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1.
Alison Pawley 《Contributions to Mineralogy and Petrology》2000,138(3):284-291
The low-pressure stability of clinohumite has been investigated in phase-equilibrium experiments on the reaction forsterite + brucite = clinohumite.
The reaction was bracketed between 2.45 and 2.84 GPa at 650 °C, extending to between 1.37 and 1.57 GPa at 850 °C. At temperatures
above the reaction brucite = periclase + vapour, the reaction clinohumite = forsterite + vapour was bracketed between 1.27
and 1.52 GPa at 900 °C, rising to between 1.90 and 2.00 GPa at 1000 °C. The position of the reaction forsterite + brucite = clinohumite
is ∼0.5 GPa below the position determined in previous work, the difference arising either from pressure uncertainties in both
studies, from enhanced reaction to clinohumite in this study due to the presence of excess brucite in the starting material,
or from different concentrations of defects in the two samples. The brackets on the reaction were combined with other measured
and estimated thermodynamic data for clinohumite to determine its enthalpy of formation and entropy, in a revised version
of the thermodynamic dataset of Holland and Powell (1998). The values obtained were ΔH
f
=−9607.29±3.05 kJ mol−1, S=445 J mol−1 K−1. These data were used to calculate positions of other reactions involving clinohumite. The calculations suggest a larger
stability field for clinohumite than implied by the results of previous experimental studies, indicating a need for more high-pressure
phase-equilibrium studies to provide better thermodynamic data.
Received: 30 April 1999 / Accepted: 8 November 1999 相似文献
2.
D. L. Kohlstedt H. Keppler D. C. Rubie 《Contributions to Mineralogy and Petrology》1996,123(4):345-357
The solubility of hydroxyl in the α, β and γ phases of (Mg,Fe)2SiO4 was investigated by hydrothermally annealing single crystals of San Carlos olivine. Experiments were performed at a temperature
of 1000° or 1100 °C under a confining pressure of 2.5 to 19.5 GPa in a multianvil apparatus with the oxygen fugacity buffered
by the Ni:NiO solid-state reaction. Hydroxyl solubilities were determined from infrared spectra obtained of polished thin
sections in crack-free regions ≤100 μm in diameter. In the α-stability field, hydroxyl solubility increases systematically
with increasing confining pressure, reaching a value of ∼20,000 H/106Si (1200 wt ppm H2O) at the α-β phase boundary near 13 GPa and 1100 °C. In the β field, the hydroxyl content is ∼400,000 H/106Si (24,000 wt ppm H2O) at 14–15 GPa and 1100 °C. In the γ field, the solubility is ∼450,000 H/106Si (27,000 wt ppm H2O) at 19.5 GPa and 1100 °C. The observed dependence of hydroxyl solubility with increasing confining pressure in the α phase
reflects an increase in water fugacity with increasing pressure moderated by a molar volume term associated with the incorporation
of hydroxyl ions into the olivine structure. Combined with published results on the dependence of hydroxyl solubility on water
fugacity, the present results for the α phase can be summarized by the relation C
OH
= A(T)f nH2Oexp(−PΔV/RT), where A(T) = 1.1 H/106Si/MPa at 1100 °C, n = 1, and ΔV = 10.6×10–6 m3/mol. These data demonstrate that the entire present-day water content of the upper mantle could be incorporated in the mineral
olivine alone; therefore, a free hydrous fluid phase cannot be stable in those regions of the upper mantle with a normal concentration
of hydrogen. Free hydrous fluids are restricted to special tectonic environments, such as the mantle wedge above a subduction
zone.
Received: 10 February 1995 / Accepted: 23 October 1995 相似文献
3.
High temperature stability limit of phase egg, AlSiO3(OH) 总被引:1,自引:1,他引:0
Shigeaki Ono 《Contributions to Mineralogy and Petrology》1999,137(1-2):83-89
The stability relations of phase egg, AlSiO3(OH), have been investigated at pressures from 7 to 20 GPa, and temperatures from 900 to 1700 °C in a multi-anvil apparatus.
At the lower pressures phase egg breaks down according to the univariant reaction, phase egg = stishovite + topaz-OH, which
extends from 1100 °C at 11 GPa to 1400 °C at 13 GPa where it terminates at an invariant point involving corundum. At pressures
above the invariant point, the stability of phase egg is limited by the breakdown reaction, phase egg = stishovite + corundum + fluid,
which extends from the invariant point to 1700 °C at 20 GPa. Stishovite crystallized in the Al2O3-SiO2-H2O system contains Al2O3, and the amount of Al2O3 increases with increasing temperature. It is inferred that the Al2O3 content is controlled by the charge-balanced substitution of Si4+ by Al3+ and H+. Aluminum-bearing stishovite coexisting with an H2O-rich fluid may contain a certain amount of water. Therefore, phase egg and stishovite in a subducting slab could transport
some H2O into the deep Earth.
Received: 14 October 1998 / Accepted: 19 May 1999 相似文献
4.
T. Okada W. Utsumi H. Kaneko M. Yamakata O. Shimomura 《Physics and Chemistry of Minerals》2002,29(7):439-445
An experimental technique to make real-time observations at high pressure and temperature of the diamond-forming process
in candidate material of mantle fluids as a catalyst has been established for the first time. In situ X-ray diffraction experiments
using synchrotron radiation have been performed upon a mixture of brucite [Mg(OH)2] and graphite as starting material. Brucite decomposes into periclase (MgO) and H2O at 3.6 GPa and 1050 °C while no periclase is formed after the decomposition of brucite at 6.2 GPa and 1150 °C, indicating
that the solubility of the MgO component in H2O greatly increases with increasing pressure. The conversion of graphite to diamond in aqueous fluid has been observed at
7.7 GPa and 1835 °C. Time-dependent X-ray diffraction profiles for this transformation have been successfully obtained.
Received: 17 July 2001 / Accepted: 18 February 2002 相似文献
5.
The melting reaction: albite(solid)+ H2O(fluid) =albite-H2O(melt) has been determined in the presence of H2O–NaCl fluids at 5 and 9.2 kbar, and results compared with those obtained in presence of H2O–CO2 fluids. To a good approximation, albite melts congruently at 9 kbar, indicating that the melting temperature at constant
pressure is principally determined by water activity. At 5 kbar, the temperature (T)- mole fraction (X
(H2O) ) melting relations in the two systems are almost coincident. By contrast, H2O–NaCl mixing at 9 kbar is quite non-ideal; albite melts ∼70 °C higher in H2O–NaCl brines than in H2O–CO2 fluids for X
(H2O) =0.8 and ∼100 °C higher for X
(H2O) =0.5. The melting temperature of albite in H2O–NaCl fluids of X
(H2O)=0.8 is ∼100 °C higher than in pure water. The P–T curves for albite melting at constant H2O–NaCl show a temperature minimum at about 5 kbar. Water activities in H2O–NaCl fluids calculated from these results, from new experimental data on the dehydration of brucite in presence of H2O–NaCl fluid at 9 kbar, and from previously published experimental data, indicate a large decrease with increasing fluid pressure
at pressures up to 10 kbar. Aqueous brines with dissolved chloride salt contents comparable to those of real crustal fluids
provide a mechanism for reducing water activities, buffering and limiting crustal melting, and generating anhydrous mineral
assemblages during deep crustal metamorphism in the granulite facies and in subduction-related metamorphism. Low water activity
in high pressure-temperature metamorphic mineral assemblages is not necessarily a criterion of fluid absence or melting, but
may be due to the presence of low a
(H2O) brines.
Received: 17 March 1995/Accepted: 9 April 1996 相似文献
6.
K. Shinoda M. Yamakata T. Nanba H. Kimura T. Moriwaki Y. Kondo T. Kawamoto N. Niimi N. Miyoshi N. Aikawa 《Physics and Chemistry of Minerals》2002,29(6):396-402
Infrared absorption spectra of brucite Mg (OH)2 were measured under high pressure and high temperature from 0.1 MPa 25 °C to 16 GPa 360 °C using infrared synchrotron radiation
at BL43IR of Spring-8 and a high-temperature diamond-anvil cell. Brucite originally has an absorption peak at 3700 cm−1, which is due to the OH dipole at ambient pressure. Over 3 GPa, brucite shows a pressure-induced absorption peak at 3650 cm−1. The pressure-induced peak can be assigned to a new OH dipole under pressure. The new peak indicates that brucite has a new
proton site under pressure and undergoes a high-pressure phase transition. From observations of the pressure-induced peak
under various P–T condition, a stable region of the high-pressure phase was determined. The original peak shifts to lower wavenumber at −0.25 cm−1 GPa−1, while the pressure-induced peak shifts at −5.1 cm−1 GPa−1. These negative dependences of original and pressure-induced peak shifts against pressure result from enhanced hydrogen bond
by shortened O–H···O distance, and the two dependences must result from the differences of hydrogen bond types of the original
and pressure-induced peaks, most likely from trifurcated and bent types, respectively. Under high pressure and high temperature,
the pressure-induced peak disappears, but a broad absorption band between 3300 and 3500 cm−1 was observed. The broad absorption band may suggest free proton, and the possibility of proton conduction in brucite under
high pressure and temperature.
Received: 16 July 2001 / Accepted: 25 December 2001 相似文献
7.
The breakdown of potassium feldspar at high water pressures 总被引:1,自引:0,他引:1
Pauline Thompson Ian Parsons Colin M. Graham Brian Jackson 《Contributions to Mineralogy and Petrology》1998,130(2):176-186
The equilibrium position of the reaction between sanidine and water to form “sanidine hydrate” has been determined by reversal
experiments on well characterised synthetic starting materials in a piston cylinder apparatus. The reaction was found to lie
between four reversed brackets of 2.35 and 2.50 GPa at 450 °C, 2.40 and 2.59 GPa at 550 °C, 2.67 and 2.74 GPa at 650 °C, and
2.70 and 2.72 GPa at 680 °C. Infrared spectroscopy showed that the dominant water species in sanidine hydrate was structural
H2O. The minimum quantity of this structural H2O, measured by thermogravimetric analysis, varied between 4.42 and 5.85 wt% over the pressure range of 2.7 to 3.2 GPa and
the temperature range of 450 to 680 °C. Systematic variation in water content with pressure and temperature was not clearly
established. The maximum value was below 6.07 wt%, the equivalent of 1 molecule of H2O per formula unit. The water could be removed entirely by heating at atmospheric pressure to produce a metastable, anhydrous,
hexagonal KAlSi3O8 phase (“hexasanidine”) implying that the structural H2O content of sanidine hydrate can vary. The unit cell parameters for sanidine hydrate, measured by powder X-ray diffraction,
were a = 0.53366 (±0.00022) nm and c = 0.77141 (±0.00052) nm, and those for hexasanidine were a = 0.52893 (±0.00016) nm and c = 0.78185 (±0.00036) nm. The behaviour and properties of sanidine hydrate appear to be analogous to those of the hydrate
phase cymrite in the equivalent barium system. The occurrence of sanidine hydrate in the Earth would be limited to high pressure
but very low temperature conditions and hence it could be a potential reservoir for water in cold subduction zones. However,
sanidine hydrate would probably be constrained to granitic rock compositions at these pressures and temperatures.
Received: 6 May 1997 / Accepted: 2 October 1997 相似文献
8.
R. G. Trønnes 《Mineralogy and Petrology》2002,74(2-4):129-148
Summary The phase relations of K-richterite, KNaCaMg5Si8O22(OH)2, and phlogopite, K3Mg6 Al2Si6O20(OH)2, have been investigated at pressures of 5–15 GPa and temperatures of 1000–1500 °C. K-richterite is stable to about 1450 °C
at 9–10 GPa, where the dp/dT-slope of the decomposition curve changes from positive to negative. At 1000 °C the alkali-rich,
low-Al amphibole is stable to more than 14 GPa. Phlogopite has a more limited stability range with a maximum thermal stability
limit of 1350 °C at 4–5 GPa and a pressure stability limit of 9–10 GPa at 1000 °C. The high-pressure decomposition reactions
for both of the phases produce relatively small amounts of highly alkaline water-dominated fluids, in combination with mineral
assemblages that are relatively close to the decomposing hydrous phase in bulk composition. In contrast, the incongruent melting
of K-richterite and phlogopite in the 1–3 GPa range involves a larger proportion of hydrous silicate melts.
The K-richterite breakdown produces high-Ca pyroxene and orthoenstatite or clinoenstatite at all pressures above 4 GPa. At
higher pressures additional phases are: wadeite-structured K2SiVISiIV
3O9 at 10 GPa and 1500 °C, wadeite-structured K2SiVISiIV
3O9 and phase X at 15 GPa and 1500 °C, and stishovite at 15 GPa and 1100 °C. The solid breakdown phases of phlogopite are dominated
by pyrope and forsterite. At 9–10 GPa and 1100–1400 °C phase X is an additional phase, partly accompanied by clinoenstatite
close to the decomposition curve. Phase X has variable composition. In the KCMSH-system (K2CaMg5Si8O22(OH)2) investigated by Inoue et al. (1998) and in the KMASH-system investigated in this report the compositions are approximately K4Mg8Si8O25(OH)2 and K3.7Mg7.4Al0.6Si8.0O25(OH)2, respectively.
Observations from natural compositions and from the phlogopite-diopside system indicate that phlogopite-clinopyroxene assemblages
are stable along common geothermal gradients (including subduction zones) to 8–9 GPa and are replaced by K-richterite at higher
pressures. The stability relations of the pure end member phases of K-richterite and phlogopite are consistent with these
observations, suggesting that K-richterite may be stable into the mantle transition zone, at least along colder slab geotherms.
The breakdown of moderate proportions of K-richterite in peridotite in the upper part of the transition zone may be accompanied
by the formation of the potassic and hydrous phase X. Additional hydrogen released by this breakdown may dissolve in wadsleyite.
Therefore, very small amounts of hydrous fluids may be released during such a decomposition.
Received April 10, 2000; revised version accepted November 6, 2000 相似文献
9.
A previously published equation of state is examined with respect to validity of predicted fugacity values for comparison
with mineral reaction equilibria. It is found that values of f
H2O should be valid for the range from 0.0 to 0.3 and probably to 0.4 in mole fraction NaCl for temperatures from 300° to 600° C
and less accurately to 900° C. Comparison is made with existing experimental results near 630° C for the dehydration of brucite;
the agreement is excellent. Comparison with recent results at 850° C from a different experiment is also satisfactory. However,
fugacity of NaCl is not given on an absolute basis, even in this range below x
NaCl=0.4.
Received: 8 October 1994 / Accepted: 11 May 1995 相似文献
10.
Jürgen Konzett 《Contributions to Mineralogy and Petrology》1997,128(4):385-404
Experiments have been conducted in a peralkaline Ti-KNCMASH system representative of MARID-type bulk compositions to delimit
the stability field of K-richterite in a Ti-rich hydrous mantle assemblage, to assess the compositional variation of amphibole
and coexisting phases as a function of P and T, and to characterise the composition of partial melts derived from the hydrous assemblage. K-richterite is stable in experiments
from 0.5 to 8.0 GPa coexisting with phlogopite, clinopyroxene and a Ti-phase (titanite, rutile or rutile + perovskite). At
8.0 GPa, garnet appears as an additional phase. The upper T stability limit of K-richterite is 1200–1250 °C at 4.0 GPa and 1300–1400 °C at 8.0 GPa. In the presence of phlogopite, K-richterite
shows a systematic increase in K with increasing P to 1.03 pfu (per formula unit) at 8.0 GPa/1100 °C. In the absence of phlogopite, K-richterite attains a maximum of 1.14 K
pfu at 8.0 GPa/1200 °C. Titanium in both amphibole and mica decreases continuously towards high P with a nearly constant partitioning while Ti in clinopyroxene remains more or less constant. In all experiments below 6.0 GPa
ΣSi + Al in K-richterite is less than 8.0 when normalised to 23 oxygens+stoichiometric OH. Rutiles in the Ti-KNCMASH system
are characterised by minor Al and Mg contents that show a systematic variation in concentration with P(T) and the coexisting assemblage. Partial melts produced in the Ti-KNCMASH system are extremely peralkaline [(K2O+Na2O)/Al2O3 = 1.7–3.7], Si-poor (40–45 wt% SiO2), and Ti-rich (5.6–9.2 wt% TiO2) and are very similar to certain Ti-rich lamproite glasses. At 4.0 GPa, the solidus is thought to coincide with the K-richterite-out
reaction, the first melt is saturated in a phlogopite-rutile-lherzolite assemblage. Both phlogopite and rutile disappear ca.
150 °C above the solidus. At 8.0 GPa, the solidus must be located at T≤1400 °C. At this temperature, a melt is in equilibrium with a garnet- rutile-lherzolite assemblage. As opposed to 4.0 GPa, phlogopite
does not buffer the melt composition at 8.0 GPa. The experimental results suggest that partial melting of MARID-type assemblages
at pressures ≥4.0 GPa can generate Si-poor and partly ultrapotassic melts similar in composition to that of olivine lamproites.
Received: 23 December 1996 / Accepted: 20 March 1997 相似文献
11.
At the Bufa del Diente contact-metamorphic aureole, brine infiltration through metachert layers embedded in limestones produced
thick wollastonite rims, according to Cc+Qz=Wo+CO2. Fluid inclusions trapped in recrystallized quartz hosts include: (1) high salinity four phase inclusions [Th(V-L)=460–573° C; Td(salts)=350–400° C; (Na+K)Cleq=64–73 wt%; X
CO
2≤0.02]; (2) low density vapour-rich CO2-bearing inclusions [Th(L-V)≈500±100° C; X
CO
2=0.22–0.44; X
NaCl≤0.01], corresponding to densities of 0.27± 0.05 gcm−3. Petrographical observations, phase compositions and densities show that the two fluids were simultaneously trapped in the
solvus of the H2O-CO2-salts system at 500–600° C and 700±200 bars. The low density fluid was generated during brine infiltration at the solvus
via the wollastonite producing reaction. Identical fluid types were also trapped as inclusion populations in wollastonite
hosts 3 cm adjacent to quartz crystals. At room temperature, both fluid types additionally contain one quartz and one calcite
crystal, generated by the back-reaction Wo+CO2=Cc+Qz of the host with the CO2-proportion of the fluid during retrogression. All of the CO2 was removed from the fluid. On heating in the microstage, the reaction progress of the prograde reaction was estimated via
volume loss of the calcites. In vapour-rich fluids, 50% progress is reached at 490–530° C; 80% at 520–560° C; and 100% at
540–590° C, the latter representing the trapping temperatures of the original fluid at the two fluid solvus. The progress
is volume controlled. With knowledge of compositions and densities from unmodified inclusions in quartz and using the equation
of state of Duan et al. (1995) for H2O-CO2-NaCl, along with f
CO
2-values extracted from it, the reaction progress curve was recalculated in the P-T-X-space. The calculated progress curve passes through the two fluid solvus up to 380° C/210 bars, continues in the one fluid
field and meets the solvus again at trapping conditions. The P-T slope is steep, most of the reaction occurs above 450° C and there is high correspondence between calculated and measured
reaction progress. We emphasize that with the exception of quartz, back-reactions between inclusion fluids and mineral hosts
is a common process. For almost any prograde metamorphic mineral that was formed by a devolatilization reaction and that trapped
the equilibrium fluid or any peak metamorphic fluid as an inclusion, a fluid-host back-reaction exists which must occur somewhere
along the retrograde path. Such retrograde reactions may cause drastic changes in density and composition of the fluid. In
most cases, however, evidence of the evolving mineral assemblages is not given for they might form submicroscopical layers
at the inclusion walls.
Received: 15 March 1995 / Accepted: 1 June 1995 相似文献
12.
Ilya V. Veksler Yana M. Fedorchuk Troels F. D. Nielsen 《Contributions to Mineralogy and Petrology》1998,131(4):347-363
The evolution of nephelinitic melts in equilibrium with mica-bearing liquidus assemblages and melting relations have been
studied on two silica-undersaturated joins of the KAlSiO4– Mg2SiO4– Ca2SiO4– SiO2– F system at atmospheric pressure by quench runs in sealed platinum capsules. Fluorine has been added to the batch compositions
by the direct exchange of fluorine for oxygen (2F− = O2−). The first join is the pseudo-ternary Forsterite – Diopside – KAlSiO3F2 system. Forsterite, diopside, F-phlogopite and leucite crystallisation fields and a fluoride-silicate liquid immiscibility
solvus are present on the liquidus surface of the join. Sub-liquidus and sub-solidus phases include akermanite, cuspidine,
spinel, fluorite and some other minor fluorine phases. The second system is the pseudo-binary Akermanite – F-phlogopite join
that intersects the Forsterite – Diopside – KAlSiO3F2 join. Akermanite, forsterite, diopside, F-phlogopite, leucite and cuspidine are found to crystallise on the join. Forsterite
(fo) and leucite (lc) are related to F-phlogopite (phl) by a reaction with the fluorine-bearing liquid: fo + lc + l = phl,
and the reaction proceeds until forsterite or leucite are completely consumed. The reaction temperature and resulting phase
association depend on batch composition. Thus, leucite is not stable in the sub-solidus of the Akermanite – F-phlogopite join,
but is preserved in a part of the Forsterite – Diopside – KAlSiO3F2 system where forsterite reacts out, or does not crystallise at all. The phlogopite-in reaction has an important effect on
the composition of the coexisting liquid. The liquids initially saturated in forsterite evolve to extremely Ca rich, larnite-normative
residuals. The experimental data show that larnite-normative melilitolites can crystallise from evolved melilititic melts
generated from “normal” melanephelinitic parental magmas with no normative larnite. The evolution towards melilitites requires fractionation of phlogopite-bearing assemblages under volatile pressure.
Received: 3 June 1997 / Accepted: 5 January 1998 相似文献
13.
The system CaO-MgO-SiO2-CO2 at 1 GPa, metasomatic wehrlites, and primary carbonatite magmas 总被引:1,自引:0,他引:1
New experimental data in CaO-MgO-SiO2-CO2 at 1 GPa define the vapor-saturated silicate-carbonate liquidus field boundary involving primary minerals calcite, forsterite
and diopside. The eutectic reaction for melting of model calcite (1% MC)-wehrlite at 1 GPa is at 1100 °C, with liquid composition
(by weight) 72% CaCO3 (CC), 9% MgCO3 (MC), and 18% CaMgSi2O6 (Di). These data combined with previous results permit construction of the isotherm-contoured vapor-saturated liquidus surface
for the calcite/dolomite field, and part of the adjacent forsterite and diopside fields. Nearly pure calcite crystals in mantle
xenoliths cannot represent equilibrium liquids. We recently determined the complete vapor-saturated liquidus surface between
carbonates and model peridotites at 2.7 GPa; the peritectic reaction for dolomite (25% MC)-wehrlite at 2.7 GPa occurs at 1300 °C,
with liquid composition 60% CC, 29% MC, and 11% Di. The liquidus field boundaries on these two surfaces provide the road-map
for interpretation of magmatic processes in various peridotite-CO2 systems at depths between the Moho and about 100 km. Relationships among kimberlites, melilitites, carbonatites and the liquidus
phase boundaries are discussed. Experimental data for carbonatite liquid protected by metasomatic wehrlite have been reported.
The liquid trends directly from dolomitic towards CaCO3 with decreasing pressure. The 1.5 GPa liquid contains 87% CC and 4% Di, much lower in silicate components than our phase
boundary. However, the liquids contain approximately the same CaCO3 (90 ± 1 wt%) in terms of only carbonate components. For CO2-bearing mantle, all magmas at depth must pass through initial dolomitic compositions. Rising dolomitic carbonatite melt will
vesiculate and may erupt as primary magmas through cracks from about ˜70 km. If it percolates through metasomatic wehrlite
from 70 km toward the Moho at 35–40 km, primary calcic siliceous carbonatite magma can be generated with silicate content
at least 11–18% (70–40 km) on the silicate-carbonate boundary.
Received: 22 June 1998 / Accepted: 7 July 1999 相似文献
14.
In situ X-ray diffraction experiments at high pressure were carried out up to 8.9 GPa and 1100 °C to study phase transformations
of iron and two iron-silicon alloys Fe0.91Si0.09 and Fe0.83Si0.17. For iron, the transformation from the bcc phase to the fcc phase was observed at pressures 3.8–8.2 GPa and temperatures
that are consistent with previous in situ X-ray diffraction studies. Reversal of the transformation of iron was found to be
sensitive to temperature; hysteresis of the transformation increased from 25 °C at 3.8 GPa to 100 °C at 7.0 GPa, primarily
because the bcc-fcc phase boundary has a negative Clayperon slope. In the binary system Fe-Si, the observations of the present
study indicate that the ferrite (bcc phase)-stabilizing behavior of silicon persists at high pressures and that the maximum
solubility of silicon in the fcc phase increases with increasing pressure: (1) the transformation from the bcc phase to the
fcc phase was observed in Fe0.91Si0.09 at 6.0, 7.4 and 8.9 GPa and the temperatures measured at the onset of the transformations were 300 °C higher than those in
iron at similar pressures, (2) the transformation rate in Fe0.91Si0.09 was extremely sluggish compared to that of iron, and (3) the bcc-fcc phase transformation was not observed in Fe0.91Si0.09 at 4.7 GPa up to 1000 °C and in Fe0.83Si0.17 at 8.2 GPa and 1100 °C.
Received: 1 June 1998 / Revised, accepted: 9 October 1998 相似文献
15.
H. Fukui O. Ohtaka T. Nagai T. Katsura K. Funakoshi W. Utsumi 《Physics and Chemistry of Minerals》2000,27(6):367-370
Using the high-pressure differential thermal analysis (HP-DTA) system in a cubic multianvil high-pressure apparatus, we measured
the melting points of portlandite, Ca(OH)2, up to 6 GPa and 1000 °C. We detected endothermic behavior at the temperature and pressure conditions of 800 °C and 2.5 GPa,
769 °C and 3.5 GPa, 752 °C and 4.0 GPa, 686 °C and 5.0 GPa, and 596 °C and 6.0 GPa, respectively, due to melting of portlandite.
By in situ X-ray studies under pressure, the melting of portlandite was observed at 730 °C and 4.32 GPa and at 640 °C and 5.81 GPa,
respectively. Results of both HP-DTA and X-ray studies were consistent within experimental error. The melting is congruent
and has a negative Clapeyron slope, indicating that liquid Ca(OH)2 has higher densities than crystalline portlandite in this pressure range.
Received: 19 June 1999 / Revised, accepted: 11 September 1999 相似文献
16.
I. Gavrieli Alan Matthews J. B. Holland 《Contributions to Mineralogy and Petrology》1996,125(2-3):251-262
The hydrothermal reaction between grossular and 1 molar manganese chloride solution was studied at 2 kbar and 600 °C at various
bulk Ca/(Ca+Mn) compositions:
Ca3Al2Si3O12+3Mn2+(aq) ⇔ Mn3Al2Si3O12+3Ca2+(aq)
The reaction products are garnets of the spessartine-grossular solid-solution series which discontinuously armour the dissolving
grossular grains. The first garnet to crystallize is spessartine rich (X
gt
Mn≥0.95), reflecting the high Mn content of the solution, but as the reaction proceeds more calcium-rich garnets progressively
overgrow the initial products. The armouring product layer is detached from the dissolving grossular, which allows the progressive
overgrowth to occur on both its external and internal surfaces and results in the development of a two directional Ca/(Ca+Mn)
zoning pattern in the product grains. The compositional changes in the run products are consistent with attainment of heterogeneous
equilibrium between the external rims of the spessartine-grossular garnets and the bulk solutions in runs of duration ≥24
hours. Plots of ln KD versus X
gt
Ca maxima show linear variations that are not consistent with the ideal mixing that has been proposed for spessartine-grossular
garnets at temperatures of 900 to 1200 °C. The data rather fit a regular solution model with the parameters ΔG° (600 °C, 2 kbar)=−8.0±0.8 kJ/mol and w
gt
CaMn=2.6±2.0 kJ/mol. Existing solubility measurements and thermodynamic data from other Ca and Mn silicates support the calculated
data. Grossular activities calculated using the w
gt
CaMn parameter indicate that even in manganese-rich metapelites pressure estimates calculated using the garnet-plagioclase-Al2SiO5-quartz barometer will not be increased by more than 0.2 kbar.
Received: 18 January 1995/Accepted: 4 June 1996 相似文献
17.
T. J. Williams Philip A. Candela Philip M. Piccoli 《Contributions to Mineralogy and Petrology》1995,121(4):388-399
Experiments were performed in the three phase system high-silica rhyolite melt+low-salinity aqueous vapor+hydrosaline brine,
to investigate the partitioning equilibria for copper in magmatic-hydrothermal systems at 800° C and 1 kbar, and 850° C and
0.5 kbar. Daqm/mlt
Cu and apparent equilibrium constants, Kaqm/mlt
Cu,Na, between the aqueous mixture (aqm=quenched vapor+brine) and the silicate melt (mlt) are calculated. Daqm/mlt
Cu increases with increasing aqueous chloride concentration and is a function of pressure. Kaqm/mlt
Cu,Na=215(±73) at 1 kbar and 800° C and Kaqm/mlt
Cu,Na=11(±6) at 0.5 kbar and 850°C. Decreasing pressure from 1 to 0.5 kbar lowers Kaqm/mlt
Cu,Na by a factor of approximately 20. Data revealed no difference in Kaqm/mlt
Cu,Na or Daqm/mlt
Cu as a function of the melt aluminium saturation index. Within the 2-phase field the Kaqm/mlt
Cu,Na show no variation with total aqueous chloride, indicating that copper-sodium exchange between the vapor, brine and silicate
melt is independent of the mass proportion of vapor and brine. Model copper-sodium apparent equilibrium constants for the
hydrosaline brine and the silicate melt revealed a negative dependence on pressure. Model apparent equilibrium constants for
copper-sodium exchange between the brine and vapor were close to unity at 1 kbar and 800° C.
Received: 27 June 1994/Accepted: 30 March 1995 相似文献
18.
The high-pressure stability of zoisite and phase relationships of zoisite-bearing assemblages 总被引:5,自引:0,他引:5
The fluid-absent reaction 12 zoisite = 3 lawsonite + 7 grossular + 8 kyanite + 1 coesite was experimentally reversed in the
model system CaO-Al2O3-SiO2-H2O (CASH) using a multi-anvil apparatus. The upper pressure stability limit for zoisite was found to extend to 5.0 GPa at 700 °C
and to 6.6 GPa at 950 °C. Additional experiments both in the H2O-SiO2-saturated and in the H2O-Al2O3-saturated portions of CASH provide further constraints on high pressure phase relationships of lawsonite, zoisite, grossular,
kyanite, coesite, and an aqueous fluid. Consistency of the present experiments with the H2O-saturated breakdown of lawsonite is demonstrated by thermodynamic analysis using linear programming techniques. Two sets
of data consistent with databases of Berman (1988) and Holland and Powell (1990) were retrieved combining experimental phase
relationships, calorimetric constraints, and recently measured elastic properties of solid phases. The best fits result in
G
f
,1,298
∘,zoisite=−6,499,400 J and S
1,298
∘,zoisite=302 J/K, and G
f
,1,298
∘,lawsonite=−4,514,600 J and S
1,298
∘,lawsonite=220 J/K for the dataset of Holland and Powell, and G
f
,1,298
∘,zoisite=−6,492,120 J and S
1,298
∘,zoisite=304 J/K, and G
f
,1,298
∘,lawsonite=−4,513,000 J and S
1,298
∘,lawsonite= 218 J/K for the dataset of Berman. Examples of the usage of zoisite as a geohygrometer and as a geobarometer in rocks metamorphosed
at eclogite facies conditions are worked, profiting from the thermodynamic properties retrieved here.
Received: 23 December 1996 / Accepted: 29 August 1997 相似文献
19.
Andrea Orlando Yves Thibault Alan D. Edgar 《Contributions to Mineralogy and Petrology》2000,139(2):136-145
Experiments ranging from 2 to 3 GPa and 800 to 1300 °C and at 0.15 GPa and 770 °C were performed to investigate the stability
and mutual solubility of the K2ZrSi3O9 (wadeite) and K2TiSi3O9 cyclosilicates under upper mantle conditions. The K2ZrSi3O9–K2TiSi3O9 join exhibits complete miscibility in the P–T interval investigated. With increasing degree of melting the solid solution becomes progressively enriched in Zr, indicating
that K2ZrSi3O9 is the more refractory end member. At 2 GPa, in the more complex K2ZrSi3O9–K2TiSi3O9–K2Mg6Al2Si6O20(OH)4 system, the presence of phlogopite clearly limits the extent of solid solution of the cyclosilicate to more Zr-rich compositions
[Zr/(Zr + Ti) > 0.85], comparable to wadeite found in nature, with TiO2 partitioning strongly into the coexisting mica and/or liquid. However, at 1200 °C, with increasing pressure from 2 to 3 GPa,
the partitioning behaviour of TiO2 changes in favour of the cyclosilicate, with Zr/(Zr + Ti) of the K2(Zr,Ti)Si3O9 phase decreasing from ∼0.9 to ∼0.6. The variation in the Ti content of the coexisting phlogopite is related to its degree
of melting to forsterite and liquid, following the major substitution VITi+VI□=2VIMg.
Received: 26 January 1999 / Accepted: 10 January 2000 相似文献
20.
H2O activity in concentrated NaCl solutions at high pressures and temperatures measured by the brucite-periclase equilibrium 总被引:1,自引:0,他引:1
H2O activities in concentrated NaCl solutions were measured in the ranges 600°–900° C and 2–15 kbar and at NaCl concentrations
up to halite saturation by depression of the brucite (Mg(OH)2) – periclase (MgO) dehydration equilibrium. Experiments were made in internally heated Ar pressure apparatus at 2 and 4.2
kbar and in 1.91-cm-diameter piston-cylinder apparatus with NaCl pressure medium at 4.2, 7, 10 and 15 kbar. Fluid compositions
in equilibrium with brucite and periclase were reversed to closures of less than 2 mol% by measuring weight changes after
drying of punctured Pt capsules. Brucite-periclase equilibrium in the binary system was redetermined using coarsely crystalline
synthetic brucite and periclase to inhibit back-reaction in quenching. These data lead to a linear expression for the standard
Gibbs free energy of the brucite dehydration reaction in the experimental temperature range: ΔG° (±120J)=73418–134.95T(K). Using this function as a baseline, the experimental dehydration points in the system MgO−H2O−NaCl lead to a simple systematic relationship of high-temperature H2O activity in NaCl solution. At low pressure and low fluid densities near 2 kbar the H2O activity is closely approximated by its mole fraction. At pressures of 10 kbar and greater, with fluid densities approaching
those of condensed H2O, the H2O activity becomes nearly equal to the square of its mole fraction. Isobaric halite saturation points terminating the univariant
brucite-periclase curves were determined at each experimental pressure. The five temperature-composition points in the system
NaCl−H2O are in close agreement with the halite saturation curves (liquidus curves) given by existing data from differential thermal
analysis to 6 kbar. Solubility of MgO in the vapor phase near halite saturation is much less than one mole percent and could
not have influenced our determinations. Activity concentration relations in the experimental P-T range may be retrieved for the binary system H2O-NaCl from our brucite-periclase data and from halite liquidus data with minor extrapolation. At two kbar, solutions closely
approach an ideal gas mixture, whereas at 10 kbar and above the solutions closely approximate an ideal fused salt mixture,
where the activities of H2O and NaCl correspond to an ideal activity formulation. This profound pressure-induced change of state may be characterized
by the activity (a) – concentration (X) expression: a
H
2O=X
H
2O/(1+αX
NaCl), and a
NaCl=(1+α)(1+α)[X
NaCl/(1+αX
NaCl)](1+α). The parameter α is determined by regression of the brucite-periclase H2O activity data: α=exp[A–B/ϱH
2O ]-CP/T, where A=4.226, B=2.9605, C=164.984, and P is in kbar, T is in Kelvins, and ϱH
2O is the density of H2O at given P and T in g/cm3. These formulas reproduce both the H2O activity data and the NaCl activity data with a standard deviation of ±0.010. The thermodynamic behavior of concentrated NaCl solutions at
high temperature and pressure is thus much simpler than portrayed by extended Debye-Hückel theory. The low H2O activity at high pressures in concentrated supercritical NaCl solutions (or hydrosaline melts) indicates that such solutions
should be feasible as chemically active fluids capable of coexisting with solid rocks and silicate liquids (and a CO2-rich vapor) in many processes of deep crustal and upper mantle metamorphism and metasomatism.
Received: 1 September 1995 / Accepted: 24 March 1996 相似文献