently formed during metamorphism, as graphite in schist reacted with hematite in quartzite. Local oxidation of graphite formed CO2 which triggered dehydration reactions along the schistquartzite contact. This process created a C-O-H fluid which infiltrated into overlying rocks. Upward infiltration, local fluid-rock equilibration and additional infiltration proceeded until the composition of the infiltrating fluid evolved to that in equilibrium with the infiltrated rock. This point occurs very close to the staurolite-biotite isograd. Pelitic rocks structurally above this isograd show no petrographic evidence of infiltration, even though calculations indicate that volumetric fluid/rock ratios may have exceeded 15 and thin, rare calc-silicate beds show extensive K-metasomatism and quartz veining. 相似文献
4.
Near-liquidus phase relationships of a spinel lherzolite-bearing olivine melilitite from Tasmania were investigated over a P, T range with varying
,
, and
. At 30 kb under MH-buffered conditions, systematic changes of liquidus phases occur with increasing
(
= CO2/CO2 +H2O+olivine melilitite). Olivine is the liquidus phase in the presence of H2O alone and is joined by clinopyroxene at low
. Increasing
eliminates olivine and clinopyroxene becomes the only liquidus phase. Further addition of CO2 brings garnet+orthopyroxene onto the liquidus together with clinopyroxene, which disappears with even higher CO2. The same systematic changes appear to hold at higher and lower pressures also, only that the phase boundaries are shifted to different
. The field with olivine- +clinopyroxene becomes stable to higher
with lower pressure and approaches most closely the field with garnet+orthopyroxene+clinopyroxene at about 27 kb, 1160 °C,
0.08 and
0.2 (i.e., 6–7% CO2+ 7–8% H2O). Olivine does not coexist with garnet+orthopyroxene+clinopyroxene under these MH-buffered conditions. Lower oxygen fugacities do not increase the stability of olivine to higher
and do not change the phase relationships and liquidus temperatures drastically. Thus, it is inferred that olivine melilitite 2927 originates as a 5% melt (inferred from K2
O and P2O5 content) from a pyrolite source at about 27kb, 1160 dg with about 6–7% CO2 and 7–8% H2O dissolved in the melt. The highly undersaturated character of the melt and the inability to find olivine together with garnet and orthopyroxene on the liquidus (in spite of the close approach of the respective liquidus fields) can be explained by reaction relationships of olivine and clinopyroxene with orthopyroxene, garnet and melt in the presence of CO2. 相似文献
5.
The partition of Ni between olivine and monosulfide-oxide liquid has been investigated at 1300–1395° C,
=10–8-9–10–6.8, and
=10–2.0–10–0.9, over the composition range 20–79 mol. % NiS. The product olivine compositions varied from Fo98 to Fo59 and from 0.06 to 3.11 wt% NiO. The metal/sulfur ratio of the sulfide-oxide liquid increases with increase in
, decrease in
, and increase in NiS content. The Ni/Fe exchange reaction has been perfectly reversed using natural olivine and pure forsterite as starting materials. The FeO and NiO contents of olivine from runs equilibrated at the same
and
form isobaric distributions with NiS content, which, to a first approximation, are dependent at constant temperature and total pressure on a variable term, –0.5 log (
/
). The Ni/Fe distribution coefficient (K
D3) exhibits only a weak decrease from 35 to 29 with increase in
from the IW buffer to close to the FMQ buffer. At
values higher than FMQ, the sulfide-oxide liquid has the approximate composition (Ni,Fe)3±xS2K
D358. The present K
D3 vs O/(S+O) data define a trend which extrapolates to K
D320 at 10 wt% oxygen in the sulfide-oxide liquid. The compositions of olivine and Ni-Cu sulfides associated with early-magmatic basic rocks and komatiites are consistent, at 1400° C, with a value of -log (
/
) of about 7.7, which is equivalent to 0.0 wt% oxygen in the hypothesized immiscible sulfide-oxide liquid. Therefore, K
D3 would not be reduced significantly from the 30 to 35 range for sulfide-oxide liquids with low oxygen contents. 相似文献
6.
Chang-Jo F. Chung 《Mathematical Geology》1993,25(7):851-865
Multivariate statistical analyses have been extensively applied to geochemical measurements to analyze and aid interpretation of the data. Estimation of the covariance matrix of multivariate observations is the first task in multivariate analysis. However, geochemical data for the rare elements, especially Ag, Au, and platinum-group elements, usually contain observations the below detection limits. In particular, Instrumental Neutron Activation Analysis (INAA) for the rare elements produces multilevel and possibly extremely high detection limits depending on the sample weight. Traditionally, in applying multivariate analysis to such incomplete data, the observations below detection limits are first substituted, for example, each observation below the detection limit is replaced by a certain percentage of that limit, and then the standard statistical computer packages or techniques are used to obtain the analysis of the data. If a number of samples with observations below detection limits is small, or the detection limits are relatively near zero, the results may be reasonable and most geological interpretations or conclusions are probably valid. In this paper, a new method is proposed to estimate the covariance matrix from a dataset containing observations below multilevel detection limits by using the marginal maximum likelihood estimation (MMLE) method. For each pair of variables, sayY andZ whose observations containing below detection limits, the proposed method consists of three steps: (i) for each variable separately obtaining the marginal MLE for the means and the variances,
,
,
, and
forY andZ: (ii) defining new variables by
and
and lettingA=C+D andB=C–D, and obtaining MLE for variances,
and
forA andB; (iii) estimating the correlation coefficient YZ by
and the covariance
YZ
by
. The procedure is illustrated by using a precious metal geochemical data set from the Fox River Sill, Manitoba, Canada. 相似文献
7.
Ignimbrites from the central North Island consist mainly of glass or its devitrified product (70–95%); their phenocryst mineralogy is varied and includes plag., hyp., ti-mag., ilm., aug., hblende, biot., san., qtz, ol., with accessory apatite, zircon and pyrrhotite. The Fe-Mg minerals can be used to divide the ignimbrites into four groups with hyp.+aug. reflecting high quench temperatures and biot.+hblende +hyp.+aug., low quench temperatures. Oxygen fugacities lie above the QMF buffer curve and even in ignimbrites with low crystal contents the solid phases apparently buffered fO2. Some ignimbrites contain the assemblage actinolite, gedrite, magnetite and hematite, reflecting post-eruption oxidation. The mineralogy also allows estimation of
using pyrrhotite and thence
,
. The assemblage biotite-sanidine can be used to estimate
and thence
. Water fugacity is calculated in a variety of ways using both biotite and hornblende as well as the combining reaction
. It is high and approaches P
total in most ignimbrites (~4kb) but is lower in unwelded pumice breccias. Comparison of temperature estimates using mineral geothermometers for the various phenocryst phases suggests that the ignimbrite magmas showed temperature differences of 60–100 °C and pressure differences of several kilobars. Individual magma chambers therefore, would have extended over several kilometres vertically. The chemical potential of water may have been constant through the magma. 相似文献
8.
The phenocryst assemblage of cummingtonite, orthopyroxene, quartz, titanomagnetite and ilmenite in rhyolites of New Zealand has been used to calculate P
total and
. The values of P
total and
depend strongly upon whether an ideal mixing, or an ordered, model is used for the solid-solutions, but in both cases
P
total.The rhyolite magma contained over 9 per cent water (by weight) when the cummingtonite phenocrysts precipitated, and possibly as much as 12 per cent, so that it is surprising that one of these rhyolites is a coherent lava. The calculated values of P
total and
are very sensitive to uncertainty in both the composition of the solid-solutions and temperature. Calculations show that
>0.7–0.8 P
total for cummingtonite to precipitate in rhyolites, and that iron-rich olivine and cummingtonite could only exist in rhyolites over a small temperature range at a pressure near 5 kilobars. Hornblende phenocrysts co-existing with fayalitic olivine in rhyolites accordingly have a very low activity of Mg7Si8O22(OH)2. 相似文献
9.
I. Tell 《Contributions to Mineralogy and Petrology》1974,43(2):99-110
Metamorphic fluorine reactions in silica deficient dolomite have been investigated between 300 and 560° C in the pressure range from 700 to 2000 bars.The equilibrium temperature for the reaction: 1 talc + 7 dolomite + 2 fluorite 2 chondrodite + 9 calcite + 5 CO2 + 1 H2O was experimentally determined as a function of the CO2-content of the CO2-H2O gas phase for the total pressure of 2000 bars. The results are given as an isobaric equilibrium curve in the
-diagram of Fig. 2. The equilibrium data were checked and confirmed by reversed reactions.Under the specified pressure conditions the equilibrium temperatures for the above reaction changes from 380° C for very low
-values to approximately 500° C for
-values around 0.5, and then remains slightly above 500° C in the
-interval between 0.5 and 1.0. The temperature conditions for the formation of chrondrodite from tremolite, dolomite, and fluorite are similar to those for the reaction including talc. 相似文献
10.
To investigate the point defect chemistry and the kinetic properties of manganese olivine Mn2SiO4, electrical conductivity () of single crystals was measured along either the [100] or the [010] direction. The experiments were carried out at temperatures T=850–1200 °C and oxygen fugacities
atm under both Mn oxide (MO) buffered and MnSiO3 (MS) buffered conditions. Under the same thermodynamic conditions, charge transport along [100] is 2.5–3.0 times faster than along [010]. At high oxygen fugacities, the electrical conductivity of samples buffered against MS is 1.6 times larger than that of samples buffered against MO; while at low oxygen fugacities, the electrical conductivity is nearly identical for the two buffer cases. The dependencies of electrical conductivity on oxygen fugacity and temperature are essentially the same for conduction along the [100] and [010] directions, as well as for samples coexisting with a solid-state buffer of either MO or MS. Hence, it is proposed that the same conduction mechanisms operate for samples of either orientation in contact with either solid-state buffer.The electrical conductivity data lie on concave upward curves on a log-log plot of vs
, giving rise to two
regimes with different oxygen fugacity exponents. In the low-
regime
, the
exponent, m, is 0, the MnSiO3-activity exponent, q, is 0, and the activation energy, Q, is 45 kJ/mol. In the high
regime
10^{ - 7} {\text{atm}}} \right)$$
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, m=1/6, q=1/4–1/3, and Q=45 and 200 kJ/mol for T<1100 °c=" and=">T>1100 °C, respectively. 相似文献
11.
Fractionation of yttrium (Y) and the rare earth elements (REEs) begins in riverine systems and continues in estuaries and the ocean. Models of yttrium and rare earth (YREE) distributions in seawater must therefore consider the fractionation of these elements in both marine and riverine systems. In this work we develop a coupled riverine/marine fractionation model for dissolved rare earths and yttrium, and apply this model to calculations of marine YREE fractionation for a simple two-box (riverine/marine) geochemical system. Shale-normalized YREE concentrations in seawater can be expressed in terms of fractionation factors (
ij
) appropriate to riverine environments (
) and seawater (
):
12.
Redox states of lithospheric and asthenospheric upper mantle 总被引：31，自引：7，他引：24
C. Ballhaus 《Contributions to Mineralogy and Petrology》1993,114(3):331-348
The oxidation state of lithospheric upper mantle is heterogeneous on a scale of at least four log units. Oxygen fugacities (
) relative to the FMQ buffer using the olivine-orthopyroxene-spinel equilibrium range from about FMQ-3 to FMQ+1. Isolated samples from cratonic Archaean lithosphere may plot as low as FMQ-5. In shallow Proterozoic and Phanerozoic lithosphere, the relative
is predominantly controlled by sliding Fe3+-Fe2+ equilibria. Spinel peridotite xenoliths in continental basalts follow a trend of increasing
with increasing refractoriness, to a relative
well above graphite stability. This suggests that any relative reduction in lithospheric upper mantle that may occur as a result of stripping lithosphere of its basaltic component is overprinted by later metasomatism and relative oxidation. With increasing pressure and depth in lithosphere, elemental carbon becomes progressively refractory and carbon-bearing equilibria more important for
control. The solubility of carbon in H2O-rich fluid (and presumably in H2O-rich small-degree melts) under the P,T conditions of Archaean lithosphere is about an order of magnitude lower than in shallow modern lithosphere, indicating that high-pressure metasomatism may take place under carbon-saturated conditions. The maximum
in deep Archaen lithosphere must be constrained by equilibria such as EMOG/D. If the marked chemical depletion and the orthopyroxene-rich nature of Archaean lithospheric xenoliths is caused by carbonatite (as opposed to komatiite) melt segregation, as suggested here, then a realistic lower
limit may be given by the H2O +C=CH4+O2 (C-H2O) equilibrium. Below C –H2O a fluid becomes CH4 rather than CO2-bearing and carbonatitic melt presumably unstable. The actual
in deep Archaean lithosphere is then a function of the activities of CO2 and MgCO3. Basaltic melts are more oxidized than samples from lithospheric upper mantle. Mid-ocean ridge (MORB) and ocean-island basalts (OIB) range between FMQ-1 (N-MORB) and about FMQ +2 (OIB). The most oxidized basaltic melts are primitive island-arc basalts (IAB) that may fall above FMQ+3. If basalts are accurate
probes of their mantle sources, then asthenospheric upper mantle is more oxidized than lithosphere. However, there is a wide range of processes that may alter melt
relative to that of the mantle source. These include partial melting, melt segregation, shifts in Fe3+/Fe2+ melt ratios upon decompression, oxygen exchange with ambient mantle during ascent, and low-pressure volatile degassing. Degassing is not very effective in causing large-scale and uniform
shifts, while the elimination of buffering equilibria during partial melting is. Upwelling graphite-bearing asthenosphere will decompress along
-pressure paths approximately parallel to the graphite saturation surface, involving reduction relative to FMQ. The relative
will be constrained to below the CCO equilibrium and will be a function of
. Upwelling asthenosphere whose graphite content has been exhausted by partial melting, or melts that have segregated and chemically decoupled from a graphite-bearing residuum will decompress along
-decompression paths controlled by continuous Fe3+-Fe2+ solid-melt equilibria. These equilibria will involve increases in
relative to the graphite saturation surface and relative to FMQ. Melts that finally segregate from that source and erupt on the earth's surface may then be significantly more oxidized than their mantle sources at depth prior to partial melting. The extent of melt oxidation relative to the mantle source may be directly proportional to the depth of graphite exhaustion in the mantle source. 相似文献
13.
Otto Zedlitz 《Mineralogy and Petrology》1965,10(1-4):130-139
Zusammenfassung Die von Dr.Baumann, Heidelberg, synthetisierten Quarze zeichnen sich nicht nur durch eine außerordentliche Klarheit, sondern auch durch eine auffallende Morphologie aus. Es werden drei grundsätzlich verschiedene Typen beschrieben. Typ I ist pseudorhombisch; eine der a-Achsen verleiht ihm stark polare Gestalt. Als größte Fläche ist das re. trig. Prisma II. St.
, entwickelt. Das Trapezoeder
erscheint an zwei Stellen vizinal. Typ II ist nach einer der Winkelhalbierenden der a-Achsen gestreckt. In dieser Richtung betrachtet erscheint der Kristall tetragonal, da auf diese Weise die unter rechtem Winkel stehenden Flächen
, (0001),
und
das Quadrat begrenzen. Dies sind zugleich die größtentwickelten Flächen. Typ III ist isometrisch; sämtliche Flächen (Prismen, beide Rhomboeder sowie das Basisendflächenpaar) sind etwa gleich stark entwickelt. In Richtung auf das pos. Rhomboeder betrachtet, erweckt dieser Typ den Eindruck eines kubischen Kristalles. Hier fehlen trig. Prisma und das Trapezoeder.
Summary Quarz crystals, grown by Dr.Baumann, Heidelberg, are remarkable not only for their extraordinary transparency but also for a conspicuous morphology. Three completely different types are described. Type I is pseudo-orthorhombic; one of the a-axes causes a strongly polar appearance. Largest face is the right trig. prism II. position . The trapezohedron appears in two positions as vicinals. Type II is alongated parallel to one of the bisectrices of the a-axes. Viewed in this direction the crystal seems to be tetragonal, as the faces , (0001), and , which are at right angles to each other, form a square; these faces are at the same time the largest ones. Typ III is isometric; all the faces (prisms, both rhombohedrons, and the pinacoid) are of approximately the same size. Viewed in the direction upon the pos. rhombohedron this type appears to be cubic. The trig. prism and the trapezohedron are here missing. Mit 4 Figuren und 3 Textabbildungen Herrn Professor Dr.F. Machatschki zum 70. Geburtstag gewidmet. 相似文献 14.
The occurrence of critical assemblages among antigorite, diopside, tremolite, forsterite, talc, calcite, dolomite and magnesite in progressively metamorphosed ophicarbonate rocks, together with experimental data, permits the construction of phase diagrams in terms of the variables P, T, and composition of a binary CO2-H2O fluid. Equilibrium constants are given for the 30 equilibria that describe all relations among the above phases. Ophicalcite, ophidolomite, and ophimagnesite assemblages occupy partially overlapping fields in the
diagram. The upper temperature limit of ophicalcite rocks lies below that of ophidolomite and ophimagnesite. The fluid phase in ophicarbonate rocks has
0.8$$
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, and there are indications that
during their progressive metamorphism is approximately equal to P
total. 相似文献
15.
Donald J. DePaolo 《Contributions to Mineralogy and Petrology》1979,69(3):265-278
Thermodynamic calculations, modified after Nicholls et al. (1971), which relate the activity of silica in a lava to the temperature and pressure conditions at which the lava could be in equilibrium with a mantle mineral assemblage, have been extended to H2O-bearing magmas by using published experimental data to derive the dependence of
on the weight fraction of H2O dissolved in a magma. A petrogenetic grid has been calculated which gives the P-T conditions under which a magma with a given
at its liquidus at 1 atm could equilibrate with a mantle mineral assemblage containing olivine (ol) and orthopyroxene (opx) for different amounts of H2O in the magma at its source. This grid is in good agreement with the results of experimental studies as summarized by Green (1971) and Brey and Green (1975). The results show that the pressure at which a given magma composition can equilibrate with ol + opx increases for increasing amounts of H2O dissolved in the magma at depth.In addition, experimental data have been used to calculate the effect of olivine crystallization and removal on the
in the residual liquid to assess the effect of low-pressure differentiation on
. The results show that if 20 % olivine is added to a basalt magma, its calculated pressure of equilibration with ol+opx increases by 4–5 kbar for a given temperature. The calculated effects of olivine removal and H2O addition on
are reasonably consistent with the silicate mixing model of Burnham (1975).Thermodynamic calculations of this type may be useful for assessing the internal consistency of certain experimental data, and in extrapolating the results to other magma compositions. The application of these calculations to determining the possible depth of origin of natural lavas appears to be limited primarily by the difficulty in determining
in a lava at its liquidus temperature. 相似文献
16.
Jonathan H. Berg 《Contributions to Mineralogy and Petrology》1977,64(1):33-52
Thermal aureoles surrounding intrusions of the Nain complex, Labrador, contain many unique or unusual mineral assemblages in aluminous gneisses and granulites, ironstones, and ultramafic rocks. Some of the limiting assemblages are (in addition to feldspars±pyrrhotite±ilmenite±graphite ±biotite±magnetite): Ga-Ol-Hy-Sp, Ga-Cd-Hy-Sp, Ga-Hy-Ol-Qz, Cd-Hy-Os-Qz, Ga-Cd-Sp-Si, Cd-Sp-Co-Si, Ga-Ol-Hy-Sp, Ga-Cd-Hy-Sp, Hy-Ol-Qz-Aug, and Ol-Hy-Sp(±Chl±Ca-amph±Aug). On the basis of some of these assemblages are (in addition to feldspars±pyrrhotite±ilmenite±graphite from 3.7–6.6 kbar and temperatures from 645–915 ° C. The paucity of hydrous phases, the preponderance of Ksp-Plag-Qz or even Cd-Ksp-Qz without evidence of a melt at these temperatures, the stable occurrence of osumilite, and the common presence of graphite suggest that
was extremely low. The presence of graphite-pyrrhotite, the compositions of ilmenites, the compositions of coexisting Fe-Ti oxides, and other mineralogical data indicate the
was relatively low and, despite the wide range in bulk compositions and rock types, may have followed an approximately buffered trend. It is possible that the magmas of the Nain complex may have acted as an external
buffer for the aureole rocks. The unique nature of these mineral assemblages appears to be a function of the extremely low
. 相似文献
17.
Devolatilization equilibria in graphite-pyrite-pyrrhotite bearing pelites with application to magma-pelite interaction 总被引：1，自引：0，他引：1
The proportions of species in a C-O-H-S fluid in equilibrium with graphite, pyrite and pyrrhotite were calculated for a range of pressure, temperature and
conditions, using the equilibrium constants and mass balance method, for ideal and non-ideal mixing in the fluid. Under typical metamorphic conditions, H2O, CO2, CH4 and H2S are the principal fluid species with H2S favored by higher temperatures, lower pressures and lower
conditions. The dominance of H2S in the fluid at high temperatures leads to values of
becoming significantly less than 1, and causes hydrous minerals to dehydrate at lower temperatures than the case when
. The production of H2S-bearing fluids provides a mechanism for the selective transfer of sulfur from a graphite-pyrite-pyrrhotite bearing pelite into a pluton via a fluid phase, without requiring wholesale melting and assimilation of rocks. Such a process is feasible if a magma is intruded by stoping, which allows a significant volume of pelite country rock to be raised rapidly to temperatures approaching that of the magma. H2S-bearing fluids produced from graphite-pyrite-pyrrhotite pelites (due either to magmatic intrusion or regional metamorphism) may also mobilize ore-forming metals as sulfide complexes. 相似文献
18.
Trace element analyses of 1-atm and high-pressure experiments show that in komatiite and peridotite, the olivine (OL)/liquid (L) distribution coefficient for Al2O3 (
) increases with pressure and temperature. Olivine in equilibrium with liquid accepts as much as 0.2 wt% Al2O3 in solution at 6 GPa. Convergence to equilibrium compositions at this high level is shown by cation diffusion of Al into synthetic forsterite crystals of low-Al contents in the presence of melt. Convergence to low-Al equilibrium compositions at lower P and T is shown by diffusion of Al out of synthetic forsterite with high initial Al content. Isobaric and isothermal experimental data subsets reveal that temperature and pressure variations both have real effects on
. Variation in silicate melt composition has no detectable effect on
within the limited range of experimentally investigated mixtures. Least-squares regression for 24 experiments, using komatiite and peridotite, performed at 1 atm to 6 GPa and 1300 to 1960°C, gives the best fit equation:
Increase in
with increasingly higher-pressure melting is consistent with incorporation of a spinel-like component of low molar volume into olivine, although other substitutions possibly involving more complex coupling cannot be ruled out. High P-T ultrabasic melting residues, if pristine, may be recognized by the high
calculated from microprobe analyses of Al2O3 concentrations in residual olivines and estimated Al2O3 concentration in the last liquid removed. In general the low levels of Al in natural olivine from mantle xenoliths suggest that pristine residues are rarely recovered. 相似文献
19.
Ján Veizer 《Contributions to Mineralogy and Petrology》1973,38(4):261-278
Recycling as outlined by Garrels and Mackenzie (1971) is the basic process responsible for the formation, preservation, destruction
and composition of sedimentary masses during geologic history. However, several sedimentological and geochemical trends are
difficult to reconcile with a simple recycling model and would therefore require an evolutionary approach superimposed on
the general recycling. These evolutionary trends are observable on an integrated time scale of the order of 108–109 years. The author believes that the majority of the observed “apparent” sedimentological and geochemical trends might be
compatible with two to three variables, such as the evolution of the crust,
and possibly
. 相似文献
20.
Single crystal Raman spectra of pyrite-type RuS2, RuSe2, OsS2, OsSe2, PtP2, and PtAs2 are presented and discussed with reference to the energies of the X-X stretching modes
x-x (A
g, F
g) and the X2 librations
(E, 2Fg). The main results obtained are (i) strong Raman resonance effects, (ii) different sequences for
x-x (A
g) and
(E
g), i.e.,
R_{x_2 } $$
" align="middle" border="0">
for PtP2 and PtAs2 and
R_{x_2 } $$
" align="middle" border="0">
for OsS2, owing to the interplay of intraionic and interionic lattice forces, (iii) greater strengths for the intraionic P-P and As-As bonds compared to the S-S and Se-Se bonds, respectively, and (iv) a strong influegnce of the metal ions on the strength of the X-X bonds.This is contribution LXI of a series of papers on lattice vibration spectra 相似文献
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