共查询到20条相似文献,搜索用时 31 毫秒
1.
Activities of CoO in (Co,Mn)O solid solutions in contact with metallic Co have been determined on ten compositions ranging
from 0.12 to 0.84 XCoO in order to calibrate the divariant equilibrium between (Co,Mn)O oxide solutions and Co metal as an oxygen fugacity sensor
for application in experimental petrology. Experiments were conducted over the temperature range 900–1300 K at 1 bar, using
an electrochemical technique with oxygen-specific calcia-stabilized zirconia (CSZ) electrolytes. Co + CoO or Fe + FeO was
used as the reference electrode. Compositions of the (Co,Mn)O solid solutions were measured after each run by electron microprobe,
and these were checked for internal consistency by measuring the lattice parameter by X-ray diffraction. Activity–composition
relations were fitted to the Redlich–Kister formalism. (Co,Mn)O solid solutions exhibit slight positive deviations from ideality,
which are symmetrical (corresponding to a regular solution mixing model) across the entire composition range with A0
G = 3690(±47) Jmol−1. Excess entropies and enthalpies were also derived from the emf data and gave Sex=0.77(±0.08) JK−1 mol−1 and Hex=4558(±90) Jmol−1 respectively. The experimental data from this study have been used to formulate the (Co,Mn)O/Co oxygen fugacity sensor to
give an expression:
where μO2
CoCoO=−492,186 + 509.322 T − 53.284 T lnT + 0.02518 T2, taken from O'Neill and Pownceby (1993).
Received: 10 September 1999 / Accepted: 4 April 2000 相似文献
2.
S. A. T. Redfern G. Artioli R. Rinaldi C. M. B. Henderson K. S. Knight B. J. Wood 《Physics and Chemistry of Minerals》2000,27(9):630-637
The partitioning of Fe and Mg between the M1 and M2 octahedral sites of olivine has been investigated by in situ time-of-flight
neutron powder diffraction. The degree of M-cation order was determined from direct measurements of site occupancies in a
synthetic sample of Fo50Fa50 heated to 1250 °C at the Fe-FeO oxygen buffer. Fe shows slight preference for M1 at temperatures
below about 600 °C, progressively disordering on heating to this temperature. Above 630 °C, the temperature at which site
preferences cross over (T
cr), Fe preferentially occupies M2, becoming progressively more ordered into M2 on increasing temperature. The cation-ordering
behaviour is discussed in relation to the temperature dependence of the M1 and M2 site geometries, and it is suggested that
vibrational entropy, crystal field effects and changes in bond characteristics play a part in the cross-over of partitioning
behaviour. The temperature dependence of site ordering is modelled using a Landau expansion of the free energy of ordering
of the type ΔG = −hQ + gTQ + (T − T
c)Q
2 + Q
4, with a/h = 0.00406 K−1, b/h = 2.3, T
c = 572 K and g/h = 0.00106 K−1. These results suggest that the high-temperature ordering behaviour across the forsterite-fayalite join will have a bearing
on the activity-composition relations of this important rock-forming mineral, and indicate that Fe-Mg olivine solid solutions
become less ideal as temperature increases.
Received: 12 August 1999 / Accepted: 25 April 2000 相似文献
3.
Summary
Kristiansenite occurs as a late hydrothermal mineral in vugs in an amazonite pegmatite at Heftetjern, T?rdal, Telemark, Norway.
Tapering crystals, rarely up to 2 mm long, are colourless, white, or slightly yellowish. The mineral has the ideal composition
Ca2ScSn(Si2O7)(Si2O6OH) and is triclinic C1 with cell parameters a = 10.028(1), b = 8.408(1), c = 13.339(2) ?, α = 90.01(1), β = 109.10(1), γ = 90.00(1)°, V = 1062.7(3) ?3 (Z = 4). It has a monoclinic cell within ∼ 0.1 ? and is polysynthetically twinned on {010} by metric merohedry. The strongest
reflections in the X-ray powder pattern are [d in ?, (I
obs), (hkl)]: 5.18 (53) (1–11), 3.146 (100) (004), 3.089 (63) (−222), 2.901 (19) (221), 2.595 (34) (222), 2.142 (17) (−3–31). The Mohs’
hardness is 5?–6; Dcalc. = 3.64 g/cm3; only a mean refractive index of 1.74 could be measured. Scandium enrichment in the Heftetjern pegmatite and the crystal
chemistry of scandium are briefly discussed.
Received April 30, 2001; accepted July 28, 2001 相似文献
4.
Summary ?A single-crystal X-ray investigation was performed on crystals of P21/c natural pigeonite with varying Ca and Fe* ( = Fe2+ + Mn2+) contents, in order to verify the effect of microtextural disorder on structure refinements and to constrain the crystal
chemistry of pigeonite. Antiphase domains and exsolution lamellae affect differently the refinement results. In a crystal
free of exsolution the structure obtained after refinement with all reflections is an average of that of the antiphase domains
and of their boundaries, whereas in an exsolved crystal it represents only the structure of the prevailing pigeonite lamellae.
The refinement using only h + k odd reflections seems to give the structure of the Ca-free pigeonite characteristic of the antiphase domains rather than
that of Ca-rich domain walls. The ratio of the scale factors in refinements with all reflections and with only h + k odd reflections allows the ratios of the exsolved augite and pigeonite phases to be estimated.
The crystal chemistry of the investigated samples follows the trends outlined by data on Ca-free and Fe-free synthetic samples.
In particular, it is shown that Ca and Fe* substitution for Mg induce similar changes in the average structure, i.e. both induce an expansion in the M1 polyhedron and
decrease the difference between the M2–O3 distances.
Received October 18, 2001; revised version accepted February 15, 2002 相似文献
5.
Summary The complexation of aluminium(III) and silicon(IV) was studied in a simplified seawater medium (0.6 M Na(Cl)) at 25 °C. The
measurements were performed as potentiometric titrations using a hydrogen electrode with OH
− ions being generated coulometrically. The total concentrations of Si(IV) and Al(III) respectively [Si
tot
] and [Al
t
ot], and −log[H
+] were varied within the limits 0.3 < [Si
tot
] < 2.5 mM, 0.5 < [Al
tot
] < 2.6 mM, and 2 ≤ -log[H
+] ≤ 4.2. Within these ranges of concentration, evidence is given for the formation of an AlSiO(OH)
3
2+
complex with a formation constant log β1,1-1 = −2.75 ± 0.1 defined by the reaction
Al
3++Si (OH)4 ↔ AlOSi(OH)
3
2+
+H
+
An extrapolation of this value to I=0 gives log β1,1-1 = −2.30. The calculated value of log K (Al
3++SiO(OH)
3
−
↔ AlOSi(OH)
3
2+
) = 6.72 (I=0.6 M) can be compared with corresponding constants for the formation of AlF
2+ and AlOH
2+ , which are equal to 6.16 and 8.20. Obviously, the stability of these Al(III) complexes decreases within the series OH
−>SiO(OH)
3
−
> F
− 相似文献
6.
Enthalpies of drop solution (ΔH
drop-sol) of CaGeO3, Ca(Si0.1Ge0.9)O3, Ca(Si0.2Ge0.8)O3, Ca(Si0.3Ge0.7)O3 perovskite solid solutions and CaSiO3 wollastonite were measured by high-temperature calorimetry using molten 2PbO · B2O3 solvent at 974 K. The obtained values were extrapolated linearly to the CaSiO3 end member to give ΔH
drop-sol of CaSiO3 perovskite of 0.2 ± 4.4 kJ mol−1. The difference in ΔH
drop-sol between CaSiO3, wollastonite, and perovskite gives a transformation enthalpy (wo → pv) of 104.4 ± 4.4 kJ mol−1. The formation enthalpy of CaSiO3 perovskite was determined as 14.8 ± 4.4 kJ mol−1 from lime + quartz or −22.2 ± 4.5 kJ mol−1 from lime + stishovite. A comparison of lattice energies among A2+B4+O3 perovskites suggests that amorphization during decompression may be due to the destabilizing effect on CaSiO3 perovskite from a large nonelectrostatic energy (repulsion energy) at atmospheric pressure. By using the formation enthalpy
for CaSiO3 perovskite, phase boundaries between β-Ca2SiO4 + CaSi2O5 and CaSiO3 perovskite were calculated thermodynamically utilizing two different reference points [where ΔG(P,T )=0] as the measured phase boundary. The calculations suggest that the phase equilibrium boundary occurs between 11.5 and
12.5 GPa around 1500 K. Its slope is still not well constrained.
Received: 20 September 2000 / Accepted: 17 January 2001 相似文献
7.
K.-D. Grevel A. Navrotsky W. A. Kahl D. W. Fasshauer J. Majzlan 《Physics and Chemistry of Minerals》2001,28(7):475-487
Calorimetric and P–V–T data for the high-pressure phase Mg5Al5Si6O21(OH)7 (Mg-sursassite) have been obtained. The enthalpy of drop solution of three different samples was measured by high-temperature
oxide melt calorimetry in two laboratories (UC Davis, California, and Ruhr University Bochum, Germany) using lead borate (2PbO·B2O3) at T=700 ∘C as solvent. The resulting values were used to calculate the enthalpy of formation from different thermodynamic datasets;
they range from −221.1 to −259.4 kJ mol−1 (formation from the oxides) respectively −13892.2 to −13927.9 kJ mol−1 (formation from the elements). The heat capacity of Mg5Al5Si6O21(OH)7 has been measured from T=50 ∘C to T=500 ∘C by differential scanning calorimetry in step-scanning mode. A Berman and Brown (1985)-type four-term equation represents
the heat capacity over the entire temperature range to within the experimental uncertainty: C
P
(Mg-sursassite) =(1571.104 −10560.89×T
−0.5−26217890.0 ×T
−2+1798861000.0×T
−3) J K−1 mol−1 (T in K). The P
V
T behaviour of Mg-sursassite has been determined under high pressures and high temperatures up to 8 GPa and 800 ∘C using a MAX 80 cubic anvil high-pressure apparatus. The samples were mixed with Vaseline to ensure hydrostatic pressure-transmitting
conditions, NaCl served as an internal standard for pressure calibration. By fitting a Birch-Murnaghan EOS to the data, the
bulk modulus was determined as 116.0±1.3 GPa, (K
′=4), V
T,0
=446.49 3 exp[∫(0.33±0.05) × 10−4 + (0.65±0.85)×10−8
T dT], (K
T/T)
P
= −0.011± 0.004 GPa K−1. The thermodynamic data obtained for Mg-sursassite are consistent with phase equilibrium data reported recently (Fockenberg
1998); the best agreement was obtained with Δf
H
0
298 (Mg-sursassite) = −13901.33 kJ mol−1, and S
0
298 (Mg-sursassite) = 614.61 J K−1 mol−1.
Received: 21 September 2000 / Accepted: 26 February 2001 相似文献
8.
Detlef W. Fasshauer Niranjan D. Chatterjee Ladislav Cemic 《Contributions to Mineralogy and Petrology》1998,133(1-2):186-198
Heat capacity, thermal expansion, and compressibility data have been obtained for a number of selected phases of the system
NaAlSiO4-LiAlSiO4-Al2O3-SiO2-H2O. All C
p
measurements have been executed by DSC in the temperature range 133–823 K. The data for T ≥ 223 K have been fitted to the function C
p
(T) = a + cT
−2 + dT
−0.5 + fT
−3, the fit parameters being The thermal expansion data (up to 525 °C) have been fitted to the function V
0(T) = V
0(T) [1 + v
1 (T−T
0) + v
2 (T−T
0)2], with T
0 = 298.15 K. The room-temperature compressibility data (up to 6 GPa) have been smoothed by the Murnaghan equation of state.
The resulting parameters are These data, along with other phase property and reaction reversal data from the literature, have
been simultaneously processed by the Bayes method to derive an internally consistent thermodynamic dataset (see Tables 6 and
7) for the NaAlSiO4-LiAlSiO4-Al2O3-SiO2-H2O quinary. Phase diagrams generated from this dataset are compatible with cookeite-, ephesite-, and paragonite-bearing assemblages
observed in metabauxites and common metasediments. Phase diagrams obtained from the same database are also in agreement with
the cookeite-free, petalite-, spodumene-, eucryptite-, and bikitaite-bearing assemblages known to develop in the subsolidus
phase of recrystallization of␣lithium-bearing pegmatites. It is gratifying to note that the cookeite phase relations predicted
earlier by Vidal and Goffé (1991) in the context of the system Li2O-Al2O3-SiO2-H2O agree with our results in a general way.
Received: 19 May 1998 / Accepted: 25 June 1998 相似文献
9.
Assessment of heavy-metal contamination of floodplain soils due to mining and mineral processing in the Harz Mountains, Germany 总被引:9,自引:2,他引:7
2 study area was assessed with respect to its heavy-metal load on the basis of the current guideline values. The heavy-metal
loads of the soils in the study area have ranges of <0.2–200 mg kg−1 for Cd, <10–30,000 mg kg−1 for Pb, 7–10,000 mg kg−1 for Cu and 50–55,000 mg kg−1 for Zn. Mobility of the heavy metals was determined by extraction at different pH values. The acid neutralisation capacity
(ANCx) at these pH values was also determined to estimate the probability that the pH can drop to pH=x. The ANC values in the study area ranged from 6 to 3000 mmol H+ kg−1, from −33 to 800 mmol H+ kg−1 and from −74 to 160 mmol H+ kg−1 for ANC3.5, ANC5.0 and ANC6.2, respectively. Together with pedological data, the extraction experiments permit differentiation between soil units that
have been placed in the same environmental hazard class on the basis of total heavy-metal loads.
Received: 10 August 1998 · Accepted: 14 August 1999 相似文献
10.
The high-pressure stability of zoisite and phase relationships of zoisite-bearing assemblages 总被引:5,自引:0,他引:5
The fluid-absent reaction 12 zoisite = 3 lawsonite + 7 grossular + 8 kyanite + 1 coesite was experimentally reversed in the
model system CaO-Al2O3-SiO2-H2O (CASH) using a multi-anvil apparatus. The upper pressure stability limit for zoisite was found to extend to 5.0 GPa at 700 °C
and to 6.6 GPa at 950 °C. Additional experiments both in the H2O-SiO2-saturated and in the H2O-Al2O3-saturated portions of CASH provide further constraints on high pressure phase relationships of lawsonite, zoisite, grossular,
kyanite, coesite, and an aqueous fluid. Consistency of the present experiments with the H2O-saturated breakdown of lawsonite is demonstrated by thermodynamic analysis using linear programming techniques. Two sets
of data consistent with databases of Berman (1988) and Holland and Powell (1990) were retrieved combining experimental phase
relationships, calorimetric constraints, and recently measured elastic properties of solid phases. The best fits result in
G
f
,1,298
∘,zoisite=−6,499,400 J and S
1,298
∘,zoisite=302 J/K, and G
f
,1,298
∘,lawsonite=−4,514,600 J and S
1,298
∘,lawsonite=220 J/K for the dataset of Holland and Powell, and G
f
,1,298
∘,zoisite=−6,492,120 J and S
1,298
∘,zoisite=304 J/K, and G
f
,1,298
∘,lawsonite=−4,513,000 J and S
1,298
∘,lawsonite= 218 J/K for the dataset of Berman. Examples of the usage of zoisite as a geohygrometer and as a geobarometer in rocks metamorphosed
at eclogite facies conditions are worked, profiting from the thermodynamic properties retrieved here.
Received: 23 December 1996 / Accepted: 29 August 1997 相似文献
11.
A. Pavese V. Diella V. Pischedda M. Merli R. Bocchio M. Mezouar 《Physics and Chemistry of Minerals》2001,28(4):242-248
The thermoelastic parameters of natural andradite and grossular have been investigated by high-pressure and -temperature
synchrotron X-ray powder diffraction, at ESRF, on the ID30 beamline. The P–V–T data have been fitted by Birch-Murnaghan-like EOSs, using both the approximated and the general form. We have obtained for
andradite K
0=158.0(±1.5) GPa, (dK/dT )0=−0.020(3) GPa K−1 and α0=31.6(2) 10−6 K−1, and for grossular K
0=168.2(±1.7) GPa, (dK/dT)0=−0.016(3) GPa K−1 and α0=27.8(2) 10−6 K−1. Comparisons between the present issues and thermoelastic properties of garnets earlier determined are carried out.
Received: 7 July 2000 / Accepted: 20 October 2000 相似文献
12.
Interactions between several silicate and metallic phases are studied by applying a self consistent thermodynamic approach
and using recent thermodynamic data. We compute proportions and compositions of oxidized silicates and of reduced metallic
phase in equilibrium at various temperatures and oxygen fugacities. The empirically observed activity-composition relationships
for ternary metallic alloys are used and their applications to a general thermodynamic expression for a non-regular ternary
system is explicitly discussed. We show that the stability limits of olivines and pyroxenes with respect to precipitation
of metallic phases under reducing conditions are directly related to the presence of nickel impurities. We precisely evaluate
the modifications of the stability limits as a function of nickel content. For typical mantle olivines [Fe/(Fe+Mg) = 0.1]
the stability limits are given for values of x
Ni= Ni/(Ni+Fe+Mg) ranging from 10 ppm to 1% by: ln f
O2=−39.83+ 7.86 ln x
Ni, ln f
O2=−14.68+6.21 ln x
Ni, at 900 K and 1600 K, respectively.
Received: 17 November 1999 / Accepted: 14 May 2000 相似文献
13.
Lars Chresten Lund-Hansen Thorbjørn Joest Andersen Morten Holtegaard Nielsen Morten Pejrup 《Estuaries and Coasts》2010,33(6):1442-1451
Optical constituents as suspended particulate matter (SPM), chlorophyll (Chl-a), colored dissolved organic matter (CDOM),
and grain sizes were obtained on a transect in the arctic fjord-type estuary Kangerlussuaq (66°) in August 2007 along with
optical properties. These comprised diffuse attenuation coefficient of downwelling PAR (K
d(PAR)), upwelling PAR (K
u(PAR)), particle beam attenuation coefficient (c
p), and irradiance reflectance R(−0, PAR). PAR is white light between 400 and 700 nm. The estuary receives melt water from the Greenland Inland Ice and stations
covered a transect from the very high turbid melt water outlet to clear marine waters. Results showed a strong spatial variation
with high values as for suspended matter concentrations, CDOM, diffuse attenuation coefficient K
d(PAR), particle beam attenuation coefficients (c
p), and reflectance R(−0, PAR) at the melt water outlet. Values of optical constituents and properties decreased with distance from the melt water
outlet to a more or less constant level in central and outer part of the estuary. There was a strong correlation between inorganic
suspended matter (SPMI) and diffuse attenuation coefficient K
d(PAR) (r
2 = 0.92) and also for particle beam attenuation coefficient (c
p; r
2 = 0.93). The obtained SPMI specific attenuation—K
d*(PAR) = 0.13 m2 g−1 SPMI—and the SPMI specific particle beam attenuation—c
p* = 0.72 m2 g−1—coefficients were about two times higher than average literature values. Irradiance reflectance R(−0, PAR) was comparatively high (0.09−0.20) and showed a high (r
2 = 0.80) correlation with K
u(PAR). Scattering dominated relative to absorption—b(PAR)/a(PAR) = 12.3. Results strongly indicated that the high values in
the optical properties were related to the very fine particle sizes (mean = 2–6 μm) of the suspended sediment. Data and results
are discussed and compared to similar studies from both temperate and tropical estuaries. 相似文献
14.
N. V. Zubkova D. Yu. Pushcharovsky G. Giester E. Tillmanns I. V. Pekov D. A. Kleimenov 《Mineralogy and Petrology》2002,75(1-2):79-88
Summary
The crystal structure of arsentsumebite, ideally, Pb2Cu[(As, S)O4]2(OH), monoclinic, space group P21/m, a = 7.804(8), b = 5.890(6), c = 8.964(8) ?, β = 112.29(6)°, V = 381.2 ?3, Z = 2, dcalc. = 6.481 has been refined to R = 0.053 for 898 unique reflections with I> 2σ(I). Arsentsumebite belongs to the brackebuschite group of lead minerals with the general formula Pb2
Me(XO4)2(Z) where Me = Cu2+, Mn2+, Zn2+, Fe2+, Fe3+; X = S, Cr, V, As, P; Z = OH, H2O. Members of this group include tsumebite, Pb2Cu(SO4)(PO4)(OH), vauquelinite, Pb2Cu(CrO4)(PO4)(OH), brackebuschite, Pb2 (Mn, Fe)(VO4)2(OH), arsenbracke buschite, Pb2(Fe, Zn)(AsO4)2(OH, H2O), fornacite, Pb2Cu(AsO4)(CrO4)(OH), and feinglosite, Pb2(Zn, Fe)[(As, S)O4]2(H2O). Arsentsumebite and all other group members contain M = M–T chains where M = M means edge-sharing between MO6 octahedra and M–T represents corner sharing between octahedra and XO4 tetrahedra. A structural relationship exists to tsumcorite, Pb(Zn, Fe)2(AsO4)2 (OH, H2O)2 and tsumcorite-group minerals Me(1)Me(2)2(XO4)2(OH, H2O)2.
Received June 24, 2000; revised version accepted February 8, 2001 相似文献
15.
Summary. ?Ca-tourmaline has been synthesized hydrothermally in the presence of Ca(OH)2 and CaCl2-bearing solutions of different concentration at T = 300–700 °C at a constant fluid pressure of 200 MPa in the system CaO-MgO-Al2O3-SiO2-B2O3-H2O-HCl. Synthesis of tourmaline was possible at 400 °C, but only above 500 °C considerable amounts of tourmaline formed. Electron
microprobe analysis and X-ray powder data indicate that the synthetic tourmalines are essentially solid solutions between
oxy-uvite, CaMg3- Al6(Si6O18)(BO3)3(OH)3O, and oxy-Mg-foitite, □(MgAl2)Al6(Si6O18)(BO3)3(OH)3O. The amount of Ca ranges from 0.36 to 0.88 Ca pfu and increases with synthesis temperature as well as with bulk Ca-concentration
in the starting mixture. No hydroxy-uvite, CaMg3(MgAl5)(Si6O18)(BO3)3(OH)3(OH), could be synthesized. All tourmalines have < 3 Mg and > 6 Al pfu. The Al/(Al + Mg)-ratio decreases from 0.80 to 0.70
with increasing Ca content. Al is coupled with Mg and Ca via the substitutions Al2□Mg−2Ca−1 and AlMg−1H−1. No single phase tourmaline could be synthesized. Anorthite ( + quartz in most runs) has been found coexisting with tourmaline.
Other phases are chlorite, tremolite, enstatite or cordierite.
Between solid and fluid, Ca is strongly fractionated into tourmaline ( + anorthite). The concentration ratio D = Ca(fluid)/Ca(tur) increases from 0.20 at 500 °C up to 0.31 at 700 °C. For the assemblage turmaline + anorthite + quartz + chlorite or tremolite
or cordierite, the relationship between Ca content in tourmaline and in fluid with temperature can be described by the equation
(whereby T = temperature in °C, Ca(tur) = amount of Ca on the X-site in tourmaline, Ca( fluid) = concentration of Ca2+ in the fluid in mol/l). The investigations may serve as a first guideline to evaluate the possibility to use tourmaline as
an indicator for the fluid composition.
Received July 24, 1998;/revised version accepted October 21, 1999 相似文献
Zusammenfassung. ?Synthese von Ca-Turmelin im System CaO-MgO-Al 2 O 3 -SiO 2 -B 2 O 3 -H 2 O-HCl Im System CaO-MgO-Al2O3-SiO2-B2O3-H2O-HCl wurde Ca-Turmalin hydrothermal aus Ca(OH)2 and CaCl2-haltigen L?sungen bei T = 300–700 °C und einem konstanten Fluiddruck von 200 MPa synthetisiert. Die Synthese von Turmalin war m?glich ab 400 °C, aber nur oberhalb von 500 °C bildeten sich deutliche Mengen an Turmalin. Elektronenstrahl-Mikrosondenanalysen und R?ntgenpulveraufnahmen zeigen, da? Mischkristalle der Reihe Oxy-Uvit, CaMg3Al6(Si6O18)(BO3)3(OH)3O, und Oxy-Mg-Foitit, □(MgAl2)Al6(Si6O18)(BO3)3(OH)3O gebildet wurden. Der Anteil an Ca variiert zwischen 0.36 und 0.88 Ca pfu und nimmt mit zunehmender Synthesetemperatur und zunehmender Ca-Konzentration im System zu. Hydroxy-Uvit, CaMg3(MgAl5) (Si6O18)(BO3)3(OH)3(OH), konnte nicht synthetisiert werden. Alle Turmaline haben < 3 Mg und > 6 Al pfu. Dabei nimmt das Al/(Al + Mg)- Verh?ltnis mit zunehmendem Ca-Gehalt von 0.80 auf 0.70 ab. Al ist gekoppelt mit Mg und Ca über die Substitutionen Al2□Mg−2Ca−1 und AlMg−1H−1. Einphasiger Turmalin konnte nicht synthetisiert werden. Anorthit (+ Quarz in den meisten F?llen) koexistiert mit Turmalin. Andere Phasen sind Chlorit, Tremolit, Enstatit oder Cordierit. Ca zeigt eine deutliche Fraktionierung in den Festk?rpern Turmalin (+ Anorthit). Das Konzentrationsverh?ltnis D = Ca(fluid)/Ca(tur) nimmt von 0.20 bei 500 °C auf 0.31 bei 700 °C zu. Für die Paragenese Turmalin + Anorthit + Quarz mit Chlorit oder Tremolit oder Cordierit gilt folgende Beziehung zwischen Ca-Gehalt in Turmalin und Fluid und der Temperatur: (wobei T = Temperatur in °C, Ca(tur) = Anteil an Ca auf der X-Position in Turmalin, Ca(fluid) = Konzentration von Ca2+ im Fluid in mol/l). Die Untersuchungen dienen zur ersten Absch?tzung, ob Turmalin als Fluidindikator petrologisch nutzbar ist.
Received July 24, 1998;/revised version accepted October 21, 1999 相似文献
16.
The heat capacity of end-member titanite and (CaTiSiO5) 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 P21/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 P21/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 (CaTiSiO5) 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
17.
Alison Pawley 《Contributions to Mineralogy and Petrology》2000,138(3):284-291
The low-pressure stability of clinohumite has been investigated in phase-equilibrium experiments on the reaction forsterite + brucite = clinohumite.
The reaction was bracketed between 2.45 and 2.84 GPa at 650 °C, extending to between 1.37 and 1.57 GPa at 850 °C. At temperatures
above the reaction brucite = periclase + vapour, the reaction clinohumite = forsterite + vapour was bracketed between 1.27
and 1.52 GPa at 900 °C, rising to between 1.90 and 2.00 GPa at 1000 °C. The position of the reaction forsterite + brucite = clinohumite
is ∼0.5 GPa below the position determined in previous work, the difference arising either from pressure uncertainties in both
studies, from enhanced reaction to clinohumite in this study due to the presence of excess brucite in the starting material,
or from different concentrations of defects in the two samples. The brackets on the reaction were combined with other measured
and estimated thermodynamic data for clinohumite to determine its enthalpy of formation and entropy, in a revised version
of the thermodynamic dataset of Holland and Powell (1998). The values obtained were ΔH
f
=−9607.29±3.05 kJ mol−1, S=445 J mol−1 K−1. These data were used to calculate positions of other reactions involving clinohumite. The calculations suggest a larger
stability field for clinohumite than implied by the results of previous experimental studies, indicating a need for more high-pressure
phase-equilibrium studies to provide better thermodynamic data.
Received: 30 April 1999 / Accepted: 8 November 1999 相似文献
18.
The lattice constants of paragonite-2M1, NaAl2(AlSi3)O10(OH)2, were determined to 800 °C by the single-crystal diffraction method. Mean thermal expansion coefficients, in the range 25–600 °C,
were: αa = 1.51(8) × 10−5, αb = 1.94(6) × 10−5, αc = 2.15(7) × 10−5 °C−1, and αV = 5.9(2) × 10−5 °C−1. At T higher than 600 °C, cell parameters showed a change in expansion rate due to a dehydroxylation process. The structural refinements
of natural paragonite, carried out at 25, 210, 450 and 600 °C, before dehydroxylation, showed that the larger thermal expansion
along the c parameter was mainly due to interlayer thickness dilatation. In the 25–600 °C range, Si,Al tetrahedra remained quite unchanged,
whereas the other polyhedra expanded linearly with expansion rate proportional to their volume. The polyhedron around the
interlayer cation Na became more regular with temperature. Tetrahedral rotation angle α changed from 16.2 to 12.9°. The structure
of the new phase, nominally NaAl2 (AlSi3)O11, obtained as a consequence of dehydroxylation, had a cell volume 4.2% larger than that of paragonite. It was refined at room
temperature and its expansion coefficients determined in the range 25–800 °C. The most significant structural difference from
paragonite was the presence of Al in fivefold coordination, according to a distorted trigonal bipyramid. Results confirm the
structural effects of the dehydration mechanism of micas and dioctahedral 2:1 layer silicates. By combining thermal expansion
and compressibility data, the following approximate equation of state in the PTV space was obtained for paragonite: V/V
0 = 1 + 5.9(2) × 10−5
T(°C) − 0.00153(4) P(kbar).
Received: 12 July 1999 / Revised, accepted: 7 December 1999 相似文献
19.
Benita Putlitz Alan Matthews John W. Valley 《Contributions to Mineralogy and Petrology》2000,138(2):114-126
Oxygen and hydrogen stable isotope ratios of eclogite-facies metagabbros and metabasalts from the Cycladic archipelago (Greece)
document the scale and timing of fluid–rock interaction in subducted oceanic crust. Close similarities are found between the
isotopic compositions of the high-pressure rocks and their ocean-floor equivalents. High-pressure minerals in metagabbros
have low δ18O values: garnet 2.6 to 5.9‰, glaucophane 4.3 to 7.1‰; omphacite 3.5 to 6.2‰. Precursor actinolite that was formed during
the hydrothermal alteration of the oceanic crust by seawater analyses at 3.7 to 6.3‰. These compositions are in the range
of the δ18O values of unaltered igneous oceanic crust and high-temperature hydrothermally altered oceanic crust. In contrast, high-pressure
metabasalts are characterised by 18O-enriched isotopic compositions (garnet 9.2 to 11.5‰, glaucophane 10.6 to 12.5‰, omphacite 10.2 to 12.8‰), which are consistent
with the precursor basalts having undergone low-temperature alteration by seawater. D/H ratios of glaucophane and actinolite
are also consistent with alteration by seawater. Remarkably constant oxygen isotope fractionations, compatible with isotopic
equilibrium, are observed among high-pressure minerals, with Δglaucophane−garnet = 1.37 ± 0.24‰ and Δomphacite−garnet = 0.72 ± 0.24‰. For the estimated metamorphic temperature of 500 °C, these fractionations yield coefficients in the equation
Δ = A * 106/T
2 (in Kelvin) of Aglaucophane−garnet = 0.87 ± 0.15 and Aomphacite−garnet = 0.72 ± 0.24. A fractionation of Δglaucophane–actinolite = 0.94 ± 0.21‰ is measured in metagabbros, and indicates that isotopic equilibrium was established during the metamorphic
reaction in which glaucophane formed at the expense of actinolite. The preservation of the isotopic compositions of gabbroic
and basaltic oceanic crust and the equilibrium fractionations among minerals shows that high-pressure metamorphism occurred
at low water/rock ratios. The isotopic equilibrium is only observed at hand-specimen scale, at an outcrop scale isotopic compositional
differences occur among adjacent rocks. This heterogeneity reflects metre-scale compositional variations that developed during
hydrothermal alteration by seawater and were subsequently inherited by the high-pressure metamorphic rocks.
Received: 4 January 1999 / Accepted: 7 July 1999 相似文献
20.
The Archean Shawmere anorthosite lies within the granulite facies portion of the Kapuskasing Structural Zone (KSZ), Ontario,
and is crosscut by numerous linear alteration veins containing calcite + quartz ± dolomite ± zoisite ± clinozoisite ± margarite ±paragonite ± chlorite.
These veins roughly parallel the trend of the Ivanhoe Lake Cataclastic Zone. Equilibria involving clinozoisite + margarite + quartz ± calcite
± plagioclase show that the vein minerals were stable at T < 600 °C, XCO2 < 0.4 at P ≈ 6 kbar. The stabilities of margarite and paragonite in equilibrium with quartz are also consistent with T < 600 °C and XCO2 < 0.4 at 6 kbar. Additional assemblages consisting of calcite + clinochlore + quartz + talc + margarite indicate T < 500 °C with XCO2 > 0.9. Thus, vein formation, while clearly retrograde, spanned a range of temperatures, and fluid compositions evolved from
H2O-rich to CO2-rich. The calcite in the retrograde veins has δ18O values that range from 8.4 to 11.2‰ (average = +9.7 ± 0.9‰) and δ13C values that range from −3.9 to −1.6‰ (average = −3.1 ± 0.6‰). These values indicate that the fluids from which calcite precipitated
underwent extensive exchange with the anorthosite and other crustal lithologies. The fluids may have been initially derived
either from devolatilization of metamorphic rocks or crystallization of igneous rocks in the adjacent Abitibi subprovince.
Vein quartz contains CO2-rich fluid inclusions (final melting T = −57.0 to −58.7 °C) that range in size from 5 to 17 μm. Measured homogenization temperatures (T h) range from −44.0 to 14.5 °C, however for most inclusions (46 of S1), T h = −44.0 to −21.1 °C (ρCO2 ≈ 1.13 to 1.05 g/cm3). At 400 to 600 °C, these densities correspond to pressures of 3.5 to 7 kbar, which is the best estimate of pressures of
vein formation. It has been argued that some high density CO2-rich fluid inclusions found in the KSZ were formed during peak metamorphism and thus document the presence of a CO2-rich fluid during peak granulite facies metamorphism (Rudnick et al. 1984). The association of high density CO2-rich fluid inclusions with clearly retrograde veins documents the formation of similar composition and density inclusions
after the peak of metamorphism. Thus, the coincidence of entrapment pressures calculated from fluid inclusion density measurements
with peak metamorphic pressures alone should not be considered strong evidence for peak metamorphic inclusion entrapment.
All fluid inclusion results are consistent with an initially semi-isobaric retrograde P–T path.
Received: 2 April 1996 / Accepted: 15 November 1996 相似文献