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1.
OH absorption coefficients of rutile and cassiterite deduced from nuclear reaction analysis and FTIR spectroscopy 总被引:1,自引:0,他引:1
Summary The OH content of four rutile and two cassiterite single-crystals was studied by nuclear reaction analysis (NRA) and by polarised
FTIR microspectroscopy. The OH absorption bands of both minerals are centered around 3300 cm−1 with different absorption features. The analytical H2O content determined by NRA ranges from 70 to 820 wt.ppm. The integrated molar absorption coefficients deduced from the total
integrated OH absorbances are equal to 38000 lċmol−1
H2Oċcm−2 for rutile and 65000 lċmol−1
H2Oċcm−2 for cassiterite. For both minerals the absorption coefficients are significantly smaller than those expected from the linear
calibration curves given by Paterson (1982) and by Libowitzky and Rossman (1997).
Received January 4, 2000; revised version accepted April 10, 2000 相似文献
Zusammenfassung OH-Absorptionskoeffizienten von Rutil und Cassiterit ermittelt durch Kernreaktions-Analyse und FTIR Spektroskopie Der OH-Gehalt von vier Rutil- und zwei Cassiterit-Einkristallen wurde mittels Kernreaktions-Analyse (NRA) und polarisierter FTIR Mikrospektroskopie untersucht. Die OH Absorptionsbanden beider Minerale sind um 3.300 cm−1 zentriert, mit unterschiedlichen Absorptionserscheinungen. Der analytische H2O-Gehalt, der mit NRA bestimmt wurde, schwankt von 70 bis 820 Gew.ppm. Die integrierten molaren Absorptionskoeffizienten, die auf den gesamten integrierten OH-Absorptionen basieren, betragen etwa 38.000 lċmol−1 H2Oċcm−2 für Rutil and 65.000 lċmol−1 H2Oċcm−2 für Cassiterit. Für beide Minerale sind die Absorptionskoeffizienten signifikant kleiner als die, die auf Grund der linearen Kalibrationskurven von Paterson (1982) und Libowitzky und Rossmann (1997) zu erwarten sind.
Received January 4, 2000; revised version accepted April 10, 2000 相似文献
2.
Pascal Richet Alan Whittington François Holtz Harald Behrens Susanne Ohlhorst Max Wilke 《Contributions to Mineralogy and Petrology》2000,138(4):337-347
A review of published and newly measured densities for 40 hydrous silicate glasses indicates that the room-temperature partial
molar volume of water is 12.0 ± 0.5 cm3/mol. This value holds for simple or mineral compositions as well as for complex natural glasses, from rhyolite to tephrite
compositions, prepared up to 10–20 kbar pressures and containing up to 7 wt% H2O. This volume does not vary either with the molar volume of the water-free silicate phase, with its degree of polymerization
or with water speciation. Over a wide range of compositions, this constant value implies that the volume change for the reaction
between hydroxyl ions and molecular water is zero and that, at least in glasses, speciation does not depend on pressure. Consistent
with data from Ochs and Lange (1997, 1999), systematics in volume expansion for SiO2–M2O systems (M=H, Li, Na, K) suggests that the partial molar thermal expansion coefficient of H2O is about 4 × 10−5 K−1 in silicate glasses.
Received: 30 June 1999 / Accepted: 5 November 1999 相似文献
3.
The IR spectrum of an alpine, hydrothermally formed diopside containing 17 wt ppm H2O consists of three main OH absorption bands centred at 3647, 3464 and 3359 cm−1. Jadeite from a Californian vein occurrence is characterised by bands at 3616 and 3557 cm−1 and contains about 197 wt ppm H2O. Based on the pleochroic scheme of the OH absorption bands in diopside, OH defect incorporation models are derived on the
basis of fully occupied cation sites and under the assumption of M1 and M2 site vacancies; OH defects replacing O2 oxygen
atoms are most common. The less pronounced OH pleochroism and the broad band absorption pattern of jadeite indicate a high
degree of OH defect disordering. The pleochroic scheme of the main absorption bands at 3616 and 3557 cm−1 implies partial replacement of O2 oxygen atoms by OH dipoles pointing to vacant Si sites. Under the assumption of M1 and
M2 site vacancies, O1–H and O2–H defects are also derivable. OH incorporation modes assuming Si-vacancies should be considered
for jadeite-rich clinopyroxenes formed in deep crust and upper mantle regions. 相似文献
4.
The polarized single-crystal Raman spectra of synthetic H2O-containing alkali-free beryl were recorded at room and low temperatures, and the polarized single-crystal IR spectra at
room temperature. The H2O molecule in the channel cavities is characterized by a Raman-active symmetric stretching vibration (ν1) at 3607 cm−1 and an IR-active asymmetric stretch (ν3) at 3700 cm−1 at room temperature. At low temperatures this ν3 mode is observed in the Raman. Weak ν1 and ν3 modes of a second type of H2O are also observed in the Raman spectra but only at 5 K. The H⋯·H vector of the most abundant type of H2O is parallel to the channel axis of beryl along [0 0 0 1]. The components of the polarizability tensor of the ν1 mode of H2O are similar to, but not exactly the same as, those of a free H2O molecule. The Raman measurements indicate that the H2O molecule is rotationally disordered around [0 0 0 1]. External translation and librational modes of H2O could be observed as overtones with the internal H2O-stretching modes. In the case of the librational motions, normal modes could also be observed directly in the Raman spectra
at ∼200 cm−1. The energies of the translational modes can be determined from an analysis of the overtones and are about 9 cm−1 in energy (i.e., Tz). The energies of the librational modes are about 210 cm−1 for Rx and 190 cm−1 for Ry.
Received: 8 April 1999 / Accepted: 5 April 2000 相似文献
5.
Sigurdur Jakobsson 《Contributions to Mineralogy and Petrology》1997,127(1-2):129-135
The concentrations of water and carbon dissolved in an icelandite glass quenched from 1400 °C and 10 kbar were measured using
Fourier transform infra-red spectroscopy and elemental analyses of carbon and hydrogen. Only carbon dioxide and water were
observed in the fluid phase as analysed after quenching with a qudrupole mass analyser. The mole fraction of carbon dioxide
in the fluid phase ranged from 0.36 to 0.95. Carbon is dissolved as carbonate except at the highest CO2 fluid fugacity, where a small amount of molecular CO2 is observed. Dissolved carbon in the glasses, calculated as CO2, remained constant at approximately 1 wt %, in spite of the different CO2 fluid fugacities. Water was dissolved as molecular water and as hydroxyl groups, the hydroxyl concentration in the quenched
glasses remaining almost constant over the whole interval, whereas the molecular water dissolves in accordance with Henry's
law. Molecular water peaks at 5200␣cm−1 and 1630 cm−1, the hydroxyl peak at 4500␣cm−1, and the carbonate peaks at 1400 cm−1–1550 cm−1 have been calibrated using elemental analyses of C and H in the quenched glasses. As molecular water decreases in the melt
the higher wavenumber carbonate peak is observed to move towards the molecular water peak at 1630 cm−1 causing a split of the carbonate peaks, ranging from 45 cm−1 to 100 cm−1.
Received: 15 November 1995 / Accepted: 21 September 1996 相似文献
6.
Anton Beran Dominik Talla Zdenek Losos Jiri Pinkas 《Physics and Chemistry of Minerals》2010,37(3):159-166
The infrared (IR) spectra of gem-quality baryte crystals from different occurrences are characterized by relatively weak but
strongly pleochroic absorption bands at 3,280, 3,220, 3,155, and 3,115 cm−1. These bands are assigned to anti-symmetric and symmetric OH stretching vibrations of two types of H2O molecules localized on vacant Ba sites. The H–H axis of the H2O I molecule is slightly tilted from the a-axis direction, its twofold axis being nearly parallel to the b-axis, thus defining the plane of the H2O molecule practically parallel to (001). The H2O II molecule has its H–H axis parallel to the b-axis direction, with its plane lying approximately parallel to (101). The values of the total water contents of the baryte
crystals, calculated on the basis of IR spectroscopic data, are ranging from about 1.7–3.8 wt.ppm. The possible presence of
H3O+ ions is also discussed. 相似文献
7.
Cordierite precursors were prepared by a sol-gel process using tetraethoxysilane, aluminum sec.-butoxide, and Mg metal flakes
as starting materials. The precursors were treated by 15-h heating steps in intervals of 100 °C from 200 to 900 °C; they show
a continuous decrease in the analytical water content with increasing preheating temperatures. The presence of H2O and (Si,Al)–OH combination modes in the FTIR powder spectra prove the presence of both H2O molecules and OH groups as structural components, with invariable OH concentrations up to preheating temperatures of 500
°C. The deconvolution of the absorptions in the (H2O,OH)-stretching vibrational region into four bands centred at 3584, 3415, 3216 and 3047 cm−1 reveals non-bridging and bridging H2O molecules and OH groups. The precursor powders remain X-ray amorphous up to preheating temperatures of 800 °C. Above this
temperature the precursors crystallize to μ-cordierite; at 1000 °C the structure transforms to α-cordierite. Close similarities
exist in the pattern of the 1400–400 cm−1 lattice vibrational region for precursors preheated up to 600 °C. Striking differences are evident at preheating temperatures
of 800 °C, where the spectrum of the precursor powder corresponds to that of conventional cordierite glass. Bands centred
in the “as-prepared” precursor at 1137 and 1020 cm−1 are assigned to Si–O-stretching vibrations. A weak absorption at 872 cm−1 is assigned to stretching modes of AlO4 tetrahedral units and the same assignment holds for a band at 783 cm−1 which appears in precursors preheated at 600 °C. With increasing temperatures, these bands show a significant shift to higher
wavenumbers and the Al–O stretching modes display a strong increase in their intensities. (Si,Al)–O–(Si,Al)-bending modes
occur at 710 cm−1 and the band at 572 cm−1 is assigned to stretching vibrations of AlO6 octahedral units. A strong band around 440 cm−1 is essentially attributed to Mg–O-stretching vibrations. The strongly increasing intensity of the 872 and 783 cm−1 bands demonstrates a clear preference of Al for a fourfold-coordinated structural position in the precursors preheated at
high temperatures. The observed band shift is a strong indication for increasing tetrahedral network condensation along with
changes in the Si–O and Al–O distances to tetrahedra dimensions similar to those occurring in crystalline cordierite. These
structural changes are correlated to the dehydration process starting essentially above 500 °C, clearly demonstrating the
inhibiting role of H2O molecules and especially of OH groups.
Received: 1 March 2002 / Accepted: 26 June 2002 相似文献
8.
Relative humidity (
P\textH 2 \textO P_{{{\text{H}}_{ 2} {\text{O}}}} , partial pressure of water)-dependent dehydration and accompanying phase transitions in NAT-topology zeolites (natrolite,
scolecite, and mesolite) were studied under controlled temperature and known
P\textH 2 \textO P_{{{\text{H}}_{ 2} {\text{O}}}} conditions by in situ diffuse-reflectance infrared Fourier transform spectroscopy and parallel X-ray powder diffraction.
Dehydration was characterized by the disappearance of internal H2O vibrational modes. The loss of H2O molecules caused a sequence of structural transitions in which the host framework transformation path was coupled primarily
via the thermal motion of guest Na+/Ca2+ cations and H2O molecules. The observation of different interactions of H2O molecules and Na+/Ca2+ cations with host aluminosilicate frameworks under high- and low-
P\textH 2 \textO P_{{{\text{H}}_{ 2} {\text{O}}}} conditions indicated the development of different local strain fields, arising from cation–H2O interactions in NAT-type channels. These strain fields influence the Si–O/Al–O bond strength and tilting angles within and
between tetrahedra as the dehydration temperature is approached. The newly observed infrared bands (at 2,139 cm−1 in natrolite, 2,276 cm−1 in scolecite, and 2,176 and 2,259 cm−1 in mesolite) result from strong cation–H2O–Al–Si framework interactions in NAT-type channels, and these bands can be used to evaluate the energetic evolution of Na+/Ca2+ cations before and after phase transitions, especially for scolecite and mesolite. The 2,176 and 2,259 cm−1 absorption bands in mesolite also appear to be related to Na+/Ca2+ order–disorder that occur when mesolite loses its Ow4 H2O molecules. 相似文献
9.
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
10.
To interpret the degassing of F-bearing felsic magmas, the solubilities of H2O, NaCl, and KCl in topaz rhyolite liquids have been investigated experimentally at 2000, 500, and ≈1 bar and 700° to 975 °C.
Chloride solubility in these liquids increases with decreasing H2O activity, increasing pressure, increasing F content of the liquid from 0.2 to 1.2 wt% F, and increasing the molar ratio
of ((Al + Na + Ca + Mg)/Si). Small quantities of Cl− exert a strong influence on the exsolution of magmatic volatile phases (MVPs) from F-bearing topaz rhyolite melts at shallow
crustal pressures. Water- and chloride-bearing volatile phases, such as vapor, brine, or fluid, exsolve from F-enriched silicate
liquids containing as little as 1 wt% H2O and 0.2 to 0.6 wt% Cl at 2000 bar compared with 5 to 6 wt% H2O required for volatile phase exsolution in chloride-free liquids. The maximum solubility of Cl− in H2O-poor silicate liquids at 500 and 2000 bar is not related to the maximum solubility of H2O in chloride-poor liquids by simple linear and negative relationships; there are strong positive deviations from ideality
in the activities of each volatile in both the silicate liquid and the MVP(s). Plots of H2O versus Cl− in rhyolite liquids, for experiments conducted at 500 bar and 910°–930 °C, show a distinct 90° break-in-slope pattern that
is indicative of coexisting vapor and brine under closed-system conditions. The presence of two MVPs buffers the H2O and Cl− concentrations of the silicate liquids. Comparison of these experimentally-determined volatile solubilities with the pre-eruptive
H2O and Cl− concentrations of five North American topaz and tin rhyolite melts, determined from melt inclusion compositions, provides
evidence for the exsolution of MVPs from felsic magmas. One of these, the Cerro el Lobo magma, appears to have exsolved alkali
chloride-bearing vapor plus brine or a single supercritical fluid phase prior to entrapment of the melt inclusions and prior
to eruption.
Received: 6 November 1995 / Accepted: 29 January 1998 相似文献
11.
S. Karampelas E. Fritsch T. Zorba K. M. Paraskevopoulos S. Sklavounos 《Mineralogy and Petrology》2005,85(1-2):45-52
Summary The infrared absorption spectrum of amethyst in the region of stretching vibrations of X–OH groups reveals several bands that
have been used for the separation of natural from synthetic amethyst. The intensity and shape of these bands have been measured
as a function of crystallographic orientation. Using a resolution of 0.5 cm−1 the 3595 cm−1 band is present in all infrared spectra of natural amethyst and in some rare synthetic ones. If present in synthetic amethyst,
its full width at half maximum (FWHM) is about 7 cm−1 whereas it is about 3 cm−1 in all natural samples. This new criterion, unlike the previous ones, seems appropriate to separate natural from synthetic
amethyst in all cases. 相似文献
12.
Cyril Aubaud Marc M. Hirschmann Anthony C. Withers Richard L. Hervig 《Contributions to Mineralogy and Petrology》2008,156(5):607-625
To understand partitioning of hydrogen between hydrous basaltic and andesitic liquids and coexisting clinopyroxene and garnet,
experiments using a mid-ocean ridge basalt (MORB) + 6 wt.% H2O were conducted at 3 GPa and 1,150–1,325°C. These included both isothermal and controlled cooling rate crystallization experiments,
as crystals from the former were too small for ion microprobe (SIMS) analyses. Three runs at lower bulk water content are
also reported. H2O was measured in minerals by SIMS and in glasses by SIMS, Fourier Transform infrared spectroscopy (FTIR), and from oxide
totals of electron microprobe (EMP) analyses. At 3 GPa, the liquidus for MORB with 6 wt.% H2O is between 1,300 and 1,325°C. In the temperature interval investigated, the melt proportion varies from 100 to 45% and the
modes of garnet and clinopyroxene are nearly equal. Liquid composition varies from basaltic to andesitic. The crystallization
experiments starting from above the liquidus failed to nucleate garnets, but those starting from below the liquidus crystallized
both garnet and clinopyroxene. SIMS analyses of glasses with >7 wt.% H2O yield spuriously low concentrations, perhaps owing to hydrogen degassing in the ultra-high vacuum of the ion microprobe
sample chamber. FTIR and EMP analyses show that the glasses have 3.4 to 11.9 wt.% water, whilst SIMS analyses indicate that
clinopyroxenes have 1,340–2,330 ppm and garnets have 98–209 ppm H2O. D
H
cpx−gt is 11 ± 3, D
H
cpx−melt is 0.023 ± 0.005 and D
H
gt−melt is 0.0018 ± 0.0006. Most garnet/melt pairs have low values of D
H
gt−melt, but D
H
gt−melt increases with TiO2 in the garnet. As also found by previous studies, values of D
H
cpx−melt increase with Al2O3 of the crystal. For garnet pyroxenite, estimated values of D
H
pyroxenite−melt decrease from 0.015 at 2.5 GPa to 0.0089 at 5 GPa. Hydration will increase the depth interval between pyroxenite and peridotite
solidi for mantle upwelling beneath ridges or oceanic islands. This is partly because the greater pyroxene/olivine ratio in
pyroxenite will tend to enhance the H2O concentration of pyroxenite, assuming that neighboring pyroxenite and peridotite bodies have similar H2O in their pyroxenes.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
13.
The diffusivity of water has been investigated for a haplogranitic melt of anhydrous composition Qz28Ab38Or34 (in wt %) at temperatures of 800–1200°C and at pressures of 0.5–5.0 kbar using the diffusion couple technique. Water contents
of the starting glass pairs varied between 0 and 9 wt %. Concentration-distance profiles for the different water species (molecular
water and hydroxyl groups) were determined by near-infrared microspectroscopy. Because the water speciation of the melt is
not quenchable (Nowak 1995; Nowak and Behrens 1995; Shen and Keppler 1995), the diffusivities of the individual species can
not be evaluated directly from these profiles. Therefore, apparent chemical diffusion coefficients of water (D
water) were determined from the total water profiles using a modified Boltzmann-Matano analysis. The diffusivity of water increases
linearly with water content <3 wt % but exponentially at higher water contents. The activation energy decreases from 64 ± 10 kJ/mole
for 0.5 wt % water to 46 ± 5 kJ/mole for 4 wt % water but remains constant at higher water contents. A small but systematic
decrease of D
water with pressure indicates an average activation volume of about 9 cm3/mole. The diffusivity (in cm2/s) can be calculated for given water content (in wt %), T (in K) and P (in kbar) by
in the ranges 1073 K ≤ T ≤ 1473 K; 0.5 kbar ≤ P≤ 5␣kbar; 0.5 wt % ≤ C
water ≤ 6 wt %. The absence of alkali concentration gradients in the glasses after the experiments shows that interdiffusion of
alkali and H+ or H3O+ gives no contribution to the transport of water in aluminosilicate melts. The H/D interdiffusion coefficients obtained at
800°C and 5 kbar using glass pieces with almost the same molar content of either water or deuterium oxide are almost identical
to the chemical diffusivities of water. This indicates that protons are transported by the neutral component H2O under these conditions.
Received: 26 March 1996 / Accepted: 23 August 1996 相似文献
14.
Monika Koch-Müller Stanislav S. Matsyuk Dieter Rhede Richard Wirth Natasha Khisina 《Physics and Chemistry of Minerals》2006,33(4):276-287
The incorporation of hydrogen in mantle olivine xenocrysts from the Udachnaya kimberlite pipe was investigated by Fourier-transform infrared spectroscopy and secondary ion mass spectrometry (SIMS). IR spectra were collected in the OH stretching region on oriented single crystals using a conventional IR source at ambient conditions and in situ at temperatures down to −180°C as well as with IR synchrotron radiation. The IR spectra of the samples are complex containing more than 20 strongly polarized OH bands in the range 3,730–3,330 cm−1. Bands at high energies (3,730–3,670 cm−1) were assigned to inclusions of serpentine, talc and the 10 Å phase. All other bands are believed to be intrinsic to olivine. The corresponding point defects are (a) associated with vacant Si sites (3,607 cm−1 E || a, 3,597 E || a, 3,571 cm−1 E || c, 3,567 E || c, and 3,556 E || b), and (b) with vacant M1 sites (most of the bands polarized parallel to a). From the pleochroic behavior and position of the OH bands associated with the vacant M1 sites, we propose two types of hydrogen—one bonded to O1 and another to O2, so that both OH vectors are strongly aligned parallel to a. The O2–H groups may be responsible for the OH bands at higher wavenumbers than those for the O1–H groups. The multiplicity of the corresponding OH bands in the spectra can be explained by different chemical environments and by slightly different distortions of the M1 sites in these high-pressure olivines. Four samples were investigated by SIMS. The calculated integral molar absorption coefficient using the IR and SIMS results of 37,500±5,000 L mol H2O cm−2 is within the uncertainties slightly higher than the value determined by Bell et al. (J Geophys Res 108(B2):2105–2113, 2003) (28,450±1,830 L mol H2O cm−2). The reason for the difference is the different distributions of the absorption intensity of the spectra of both studies (mean wavenumber 3,548 vs. 3,570 cm−1). Olivine samples with a mean wavenumber of about 3,548 cm−1 should be quantified with the absorption coefficient as determined in this study; those containing more bands at higher wavenumber (mean wavenumber 3,570 cm−1) should be quantified using the value determined by Bell et al. (J Geophys Res 108(B2):2105–2113, 2003).
相似文献
Monika Koch-MüllerEmail: Phone: +49-331-2881492 |
15.
One well-defined OH Raman band at 3651 ± 1 cm−1 and one weak feature near 3700 ± 5 cm−1 are recognized for the hydrous γ-phase of Mg2SiO4. Like the hydrous β-phase, the H2O content in the γ-phase shifts most of the corresponding silicate modes towards lower frequencies. Variations in Raman spectra
of the hydrous γ-phase were investigated up to about 200 kbar at room temperature and in the range 81–873 K at atmospheric pressure. Unlike
the anhydrous γ-phase, which remains intact up to at least 873 K, the hydrous γ-phase sometimes converts to a defective forsterite structure above 800 K. Although the hydrous γ-phase remains intact up to at least 800 K, Raman signals of the OH bands disappear completely above 423 K. The Raman frequency
of the well-defined OH band decreases linearly with increasing temperature between 81 and 423 K. In the region of the silicate
vibrations, the Raman frequencies of the two most intense bands increase nonlinearly with increasing pressure, and decrease
with increasing temperature. The frequencies for all other weak bands, however, decreased linearly with increasing temperature.
The latter most likely reflects the larger scatter of the data for the weak bands.
Received: 27 April 2001 / Accepted: 12 September 2001 相似文献
16.
Diffusion of water was experimentally investigated for melts of albitic (Ab) and quartz-orthoclasic (Qz29Or71, in wt %) compositions with water contents in the range of 0 to 8.5 wt % at temperatures of 1100 to 1200 °C and at pressures
of 1.0 and 5.0 kbar. Apparent chemical diffusion coefficients of water (D
water) were determined from concentration-distance profiles measured by FTIR microspectroscopy. Under the same P-T condition and water content the diffusivity of water in albitic, quartz-orthoclasic and haplogranitic (Qz28Ab38 Or34, Nowak and Behrens, this issue) melts is identical within experimental error. Comparison to data published in literature
indicates that anhydrous composition only has little influence on the mobility of water in polymerized melts but that the
degree of polymerization has a large effect. For instance, Dwater is almost identical for haplogranitic and rhyolitic melts with 0.5–3.5 wt % water at 850 °C but it is two orders of magnitude
higher in basaltic than in haplogranitic melts with 0.2–0.5 wt % water at 1300 °C. Based on the new water diffusivity data,
recently published in situ near-infrared spectroscopic data (Nowak 1995; Nowak and Behrens 1995), and viscosity data (Schulze et al. 1996) for hydrous
haplogranitic melts current models for water diffusion in silicate melts are critically reviewed. The NIR spectroscopy has
indicated isolated OH groups, pairs of OH groups and H2O molecules as hydrous species in polymerized silicate melts. A significant contribution of isolated OH groups to the transport
of water is excluded for water contents above 10 ppm by comparison of viscosity and water diffusion data and by inspection
of concentration profiles from trace water diffusion. Spectroscopic measurements have indicated that the interconversion of
H2O molecules and OH pairs is relatively fast in silicate glasses and melts even at low temperature and it is inferred that
this reaction is an active step for migration of water. However, direct jumps of H2O molecules from one cavity within the silicate network to another one can not be excluded. Thus, we favour a model in which
water migrates by the interconversion reaction and, possibly, small sequences of direct jumps of H2O molecules. In this model, immobilization of water results from dissociation of the OH pairs. Assuming that the frequency
of the interconversion reaction is faster than that of diffusive jumps, OH pairs and water molecules can be treated as a single
diffusing species having an effective diffusion coefficient . The shape of curves of Dwater versus water content implies that increases with water content. The change from linear to exponential dependence of Dwater between 2 and 3 wt % water is attributed to the influence of the dissociation reaction at low water content and to the modification
of the melt structure by incorporation of OH groups.
Received: 26 March 1996 / Accepted: 23 August 1996 相似文献
17.
Hydroxyl defects in garnets from mantle xenoliths in kimberlites of the Siberian platform 总被引:12,自引:0,他引:12
A suite of more than 200 garnet single crystals, extracted from 150 xenoliths, covering the whole range of types of garnet
parageneses in mantle xenoliths so far known from kimberlites of the Siberian platform and collected from nearly all the kimberlite
pipes known in that tectonic unit, as well as some garnets found as inclusions in diamonds and olivine megacrysts from such
kimberlites, were studied by means of electron microprobe analysis and single-crystal IR absorption spectroscopy in the v
OH vibrational range in search of the occurrence, energy and intensity of the v
OH bands of hydroxyl defects in such garnets and its potential use in an elucidation of the nature of the fluid phase in the
mantle beneath the Siberian platform. The v
OH single-crystal spectra show either one or a combination of two or more of the following major v
OH bands, I 3645–3662 cm−1, II 3561–3583 cm−1, III 3515–3527 cm−1, and minor bands, Ia 3623–3631 cm−1, IIa 3593–3607 cm−1. The type of combination of such bands in the spectrum of a specific garnet depends on the type of the rock series of the
host xenolith, Mg, Mg-Ca, Ca, Mg-Fe, or alkremite, on the xenolith type as well as on the chemical composition of the respective
garnet. Nearly all garnets contain band systems I and II. Band system III occurs in Ti-rich garnets, with wt% TiO2 > ca. 0.4, from xenoliths of the Mg-Ca and Mg-Fe series, only. The v
OH spectra do not correspond to those of OH− defects in synthetic pyropes or natural ultra-high pressure garnets from diamondiferous metamorphics. There were no indications
of v
OH from inclusions of other minerals within the selected 60 × 60 μm measuring areas in the garnets. The v
OH spectra of pyrope-knorringite- and pyrope-knorringite-uvarovite-rich garnets included in diamonds do not show band systems
I to III. Instead, they exhibit one weak, broad band (Δv
OH 200–460 cm−1) near 3570 cm−1, a result that was also obtained on pyrope-knorringite-rich garnets extracted from two olivine megacrysts. The quantitative
evaluation, on the basis of relevant existing calibrational data (Bell et al. 1995), of the sum of integral intensities of
all v
OH bonds of the garnets studied yielded a wide range of “water” concentrations within the set of the different garnets, between
values below the detection limit of our single-crystal IR method, near 2 × 10−4 wt%, up to 163 × 10−4 wt%. The “water” contents vary in a complex manner in garnets from different xenolith types, obviously depending on a large
number of constraints, inherent in the crystal chemistry as well as the formation conditions of the garnets during the crystallization
of their mantle host rocks. Secondary alteration effects during uplift of the kimberlite, play, if any, only a minor role.
Despite the very complex pattern of the “water” contents of the garnets, preventing an evaluation of a straightforward correlation
between “water” contents of the garnets and the composition of the mantle's fluid phase during garnet formation, at least
two general conclusions could be drawn: (1) the wide variation of “water” contents in garnets is not indicative of regional
or local differences in the composition of the mantle's fluid phase; (2) garnets formed in the high-pressure/high-temperature
diamond-pyrope facies invariably contain significantly lower amounts of “water” than garnets formed under the conditions of
the graphite-pyrope facies. This latter result (2) may point to significantly lower f
H2O and f
O2 in the former as compared to the latter facies.
Received: 25 November 1997 / Accepted: 9 March 1998 相似文献
18.
Pierre Agrinier Nathalie Jendrzejewski 《Contributions to Mineralogy and Petrology》2000,139(3):265-272
The Beer–Lambert law is traditionally used to determine water and carbon concentrations in glasses from their infrared (IR)
spectra. In practice, this method requires estimation of the thickness and density of the glass as well as the calibration
of the molecular absorptivities of the species concerned. All of these parameters can be sources of practical difficulties
and analytical uncertainty. These weaknesses in the application of the Beer–Lambert law have been overcome by an empirical
analysis of the infrared spectra. Using a set of 292 spectra obtained on 113 natural and experimental tholeiitic glasses (SiO2 48.5–51 wt%; water contents 0–4000 ppm H2O), it can be shown that the thickness–density (ρ d) product of a glass sample can be directly and reliably inferred from
its IR spectrum. This allows the Beer–Lambert law to be rewritten. The new form no longer requires thickness or density estimations
to determine volatile contents. Moreover, if needed, the thickness of the glass slab can also be accurately determined from
the IR spectra. This new method is developed for quantitative determination of water concentrations in MORB glasses but can
also be applied to any minor species (carbon, sulfur, etc.) provided it is active in the IR domain and that a suitable independent
frequency of IR absorption can be identified. Precision is about 60 ppm H2O on O–H− contents. This method, tested on natural and experimental MORB-type glasses, can be applied to any chemical composition provided
a set of reference spectra is available.
Received: 16 September 1999 / Accepted: 18 February 2000 相似文献
19.
A. N. Platonov A. N. Tarashchan K. Langer M. Andrut G. Partzsch S. S. Matsyuk 《Physics and Chemistry of Minerals》1998,25(3):203-212
A selected set of five different kyanite samples was analysed by electron microprobe and found to contain chromium between <0.001 and 0.055 per formula unit (pfu). Polarized electronic absorption spectroscopy on oriented single crystals,
R1, R2-sharp line luminescence and spectra of excitation of λ3- and λ4-components of R1-line of Cr3+-emission had the following results: (1) The Fe2+–Ti4+ charge transfer in c-parallel chains of edge connected M(1) and M(2) octahedra shows up in the electronic absorption spectra
as an almost exclusively c(||Z′)-polarized, very strong and broad band at 16000 cm−1 if <, in this case the only band in the spectrum, and at an invariably lower energy of 15400 cm−1 in crystals with ≥ . The energy difference is explained by an expansion of the Of–Ok, and Ob–Om edges, by which the M(1) and M(2) octahedra are interconnected (Burnham 1963), when Cr3+ substitutes for Al compared to the chromium-free case. (2) The Cr3+ is proven in two greatly differing crystal fields a and b, giving rise to two sets of bands, derived from the well known
dd transitions of Cr3+
4A2g→4T2g(F)(I), →4T1g(F)(II), and →4T1g(P)(III). Band energies in the two sets a and b, as obtained by absorption, A, and excitation, E, agree well: I: 17300(a, A),
17200(a, E), 16000(b, A), 16200(b, E); II: 24800(a, A), 24400(a, E); 22300(b, A), 22200(b, E); III: 28800(b,A) cm−1. Evaluation of crystal field parameters from the bands in the electronic spectra yield Dq(a)=1730 cm−1, Dq(b)=1600 cm−1, B(a)=790 cm−1, B(b)=620 cm−1 (errors ca. ±10 cm−1), again in agreement with values extracted from the λ3, λ4 excitation spectra. The CF-values of set a are close to those typical of Cr3+ substituting for Al in octahedra of other silicate minerals without constitutional OH− as for sapphirine, mantle garnets or beryl, and are, therefore, interpreted as caused by Cr3+ substituting for Al in some or all of the M(1) to M(4) octaheda of the kyanite structure, which are crystallographically
different but close in their mean Al–O distances, ranging from 1.896 to 1.919 A (Burnham 1963), and slight degrees of distortion.
Hence, band set a originates from substitutive Cr3+ in the kyanite structural matrix. The CF-data of Cr3+ type b, expecially B, resemble those of Cr3+ in oxides, especially of corundum type solid solutions or eskolaite. This may be interpreted by the assumption that a fraction
of the total chromium contents might be allocated in a precursor of a corundum type exsolution.
Received: 3 January 1997 / Revised, accepted: 2 May 1997 相似文献
20.
A. K. Kleppe A. P. Jephcoat H. Olijnyk A. E. Slesinger S. C. Kohn B. J. Wood 《Physics and Chemistry of Minerals》2001,28(4):232-241
Raman spectra of hydrous β-Mg2SiO4 (1.65 wt% H2O) have been measured in a diamond-anvil cell with helium as a pressure-transmitting medium at room temperature to 50 GPa.
We observe three OH-stretching modes, a doublet with components at 3329 and 3373 cm−1, which decrease linearly with pressure, and a single mode at 3586 cm−1, which remains nearly constant up to 24 GPa before decreasing at higher pressures. Assessment of the mode frequencies and
their pressure dependence, together with previous results from X-ray and IR data, are consistent with protonation of the O1
site in agreement with previous studies. Strict assignment of Raman activity awaits detailed structural models. The nature
of the protonation in wadsleyite may require more specific experimental probes for full solution of the hydrogen-site problem.
Received: 18 July 2000 / Accepted: 22 November 2000 相似文献