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1.
Dagma Derdau Robert Freer Kate Wright 《Contributions to Mineralogy and Petrology》1998,133(1-2):199-204
Oxygen exchange experiments have been performed between single crystals of sanidine feldspar and oxygen gas enriched in 18O, at temperatures in the range 869–1053 °C, total pressure 1 atmosphere, for times up to 28 days. Oxygen isotope diffusion
profiles in a direction perpendicular to (001) were determined with an ion microprobe. The experimental data obey a single
Arrhenius relationship of the form D = 8.4 × 10−11 exp. (−245 ± 15 kJ mol−1/RT) m2s−1. The results indicate that oxygen diffusion in anhydrous sanidine feldspar is marginally slower than oxygen diffusion in
anhydrous anorthite. Comparison with published atomistic simulation studies suggests that oxygen transport in feldspar is
by an interstitial mechanism.
Received: 17 October 1997 / Accepted: 6 July 1998 相似文献
2.
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
3.
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
4.
Stichtite, a rare (14 known localities worldwide) hydrated carbonate-hydroxide of Mg and Cr with ideal formula Mg6Cr2 (OH)16 CO3 · 4H2O, occurs exclusively in Cr-rich serpentinites of ophiolites or greenstone belts. Physical properties (hardness = 1.5–2, specific
gravity = 2.16–2.2, perfect basal [0001] cleavage, grain size commonly < 100 μm) resemble talc, but the mineral has an attractive
purple to lilac color; chemical analyses demonstrate it to be a non-silicate. Stichtite generally occurs as irregular to rounded
masses (< 1 cm – 30 cm across) and as veinlets (< 1 mm – > 2 cm wide) within serpentinite. Macroscopic and microscopic textures,
such as crosscutting veinlets and stringers, demonstrate that stichtite formation invariably post-dated serpentinization.
In some specimens stichtite surrounds relict grains of Cr-rich spinel; in others stichtite has completely replaced euhedral
or subhedral chromites. Chemical analyses of stichtites reveal substantial substitution of Al and Fe3+ for Cr in specimens from many localities, reflecting a possible compositional continuum between stichtite and rhombohedral
polymorphs hydrotalcite (Mg6Al2 (OH)16 CO3 · 4H2O) and pyroaurite (Mg6Fe2 (OH)16 CO3 · 4H2O). We report the first electron microprobe analyses of stichtites from seven localities, and summarize all available published
chemical data. Stichtites very likely inherited part of their trivalent cation chemistry from precursor Cr-rich spinels, but
stichtite growth apparently post-dated characteristic “ferritchromit” alteration, as demonstrated by the depletion of Al and
enrichment in Fe3+ in stichtite relative to primary chromite core compositions. Stichtite appears to form by reaction between serpentine and
altered chromite, during addition of substantial fluid, either as separate H2O and CO2 phases, or as a mixed volatile phase. Such reactions must involve removal of substantial SiO2, possibly by transport and remote deposition of silica by throughgoing aqueous and carbonic fluid.
Received: 4 April 1996 / Accepted: 16 September 1996 相似文献
5.
Assessment of natural attenuation of aromatic hydrocarbons in groundwater near a former manufactured-gas plant, South Carolina, USA 总被引:1,自引:0,他引:1
J. E. Landmeyer F. H. Chapelle M. D. Petkewich P. M. Bradley 《Environmental Geology》1998,34(4):279-292
Shallow, anaerobic groundwater near a former manufactured-gas plant (MGP) in Charleston, South Carolina, USA, contains mono-
and polycyclic aromatic hydrocarbons (MAHs and PAHs, respectively). Between 1994 and 1997, a combination of field, laboratory,
and numerical-flow and transport-model investigations were made to assess natural attenuation processes affecting MAH and
PAH distributions. This assessment included determination of adsorption coefficients (K
ad
) and first-order biodegradation rate constants (K
bio
) using aquifer material from the MGP site and adjacent properties. Naphthalene adsorption (K
ad
=1.35×10–7 m3/mg) to aquifer sediments was higher than toluene adsorption (K
ad
=9.34×10–10 m3/mg), suggesting preferential toluene transport relative to naphthalene. However, toluene and benzene distributions measured
in January 1994 were smaller than the naphthalene distribution. This scenario can be explained, in part, by the differences
between biodegradation rates of the compounds. Aerobic first-order rate constants of 14C-toluene, 14C-benzene, and 14C-naphthalene degradation were similar (–0.84, –0.03, and 0.88 day–1, respectively), but anaerobic rate constants were higher for toluene and benzene (–0.002 and –0.00014 day–1, respectively) than for naphthalene (–0.000046 day–1). Both areal and cross-sectional numerical simulations were used to test the hypothesis suggested by these rate differences
that MAH compounds will be contained relative to PAHs. Predictive simulations indicated that the distributions of toluene
and benzene reach steady-state conditions before groundwater flow lines discharge to an adjacent surface-water body, but do
discharge low concentrations of naphthalene. Numerical predictions were "audited" by measuring concentrations of naphthalene,
toluene, and benzene at the site in early 1997. Measured naphthalene and toluene concentrations were substantially reduced
and the areal extent of contamination smaller than was both observed in January 1994 and predicted for 1997. Measured 1997
benzene concentrations and distribution were shown to be relatively unchanged from those measured in 1994, and similar to
predictions for 1997.
Received: 26 June 1997 · Accepted: 25 August 1997 相似文献
6.
M. Liu J. C. Peterson Richard A. Yund 《Contributions to Mineralogy and Petrology》1997,126(3):217-223
The growth rates of albite and pyroxene (enstatite + diopside + spinel) reaction rims were measured at 1000°C and ˜700 MPa
and found to be parabolic indicating diffusion-controlled growth. The parabolic rate constants for the pyroxene (+ spinel)
rims in samples with 0.5 wt% H2O added or initially vacuum dried at 25°C and 250°C are 1.68 ± 0.09, 0.54 ± 0.05 and 0.25 ± 0.06 μm2/h, respectively. The values for albite rim growth in samples initially dried at 60°C and with 0.1 wt% H2O added are 0.25 ± 0.04 and 0.33 ± 0.03 μm2/h, respectively. The latter values were used to derive the product of the grain boundary diffusion coefficient D′A, where A = SiO2, NaAlO2, or NaAlSi−1, and the grain boundary thickness δ in albite. The calculated D′SIO2δ in the albite aggregate for the situations of two different water contents are about 9.9 × 10−23 and 1.4 × 10−22 m3 s−1, respectively. Both the rate constants and the calculated D′Aδ demonstrate that the effect of water content on the grain boundary diffusion rate in monomineralic albite and polymineralic
pyroxene (+ spinel) aggregates is small, consistent with recent studies of monomineralic enstatite and forsterite rims.
Received: 1 July 1995 / Accepted: 1 August 1996 相似文献
7.
Craig S. Schwandt Randall T. Cygan Henry R. Westrich 《Contributions to Mineralogy and Petrology》1998,130(3-4):390-396
Magnesium self-diffusion coefficients were determined experimentally for diffusion parallel to each of the three crystallographic
directions in natural orthoenstatite (En88Fs12). Experiments were conducted at 1 atm in CO-CO2 gas mixing furnaces, which provided oxygen fugacities equivalent to the iron-wüstite buffer. Diffusion of 25Mg was induced in polished samples of oriented orthoenstatite using a film of isotopically enriched 25MgO as the source material. Very short (<0.15 μm) diffusional penetration profiles were measured by ion microprobe depth profiling.
The diffusion coefficients determined for four temperatures (900, 850, 800, 750 °C) provide the activation energies, E
a
, and frequency factors, D
o, where D = D
o exp (−E
a
/RT) for Mg self-diffusion parallel to each crystallographic direction: a-axis, E
a
= 360 ± 52 kJ/mole and D
o = 1.10 × 10−4 m2/s; b-axis, E
a
= 339 ± 77 kJ/mole and D
o = 6.93 × 10−6 m2/s and c-axis, E
a
= 265 ± 66 kJ/mole and D
o = 4.34 × 10−9 m2/s. In this temperature range, any possible anisotropy of cation diffusion is very small, however the activation energy for
diffusion parallel to the c-axis (001) is the lowest and the activation energies for diffusion parallel to the a-axis (100) and b-axis (010) are higher. Application of these diffusion results to the silicate phases of the Lowicz mesosiderite meteorite
provides cooling rates for the silicate portion of the meteorite (4–11 °C/100 years) that are similar, although slower, to
previous estimates. These silicate cooling rates are still several orders of magnitude faster than the cooling rates (0.1 °C/106 years) for the metal portions.
Received: 22 January 1997 / Accepted: 2 October 1997 相似文献
8.
The Janggun iron deposits, Republic of␣Korea, occur as lens-shaped magnesian skarn, magnetite and base-metal sulfide orebodies
developed in the Cambrian Janggun Limestone Formation. Mineralization stage of the deposits can be divided into two separate
events. The skarn stage (107 Ma) consists of magnetite, pyrrhotite, base-metal sulfides, carbonates and magnesian skarn minerals.
The hydrothermal stage (70 Ma) consists of base-metal sulfides, native bismuth, bismuthinite, tetrahedrite, boulangerite,
bournonite and stannite. Mineral assemblages, chemical compositions and thermodynamic considerations indicate that formation
temperatures, −log fs2 and −log fo2 values of ore fluids from the skarn stage were 433 to 345 °C, 8.1 to 9.7 bar and 29.4 to 31.6 bar, and the hydrothermal stage
was 245 to 315 °C, 10.4 to 13.2 bar and 33.6 to 35.4 bar, respectively. Thermochemical considerations indicate that the XCO2 during magnesian skarnization ranged from 0.06 to 0.09, and the activity of H+ presumably decreased when the fluids equilibrated with host dolomitic limestone which resulted in a pH change from about
6.1 to 7.8, and decreases in fo2 and fs2. The δ34S values of ore sulfides have a wide range from 3.2 to 11.6 ‰ (CDT). Calculated 34SH2
S values of ore fluids are 2.9 to 5.4 ‰ (skarn stage) and 8.7 to 13.5 ‰ (hydrothermal stage). These are interpreted to represent
an initial deep-seated, igneous source of sulfur which gave way to influence of oxidized sedimentary sulfur to hydrothermal
stage. The δ13C values of carbonates in ores range from −4.6 to −2.5 ‰ (PDB). It is likely that carbon in the ore fluids was a mixture of
deep-seated magmatic carbon and dissolved carbon of dolomitic limestone. The δ18OH2
O and δD values (SMOW) of water in the ore fluids were 14.7 to 1.8 and −85 to −73 ‰ during the skarn stage and 11.1 to −0.2
and −87 to −80 ‰ in the hydrothermal stage.
Received: 5 March 1997 / Accepted: 28 August 1997 相似文献
9.
John Ayers 《Contributions to Mineralogy and Petrology》1998,132(4):390-404
Recently measured partition coefficients for Rb, Th, U, Nb, La (Ce), Pb, Sr, Sm, Zr, and Y between lherzolite assemblage
minerals and H2O-rich fluid (Ayers et al. 1997; Brenan et al. 1995a,b) are used in a two-component local equilibrium model to assess the
effects of interaction between slab-derived aqueous fluids and wedge lherzolite on the trace element and isotopic composition
of island arc basalts (IAB). The model includes four steps representing chemical processes, with each process represented
by one equation with one adjustable parameter, in which aqueous fluid: (1) separates from eclogite in the subducted slab (Rayleigh
distillation, mass fraction of fluid released F
fluid); (2) ascends through the mantle wedge in isolated packets, exchanging elements and isotopes with depleted lherzolite (zone
refining, the rock/fluid mass ratio n); (3) mixes with depleted lherzolite (physical mixing, the mass fraction of fluid in the mixture X
fluid); (4) induces melting to form primitive IAB (batch melting, mass fraction of melt F
melt). The amount of mantle lherzolite processed by the fluid in step (2) determines its isotopic and trace element signature
and the relative contributions of slab and wedge to primitive IAB. Assuming an average depleted lherzolite composition and
mineralogy (70% olivine, 26% orthopyroxene, 3% clinopyroxene and 1% ilmenite) and using nonlinear regression to adjust parameter
values to obtain an optimal fit to the average composition of IAB (McCulloch and Gamble 1991) yields values of F
fluid= 0.20, n= 26, X
fluid= 0.17, and F
melt= 0.15, with r
2= 0.995 and the average relative error in trace element concentration = 6%. The average composition of IAB can also effectively
be modeled with no contribution from the slab other than H2O (i.e., skip model step 1): n= 27, X
fluid= 0.21, F
melt= 0.17, with r
2= 0.992. By the time the fluid reaches the IAB source, exchange with depleted wedge lherzolite reduces the 87Sr/86Sr ratio isotopic composition to near-mantle values and the slab contribution to <50% for all but the most incompatible elements
(e.g., Pb). The IAB may retain the slab signature for elements such as B and Be that are highly incompatible and that have
very low concentrations in the depleted mantle wedge. The relatively high equilibrium D
mineral
/
fluid values measured by Ayers et al. (1997), Brenan et al. (1995a) and Stalder et al. (1998) suggest that large amounts of fluid
(>5 wt%) must be added to lherzolite in the IAB source. Decreasing X
fluid below 0.05 causes model results to have unacceptably high levels of error and petrologically unreasonable values of F
melt. That H2O contents of IAB are generally <6 wt% suggests that not all of the H2O that metasomatizes the IAB source remains in the source to dissolve in the subsequently formed melt. Modeling of the compositions
of specific primitive IAB from oceanic settings with low sediment input and depleted mantle wedges (Tonga, Marianas) shows
a generally lower level of fluid-wedge interaction (low n), and therefore a larger slab component in primitive IAB.
Received: 6 October 1997 / Accepted: 8 May 1998 相似文献
10.
Diffusion of tetravalent cations in zircon 总被引:18,自引:1,他引:18
D. J. Cherniak J. M. Hanchar E. B. Watson 《Contributions to Mineralogy and Petrology》1997,127(4):383-390
Diffusion rates for the three tetravalent cations U, Th and Hf have been measured in synthetic zircon. Diffusant sources
included oxide powders and ground pre-synthesized silicates. Rutherford backscattering spectrometry (RBS) was used to measure
depth profiles. Over the temperature range 1400–1650 °C, the following Arrhenius relations were obtained (diffusion coefficients
in m2sec−1):
log D
Th = (1.936 ± 0.9820) + (− 792 ± 34 kJ mol−1 /2.303 RT)
log D
U = (0.212 ± 2.440) + (− 726 ± 83 kJ mol−1 /2.303 RT)
log D
Hf = (3.206 ± 1.592) + (− 812 ± 54 kJ mol−1 /2.303 RT)
The data show a systematic increase in diffusivity with decreasing ionic radius (i.e., faster diffusion rates for Hf than
for U or Th), a trend also observed in our earlier study of rare earth diffusion in zircon. Diffusive fractionation may be
a factor in the Lu-Hf system given the much slower diffusion rates of tetravalent cations when compared with the trivalent
rare earths. The very slow diffusion rates measured for these tetravalent cations suggest that they are essentially immobile
under most geologic conditions, permitting the preservation of fine-scale chemical zoning and isotopic signatures of inherited
cores.
Received: 12 July 1996 / Accepted: 2 December 1996 相似文献
11.
Selenium (Se), an animal toxicant and aquifer contaminant, occurs in coal mine environments of Wyoming. There is a paucity
of information on solution-phase Se speciation in mine soils. The objectives of this study were to compare Se extraction efficiencies
of various reagents and to characterize SeO2–
3 (selenite), SeO2–
4 (selenate) and organic Se components in these extracts. Forty coal mine soils were extracted using DI (deionized) water,
hot water (0.1% CaCl2), AB-DTPA, NaOH, and KH2PO4. Each solution was analyzed for total dissolved Se, and inorganic and organic Se fractions. Both inorganic and organic Se
fractions were detected in the soil extracts. The order of Se (total, inorganic, and organic) extraction efficiency for different
reagents was DI water < hot water < AB-DTPA < NaOH < KH2PO4. The inorganic–organic Se ratios in DI water, hot water, AB-DTPA, NaOH, and KH2PO4 extracts were 60 : 40, 26 : 74, 61 : 39, 87 : 13, and 52 : 48, respectively, indicating predominance of inorganic Se in all
but the hot water extract. Selenite was the dominant inorganic species in AB-DTPA and KH2PO4 extracts, while SeO2–
4 was the major Se species in the DI water, hot water, and NaOH extracts. Significant correlations (P<0.01) were observed among extractable inorganic Se [NaOH and KH2PO4 (r=0.95); hot water and AB-DTPA (r=0.89)], total soluble Se [DI water with hot water (r=0.98) and AB-DTPA (r=0.95)], and Se species [SeO2–
3 in AB-DTPA with SeO2–
4 in NaOH (r=0.94) and SeO2–
3 in KH2PO4 (r=0.88)]. These correlations are indicative of Se extraction efficiency, thermodynamically predicted chemical transformations
(such as oxidation of SeO2–
3 to SeO2–
4), and probable interconversions between the organic and inorganic Se fractions (r=0.70 in KH2PO4 extracts); as a whole the correlations can be used as statistical validations of possible geochemical processes.
Received: 21 August 1995 · Accepted: 16 October 1995 相似文献
12.
The environmental conditions prevailing in the Chicam-Toctina drainage system (approx. 138 km2 in Córdoba, Argentina) are considered representative of a number of catchments in Argentina's Sierras Pampeanas Range. Two
groups of ions reflect the sources of dissolved species in the catchment: a) a group (Cl–, SO2–
4, and Na+) which recognizes natural and anthropogenic sources, and which exhibits significant correlations with N–
3 and NO–
2, and b) another group of components (Ca2+, Mg2+, and HCO–
3) which is clearly controlled by carbonate rocks and their waste rock products. In the headwaters, stockpiled marble quarry
mining wastes provide a more open system to CO2 gaseous exchange than the outcropping rocks, thus promoting the increase of carbonate dissolution (up to 4.88 g km–2 s–1 during the rainy season). This specific yield was 20% higher than the amount estimated for an area with fewer extended mining
activities. The dissolved load delivered by the upper reaches is subjected in the lower drainage area to various processes,
mainly controlled by the presence of the city of Alta Gracia (approx. 40,000 inhabitants). In the dry season, due to nutrient
inputs supplied by the city, photosynthetic activity plays a major role controlling stream pH. Hence, the high values of calcite
saturation indexes and the increase of CaCO3 concentration in bed sediments can be explained by calcite precipitation. Such a process could be accompanied by the coprecipitation
on calcium carbonate of low solubility heavy metal carbonates.
Received : 17 January 1997 · Accepted : 31 March 1997 相似文献
13.
George B. Morgan Antonio Acosta-Vigil David London 《Contributions to Mineralogy and Petrology》2008,155(2):257-269
This study examines the systematics and rate of alkali transport in haplogranite diffusion couples in which a chemical potential
gradient in Al is established between near water-saturated metaluminous and peraluminous liquids that differ only in their
initial content of normative corundum. At 800°C, measurable chemical diffusion of alkalis occurs throughout the entire length
(∼1 cm) of the diffusion couples in 2–6 h, indicating long range diffusive communication through melt. Alkali transport results
in homogenization of initially different Na/Al and ASI [=mol. Al2O3/(CaO + Na2O + K2O)] throughout the couples within ∼24 h, whereas initially homogenous K* evolves to become uniformly different between metaluminous
and peraluminous ends. Calculated effective binary diffusion coefficients for alkalis in experiments that do not significantly
violate the requirement of a semi-infinite chemical reservoir (0- to 2-h duration at 800°C) are similar to those observed
in previous studies: in the range of (1–8) × 10−12 m2/s. Such a magnitude of diffusivity, however, is inadequate to account for the observed changes of alkali concentrations and
molecular ratios throughout the couples in 2- to 6-h experiments. The latter changes are consistent with diffusivities estimated
via the x
2 = Dt approximation, which yields effective values around 10−9 m2/s. These observations suggest that Fick’s law alone does not adequately describe the diffusive transport of alkalis in granitic
liquids. In addition to simple ionic diffusion associated with local gradients in concentration or chemical potential of the
diffusing component described by Fick’s second law (local diffusion), alkali transport through melt involves system-wide diffusion (field diffusion) driven by chemical potential gradients that also include components with which the alkalis couple or complex (e.g., Al).
Field diffusion involves the coordinated migration of essentially all alkali cations, resembling a positive ionic current
that drives the system to a metastable state having a minimum energy configuration with respect to alkali distribution. The
net result is effective transport rates perhaps three orders of magnitude faster than simple local alkali diffusion, and at least seven to eight orders of magnitude faster than the diffusive equilibration of Al and Si. 相似文献
14.
I. M. Dwairi 《Environmental Geology》1998,34(1):1-4
The exchange and release properties of the natural phillipsite tuff from the Aritain area in Jordan were evaluated by studying
the exchange properties of this natural zeolite in the NH4
+–Na+ system. Exchange isotherms at 18, 35, and 50 °C showed that phillipsite exchanged NH4
+ preferably over Na+ at all temperatures. However, the selectivity coefficient for NH4
+ decreased with decreasing temperature. The release of NH4
+ from phillipsite saturated with ammonium sulfate took place in two stages characterized by different SO4
2– : NH4
+ ratios. Aritain phillipsite from NE Jordan could be processed and used as NH4
+ slow-release fertilizers. The use of NH4
+-phillipsite tuff offers an option to the widely used soluble NH4-fertilizers in agciculture to avoid environmental problems associated with nitrogen contamination of surface water and groundwater.
Received: 19 December 1996 · Accepted: 13 May 1997 相似文献
15.
Iron tracer diffusion experiments in diopside have been performed using natural and synthetic single crystals of diopside,
and stable iron tracers enriched in 54Fe, at temperatures in the range 950–1100 °C, total pressure 1 atm, for times up to 29 days. Iron isotope diffusion profiles
were determined with an ion microprobe. For experiments performed at log pO2 = −13, in directions parallel to the c axis and the b axis of two natural, low iron (Fe ∼ 1.8 at %) diopsides, the data obey
a single Arrhenius relationship of the form D = 6.22−5.9
+49.6×10−15 exp(−161.5 ± 35.0 kJ mol−1/RT) m2 s−1. A single datum for iron diffusion in iron-free, single-crystal diopside at 1050 °C, is approximately 1 order of magnitude
slower than in the natural crystals. The pO2 dependence of iron diffusion in natural crystals at 1050 °C (power exponent = 0.229 ± 0.036) indicates a vacancy mechanism;
this is consistent with the results of unpublished atomistic simulation studies. There is no evidence of anisotropy for iron
diffusion in diopside.
Received: 16 March 1999 / Accepted: 10 April 2000 相似文献
16.
Sascha André Borinski Ulrich Hoppe Sumit Chakraborty Jibamitra Ganguly Santanu Kumar Bhowmik 《Contributions to Mineralogy and Petrology》2012,164(4):571-586
We have carried out a combined theoretical and experimental study of multicomponent diffusion in garnets to address some unresolved issues and to better constrain the diffusion behavior of Fe and Mg in almandine–pyrope-rich garnets. We have (1) improved the convolution correction of concentration profiles measured using electron microprobes, (2) studied the effect of thermodynamic non-ideality on diffusion and (3) explored the use of a mathematical error minimization routine (the Nelder-Mead downhill simplex method) compared to the visual fitting of concentration profiles used in earlier studies. We conclude that incorporation of thermodynamic non-ideality alters the shapes of calculated profiles, resulting in better fits to measured shapes, but retrieved diffusion coefficients do not differ from those retrieved using ideal models by more than a factor of 1.2 for most natural garnet compositions. Diffusion coefficients retrieved using the two kinds of models differ only significantly for some unusual Mg–Mn–Ca-rich garnets. We found that when one of the diffusion coefficients becomes much faster or slower than the rest, or when the diffusion couple has a composition that is dominated by one component (>75 %), then profile shapes become insensitive to one or more tracer diffusion coefficients. Visual fitting and numerical fitting using the Nelder-Mead algorithm give identical results for idealized profile shapes, but for data with strong analytical noise or asymmetric profile shapes, visual fitting returns values closer to the known inputs. Finally, we have carried out four additional diffusion couple experiments (25–35 kbar, 1,260–1,400 °C) in a piston-cylinder apparatus using natural pyrope- and almandine-rich garnets. We have combined our results with a reanalysis of the profiles from Ganguly et al. (1998) using the tools developed in this work to obtain the following Arrhenius parameters in D = D 0 exp{–[Q 1bar + (P–1)ΔV +]/RT} for D Mg* and D Fe*: Mg: Q 1bar = 228.3 ± 20.3 kJ/mol, D 0 = 2.72 (±4.52) × 10−10 m2/s, Fe: Q 1bar = 226.9 ± 18.6 kJ/mol, D 0 = 1.64 (±2.54) × 10−10 m2/s. ΔV + values were assumed to be the same as those obtained by Chakraborty and Ganguly (1992). 相似文献
17.
M. Hoyos V. Soler J. C. Cañaveras S. Sánchez-Moral E. Sanz-Rubio 《Environmental Geology》1998,33(4):231-242
The Candamo Cave contains an important group of paleolithic paintings which have been seriously deteriorated due to mass tourism.
In this work, an analysis was carried out of different climatic parameters (CO2, temperature, humidity, 222Rn) during annual cycles with the cave closed to the public and during an experimental period of controlled visits. The effect
of visits on the geochemical characteristics of karstic water was also analyzed together with the cave ventilation.
The natural variations in the cave air CO2 were above 3000 ppm, the increase produced through visits was only 100–110 ppm and since the humidity is almost permanently
at saturation point, the critical parameter which limits the visitor capacity becomes air temperature. The temperature changes
during the annual cycle are of the order of 1 °C in the external part and less than 0.5 °C in the internal part of the cave
and a maximum increase of 0.13 °C was observed during the period of the visits. The 222Rn and CO2 concentration minimums in the summer period (July–October) show that this is the most propitious time for visits, since the
greatest ventilation is produced in the cave at this time and, therefore, the greatest capacity for recovery. The geochemistry
of the water, on the other hand, indicated that this is the period of the year in which processes of wall corrosion can be
most easily introduced, although this would be of limited magnitude. The visitor capacity calculated was 29 visitors/day.
Received: 29 August 1996 · Accepted: 23 June 1997 相似文献
18.
Detlef W. Fasshauer Bernd Wunder Niranjan D. Chatterjee Günther W. H. Höhne 《Contributions to Mineralogy and Petrology》1998,131(2-3):210-218
The heat capacity of synthetic, stoichiometric wadeite-type K2Si4O9 has been measured by DSC in the 195≤T(K)≤598 range. Near the upper temperature limit of our data, the heat capacity observed by DSC agrees with that reported by
Geisinger et al. (1987) based on a vibrational model of their infrared and Raman spectroscopic data. However, with decreasing
temperature, the Cp observed by DSC is progressively higher than that predicted from the vibrational model, suggesting that
the standard entropy of K2Si4O9 is likely to be larger than 198.9 ± 4.0 J/K · mol computed from the spectroscopic data. A fit to the DSC data gave: Cp(T) = 499.13 (±1.87) − 4.35014 · 103(±3.489 · 101) · T
−0.5, with T in K and average absolute percent deviation of 0.37%. The room-temperature compressibilities of kalsilite and leucite, hitherto
unknown, have been measured as well. The data, fitted to the Murnaghan equation of state, gave K
o = 58.6 GPa, K
o
′ = 0.1 for kalsilite and K
o = 45 GPa, K
o
′ = 5.7 for α-leucite. Apart from the above mentioned data on the properties of the individual phases, we have also obtained
reaction-reversals on four equilibria in the system K2O-Al2O3-SiO2. The Bayesian method has been used simultaneously to process the properties of 13 phases and 15 reactions between them to
derive an internally consistent thermodynamic dataset for the K2O-Al2O3-SiO2 ternary. The enthalpy of formation of K2Si4O9 wadeite is in perfect agreement with its revised calorimetric value, the standard entropy is 232.1 ± 10.4 J/K · mol, ∼15%
higher than that implied by vibrational modeling. The phase diagram, generated from our internally consistent thermodynamic
dataset, shows that for all probable P-T trajectories in the subduction regime, the stable pressure-induced decomposition of K-feldspar will produce coesite + kalsilite rather than coesite + kyanite + K2Si4O9 (cf. Urakawa et al. 1994).
Received: 11 June 1997 / Accepted: 2 December 1997 相似文献
19.
Pb diffusion in rutile 总被引:16,自引:0,他引:16
D. J. Cherniak 《Contributions to Mineralogy and Petrology》2000,139(2):198-207
Diffusion of Pb was measured in natural and synthetic rutile under dry, 1 atmosphere conditions, using mixtures of Pb titanate
or Pb sulfide and TiO2 as the sources of diffusant. Pb depth profiles were then measured with Rutherford Backscattering Spectrometry (RBS). Over
the temperature range 700–1100 °C, the following Arrhenius relation was obtained for the synthetic rutile: D=3.9 × 10−10exp(−250 ± 12 kJ mol−1/RT) m2s−1. Results for diffusion in natural and synthetic rutile were quite similar, despite significant differences in trace element
compositions. Mean closure temperatures calculated from the diffusion parameters are around 600 °C for rutile grains of ∼100 μm
size. This is about 100 °C higher than rutile closure temperature determinations from past field-based studies, suggesting
that rutile is more resistant to Pb loss through volume diffusion than previously thought.
Received: 28 June 1999 / Accepted: 29 December 1999 相似文献
20.
Part I of this contribution (Gardés et al. in Contrib Mineral Petrol, 2010) reported time- and temperature-dependent experimental growth of polycrystalline forsterite-enstatite double layers between
single crystals of periclase and quartz, and enstatite single layers between forsterite and quartz. Both double and single
layers displayed growth rates decreasing with time and pronounced grain coarsening. Here, a model is presented for the growth
of the layers that couples grain boundary diffusion and grain coarsening to interpret the drop of the growth rates. It results
that the growth of the layers is such that (Δx)2 ∝ t
1−1/n
, where Δx is the layer thickness and n the grain coarsening exponent, as experimentally observed. It is shown that component transport occurs mainly by grain boundary
diffusion and that the contribution of volume diffusion is negligible. Assuming a value of 1 nm for the effective grain boundary
width, the following Arrhenius laws for MgO grain boundary diffusion are derived: log D
gb,0Fo (m2/s) = −2.71 ± 1.03 and E
gbFo = 329 ± 30 kJ/mol in forsterite and log D
gb,0En (m2/s) = 0.13 ± 1.31 and E
gbEn = 417 ± 38 kJ/mol in enstatite. The different activation energies are responsible for the changes in the enstatite/forsterite
thickness ratio with varying temperature. We show that significant biases are introduced if grain boundary diffusion-controlled
rim growth is modelled assuming constant bulk diffusivities so that differences in activation energies of more than 100 kJ/mol
may arise. It is thus important to consider grain coarsening when modelling layered reaction zones because they are usually
polycrystalline and controlled by grain boundary transport. 相似文献