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1.
Molecular Orbital Study on the Optimized Geometries and Spectroscopic Parameters of Borate Polyhedra
In this paper several methods including MNDO, multiple scattering Xα and ab initio self-consistent-field MO theories have been used to calculate the minimum energy geometries, force constants, vibrational frequencies ,and ^11B quadruple coupling constants of B-O polyhedra such as [BO3],[BO4],[OB2] and [OB3].The results are in good agreement with the experimental and calcu-lated values so far published by other authors. 相似文献
2.
Andreas Tennie Radegund Hoffbauer Stephan Hoernes 《Contributions to Mineralogy and Petrology》1998,133(4):346-355
The oxygen isotope fractionation between kyanite and calcium carbonate has been investigated experimentally at four temperatures
in the range between 625 and 775 °C at 13 kbar. Because of low exchange rates, the isotopic reaction was enhanced by polymorphic
transformation of andalusite to kyanite. With this experimental modification a close approach to equilibrium was reached in
all runs. The temperature dependence of the equilibrium fractionation is described by the equation 1000 ln ky-cc=−2.62×106/T
2. Application of the experimental results to natural quartz-kyanite-garnet assemblages indicates the preservation of the oxygen
isotope composition of kyanite acquired during its formation, reflecting its extremely low oxygen diffusivity. This refractory
behaviour restricts the use of kyanite for thermometry but opens the possibility to use its O-isotope composition as an indicator
for recognition of polymetamorphic rock histories and reconstruction of the prograde evolution of a metamorphic sequence.
Received: 8 June 1998 / Accepted: 24 August 1998 相似文献
3.
Matteo Alvaro Fernando Cámara M. Chiara Domeneghetti Fabrizio Nestola Vittorio Tazzoli 《Contributions to Mineralogy and Petrology》2011,162(3):599-613
A natural Ca-poor pigeonite (Wo6En76Fs18) from the ureilite meteorite sample PCA82506-3, free of exsolved augite, was studied by in situ high-temperature single-crystal
X-ray diffraction. The sample, monoclinic P21/c, was annealed up to 1,093°C to induce a phase transition from P21/c to C2/c symmetry. The variation with increasing temperature of the lattice parameters and of the intensity of the b-type reflections (h + k = 2n + 1, present only in the P21/c phase) showed a displacive phase transition P21/c to C2/c at a transition temperature T
Tr = 944°C, first order in character. The Fe–Mg exchange kinetics was studied by ex situ single-crystal X-ray diffraction in
a range of temperatures between the closure temperature of the Fe–Mg exchange reaction and the transition temperature. Isothermal
disordering annealing experiments, using the IW buffer, were performed on three crystals at 790, 840 and 865°C. Linear regression
of ln k
D versus 1/T yielded the following equation:
ln k\textD = - 3717( ±416)/T(K) + 1.290( ±0.378); (R2 = 0.988) \ln \,k_{\text{D}} = - 3717( \pm 416)/T(K) + 1.290( \pm 0.378);\quad (R^{2} = 0.988) . The closure temperature (T
c) calculated using this equation was ∼740(±30)°C. Analysis of the kinetic data carried out taking into account the e.s.d.'s
of the atomic fractions used to define the Fe–Mg degree of order, performed according to Mueller’s model, allowed us to retrieve
the disordering rate constants C
0
K
dis+ for all three temperatures yielding the following Arrhenius relation:
ln( C0 K\textdis + ) = ln K0 - Q/(RT) = 20.99( ±3.74) - 26406( ±4165)/T(K); (R2 = 0.988) \ln \left( {C_{0} K_{\text{dis}}^{ + } } \right) = \ln \,K_{0} - Q/(RT) = 20.99( \pm 3.74) - 26406( \pm 4165)/T(K);\quad (R^{2} = 0.988) . An activation energy of 52.5(±4) kcal/mol for the Fe–Mg exchange process was obtained. The above relation was used to calculate
the following Arrhenius relation modified as a function of X
Fe (in the range of X
Fe = 0.20–0.50):
ln( C0 K\textdis + ) = (21.185 - 1.47X\textFe ) - \frac(27267 - 4170X\textFe )T(K) \ln \left( {C_{0} K_{\text{dis}}^{ + } } \right) = (21.185 - 1.47X_{\text{Fe}} ) - {\frac{{(27267 - 4170X_{\text{Fe}} )}}{T(K)}} . The cooling time constant, η = 6 × 10−1 K−1 year−1 calculated on the PCA82506-3 sample, provided a cooling rate of the order of 1°C/min consistent with the extremely fast late
cooling history of the ureilite parent body after impact excavation. 相似文献
4.
K. Putirka Marie Johnson Rosamond Kinzler John Longhi David Walker 《Contributions to Mineralogy and Petrology》1996,123(1):92-108
Models for estimating the pressure and temperature of igneous rocks from co-existing clino-pyroxene and liquid compositions
are calibrated from existing data and from new data obtained from experiments performed on several mafic bulk compositions
(from 8–30 kbar and 1100–1475° C). The resulting geothermobarometers involve thermodynamic expressions that relate temperature
and pressure to equilibrium constants. Specifically, the jadeite (Jd; NaAlSi2O6)–diopside/hedenbergite (DiHd; Ca(Mg, Fe) Si2O6) exchange equilibrium between clinopyroxene and liquid is temperature sensitive. When compositional corrections are made
to the calibrated equilibrium constant the resulting geothermometer is
(i) 104
T=6.73−0.26* ln [Jdpx*Caliq*FmliqDiHdpx*Naliq*Alliq] −0.86* ln [MgliqMgliq+Feliq]+0.52*ln [Caliq]
an expression which estimates temperature to ±27 K. Compared to (i), the equilibrium constant for jadeite formation is more
sensitive to pressure resulting in a thermobarometer
(ii) P=−54.3+299* T104+36.4* T104 ln [Jdpx[Siliq]2*Naliq*Alliq] +367*[Naliq*Alliq]
which estimates pressure to ± 1.4 kbar. Pressure is in kbar, T is in Kelvin. Quantities such as Naliq represent the cation fraction of the given oxide (NaO0.5) in the liquid and Fm=MgO+FeO. The mole fractions of Jd and diopside+hedenbergite (DiHd) components are calculated from a
normative scheme which assigns the lesser of Na or octahedral Al to form Jd; any excess AlVI forms Calcium Tschermak’s component (CaTs; CaAlAlSiO6); Ca remaining after forming CaTs and CaTiAl2O6 is taken as DiHd. Experimental data not included in the regressions were used to test models (i) and (ii). Error on predictions
of T using model (i) is ±40 K. A pressure-dependent form of (i) reduces this error to ±30 K. Using model (ii) to predict pressures,
the error on mean values of 10 isobaric data sets (0–25 kbar, 118 data) is ±0.3 kbar. Calculating thermodynamic properties
from regression coefficients in (ii) gives VJd
f of 23.4 ±1.3 cm3/mol, close to the value anticipated from bar molar volume data (23.5 cm3/mol). Applied to clinopyroxene phenocrysts from Mauna Kea, Hawaii lavas, the expressions estimate equilibration depths as
great as 40 km. This result indicates that transport was sufficiently rapid that at least some phenocrysts had insufficient
time to re-equilibrate at lower pressures.
Received: 16 May 1994/Accepted: 15 June 1995 相似文献
5.
Tyler B. Coplen 《Geochimica et cosmochimica acta》2007,71(16):3948-3957
The δ18O of ground water (−13.54 ± 0.05 ‰) and inorganically precipitated Holocene vein calcite (+14.56 ± 0.03 ‰) from Devils Hole cave #2 in southcentral Nevada yield an oxygen isotopic fractionation factor between calcite and water at 33.7 °C of 1.02849 ± 0.00013 (1000 ln αcalcite-water = 28.09 ± 0.13). Using the commonly accepted value of ∂(αcalcite-water)/∂T of −0.00020 K−1, this corresponds to a 1000 ln αcalcite-water value at 25 °C of 29.80, which differs substantially from the current accepted value of 28.3. Use of previously published oxygen isotopic fractionation factors would yield a calcite precipitation temperature in Devils Hole that is 8 °C lower than the measured ground water temperature. Alternatively, previously published fractionation factors would yield a δ18O of water, from which the calcite precipitated, that is too negative by 1.5 ‰ using a temperature of 33.7 °C. Several lines of evidence indicate that the geochemical environment of Devils Hole has been remarkably constant for at least 10 ka. Accordingly, a re-evaluation of calcite-water oxygen isotopic fractionation factor may be in order.Assuming the Devils Hole oxygen isotopic value of αcalcite-water represents thermodynamic equilibrium, many marine carbonates are precipitated with a δ18O value that is too low, apparently due to a kinetic isotopic fractionation that preferentially enriches 16O in the solid carbonate over 18O, feigning oxygen isotopic equilibrium. 相似文献
6.
In order to develop a model for simulating naturally occurring chromian spinel compositions, we have processed published
experimental data on chromian spinel-melt equilibrium. Out of 259 co-existing spinel-melt experiments reported in the literature,
we have selected 118 compositions on the basis of run time, melt composition and experimental technique. These data cover
a range of temperatures 1150–1500° C, oxygen fugacities of −13<log f
O2< −0.7, and bulk compositions ranging from basalt and norite, to komatiite. Six major spinel components with Cr3+, Al3+, Ti4+, Mg2+, Fe3+ and Fe2+-bearing end-members were considered for the purpose of describing chromite saturation as a function of melt composition,
temperature and oxygen fugacity at 1 atmosphere pressure (0.101 MPa). The empirically calibrated mineral-melt expression based
on multiple linear regressions is:
K
Sp
i
=A/T(K)+B log f
O2+C ln (Fe3+/Fe2+)L+D ln R
L
+E,
where K
Sp
i
is an equilibrium constant and R
L
is a melt structure-chemical parameter (MSCP). Twenty-eight forms of equilibrium constants were considered, including single distribution coefficients, exchange equilibrium
constants, formation constants for AB2O4 components, as well as simple “spinel cation ratios”. For each form of the equilibrium constants, a set of 16 combinations
of the MSCPs have been investigated. The MSCP is present in the form of composite ratios [e.g., Si/O, NBO/T,(Al+Si)/Si, or (Na+K)/Al] or as simple cation ratios (e.g.,
Mg/Fe2+). For the calculation of Fe3+ and Fe2+ species in silicate melts, we used existing equations, whereas the Fe3+/Fe2+ ratio of spinels was calculated from the spinel stoichiometry. The regression parameters that best repoduce the experimental
data were for the following constants: (Fe3+/Fe2+)
Sp
, (Mg/Fe2+)
Sp
/(Mg/Fe2+)
L
, (Cr/Al)
Sp
/ (Cr/Al)
L
, K
FeCr2O4, and Ti
Sp
/Ti
L
. These expressions have been combined into a single program called SPINMELT, which calculates chromite crystallization temperature
and composition at a given f
O2 with an average accuracy of ∼10° C and 1–2 mol%. An example of the use of SPINMELT is presented for a magma parental to the
Bushveld Complex.
Received: 30 May 1995/Accepted: 1 November 1995 相似文献
7.
Donald C. Thorstenson 《Geochimica et cosmochimica acta》2004,68(11):2449-2465
Theory is derived from the work of Urey (Urey H. C. [1947] The thermodynamic properties of isotopic substances. J. Chem. Soc. 562-581) to calculate equilibrium constants commonly used in geochemical equilibrium and reaction-transport models for reactions of individual isotopic species. Urey showed that equilibrium constants of isotope exchange reactions for molecules that contain two or more atoms of the same element in equivalent positions are related to isotope fractionation factors by α = (Kex)1/n, where n is the number of atoms exchanged. This relation is extended to include species containing multiple isotopes, for example 13C16O18O and 1H2H18O. The equilibrium constants of the isotope exchange reactions can be expressed as ratios of individual isotope equilibrium constants for geochemical reactions. Knowledge of the equilibrium constant for the dominant isotopic species can then be used to calculate the individual isotope equilibrium constants.Individual isotope equilibrium constants are calculated for the reaction CO2g = CO2aq for all species that can be formed from 12C, 13C, 16O, and 18O; for the reaction between 12C18O2aq and 1H218Ol; and among the various 1H, 2H, 16O, and 18O species of H2O. This is a subset of a larger number of equilibrium constants calculated elsewhere (Thorstenson D. C. and Parkhurst D. L. [2002] Calculation of individual isotope equilibrium constants for implementation in geochemical models. Water-Resources Investigation Report 02-4172. U.S. Geological Survey). Activity coefficients, activity-concentration conventions for the isotopic variants of H2O in the solvent 1H216Ol, and salt effects on isotope fractionation have been included in the derivations. The effects of nonideality are small because of the chemical similarity of different isotopic species of the same molecule or ion. The temperature dependence of the individual isotope equilibrium constants can be calculated from the temperature dependence of the fractionation factors.The derivations can be extended to calculation of individual isotope equilibrium constants for ion pairs and equilibrium constants for isotopic species of other chemical elements. The individual isotope approach calculates the same phase isotopic compositions as existing methods, but also provides concentrations of individual species, which are needed in calculations of mass-dependent effects in transport processes. The equilibrium constants derived in this paper are used to calculate the example of gas-water equilibrium for CO2 in an acidic aqueous solution. 相似文献
8.
In situ x-ray data on molar volumes of periclase and tungsten have been collected over the temperature range from 300 K to melting.
We determine the temperature by combining the technique of spectroradiometry and electrical resistance wire heating. The thermal
expansion (α) of periclase between 300 and 3100 K is given by α=2.6025 10−5+1.3535 10−8 T+6.5687 10−3 T−1−1.8281 T−2.
For tungsten, we have (300 to 3600 K) α=7.862 10−6+6.392 10−9 T.
The data at 298 K for periclase is: molar volume 11.246 (0.031) cm3, α=3.15 (0.07) 10−5 K−1, and for tungsten: molar volume 9.55 cm3, α=9.77 (10.08) 10−6 K−1.
Received: July 18, 1996 / Revised, accepted: February 14, 1997 相似文献
9.
Temperature-dependent isotopic fractionation of lithium between clinopyroxene and high-pressure hydrous fluids 总被引:2,自引:1,他引:2
Bernd Wunder Anette Meixner Rolf L. Romer Wilhelm Heinrich 《Contributions to Mineralogy and Petrology》2006,151(1):112-120
The fractionation of lithium isotopes between synthetic spodumene as representative of Li-bearing clinopyroxene and Cl- and
OH-bearing aqueous fluids was experimentally determined between 500 and 900°C at 2.0 GPa. In all the experiments, 7Li was preferentially partitioned into the fluid. The fractionation is temperature dependent and approximated by the equation
Δ7Li(clinopyroxene–fluid)=−4.61×(1,000/T [K]) + 2.48; R
2=0.86. Significant Li isotopic fractionation of about 1.0‰ exists even at high temperatures of 900°C. Using neutral and weakly
basic fluids revealed that the amount of fractionation is not different. The Li isotopic fractionation between altered basalt
and hot spring water (350°C) in natural samples is in good agreement with our experimentally determined fractionation curve.
The data confirm earlier speculations drawn from the Li isotopic record of dehydrated metamorphic rocks that fluids expelled
from a dehydrating slab carry heavier Li into the mantle wedge, and that a light Li component is introduced into the deeper
mantle. Li and Li isotopes are redistributed among wedge minerals as fluids travel across the wedge into hotter regions of
arc magma production. This modifies the Li isotopic characteristics of slab-derived fluids erasing their source memory, and
explains the absence of cross-arc variations of Li isotopes in arc basalts. 相似文献
10.
Oxygen isotope partitioning between calcite and tremolite was experimentally calibrated in the presence of small amounts of a supercritical CO2–H2O fluid at temperatures from 520 to 680° C and pressures from 3 to 10 kbar. The experiments were carried out within the stability field of the calcite-tremolite assemblage based on phase equilibrium relationships in the system CaO–MgO–SiO2–CO2–H2O, so that decomposition of calcite and tremolite was avoided under the experimental conditions. Appropriate proportions of carbon dioxide to water were used to meet this requirement. Large weight ratios of mineral to fluid were employed in order to make the isotopic exchange between calcite and tremolite in the presence of a fluid close to that without fluid. The data processing method for isotopic exchange in a three-phase system has been applied to extrapolate partial equilibrium data to equilibrium values. The determined fractionation factors between calcite (Cc) and tremolite (Tr) are expressed as:1031n Cc-Tr=3.80 × 106/T
2-1.67By combining the present data with the experimental calibrations of Clayton et al. (1989) on the calcite-quartz system, we obtain the fractionation for the quartztremolite system: 1031n Qz-Tr=4.18 × 106/T
2-1.67Our experimental calibrations are in good agreement with the theoretical calculations of Hoffbauer et al. (1994) and the empirical estimates of Bottinga and Javoy (1975) based on isotopic data from naturall assemblages. At 700 C good agreement also exists between our experimental data and theoretical values calculated by Zheng (1993b). With decreasing temperature, however, an increasing difference between these data appears.Retrograde isotopic reequilibration by oxygen diffusion may be common for amphibole relative to diopside in metamorphic rocks. However, isotopic equilibrium in amphibole can be preserved in cases of rapid cooling. 相似文献
11.
12.
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
13.
Stable oxygen isotopic fractionation during inorganic calcite precipitation was experimentally studied by spontaneous precipitation at various pH (8.3 < pH < 10.5), precipitation rates (1.8 < log R < 4.4 μmol m− 2 h− 1) and temperatures (5, 25, and 40 °C) using the CO2 diffusion technique.The results show that the apparent stable oxygen isotopic fractionation factor between calcite and water (αcalcite–water) is affected by temperature, the pH of the solution, and the precipitation rate of calcite. Isotopic equilibrium is not maintained during spontaneous precipitation from the solution. Under isotopic non-equilibrium conditions, at a constant temperature and precipitation rate, apparent 1000lnαcalcite–water decreases with increasing pH of the solution. If the temperature and pH are held constant, apparent 1000lnαcalcite–water values decrease with elevated precipitation rates of calcite. At pH = 8.3, oxygen isotopic fractionation between inorganically precipitated calcite and water as a function of the precipitation rate (R) can be described by the expressionsat 5, 25, and 40 °C, respectively.The impact of precipitation rate on 1000lnαcalcite–water value in our experiments clearly indicates a kinetic effect on oxygen isotopic fractionation during calcite precipitation from aqueous solution, even if calcite precipitated slowly from aqueous solution at the given temperature range. Our results support Coplen's work [Coplen T. B. (2007) Calibration of the calcite–water oxygen isotope geothermometer at Devils Hole, Nevada, a natural laboratory. Geochim. Cosmochim. Acta 71, 3948–3957], which indicates that the equilibrium oxygen isotopic fractionation factor might be greater than the commonly accepted value. 相似文献
14.
利用增量方法和同位素交换技术,对角闪石族矿物的氧同位素分馏进行了理论计算和实验测定。理论结果表明,不同化学成分的角闪石之间存在一定的氧同位素分馏,其13O富集顺序为:钠闪石>蓝闪石>铁闪石>阳起石=镁铁门石≥直闪石≥透闪石>普通角闪石>铝直闪石>韭闪石。高温条件下(>500℃),角闪石相对于水亏损18O达1‰至3‰。实验进行在有少量流体存在的条件下,温度为520℃至680℃。所确定的方解石-透闪石氧同位素分馏系数与理论计算值在误差范围内完全一致。理论和实验确定的石英-透闪石分馏曲线均显着低于已知的经验校准曲线,反映了变质岩中含角闪石矿物集合体内部的退化同位素再平衡。 相似文献
15.
Recent empirical and theoretical calculations of the temperature-dependant oxygen stable isotope fractionation behavior of cerussite have highlighted potential problems with earlier work on this topic. The synthetic cerussite which was used earlier by the lead author to determine fractionation factors was re-examined using energy dispersive X-ray analysis, and found to be internally contaminated with inclusions of the phase hydrocerussite at levels of 5-10% by volume. The volume of hydrocerussite present within the samples is not sufficient to explain the entire discrepancy between this work and the empirical and theoretical calculations made earlier by the second author of this paper. Regardless of the exact causes of experimental failure or kinetic effects, the hydrocerussite contamination and the difficulty of demonstrating that these experiments reached isotopic equilibrium suggest that the use of cerussite oxygen isotope fractionation factors determined by slow precipitation experiments be discontinued in favor of the empirically calibrated fractionation factor 1000 ln αcerussite-water = 2.29(106/T2) − 3.56. In addition, we have determined that the oxygen isotope fractionation factor between hydrocerussite and water at 20 °C is 1.0232. 相似文献
16.
The α − β transition of quartz was successfully observed with using a single sample by means of the rectangular parallelepiped
resonance (RPR) method. An oriented rectangular parallelepiped of α-quartz single crystal was prepared and the resonant frequencies
of 30–11 vibrational modes were measured from room temperature to 700°C. The softening of quartz crystal was observed as the
significant reduction of resonant frequencies near the α–β transition. The present study is the first application of the RPR
method to the study of phase transition. The complete set of elastic constants of α- and β-quartz were determined as a function
of temperature by the least-squares inversion of the measured frequency data obtained by a single run. This is a merit yielded
by the RPR method. It is shown near the α − β transition in both α- and β-quartz that the elastic parameters decrease proportionally
to |T−T
0|−n
, where T is temperature and T
0 is the transition temperature, 573.0°C for α-quartz and 574.3°C for β-quartz. It was also seen that linear incompressibilities
K
1 = (C
11
+C
12
+C
13)/3 and K
3 = (C
33
+2C
13)/3 decrease rapidly toward the transition, whereas, shear moduli C
44, C
S1 = (C
11
+C
33
-2C
13)/4 and C
S3 = (C
11
-C
12)/2 = C
66 decrease only slightly. The shear modulus C
S3 = C
66 increased slightly in α-quartz. The elastic properties of isotropic aggregate of quartz were calculated, and it is shown
that the longitudinal wave velocity significantly decreases at the α − β transition, whereas, the shear wave velocity decreases
only slightly. 相似文献
17.
P. Comodi G. D. Gatta P. F. Zanazzi D. Levy W. Crichton 《Physics and Chemistry of Minerals》2002,29(8):538-544
Powder diffraction measurements at simultaneous high pressure and temperature on samples of 2M1 polytype of muscovite (Ms) and paragonite (Pg) were performed at the beamline ID30 of ESRF (Grenoble), using the Paris-Edinburgh
cell. The bulk moduli of Ms, calculated from the least-squares fitting of V–P data on each isotherm using a second-order Birch–Murnaghan EoS, were: 57.0(6), 55.1(7), 51.1(7) and 48.9(5) GPa on the isotherms
at 298, 573, 723 and 873 K, respectively. The value of (∂K
T
/∂T)
was −0.0146(2) GPa K−1. The thermal expansion coefficient α varied from 35.7(3) × 10−6 K−1 at P ambient to 20.1(3) × 10−6 K−1 at P = 4 GPa [(∂α/∂P)
T
= −3.9(1) × 10−6 GPa−1 K−1]. The corresponding values for Pg on the isotherms at 298, 723 and 823 K were: bulk moduli 59.9(5), 55.7(6) and 53.8(7) GPa,
(∂K
T
/∂T)
−0.0109(1) GPa K−1. The thermal expansion coefficient α varied from 44.1(2) × 10−6 K−1 at P ambient to 32.5(2) × 10−6 K−1 at P = 4 GPa [(∂α/∂P)
T
= −2.9(1) × 10−6 GPa−1 K−1]. Thermoelastic coefficients showed that Pg is stiffer than Ms; Ms softens more rapidly than Pg upon heating; thermal expansion
is greater and its variation with pressure is smaller in Pg than in Ms.
Received: 28 January 2002 / Accepted: 5 April 2002 相似文献
18.
Oxygen isotope fractionation was experimentally studied in the quartz-wolframite-water system from 200 to 420 °C. The starting
wolframite was synthesized in aqueous solutions of Na2WO4 · 2H2O + FeCl2 · 4H2O or MnCl2 · 4H2O. The starting solutions range in salinity from 0 to 10 equivalent wt.% NaCl. Experiments were conducted in a gold-lined
stainless steel autoclave, with filling degrees of about 50%. The results showed no significant difference in equilibrium
isotope fractionation between water and wolframite, ferberite and huebnerite at the same temperature (310 °C ). The equilibrium
oxygen isotope fractionation factors of wolframite and water tend to be equal with increasing temperature above 370 °C, but
to increase significantly with decreasing temperature below 370 °C: 1000 ln αwf-H2o= 1.03×106T−2-4.91 (370 °C ±200 °C ) 1000 ln αwf-H2o = 0.21×106T −2-2.91 (420 °C -370 °C ±)
This projects was financially supported by the National Natural Science Foundation of China. 相似文献
19.
Baiyuneboite-(Ce) is a new fluor-carbonate mineral.Based on the fine data on the structure of the mineral,the factor group and normal coordinate analyses for its infrared spectrum have been carried out.The factor group analyses indicate that the site group and factor group splittings of the internal vibration bands of CO3^2- ions do not occur and that the double bands of normal modes result from two non-equal sets of CO3^2- ions in the crystal structure,The normal coordinate analyses give the stretching force constants.bend force constants and calculated frequencies of CO3^2- ions.The calculations of potential energy distribution allow us to assign v3 and v4 to the stretching vibration and the bend vibration of CO3^2- ions.respectively. 相似文献
20.
Experimental study of silicon isotope dynamic fractionation and its application in geology 总被引:1,自引:0,他引:1
Silicon shows no variation in its chemical valence in nature and exists mainly in the form of silicon-oxygen tetrahedra, so
very small silicon isotope thermodynamic fractionation occurs and the resultant silicon isotope variation is limited. Dynamic
fractionation of Si isotopes during precipitation of SiO2 from a solution is a main factor leading to substantial variations in silicon isotopes in nature. In this experimental study,
we determined the dynamic fractionation factorα for silicon isotopes during precipitation of SiO2 from the solution. And in combination of α, a theoretical explanation is presented of the considerably low δ30Si values of black smokers on modern seafloor, Archean banded magnetite-quartzite and clay minerals of weathering origin,
and of clearly high δ30Si values of siliceous rocks in shallow-sea carbonate platforms.
This paper won the Paper of Excellence in the Second National Young Scientist Symposium on Geochemistry of Minerals and Rocks. 相似文献