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1.
Thermal diffusivity (D) was measured using laser-flash analysis from oriented single-crystal low-sanidine (K0.92Na0.08Al0.99Fe3+ 0.005Si2.95O8), and three glasses near KAlSi3O8. Viscosity measurements of the three supercooled liquids, in the range 106.8 to 1012.3 Pa s, confirm near-Arrhenian behavior, varying subtly with composition. For crystal and glass, D decreases with T, approaching a constant near 1,000 K: D sat ∼ 0.65 ± 0.3 mm2 s−1 for bulk crystal and ∼0.53 ± 0.03 mm2 s−1 for the glass. A rapid decrease near 1,400 K is consistent with crossing the glass transition. Melt behavior is approximated by D = 0.475 ± 0.01 mm2 s−1. Thermal conductivity (k lat) of glass, calculated using previous heat capacity (C P) and new density data, increases with T because C P strongly increases with T. For melt, k lat reaches a plateau near 1.45 W m−1 K−1, and is always below k lat of the crystal. Melting of potassium feldspars impedes heat transport, providing positive thermal feedback that may promote further melting in continental crust.  相似文献   

2.
The dielectric constants and dissipation factors of LiAlSi2O6, CaAl2Si2O8 and CaMgSi2O6 in both the crystalline (α-spodumene, anorthite, and diopside) and amorphous forms were determined at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: spodumene κ′ 11=7.30 tan δ= 0.0007 κ′22=8.463 tan δ= 0.0002 κ′33 =11.12 tan δ= 0.0007 anorthite κ′ a *=5.47 tan δ= 0.0009 κ′b *=8.76 tan δ= 0.0010 κ′c *=7.19 tan δ= 0.0013 diopside κ′11=9.69 tan δ= 0.0016 κ′22 = 7.31 tan δ= 0.0007 κ′33=7.29 tan δ= 0.00019 LiAlSi2O6 κ′=8.07 tan δ= 0.047 amorphous CaAl2Si2O8 κ′=7.50 tan δ= 0.0024 amorphous CaMgSi2O6 κ′=8.89 tan δ= 0.0021 amorphous The dielectric properties of a spodumene glass, progressively crystallized at different conditions, were also determined. As the crystallization temperature was increased from 720 to 920° C, κ′ increased from 6.22 to 6.44. The dissipation factor, tan δ, remained constant at 0.020. Similarly, as the crystallization time at 750° C increased from 0.5 hr to 6.0 hr, κ′ increased from 6.28 to 6.35. The deviations of the measured dielectric polarizabilities as determined from the Clausius-Mosotti equation from those calculated from the sum of oxide polarizabilities according to α D(mineral, glass) = σ α D(oxides) are +7.4% for α-spodumene, +1.2% for diopside, and +28.0, +19.6 and +15.9% for amorphous spodumene, anorthitie and diopside compositions, respectively. Positive deviations in α-spodumene and anorthite are consistent with lower than normal apparent cation bond valence sums and are believed to be evidence for loosely bonded “rattling” Li and Ca ions. Diopside, with Ca and Mg ions having normal bond valence sums, exhibits no abnormal deviation from additivity. Larger positive deviations in amorphous SiO2, LiAlSi2O6, CaAl2Si2O8 and CaMgSi2O6 are postulated to arise from a combination of loosely bonded cations and disordered O= ions where the oxygen dielectric polarizability increased from its normal value of 2.0 Å3 in well-behaved oxides to 2.2–3.0 Å3 in the amorphous phases.  相似文献   

3.
Thermal diffusivity (D) of garnets with diverse chemical compositions was measured using the laser-flash technique, which is accurate (±2%) and isolates the lattice component from direct radiative transfer. Temperatures ranged from ~290 to ~1,600 K (unless limited by melting). Seven synthetic (e.g., YAG, GGG) and 15 natural garnets with two types of ionic substitution [Ca3(Fe,Al)2Si3O12 and (Mg,Fe,Ca)3Al2Si3O12] and varying amounts of OH- were examined. Cation substitution or hydroxyl incorporation lowers D from end-member values. Thermal diffusivity is constant once the temperature (T) exceeds a critical value (T sat) of ~1,100 to 1,500 K. From ~290 K to T sat, the measurements are best represented by 1/D=A+BT+CT 2 where A, B, and C are constants. These constants vary little among diverse chemical compositions, suggesting that the oxygen sublattice controls heat transport. Higher order terms are needed only when T sat is low, such as Ant Hill garnet wherein 1/D=0.049403+0.0032299T−2.3992T 2×10−6+6.0168T 3×10−10(1/D in s/mm2; T in K). The mean free path (λ, computed from D and sound velocities) is slightly larger than the lattice parameter above T sat, in accord with phonon–phonon interactions requiring non-localized modes. At most temperatures, λ is nm-sized. Large values of λ are obtained by extrapolation to a few Kelvins, suggesting that boundary scattering can only be important at extremely cold temperatures. The observed behavior with T and chemical composition is consistent with the damped harmonic oscillator model. Phonon transport is best represented by inverse thermal diffusivity wherein 1/D goes as T n where n is between 1 and 3 up to ~200 K, depends on a quadratic or cubic polynomial at moderate T, but is constant above T sat. The predicted and observed temperature response of 1/D mimics the well-known form for heat capacity, in that acoustic modes control heat transport near cryogenic temperatures, optic phonons dominate above ambient temperature, and a limit analogous to that of Dulong and Petit is reached at very high temperature, due to full population of discrete phonon states.  相似文献   

4.
The synthetic amphibole Na0.95(Li0.95Mg1.05)Mg5Si8O22(OH)2 was studied in situ at high-T, using IR OH-stretching spectroscopy and synchrotron X-ray powder diffraction. At room-T the sample has P21 /m symmetry, as shown by the FTIR spectrum. It shows in the OH region two well-defined and intense absorptions at 3,748 and 3,712 cm−1, respectively, and two minor bands at 3,667 and 3,687 cm−1. The main bands are assigned to the two independent O–H groups in the primitive structure. The two minor bands evidencing the presence of small amount of vacant A-site (A□0.05). With increasing T, these bands shift continuously and merge into a unique absorption at high temperature. A change as a function of increasing T is revealed by the evolution of the refined unit-cell parameters, whose trend shows a transition to C2/m at about 320–330°C. The spontaneous scalar strain, fitted with a tricritical 2–6 Landau potential, gives a T c of 325(10)°C (β parameter = 0.27). Comparison with the second-order P21 /m ⇔ C2/m phase transition at 255°C for synthetic amphibole ANa0.8B(Na0.8Mg1.2)CMg5Si8O22(OH)2 indicates that the substitution of Na with Li at the B-sites strongly affects the thermodynamic character and the T c of the phase transition. The comparison of LNMSH amphiboles with cummingtonitic ones shows that the high-T thermodynamic behaviour is affected by A-site occupancy.  相似文献   

5.
Kojitani  H.  Nishimura  K.  Kubo  A.  Sakashita  M.  Aoki  K.  Akaogi  M. 《Physics and Chemistry of Minerals》2003,30(7):409-415
Raman spectroscopy of calcium ferrite type MgAl2O4 and CaAl2O4 and heat capacity measurement of CaAl2O4 calcium ferrite were performed. The heat-capacity of CaAl2O4 calcium ferrite measured by a differential scanning calorimeter (DSC) was represented as CP(T)=190.6–1.116 × 107T–2 + 1.491 × 109T–3 above 250 K (T in K). The obtained Raman spectra were applied to lattice dynamics calculation of heat capacity using the Kieffer model. The calculated heat capacity for CaAl2O4 calcium ferrite showed good agreement with that by the DSC measurement. A Kieffer model calculation for MgAl2O4 calcium ferrite similar to that for CaAl2O4 calcium ferrite was made to estimate the heat capacity of the former. The heat capacity of MgAl2O4 calcium ferrite was represented as CP(T)=223.4–1352T –0.5 – 4.181 × 106T –2 + 4.300 × 108T –3 above 250 K. The calculation also gave approximated vibrational entropies at 298 K of calcium ferrite type MgAl2O4 and CaAl2O4 as 97.6 and 114.9 J mol–1 K–1, respectively.  相似文献   

6.
The volume thermal expansion coefficient and the anisotropy of thermal expansion were determined for nine natural feldspars with compositions, in terms of albite (NaAlSi3O8, Ab) and anorthite (CaAl2Si2O8, An), of Ab100, An27Ab73, An35Ab65, An46Ab54, An60Ab40, An78Ab22, An89Ab11, An96Ab4 and An100 by high resolution powder diffraction with a synchrotron radiation source. Unit-cell parameters were determined from 124 powder patterns of each sample, collected over the temperature range 298–935 K. The volume thermal expansion coefficient of the samples determined by a linear fit of V/V 0 = α(T − T 0) varies with composition (X An in mol %) as:
aV = 2.90( 4 ) ×10 - 5 - 3.0( 2 ) ×10 - 7 *X\textAn + 1.8( 2 ) ×10 - 9 *X\textAn2 \alpha_{V} = 2.90\left( 4 \right) \times 10^{ - 5} - 3.0\left( 2 \right) \times 10^{ - 7} *X_{\text{An}} + 1.8\left( 2 \right) \times 10^{ - 9} *X_{\text{An}}^{2}  相似文献   

7.
Six synthetic NaScSi2O6–CaNiSi2O6 pyroxenes were studied by optical absorption spectroscopy. Five of them of intermediate (Na1−x , Ca x )(Sc1−x , Ni x )Si2O6 compositions show spectra typical of Ni2+ in octahedral coordination, more precise Ni2+ at the M1 site of the pyroxene structure. The common feature of all spectra is three broad absorption bands with maxima around 8,000, 13,000 and 24,000 cm−1 assigned to 3 A 2g → 3 T 2g, 3 A 2g → 3 T 1g and →3 T 1g (3 P) electronic spin-allowed transitions of VINi2+. A weak narrow peak at ∼14,400 cm−1 is assigned to the spin-forbidden 3 A 2g → 1 T 2g (1 D) transition of Ni2+. Under pressure the spin-allowed bands shift to higher energies and change in intensity. The octahedral compression modulus, calculated from the shift of the 3 A 2g → 3 T 2g band in the (Na0.7Ca0.3)(Sc0.7Ni0.3)Si2O6 pyroxene is evaluated as 85±20 GPa. The Racah parameter B of Ni2+(M1) is found gradually changing from ∼919 cm−1 at ambient pressure to ∼890 cm−1 at 6.18 GPa. The Ni end-member pyroxene [(Ca0.93 Ni0.07)NiSi2O6] has a spectrum different from all others. In addition to the above mentioned bands of Ni2+(M1) it displays several new relatively intense and broad extra bands, which were attributed to electronic transitions of Ni2+ at the M2 site. In difference to CaO8 polyhedron geometry of an eightfold coordination, Ni2+(M2)O8 polyhedra are assumed to be relatively large distorted octahedra. Due to different distortions and different compressibilities of the M1 and M2 sites the Ni2+(M1)- and Ni2+(M2)-bands display rather different pressure-induced behaviors, becoming more resolved in the high-pressure spectra than in that measured at atmospheric pressure. The octahedral compression modulus of Ni2+(M1) in this end-member pyroxene is evaluated as 150 ± 25 GPa, which is noticeably larger than in Ni0.3 pyroxene. This is due to a smaller size and, thus, a stiffer character of Ni2+(M1)O6 octahedron in the (Ca0.93Ni0.07)NiSi2O6 pyroxene compared to (Na0.7Ca0.3)(Sc0.7Ni0.3)Si2O6.
Monika Koch-MüllerEmail:
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8.
A novel experimental cell was developed for in situ measurements of transport phenomena in porous media using Fourier-Transform Infrared (FTIR) Spectroscopy. The technique was employed at ambient pressure in the temperatures range of 11–44 °C to study the H2O → D2O exchange between water-saturated weathered feldspars (bulk porosity of 5–19 vol% for feldspar) from granitic saprolites and a surrounding aqueous liquid. Such measurements are an important step for understanding internal weathering reactions of feldspars in soils and aquifers. Effective diffusion coefficients Deff for water in water-saturated porous feldspars were determined assuming one-dimensional diffusion in a quasi-homogeneous medium. The values of Deff vary from 7.2 × 10−10 to 1.9 × 10−11 m2/s and are 1–2 orders of magnitude lower than the diffusion coefficients (D) of protons and molecular H2O in liquid water. The activation energy for the H2O → D2O exchange process in porous feldspars ranges from 7.8 to 18.8 kJ/mol.The results imply that the effective diffusivity of water is mainly controlled by physical properties of the feldspars like porosity, pore connectivity, pore geometry and distribution. Perthitic feldspars with homogeneous pore distribution in the albitic lamellas have diffusional tortuosity factors X = D/Deff between 3 and 10 while alkali feldspars with inhomogeneously distributed and disconnected pores have much higher X values up to 129. Diffusion anisotropy has been verified for a vein perthite with diffusion perpendicular to the lamellas being faster by 0.3–0.5 log units than within the lamellas. It has to be emphasized that the study is based only on few selected feldspars, including perthitic feldspar, and additional work on samples with different weathering stages is needed to test the importance of the different parameters controlling diffusive transport in the pore system.  相似文献   

9.
 In Madagascar, hibonite occurs as a rather frequent mineral within thorianite-bearing skarns which are widespread in the Pan African granulitic formations constituting the S-E part of the Island (Tranomaro area). In these skarns, leucocratic segregations made up of CO3-scapolite to meionite (Anequivalent=89–95% which implies T≥850° C), spinel and corundum were formed at stage 1 of metasomatism in a titanite-bearing matrix consisting of scapolite (Aneq=77–88) and aluminous diopside. During stage 2 of metasomatism, scapolite from the lenses were altered to anorthite+calcite while the less calcic scapolite remained stable which indicates T≈800° C. Hibonite crystallized at the expense of corundum and spinel. Expressed as mol% of the CaAl12O19/Ca(Al10TiR2+)O19/REE(Al11R2+)O19 [+Th (Al10R2+ 2)O19] end-members (R 2+=Mg, Fe2+, Zn2+; Al=Al, Fe3+; Ti=Ti, Si), its composition varies from 26/72/2 to 50/23/27. The ideal activity of the CaAl12O19 component is about 0.25. Fluid inclusions in corundum, hibonite and anorthite are composed of nearly pure CO2. In corundum, the isochores for primary inclusions are in agreement with the P-T estimates for regional metamorphism and stage 1 metasomatism (T≈850° C, P≈5 kbar). Inclusions with the highest density in hibonite and anorthite constrain P to about 3–3.5 kbar for T=800° C. Thermodynamic calculations indicate that, in addition to a low activity of CaAl12O19, stability of hibonite in equilibrium with anorthite and calcite implies an extremely low activity of silica (below the zircon-baddeleyite buffer). By contrast the activity of CO2 may be high, in agreement with the observed fluid compositions. These results are corroborated by a short comparison with the other granulite occurrences of hibonite in Tanzania and South India. Received: 18 August 1994 / Accepted: 12 October 1995  相似文献   

10.
Four different solution models, the two-parameter Margules, the quasi-chemical (QC), the Wilson and the non-random two-liquid (NRTL) model, have been used for fitting the calorimetric excess enthalpy of solution for the following four binary silicate systems: anorthite-albite, pyrope-grossular, diopside-enstatite and diopside-Ca-Tschermak. All models except the Wilson model yield a satisfactory fit to the data but the NRTL model generally results in the lowest residuals. The use of NRTL and QC facilitates the study of the configurational and non-configurational parts of the excess entropy of mixing.Three different methods, namely those of Kohler, Wohl, and Hillert, have been used to combine binary solution properties to predict ternary solution properties. Comparison of computed excess free energy of mixing in a hypothetical solution shows that all the three methods are viable but the Kohler and Wohl methods are similar to each other and are significantly different from the Hillert method. The Kohler method with one or a combination of different binary models is recommended for predicting multicomponent solution properties.Abbreviations G ex excess free energy of mixing - H ex excess enthalpy of mixing - S ex total excess entropy of mixing - S ex c configurational excess entropy of mixing - W ij interaction energy parameter between speciesi andj - X i mole fraction of speciesi - QC quasi-chemical - NRTL non-random two-liquid - M Margules formulation - W Wohl's formulation - RK Redlich-Kister - K Bertrand-Kohler - H Hillert - Di diopside (CaMgSi2O6) - En enstatite (Mg2Si2O6) - Py pyrope (MgAl2/3SiO4) - Gr grossular (CaAl2/3SiO4) - CaTs Ca-Tschermak (CaAl2SiO6) - Ab albite (NaAlSi3O8) - An anorthite (CaAl2Si2O8)  相似文献   

11.
The behaviour of synthetic Mg-ferrite (MgFe2O4) has been investigated at high pressure (in situ high-pressure synchrotron radiation powder diffraction at ESRF) and at high temperature (in situ high-temperature X-ray powder diffraction) conditions. The elastic properties determined by the third-order Birch–Murnaghan equation of state result in K0=181.5(± 1.3) GPa, K=6.32(± 0.14) and K= –0.0638 GPa–1. The symmetry-independent coordinate of oxygen does not show significant sensitivity to pressure, and the structure shrinking is mainly attributable to the shortening of the cell edge (homogeneous strain). The lattice parameter thermal expansion is described by a0+a1*(T–298)+a2/(T–298)2, where a0=9.1(1) 10–6 K–1, a1=4.9(2) 10–9 K–2 and a2= 5.1(5) 10–2 K. The high-temperature cation-ordering reaction which MgFe-spinel undergoes has been interpreted by the ONeill model, whose parameters are = 22.2(± 1.8) kJ mol–1 and =–17.6(± 1.2) kJ mol–1. The elastic and thermal properties measured have then been used to model the phase diagram of MgFe2O4, which shows that the high-pressure transition from spinel to orthorombic CaMn2O4-like structure at T < 1700 K is preceded by a decomposition into MgO and Fe2O3.  相似文献   

12.
This work focuses on a rigorous analysis of the physical–chemical, compositional and textural relationships of amphibole stability and the development of new thermobarometric formulations for amphibole-bearing calc-alkaline products of subduction-related systems. Literature experimental results (550–1,120°C, <1,200 MPa, −1 ≤ ΔNNO ≤ +5), H2O–CO2 solubility models, a multitude of amphibole-bearing calc-alkaline products (whole-rocks and glasses, representing 38 volcanoes worldwide), crustal and high-P (1–3 GPa) mantle amphibole compositions have been used. Calcic amphiboles of basalt-rhyolite volcanic products display tschermakitic pargasite (37%), magnesiohastingsite (32%) and magnesiohornblende (31%) compositions with aluminium number (i.e. Al# = [6]Al/AlT) ≤ 0.21. A few volcanic amphiboles (~1%) show high Al# (>0.21) and are inferred to represent xenocrysts of crustal or mantle materials. Most experimental results on calc-alkaline suites have been found to be unsuitable for using in thermobarometric calibrations due to the high Al# (>0.21) of amphiboles and high Al2O3/SiO2 ratios of the coexisting melts. The pre-eruptive crystallization of consistent amphiboles is confined to relatively narrow physical–chemical ranges, next to their dehydration curves. The widespread occurrence of amphiboles with dehydration (breakdown) rims made of anhydrous phases and/or glass, related to sub-volcanic processes such as magma mixing and/or slow ascent during extrusion, confirms that crystal destabilization occurs with relatively low T–P shifts. At the stability curves, the variance of the system decreases so that amphibole composition and physical–chemical conditions are strictly linked to each other. This allowed us to retrieve some empirical thermobarometric formulations which work independently with different compositional components (i.e. Si*, AlT, Mg*, [6]Al*) of a single phase (amphibole), and are therefore easily applicable to all types of calc-alkaline volcanic products (including hybrid andesites). The Si*-sensitive thermometer and the fO2–Mg* equation account for accuracies of ±22°C (σest) and 0.4 log units (maximum error), respectively. The uncertainties of the AlT-sensitive barometer increase with pressure and decrease with temperature. Near the P–T stability curve, the error is <11% whereas for crystal-rich (porphyritic index i.e. PI > 35%) and lower-T magmas, the uncertainty increases up to 24%, consistent with depth uncertainties of 0.4 km, at 90 MPa (~3.4 km), and 7.9 km, at 800 MPa (~30 km), respectively. For magnesiohornblendes, the [6]Al*-sensitive hygrometer has an accuracy of 0.4 wt% (σest) whereas for magnesiohastingsite and tschermakitic pargasite species, H2Omelt uncertainties can be as high as 15% relative. The thermobarometric results obtained with the application of these equations to calc-alkaline amphibole-bearing products were finally, and successfully, crosschecked on several subduction-related volcanoes, through complementary methodologies such as pre-eruptive seismicity (volcano-tectonic earthquake locations and frequency), seismic tomography, Fe–Ti oxides, amphibole–plagioclase, plagioclase–liquid equilibria thermobarometry and melt inclusion studies. A user-friendly spreadsheet (i.e. AMP-TB.xls) to calculate the physical–chemical conditions of amphibole crystallization is also provided.  相似文献   

13.
The low-temperature heat capacity (C p ) of KAlSi3O8 with a hollandite structure was measured over the range of 5–303 K with a physical properties measurement system. The standard entropy of KAlSi3O8 hollandite is 166.2±0.2 J mol−1 K−1, including an 18.7 J mol−1 K−1 contribution from the configurational entropy due to disorder of Al and Si in the octahedral sites. The entropy of K2Si4O9 with a wadeite structure (Si-wadeite) was also estimated to facilitate calculation of phase equilibria in the system K2O–Al2O3–SiO2. The calculated phase equilibria obtained using Perple_x are in general agreement with experimental studies. Calculated phase relations in the system K2O–Al2O3–SiO2 confirm a substantial stability field for kyanite–stishovite/coesite–Si-wadeite intervening between KAlSi3O8 hollandite and sanidine. The upper stability of kyanite is bounded by the reaction kyanite (Al2SiO5) = corundum (Al2O3) + stishovite (SiO2), which is located at 13–14 GPa for 1,100–1,400 K. The entropy and enthalpy of formation for K-cymrite (KAlSi3O8·H2O) were modified to better fit global best-fit compilations of thermodynamic data and experimental studies. Thermodynamic calculations were undertaken on the reaction of K-cymrite to KAlSi3O8 hollandite + H2O, which is located at 8.3–10.0 GPa for the temperature range 800–1,600 K, well inside the stability field of stishovite. The reaction of muscovite to KAlSi3O8 hollandite + corundum + H2O is placed at 10.0–10.6 GPa for the temperature range 900–1,500 K, in reasonable agreement with some but not all experiments on this reaction.  相似文献   

14.
To get deeper insight into the phase relations in the end-member system Fe2SiO4 and in the system (Fe, Mg)2SiO4 experiments were performed in a multi-anvil apparatus at 7 and 13 GPa and 1,000–1,200°C as a function of oxygen fugacity. The oxygen fugacity was varied using the solid oxygen buffer systems Fe/FeO, quartz–fayalite–magnetite, MtW and Ni/NiO. The run products were characterized by electron microprobe, Raman- and FTIR-spectroscopy, X-ray powder diffraction and transmission electron microscopy. At fO2 corresponding to Ni/NiO Fe-ringwoodite transforms to ferrosilite and spinelloid according to the reaction: 9 Fe2SiO4 + O2 = 6 FeSiO3 + 5 Fe2.40Si0.60O4. Refinement of site occupancies in combination with stoichiometric Fe3+ calculations show that 32% of the total Fe is incorporated as Fe3+ according to From the Rietveld refinement we identified spl as spinelloid III (isostructural with wadsleyite) and/or spinelloid V. As we used water in excess in the experiments the run products were also analyzed for structural water incorporation. Adding Mg to the system increases the stability field of ringwoodite to higher oxygen fugacity and the spinel structure seems to accept higher Fe3+ but also water concentrations that may be linked. At oxygen fugacity corresponding to MtW conditions similar phase relations in respect to the breakdown reaction in the Fe-end-member system were observed but with a strong fractionation of Fe into spl and Mg into coexisting cpx. Thus, through this strong fractionation it is possible to stabilize very Fe-rich wadsleyite with considerable Fe3+ concentrations even at an intermediate Fe–Mg bulk composition: assuming constant K D independent on composition and a bulk composition of x Fe = 0.44 this fractionation would stabilize spl with x Fe = 0.72. Thus, spl could be a potential Fe3+ bearing phase at P–T conditions of the transition zone but because of the oxidizing conditions and the Fe-rich bulk composition needed one would expect it more in subduction zone environments than in the transition zone in senso stricto.
M. Koch-MüllerEmail:
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15.
The techniques of electron paramagnetic resonance (EPR) were used to measure the concentration ratio of Eu2+ to Eu3+ in quenched CaMgSi2O6, Ca3Si3O12, and CaAl2Si2O8 liquids as functions of partial pressure of oxygen and temperature. The redox equilibrium of the Eu ions was described by the reaction 4Eu3+ + 202? = 4Eu2+ + O2. The reduction of Eu3+ to Eu2+ was endothermic, and for CaMgSi2O6 and Ca3Al2Si3O12 liquids the mean value of ΔH0 and the standard deviation from that mean were 25 ± 7 kcal/mole.The magnitude of the Eu anomaly in the distribution coefficients is discussed in terms of the compositions of the solid and liquid phases.  相似文献   

16.
Using experimental results at 1·0 GPa for the systemsCaO–SiO2, MgO–SiO2, CaMgSi2O6–SiO2 and CaMgSi2O6–Mg2SiO4,and all the currently available phase equilibria and thermodynamicdata at 1 bar, we have optimized the thermodynamic propertiesof the liquid phase at 1·0 GPa. The new optimized thermodynamicparameters indicate that pressure has little effect on the topologyof the CaO–SiO2, CaMgSi2O6–SiO2, and CaMgSi2O6–Mg2SiO4systems but a pronounced one on the MgO–SiO2 binary. Themost striking change concerns passage of the MgSiO3 phase fromperitectic melting at 1 bar to eutectic melting at 1·0GPa. This transition is estimated to occur at 0·41 GPa.For the CaMgSi2O6–SiO2 and CaMgSi2O6–Mg2SiO4 pseudo-binaries,the size of the field clinopyroxene + liquid increases withincreasing pressure. This change is related to the shift ofthe piercing points clinopyroxene + silica + liquid (from 0·375mol fraction SiO2 at 1 bar to 0·414 at 1·0 GPa)and clinopyroxene + olivine + liquid (from 0·191 molfraction SiO2 at 1 bar to 0·331 at 1·0 GPa) thatbound the clinopyroxene + liquid field in the CaMgSi2O6·SiO2and CaMgSi2O6·Mg2SiO4 pseudo-binaries, respectively. KEY WORDS: CaO–SiO2; CaMgSi2O6–Mg2SiO4; CaMgSi2O6–SiO2; experiments; MgO–SiO2  相似文献   

17.
We have experimentally determined the tracer diffusion coefficients (D*) of 44Ca and 26Mg in a natural diopside (~Di96) as function of crystallographic direction and temperature in the range of 950–1,150 °C at 1 bar and f(O2) corresponding to those of the WI buffer. The experimental data parallel to the a*, b, and c crystallographic directions show significant diffusion anisotropy in the a–c and b–c planes, with the fastest diffusion being parallel to the c axis. With the exception of logD*(26Mg) parallel to the a* axis, the experimental data conform to the empirical diffusion “compensation relation”, converging to logD ~ −19.3 m2/s and T ~ 1,155 °C. Our data do not show any change of diffusion mechanism within the temperature range of the experiments. Assuming that D* varies roughly linearly as a function of angle with respect to the c axis in the a–c plane, at least within a limited domain of ~20° from the c-axis, our data do not suggest any significant difference between D*(//c) and D*(⊥(001)), the latter being the diffusion data required to model compositional zoning in the (001) augite exsolution lamellae in natural clinopyroxenes. Since the thermodynamic mixing property of Ca and Mg is highly nonideal, calculation of chemical diffusion coefficient of Ca and Mg must take into account the effect of thermodynamic factor (TF) on diffusion coefficient. We calculate the dependence of the TF and the chemical interdiffusion coefficient, D(Ca–Mg), on composition in the diopside–clinoenstatite mixture, using the available data on mixing property in this binary system. Our D*(Ca) values parallel to the c axis are about 1–1.5 log units larger than those Dimanov et al. (1996). Incorporating the effect of TF, the D(Ca–Mg) values calculated from our data at 1,100–1,200 °C is ~0.6–0.7 log unit greater than the experimental quasibinary D((Ca–Mg + Fe)) data of Fujino et al. (1990) at 1 bar, and ~0.6 log unit smaller than that of Brady and McCallister (1983) at 25 kb, 1,150 °C, if our data are normalized to 25 kb using activation volume (~4 and ~6 cm3/mol for Mg and Ca diffusion, respectively) calculated from theoretical considerations.  相似文献   

18.
Garnet-bearing mantle peridotites, occurring as either xenoliths in volcanic rocks or lenses/massifs in high-pressure and ultrahigh-pressure terrenes within orogens, preserve a record of deep lithospheric mantle processes. The garnet peridotite xenoliths record chemical equilibrium conditions of garnet-bearing mineral assemblage at temperatures (T) ranging from ~700 to 1,400°C and pressures (P) > 1.6–8.9 GPa, corresponding to depths of ~52–270 km. A characteristic mineral paragenesis includes Cr-bearing pyropic garnet (64–86 mol% pyrope; 0–10 wt% Cr2O3), Cr-rich diopside (0.5–3.5 wt% Cr2O3), Al-poor orthopyroxene (0–5 wt% Al2O3), high-Cr spinel (Cr/(Cr + Al) × 100 atomic ratio = 2–86) and olivine (88–94 mol% forsterite). In some cases, partial melting, re-equilibration involving garnet-breakdown, deformation, and mantle metasomatism by kimberlitic and/or carbonatitic melt percolations are documented. Isotope model ages of Archean and Proterozoic are ubiquitous, but Phanerozoic model ages are less common. In contrast, the orogenic peridotites were subjected to ultrahigh-pressure (UHP) metamorphism at temperature ranging from ~700 to 950°C and pressure >3.5–5.0 GPa, corresponding to depths of >110–150 km. The petrologic comparisons between 231 garnet peridotite xenoliths and 198 orogenic garnet peridotites revealed that (1) bulk-rock REE (rare earth element) concentrations in xenoliths are relatively high, (2) clinopyroxene and garnet in orogenic garnet peridotites show a highly fractionated REE pattern and Ce-negative anomaly, respectively, (3) Fo contents of olivines for off-cratonic xenolith are in turn lower than those of orogenic garnet and cratonic xenolith but mg-number of garnet for orogenic is less than that of off-cratonic and on-cratonic xenolith, (4) Al2O3, Cr2O3, CaO and Cr# of pyroxenes and chemical compositions of whole rocks are very different between these garnet peridotites, (5) orogenic garnet peridotites are characterized by low T and high P, off-cratonic by high T and low P, and cratonic by medium T and high P and (6) garnet peridotite xenoliths are of Archean or Proterozoic origin, whereas most of orogenic garnet peridotites are of Phanerozoic origin. Taking account of tectonic settings, a new orogenic garnet peridotite exhumation model, crust-mantle material mixing process, is proposed. The composition of lithospheric mantle is additionally constrained by comparisons and compiling of the off-cratonic, on-cratonic and orogenic garnet peridotite.  相似文献   

19.
We have studied the paleomagnetism of the middle Cretaceous Iritono granite of the Abukuma massif in northeast Japan together with 40Ar–39Ar dating. Paleomagnetic samples were collected from ten sites of the Iritono granite (102 Ma 40Ar–39Ar age) and two sites of its associated gabbroic dikes. The samples were carefully subjected to alternating field and thermal demagnetizations and to rock magnetic analyses. Most of natural remanent magnetizations show mixtures of two components: (1) H component, high coercivity (Bc > 50–90 mT) or high blocking temperature (Tb > 350–560 °C) component and (2) L component, relatively low Bc or low Tb component. H component was obtained from all the 12 sites to give a mean direction of shallow inclination and northwesterly declination (I = 29.9°, D = 311.0°, α95 = 2.7°, N = 12). This direction is different from the geocentric axial dipole field at the present latitude (I = 56.5°) and the typical direction of the Cenozoic remagnetization in northeast Japan. Since rock magnetic properties indicate that the H component of the Iritono granite is carried mainly by magnetite inclusions in plagioclase, this component probably retains a primary one. Thus the shallow inclination indicates that the Abukuma massif was located at a low latitude (16.1 ± 1.6°N) about 100 Ma and then drifted northward by about 20° in latitude. The northwesterly deflection is attributed mostly to the counterclockwise rotation of northeast Japan due to Miocene opening of the Japan Sea. According to this model, the low-pressure and high-temperature (low-P/high-T) metamorphism of the Abukuma massif, which has been well known as a typical location, would have not occurred in the present location. On the other hand, the L component is carried mainly by pyrrhotite and its mean direction shows a moderate inclination and a northwesterly declination (I = 42.8°, D = 311.5°, α95 = 3.3°, N = 9). Since this direction is intermediate between the H component and early Cenozoic remagnetization in northeast Japan, some thermal event would have occurred at lower temperature than pyrrhotite Curie point ( 320 °C) during the middle Cretaceous to early Cenozoic time to have resulted in partial remagnetization.  相似文献   

20.
The X-band EPR and magnetic susceptibility in the temperature range 4.2–300 K study of the shungite-I, natural nanostructured material from the deposit of Shunga are reported. Obtained results allow us to assign the EPR signal to conduction electrons, estimate their number, N P, and evaluate the Pauli paramagnetism contribution to shungite susceptibility. A small occupation (~5%) of the localized nonbonding π states in the zigzag edges of the open-ended graphene-like layers and/or on σ (sp 2+x ) orbitals in the curved parts of the shungite globules has been also revealed. The observed temperature dependence of the EPR linewidth can be explained by the earlier considered interaction of conduction π electrons with local phonon modes associated with the vibration of peripheral carbon atoms of the open zigzag-type edges and with peripheral carbon atoms cross-linking different nanostructures. The relaxation time T 2 and diffusion time T D are found to have comparable values (2.84 × 10−8 and 1.73 × 10−8 s at 5.2 K, respectively), and similar dependence on temperature. The magnetic measurements have revealed the suppression of orbital diamagnetism due to small amount of large enough fragments of the graphene layers.  相似文献   

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