PHASE RELATIONS OF PURE Mg2SiO4 UP TO 200 KILOBARS

Suito, Kaichi

doi:10.1016/b978-0-12-468750-9.50024-3

Cited by 70 publications

(41 citation statements)

References 11 publications

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“…In the Earth, changes of the pressure of the transition will translate into changes of its depth, so that lateral variations in temperature can create topography on the seismic discontinuity. The Clapeyron slope of the ␣ → ␤ transformation is positive (Suito, 1977;Katsura and Ito, 1989), so that a low-temperature anomaly will cause a local uplift of the 410 km discontinuity, whereas a high-temperature anomaly will cause a depression. The slope of the sp → pv + mw transformation is probably negative (Navrotsky, 1980;Ito and Takahashi, 1989), implying a depression of the 660 km discontinuity in a low-temperature environment and an uplift at high temperatures.…”

Section: Introductionmentioning

confidence: 99%

Correlation between the shear-speed structure and thickness of the mantle transition zone

Lebedev¹,

Chevrot

Hilst³

2003

Physics of the Earth and Planetary Interiors

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The 410 and 660 km seismic discontinuities that bound the mantle transition zone (TZ) are attributed to phase transformations in olivine structure. This implies that variations in TZ thickness (H TZ ) should correlate with those in TZ temperature. Pertinent seismic evidence has so far been ambiguous, however. We measure converted-wave (P ds) differential times t diff = t P 660s − t P 410s in SE Asia and Australia and compare them with S-velocity (β TZ ) estimates from regional tomographic models. Both t diff and β TZ vary on a scale of a few hundred kilometers. Inferred variations in H TZ are up to ±30 km over length scales larger than 500 km, implying ±200 K thermal heterogeneity if the effect of composition can be neglected. t diff and β TZ correlate strongly; the linear dependence of H TZ on the average temperature within the TZ is consistent with olivine Clapeyron slopes. We also show that this relationship holds on a global-scale as well, provided that the scalelengths and uncertainties of the variations in t diff and β TZ are taken into account. These results confirm that the transformations in olivine structure give rise to the 410 and 660 km discontinuities globally.

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Section: Introductionmentioning

confidence: 99%

Correlation between the shear-speed structure and thickness of the mantle transition zone

Lebedev¹,

Chevrot

Hilst³

2003

Physics of the Earth and Planetary Interiors

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“…Experiments of Kato and Kumazawa (1986) at 20 GPa have shown stability of the fl-phase within the range 1700 to 2250 ~ C; the association fi + Ilm is stable up to temperatures of 1800 ~ C, while at still higher temperatures (2000-2100 ~ C) fl-spinel and a noncubic garnet-like modification coexist. Sawamoto (1986), Logvinov (1983, Malinovsky et al (1981) have refined the positions of the phase boundaries a=fl and fl=7 for the MgzSiO4 system (see Table 1); the pressures they report are 0.5-1.5 GPa below those given by Suito (1977).…”

Section: Phase Relations In the Mgo-sioz System From Experimental Datamentioning

confidence: 93%

“…Akaogi et al (1984) have determined the heat of phase transformations in Mg2SiO4 by calorimetry as AH~ (c~=fl)=29.96_+2.93; AH~ +3.76 kJ.Mo1-1 and calculated changes in entropy of phase transformations by two methods giving AS~ =fl)=-11.72; AS~ J.K-l.mo1-1 according to Kieffer's (1980) model; AS~ (e = fl) = -10.46; AS~ (fl = 7) = -6.28 J-K-a. mol-1 based on the P-Tparameters of phase equilibria according to Suito (1977).…”

Section: Si02 (Coesite Stishovite)mentioning

confidence: 99%

“…The binary MgO-SiO2 system fundamental to mantle petrology is known within a wide range of temperatures and pressures (1000-2000 ~ C, 10-30 GPa) as a result of experimental investigations due to Ringwood (1975), Suito (1977), Akaogi and Akimoto (1977), Yagi et al (1979), Ohtani (1979), Liu (1979), Ito and Yamada (1982), Ito and Navrotsky (1985), Sawamoto (1986). Studies of individual phase transformations in this system form the basis of a geochemical interpretation of the nature of seismic discontinuites in the mantle.…”

Section: Introductionmentioning

confidence: 99%

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Computer simulation of the phase diagram for the MgO-SiO2 system at P - T parameters of the mantle transition zone

et al. 1989

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Abstract. The paper reports an attempt to study the topologies of the phase diagram for the MgO-SiO2 system at high pressure and temperature using computer simulation. Phase equilibria at MgSiO3 stoichiometry is investigated, demonstrating that the invariant point Gr + Ilm + Pv is stable at 21.6 GPa and 2270 K. A thermodynamic data base for minerals in the MgO-SiO2 system is established by supplementing the calorimetric data for low pressure phases and equations of state for low and high pressure phases with data calculated from high pressure synthesis experiments. A refined set of standard free energies of formation and phase transformations in the MgO-SiO2 system is presented. The proposed phase diagram covers a wide range of pressure (up to 25 GPa) and temperature (up to 2500 K) and forms the basis for a geochemical interpretation of the nature of seismic discontinuites in the mantle.

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“…Forsterite, Mg2SiO4, transforms to the beta phase at 13 GPa, 1000~ C (Suito 1977, Akaogi et al 1984. Tephroite, Mn2SiO4, decomposes to MnSiO3 tetragonal garnet and MnO rocksalt at 14 GPa, 1000 ~ C (Ito andMatsui 1977, Akaogi andNavrotsky 1985).…”

Section: Sample Preparationmentioning

confidence: 97%

Pressure and temperature dependence of cation distribution in Mg-Mn olivine

et al. 1988

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Abstract. Synthetic (Mgo.sa, Mno.49)2SiO4 olivine samples are heat-treated at three different pressures; 0, 8 and 12 GPa, all at the same temperature (~ 500 ~ C). X-ray structure analyses on these single crystals are made in order to see the pressure effect on cation distribution. The intersite distribution coefficient of Mg and Mn in M 1 and M 2 sites, KD = (Mn/Mg)M 1/(Mn/Mg)M 2, of these samples are 0.192 (0 GPa), 0.246 (8 GPa) and 0.281 (12 GPa), indicating cationic disordering with pressure. The small differences of cell dimensions between these samples are determined by powder X-ray diffraction. Cell dimensions b and c decrease, whereas a increases with pressure of equilibration. Cell volume decreases with pressure as a result of a large contraction of the b cell dimension. The effect of pressure on the free energy of the cation exchange reaction is evaluated by the observed relation between the cell volume and the site occupancy numbers. The magnitude of the pressure effect on cation distribution is only a fifth of that predicted from the observed change in volume combined with thermodynamic theory. This phenomenon is attributed to nonideality in this solid solution, and nonideal parameters are required to describe cation distribution determined in the present and previous experiments. We use a five-parameter equation to specify the cationic equilibrium on the basic of thermodynamic theory. It includes one energy parameter of ideal mixing, two parameters for nonideal effects, one volume parameter, and one thermal parameter originated from the lattice vibrational energy. The present data combined with some of the existing data are used to determine the five parameters, and the cation distribution in Mg-Mn olivine is described as a function of temperature, pressure, and composition. The basic framework of describing the cationic behavior in olivine-type mineral is worked out, although the result is preliminary: each of the determined parameters is not accurate enough to enable us to make a reliable prediction.

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PHASE RELATIONS OF PURE Mg2SiO4 UP TO 200 KILOBARS

Cited by 70 publications

References 11 publications

Correlation between the shear-speed structure and thickness of the mantle transition zone

Correlation between the shear-speed structure and thickness of the mantle transition zone

Computer simulation of the phase diagram for the MgO-SiO2 system at P - T parameters of the mantle transition zone

Pressure and temperature dependence of cation distribution in Mg-Mn olivine

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