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1.
The garnet-cordierite zone, the highest-grade zone of the Ryoke metamorphic rocks in the Yanai district, SW Japan, is defined
by the coexistence of garnet and cordierite in pelitic rocks. Three assemblages in this zone are studied in detail, i.e. spinel
+ cordierite + biotite, garnet + cordierite + biotite and garnet + biotite, all of which contain quartz, K-feldspar and plagioclase.
The Mg/(Fe + Mg) in the coexisting minerals decreases in the following order: cordierite, biotite, garnet and spinel. Two
facts described below are inconsistent with the paragenetic relation in the K 2OFeOMgOAl 2O 3SiO 2H 2O (KFMASH) system in terms of an isophysical variation. First, garnet and biotite in the last assemblage have Mg/(Fe + Mg)
higher than those in the second. Second, the first two assemblages are described by the reaction,
while they occur in a single outcrop. The addition of MnO, ZnO and TiO 2 to the system can resolve the inconsistencies as follows. The assemblage garnet + biotite can consist of garnet and biotite
higher in Mg/(Fe + Mg) than those in garnet + cordierite + biotite as long as they are enriched in spessartine and depleted
in Al, respectively. The assemblage garnet + cordierite + biotite becomes stable relative to spinel + cordierite + biotite
with increasing spessartine content or decreasing gahnite content and the Ti content of biotite. The constituent minerals
of the assemblages, spinel + cordierite + biotite and garnet + cordierite + biotite, preserve several reaction microstructures
indicative of prograde reactions,
and
together with retrograde reactions,
and
This suggests that the pressure-temperature path of the rocks includes an isobaric heating and an isobaric or decompressional
cooling. The high-grade areas consisting of the K-feldspar-cordierite zone, sillimanite-K-feldspar zone and garnet-cordierite
zone have prograde paths involving isobaric heating and show a southwards increase in pressure with a thermal maximum in the
middle. These high-grade zones are closely associated with the gneissose granitic rocks, suggesting that the Ryoke metamorphism,
one of the typical low-pressure type, is caused by the heat supply from the syn-tectonic granitic rocks that emplaced at the
middle level of the crust.
Received: 22 August 1997 / Accepted: 11 May 1998 相似文献
2.
Siderite, dolomite and ankerite were reacted with “>103°” phosphoric acid at temperatures up to 150°C with >99° yields achieved in less than two hours, using a modification of the McCrea (1950) technique. The oxygen fractionation factors, α, between the δ 18O of the carbonate and that of the acid-extracted CO 2 are: | Siderite | Dolomite | Ankerite | 100°C | 1.00881 | 1.00913 | 1.00901 | 150°C | 1.00771 | - | - | 相似文献
3.
The heat capacities of synthetic pyrope (Mg 3Al 2Si 2O 12), grossular (Ca 3Al 2Si 3O 12) and a solid solution pyrope 60grossular 40 (Mg 1.8Ca 1.2Al 2Si 3O 12) have been measured by adiabatic calorimetry in the temperature range 10–350 K. The samples were crystallized from glasses in a conventional piston-cylinder apparatus.The molar thermophysical properties at 298.15 K (J mol ?1 K ?1) are: | Cop | So298?So0 | Ho298?Ho0/T | Pyrope | 325.31 | 266.27 | 47852 | Grossular | 333.17 | 260.12 | 47660 | Py60Gr40 | 328.32 | 268.32 | 47990 | 相似文献
4.
The heat capacity of end-member titanite and (CaTiSiO 5) glass has been measured in the range 328–938 K using differential scanning calorimetry. The data show a weak λ-shaped anomaly
at 483 ± 5 K, presumably associated with the well-known low-pressure P2 1/a ⇆ A2/a transition, in good agreement with previous studies. A value of 0.196 ± 0.007 kJ mol −1 for the enthalpy of the P2 1/a ⇆ A2/a transition was determined by integration of the area under the curve for a temperature interval of 438–528 K, bracketing
the anomaly. The heat capacity data for end-member titanite and (CaTiSiO 5) glass can be reproduced within <1% using the derived empirical equations (temperature in K, pressure in bars):
The available enthalpy of vitrification (80.78 ± 3.59 kJ mol −1), and the new heat capacity equations for solid and glass can be used to estimate (1) the enthalpy of fusion of end-member
titanite (122.24 ± 0.2 kJ mol −1), (2) the entropy of fusion of end-member titanite (73.85 ± 0.1 J/mol K −1), and (3) a theoretical glass transition temperature of 1130 ± 55 K. The latter is in considerable disagreement with the
experimentally determined glass transition temperature of 1013 ± 3 K. This discrepancy vanishes when either the adopted enthalpy
of vitrification or the liquid heat content, or both, are adjusted.
Calculations using Eq. (2), new P−V−T data for titanite, different but also internally consistent thermodynamic data for anorthite,
rutile, and kyanite, and experimental data for the reaction: anorthite + rutile = titanite + kyanite strongly suggest: (1)
the practice to adjust the enthalpy of formation of titanite to fit phase equilibrium data may be erroneous, and (2) it is
probably the currently accepted entropy of 129.2 ± 0.8 J/mol K −1 that may need revision to a smaller value.
Received: 30 December 1999 / Accepted: 23 June 2000 相似文献
5.
The expansivity of supercooled diopside liquid has been determined using techniques of container-based dilatometry. Two thermal
strategies have been employed, one in which the sample is brought to volumetric equilibrium by long-duration dwells at low
temperatures (817 °C) and one in which scanning dilatometry of the sample has been performed at somewhat higher temperatures
(890–913 °C). The results of both experiments yield a supercooled liquid expansivity for diopside liquid in the temperature
range of 817–913 °C of 84.4 ± 2.8 × 10 −4 cm 3/mol K. The expansivity is 65% higher than that obtained for diopside melt obtained at superliquidus temperatures using the
double bob Archimedean method. Combined fitting of the new low temperature, volume–temperature data from the present study
and the superliquidus data from the literature has been performed. The combined fit yields the following equations for the
volume–temperature relationship of diopside liquid ( T=temperature in °C):
The standard error of the fit using both equations reproduces the volume–temperature data for diopside liquid within experimental
error. This result reconciles the disparate values of expansivity measured at low temperatures in the supercooled state and
at superliquidus temperatures and confirms the temperature-dependence of the expansivity of diopside liquid. Comparison with
previous low temperature estimates of melt volume and expansivity are discussed in light of these new results.
Received: 18 November 1999 / Accepted: 24 January 2000 相似文献
6.
Kinetic experiments of dolomite dissolution in water over a temperature range from 25 to 250°C were performed using a flow
through packed bed reactor. Authors chose three different size fractions of dolomite samples: 18–35 mesh, 35–60 mesh, and
60–80 mesh. The dissolution rates of the three particle size samples of dolomite were measured. The dissolution rate values
are changed with the variation of grain size of the sample. For the sample through 20–40 mesh, both the release rate of Ca
and the release rate of Mg increase with increasing temperature until 200°C, then decrease with continued increasing temperature.
Its maximum dissolution rate occurs at 200°C. The maximum dissolution rates for the sample through 40–60 mesh and 60–80 mesh
happen at 100°C. Experimental results indicate that the dissolution of dolomite is incongruent in most cases. Dissolution
of fresh dolomite was non-stoichiometric, the Ca/Mg ratio released to solution was greater than in the bulk solid, and the
ratio increases with rising temperatures from 25 to 250°C. Observations on dolomite dissolution in water are presented as
three parallel reactions, and each reaction occurs in consecutive steps as
where the second part is a slow reaction, and also the reaction could occur as follows:
The following rate equation was used to describe dolomite dissolution kinetics
where refers to one of each reaction among the above reactions; k
ij
is the rate constant for ith species in the jth reaction, a
i
stands for activity of ith aqueous species, n is the stoichimetric coefficience of ith species in the jth reaction, and define . The experiments prove that dissolved Ca is a strong inhibitor for dolomite dissolution (release of Ca) in most cases. Dissolved
Mg was found to be an inhibitor for dolomite dissolution at low temperatures. But dissolution rates of dolomite increase with
increasing the concentration of dissolved Mg in the temperature range of 200–250°C for 20–40 mesh sample, and in the temperature
range of 100–250°C for 40–80 mesh sample, whereas the Mg 2+ ion adsorption on dolomite surface becomes progressively the step controlling reaction. The following rate equation is suitable
to dolomite dissolutions at high temperatures from 200 to 250°C. where refers to dissolution rate (release of Ca), and are molar concentrations of dissolved Ca and Mg, k
ad stands for adsorption reaction rate constant, K
Mg refers to adsorption equilibrium constant.
At 200°C for 40–60 mesh sample, the release rate of Ca can be described as: 相似文献
7.
A pronounced negative correlation between the yttrium concentration in garnet ([Y] Grt) and temperature has been observed in xenotime (YPO 4)-bearing metapelites from central New England, USA. The [Y] Grt decreases roughly two orders of magnitude (∼5500 to less than 100 ppm Y) over a 150 °C interval. A regression of ln([Y] Grt) against estimated reciprocal temperature yields the following relationship:
with R 2 = 0.97. The decrease in garnet Y content is most rapid over garnet- to staurolite-zone conditions (450–550 °C) and the thermometer
has a precision of a few degrees in this range.
Received: 21 January 1999 / Accepted: 13 September 1999 相似文献
8.
Using the model of fictive ideal components, Gibbs free energies of formation of pyrope and Al 2O 3-enstatite have been determined from the experimental data on coexisting garnet and orthopyroxene and orthopyroxene and spinel in the temperature range of 1200–1600 K. The negative free energies in kJ/mol are: TK | 1200 | 1300 | 1400 | 1500 | 1600 | Pyrope | 4869.92 | 4747.05 | 4614.26 | 4462.63 | 4311.00 | Al2O3-enstatite | 1257.25 | 1244.28 | 1191.93 | 1158.67 | 1125.64 | 相似文献
9.
The density ρ of Caspian Sea waters was measured as a function of temperature (273.15–343.15) K at conductivity salinities
of 7.8 and 11.3 using the Anton-Paar Densitometer. Measurements were also made on one of the samples ( S = 11.38) diluted with water as a function of temperature ( T = 273.15–338.15 K) and salinity (2.5–11.3). These latter results have been used to develop an equation of state for the Caspian
Sea ( σ = ±0.007 kg m −3)
where ρ 0 is the density of water and the parameters A, B and C are given by
Measurements of the density of artificial Caspian Sea water at 298.15 K agree to ± 0.012 kg m −3 with the real samples. These results indicate that the composition of Caspian Sea waters must be close to earlier measurements
of the major components. Model calculations based on this composition yield densities that agree with the measured values
to ± 0.012 kg m −3. The new density measurements are higher than earlier measurements. This may be related to a higher concentration of dissolved
organic carbon found in the present samples (500 μM) which is much higher than the values in ocean waters (~65 μM). 相似文献
10.
Experimental clinopyroxenes synthesized at 850–1500 °C and 0–60 kbar in the CMS and CMAS-Cr systems and in more complex lherzolitic
systems have been used to calibrate a Cr-in-Cpx barometer and an enstatite-in-Cpx thermometer for Cr-diopsides derived from
garnet peridotites. The experiments cover a wide range of possible natural peridotitic compositions, from fertile pyrolite to refractory, high-Cr lherzolite. The barometer is based on the Cr exchange between clinopyroxene and garnet. Pressure is formulated as
a function of temperature and clinopyroxene composition:
where a
CaCrTs
Cpx=Cr−0.81·Cr#·(Na+K) and Cr#= , with elements in atoms per 6 oxygens. This formulation reproduces the experimental pressures to ±2.3 kbar (1σ) and has a
temperature dependence (1.2–2.4 kbar/50 °C, varying with composition) that is weaker than that of the widely used Al-in-Opx
barometer (2–3 kbar/50 °C). The enstatite-in-Cpx thermometer includes corrections for the effect of minor components and is
formulated as
where K)). The thermometer reproduces the experimental temperatures to ±30 °C (1σ).
The uncertainties of the present formulations are comparable to, or better than, those of the most widely used thermobarometers
for garnet peridotites. P-T estimates obtained for diamond-bearing and graphite-bearing lherzolite xenoliths and peridotitic clinopyroxene inclusions
in kimberlitic and lamproitic diamonds confirm the reliability of the thermobarometer. Cr-diopside thermobarometry appears
to be a potential tool for obtaining information on the thermal state of the upper mantle and the extent of mantle sampling
by deep-seated magmas. We consider the Cr-in-Cpx barometer to be the best alternative to the Al-in-Opx barometer for the evaluation
of pressure conditions of equilibration of natural garnet lherzolites. P-T conditions of equilibration can be directly retrieved from the composition of Cr-diopside alone, thus allowing application
to partially altered xenoliths, inclusions in diamonds, and loose grains from sediments. We foresee application of the present
thermobarometer to evaluation of the diamond potential of kimberlite and lamproite provinces and in diamond exploration where
Cr-diopside from deep mantle sources is preserved in the surficial weathering environment.
Received: 16 August 1999 / Accepted: 17 March 2000 相似文献
11.
Jarosite phases are common minerals in acidic, sulfate-rich environments. Here, we report heat capacities ( C
p) and standard entropies ( S°) for a number of jarosite samples. Most samples are close to the nominal composition AFe 3(SO 4) 2(OH) 6, where A = K, Na, Rb, and NH 4. One of the samples has a significant number of defects on the Fe sites and is called the defect jarosite; others are referred
to as A-jarosite. The samples, their compositions, and the entropies at T = 298.15 K are:
K-jarosite
|
K0.92(H3O)0.08Fe2.97(SO4)2(OH)5.90(H2O)0.10
|
427.4 ± 0.7
|
Na-jarosite
|
Na0.95(H3O)0.05Fe3.00(SO4)2(OH)6.00
|
436.4 ± 4.4
|
Rb-jarosite
|
RbFe2.98(SO4)2(OH)5.95(H2O)0.05
|
411.9 ± 4.1
|
NH4-jarosite
|
(NH4)0.87(H3O)0.13Fe3.00(SO4)2(OH)6.00
|
447.2 ± 4.5
|
Defect jarosite
|
K0.94(H3O)0.06Fe2.34(SO4)2(OH)4.01(H2O)1.99
|
412.7 ± 4.1
|
There are additional configurational entropies of 13.14 and 8.23 J mol −1 K −1 in defect and NH 4-jarosite, respectively. A detailed analysis of the synchrotron X-ray diffraction patterns showed a large anisotropic peak
broadening for defect and NH 4-jarosite. The fits to the low-temperature (approx. <12 K) C
p data showed that our samples can be divided into two groups. The first group is populated by the K-, Na-, Rb-, and NH 4-jarosite samples, antiferromagnetic at low temperatures. The second group contains the H 3O-jarosite (studied previously) and the defect jarosite. H 3O- and defect jarosite are spin glasses and their low- T
C
p was fit with the expression C
p = γT + Σ B
j
T
j
, where j = (3, 5, 7, 9). The linear term is typical for spin glasses and the sum represents the lattice contribution to C
p. Surprisingly, the C
p of the K-, Na-, Rb-, and NH 4-jarosite samples, which are usually considered to be antiferromagnetic at low temperatures, also contains a large linear
term. This finding suggests that even these phases do not order completely, but have a partial spin-glass character below
their Néel transition temperature. 相似文献
12.
The chemical potential of oxygen (µO 2) in equilibrium with magnesiowüstite solid solution (Mg, Fe)O and metallic Fe has been determined by gas-mixing experiments at 1,473 K supplemented by solid-cell EMF experiments at lower temperatures. The results give: where IW refers to the Fe-"FeO" equilibrium. The previous work of Srecec et al. ( 1987) and Wiser and Wood ( 1991) agree well with this equation, as does that of Hahn and Muan ( 1962) when their reported compositions are corrected to a new calibration curve for lattice parameter vs. composition. The amount of Fe 3+ in the magnesiowüstite solid solution in equilibrium with Fe metal was determined by Mössbauer spectroscopy on selected samples. These data were combined with literature data from gravimetric studies and fitted to a semi-empirical equation: These results were then used to reassess the activity-composition relations in (Mg, Fe) 2SiO 4 olivine solid solutions at 1,400 K, from the partitioning of Mg and Fe 2+ between olivine and magnesiowüstite in equilibrium with metallic Fe experimentally determined by Wiser and Wood ( 1991). The olivine solid solution is constrained to be nearly symmetric with
, with a probable uncertainty of less than ±0.5 kJ/mol (one standard deviation). The results also provide a useful constraint on the free energy of formation of Mg 2SiO 4.Editorial responsibility: B. Collins 相似文献
13.
Analysis of existing data and models on point defects in pure (Fe,Mg)-olivine (Phys Chem Miner 10:27–37, 1983; Phys Chem Miner 29:680–694, 2002) shows that it is necessary to consider thermodynamic non-ideality of mixing to adequately describe the concentration of
point defects over the range of measurement. In spite of different sources of uncertainties, the concentrations of vacancies
in octahedral sites in (Fe,Mg)-olivine are on the order of 10 −4 per atomic formula unit at 1,000–1,200 °C according to both the studies. We provide the first explicit plots of vacancy concentrations
in olivine as a function of temperature and oxygen fugacity according to the two models. It is found that in contrast to absolute
concentrations at ∼1,100 °C and dependence on fO 2, there is considerable uncertainty in our knowledge of temperature dependence of vacancy concentrations. This needs to be
considered in discussing the transport properties such as diffusion coefficients. Moreover, these defect models in pure (Fe,Mg)-olivine
need to be extended by considering aliovalent impurities such as Al, Cr to describe the behavior of natural olivine. We have
developed such a formulation, and used it to analyze the considerable database of diffusion coefficients in olivine from Dohmen
et al. (Phys Chem Miner this volume, 2007) (Part - I) and older data in the literature. The analysis documents unequivocally for the first time a change of diffusion
mechanism in a silicate mineral—from the transition metal extrinsic (TaMED) to the purely extrinsic (PED) domain, at fO 2 below 10 −10 Pa, and consequently, temperatures below 900 °C. The change of diffusion mechanism manifests itself in a change in fO 2 dependence of diffusivity and a slight change in activation energy of diffusion—the activation energy increases at lower temperatures. These are consistent with the predictions of Chakraborty (J Geophys Res 102(B6):12317–12331, 1997). Defect formation enthalpies in the TaMED regime (distinct from intrinsic defect formation) lie between −66 and + 15 kJ/mol
and migration energies of octahedral cations in olivine are most likely ∼ 260 kJ/mol, consistent with previous inferences
(Phys Chem 207:147–162, 1998). Plots are shown for diffusion at various constant fO 2 as well as along fO 2 buffers, to highlight the difference in behavior between the two. Considering all the diffusion data and constraints from
the point defect models, (Fe–Mg) diffusion in olivine along [001] is best described by the Master equations: (1) At oxygen
fugacities greater than 10 −10 Pa:
where T is in Kelvin, P and fO 2 is in Pascals, X
Fe is the mole fraction of the fayalite component and R is the gas constant in J/mol/K. (2) At oxygen fugacities less than 10 −10 Pa:
These equations reproduce all of the 113 experimental data points within half an order of magnitude. (3) Alternately, a global
equation averaging out the change of mechanism may be used, with somewhat larger errors in reproducing the measured diffusion
data. It underestimates data at higher temperatures, and overestimates them at lower temperatures on the average. Note that
fO 2 is not explicitly considered here, leading to additional sources of error:
To obtain diffusion coefficients along [100] and [010], log 6 needs to be subtracted from each of the above equations.
An erratum to this article can be found at 相似文献
14.
Ca-(Fe,Mg) interdiffusion experiments between natural single crystals of grossular (Ca 2.74Mg 0.15 Fe 0.23Al 1.76Cr 0.04Si 3.05O 12) and almandine (Ca 0.21Mg 0.40 Fe 2.23Mn 0.13Al 2.00Cr 0.08Si 2.99O 12 or Ca 0.43Mg 0.36Fe 2.11 Al 1.95Si 3.04O 12), were undertaken at 900–1100 °C and 30 kbar, and pressures of 15.0–32.5 kbar at 1000 °C. Samples were buffered by Fe/FeO
in most cases. Diffusion profiles were determined by electron microprobe. Across the experimental couples the interdiffusion
coefficients ( D˜) were almost independent of composition. The diffusion rates in an unbuffered sample were significantly faster than in buffered
samples. The temperature dependence of the D˜ (Ca-Fe,Mg) interdiffusion coefficients may be described by
at 30 kbar and 900–1100 °C. This activation energy is marginally higher than previous experimental studies involving Ca-free
garnets; the interdiffusion coefficients are higher than previous studies for Fe-Mg and Fe-Mn exchange in garnet. The pressure
dependence of D˜ (Ca-Fe,Mg) at 1000 °C yielded an activation volume of 11.2 cm 3 mol −1, which is higher than previous results from studies involving garnet and olivine. Comparison with simulation studies suggests
a vacancy mechanism for divalent ion migration in garnet, with extrinsic processes being dominant up to very high temperatures.
Received: 15 December 1996 / Accepted: 3 November 1998 相似文献
15.
The effects of composition on pyroxene-melt partitioning of several REE (rare earth elements), Y, and Sr were experimentally
evaluated. Using the synthetic model systems anorthite–diopside, diopside–titanite and anorthite–diopside–titanite different
diopsides were grown at atmospheric conditions in a double-ellipsoid mirror furnace. The single samples were melted and crystallised
in a Pt/Au crucible with compositions corresponding to the invariant points of these systems. Rotational motion with approximately
25 rpm around the longitudinal axis of the crucible increases the prevailing convection flows. By this means, the exclusively
diffusional transport of assembly groups onto the growing crystals is avoided. Quenching is achieved by dropping the crucible
into water. Crystals up to 2 mm were obtained and analysed by electron microprobe. No inhomogeneities or compositional zonation,
either in the diopsides or in the coexisting melts, were observed within the analytical uncertainty of the electron microprobe.
The crystallised diopsides occur as both euhedral single crystals and large symplectitic lamellar intergrowths with anorthite
or titanite. The chemical homogeneity and the texture indicate near-equilibrium conditions. The analyses show strong positive
correlations between D REE and tetrahedrally coordinated Al in diopside but are not affected by octahedral Al or Ti-concentration. By means of correlations
and mass balances the incorporation of REE can be described by 2 different coupled substitutions:
The Al-coupled incorporation of REE 3+ (1) dominates the D-values. The Na-coupled substitution (2) is of minor importance. Depending on the compositions investigated
the D-values vary by up to a factor of 10. This range overlaps most of the published pyroxene-melt partition coefficients.
Because we conducted isothermal and isobaric experiments, this overlap indicates that a wide range of D-values is a function
of composition. For the coupled substitutions (1) and (2) this indicates that the D REE strongly depends on the amount of tetrahedrally coordinated Al 3+ in clinopyroxenes.
Received: 5 January 1998 / Accepted: 11 June 1998 相似文献
16.
Interdiffusion of Fe and Mg in (Mg,Fe)O has been investigated experimentally under hydrous conditions. Single crystals of
MgO in contact with (Mg 0.73Fe 0.27)O were annealed hydrothermally at 300 MPa between 1,000 and 1,250°C and using a Ni–NiO buffer. After electron microprobe
analyses, the dependence of the interdiffusivity on Fe concentration was determined using a Boltzmann–Matano analysis. For
a water fugacity of ∼300 MPa, the Fe–Mg interdiffusion coefficient in Fe
x
Mg 1−x
O with 0.01 ≤ x ≤ 0.25 can be described by with and C = −80 ± 10 kJ mol −1. For x = 0.1 and at 1,000°C, Fe–Mg interdiffusion is a factor of ∼4 faster under hydrous than under anhydrous conditions. This enhanced
rate of interdiffusion is attributed to an increased concentration of metal vacancies resulting from the incorporation of
hydrogen. Such water-induced enhancement of kinetics may have important implications for the rheological properties of the
lower mantle.
相似文献
17.
Oxygen and carbon isotope analyses of samples from three mines in the Krivoy Rog iron formation, Ukranian SSR, are reported here. Maximum and minimum quartz-magnetite fractionation values ( ) and inferred temperature range in degrees centrigrade for each mine are: Mine | | Corresponding temperature | Sevgok | 9.4 to 14.2 | 475° to 320°C | Ugok | 10.0 to 12.7 | 450° to 355°C | Annovsky | 10.5 to 12.6 | 430° to 360°C | 相似文献
18.
The regular solid solution model has been applied to solid solubility in the monazite–xenotime systems and is verified against
the available experimental data for LaPO 4–YPO 4 and CePO 4–YPO 4 systems. The model is then used to predict the miscibility gaps in a number of other monazite–xenotime systems. The implications
for prospective two-phase monazite–xenotime fiber coatings for applications in ceramic matrix composites (CMCs) are discussed.
相似文献
19.
We report Ni, Ga, Ge and Ir concentrations for 193 irons. The compositional trends in groups IIIA and IIIB are redefined, and the suggestion by Wasson and Kimberlin that they represent a single fractionation sequence (group IIIAB) is confirmed. A new group, HIE, is similar in its properties to group IIIA but distinguished by lower Ga/Ni and Ge/Ni ratios, larger bandwidths and the formation of haxonite (Fe, Ni) 23C 6 in each of its members. A sixth member, Hassi-Jekna, has been added to group IIIC, extending its Ge range up to 70 ppm. The characteristics of these groups can be summarized as follows: Group | Structure | Ni% | Ga(ppm) | Ge(ppm) | Ir(ppm) | IIIA | Om | 7.1–9.3 | 7–23 | 32–47 | 0.17–19 | IIIB | Om | 8.4–10.5 | 16–21 | 27–46 | 0.014–0.17 | IIIC | Off-Of | 10.5–13.0 | 11–27 | 8.6–70 | 0.08–0.6 | IIIE | Og | 8.2–8.9 | 17–19 | 34–37 | 0.05–0.6 The Ge-Ni correlation is positive in IIIA, negative in IIIB and IIIC, and there is no significant correlation in IIIE. San Cristobal is identified as a member of group IAB, thereby extending the Ge and Ni range of this group to 25 ppm and 25 per cent, respectively. Previous reports of wide cooling-rate variations in group IIIAB are not substantiated, and current evidence favors a core over a raisin-bread model for this group. There appears to be no genetic relationship between group IIIAB and either the pallasites or the mesosiderites | 相似文献
20.
Concentrations of Au, As, Co, Ga, Ge, Ir, Ni and W were determined in the metal of 28 different pallasites plus 6 which are probably paired, to help elucidate their origin. Most divide into two clusters: | No. | Ni (%) | Ga (μg/g) | Ge (μg/g) | Au (μg/g) | Fa (mole %) | Main group | 19 | 7.8–11.7 | 16–26 | 29–65 | 1.7–3.0 | 11–13 | Eagle Station trio | 3 | 14–16 | 4.5–6 | 75–120 | 0.8–1.0 | 19–20 | 相似文献
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