Low-temperature heat capacities, entropies and enthalpies of Mg2SiO4 polymorphs, and α−β−γ and post-spinel phase relations at high pressure

Akaogi, Masaki; Takayama, Hajime; Kojitani, Hiroshi; Kawaji, Hitoshi; Ataké, Tooru

doi:10.1007/s00269-006-0137-3

Cited by 83 publications

(82 citation statements)

References 53 publications

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“…The ab initio phase boundary is localized at slightly higher pressures (≈1-2 GPa) than those determined by other HP-HT experiments [124,127,129,130,133] (see Figure 11a). The calculated Clapeyron slope (i.e., dP/dT = −2.53 MPa/K) agrees well with those obtained by the most part of experimental investigations (ranging from −4.0 to −2.0 MPa/K) [121,[124][125][126][127]131,132,135], while other works [129,130,133,134] suggest a more gentle slope of the phase boundary (i.e., between −2.0 and −1.0 MPa/K or even less) (see Table 5). B3LYP results are in qualitative agreement with previous GGA calculations [137][138][139], whereas LDA [137] severely underestimates transformation pressures of the post-spinel reaction (see Figure 11b).…”

Section: Phase Equilibrium Calculation At Hp-ht: the Post-spinel Phassupporting

confidence: 74%

“…Ab initio B3LYP results show an excellent agreement with the in situ LH-DAC X-ray diffraction study of Shim et al [128] and the multi-anvil experiments of Ishii et al [132], as well as with calculations based on accurate calorimetric measurements by Akaogi and Ito [126] and Akaogi et al [131] (Figure 11a; see also Figure Table 5), although a recent study found a lower enthalpy of reaction [134]. The ab initio phase boundary is localized at slightly higher pressures (≈1-2 GPa) than those determined by other HP-HT experiments [124,127,129,130,133] (see Figure 11a).…”

Section: Phase Equilibrium Calculation At Hp-ht: the Post-spinel Phassupporting

confidence: 70%

“…Table 6 shows the results of the density change calculation at P-T conditions given by Figure 11. Ab initio B3LYP phase boundary of post-spinel transformation (in bold) as compared to: (a) experimental results (multi-anvil press, laser-heated diamond-anvil cell) [124,[127][128][129][130]132,133] and calculations based on calorimetric measurements [121,125,126,131]; (b) other ab initio LDA [137] and GGA [138] calculations. Abbreviations for minerals are: rng = ringwoodite (γ-Mg 2 SiO 4 ); pc = periclase (MgO); bgm = bridgmanite (MgSiO 3 ).…”

Section: Post-spinel Reactionmentioning

confidence: 99%

“…The effect of lattice vibrations seems to be crucial to correctly predicting the high-pressure phase transformation; ab initio static enthalpy calculations [137][138][139]141] give transition pressures that are overestimated (by ≈1−2 up to 10 GPa) compared with those obtained by including vibrational contributions to thermodynamic properties (i.e., by minimizing Gibbs free energies instead of static enthalpies). [121,[124][125][126][127][128][129][130][131][132][133][134][135] and other ab initio calculations [137][138][139]. Figure 11.…”

Section: Phase Equilibrium Calculation At Hp-ht: the Post-spinel Phasmentioning

confidence: 99%

“…Owing to its geophysical implications, the Mg2SiO4 post-spinel phase transformations have been investigated by several experimental studies in the last decades [124][125][126][127][128][129][130][131][132][133][134][135]. Although experimental results are not consistent with each other concerning the P-T localization of the phase equilibrium boundary, there is general agreement about its most important thermodynamic feature; that is, the negative Clapeyron slope (i.e., dP/dT < 0) or endothermic character (i.e., ∆Hrxt > 0).…”

Section: Phase Equilibrium Calculation At Hp-ht: the Post-spinel Phasmentioning

confidence: 99%

See 4 more Smart Citations

First Principles Thermodynamics of Minerals at HP–HT Conditions: MgO as a Prototypical Material

Belmonte

2017

Minerals

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Ab initio thermodynamic properties, equation of state and phase stability of periclase (MgO, B1-type structure) have been investigated in a broad P-T range (0-160 GPa; 0-3000 K) in order to set a model reference system for phase equilibria simulations under deep Earth conditions. Phonon dispersion calculations performed on large supercells using the finite displacement method and in the framework of quasi-harmonic approximation highlight the performance of the Becke three-parameter Lee-Yang-Parr (B3LYP) hybrid density functional in predicting accurate thermodynamic functions (heat capacity, entropy, thermal expansivity, isothermal bulk modulus) and phase reaction boundaries at high pressure and temperature. A first principles Mie-Grüneisen equation of state based on lattice vibrations directly provides a physically-consistent description of thermal pressure and P-V-T relations without any need to rely on empirical parameters or other phenomenological formalisms that could give spurious anomalies or uncontrolled extrapolations at HP-HT. The post-spinel phase transformation, Mg 2 SiO 4 (ringwoodite) = MgO (periclase) + MgSiO 3 (bridgmanite), is taken as a computational example to illustrate how first principles theory combined with the use of hybrid functionals is able to provide sound results on the Clapeyron slope, density change and P-T location of equilibrium mineral reactions relevant to mantle dynamics.

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Section: Phase Equilibrium Calculation At Hp-ht: the Post-spinel Phassupporting

confidence: 74%

Section: Phase Equilibrium Calculation At Hp-ht: the Post-spinel Phassupporting

confidence: 70%

Section: Post-spinel Reactionmentioning

confidence: 99%

Section: Phase Equilibrium Calculation At Hp-ht: the Post-spinel Phasmentioning

confidence: 99%

Section: Phase Equilibrium Calculation At Hp-ht: the Post-spinel Phasmentioning

confidence: 99%

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First Principles Thermodynamics of Minerals at HP–HT Conditions: MgO as a Prototypical Material

Belmonte

2017

Minerals

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The mantle transition zone beneath West Antarctica: Seismic evidence for hydration and thermal upwellings

Emry

Nyblade

Julià

et al. 2015

Geochem Geophys Geosyst

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Although prior work suggests that a mantle plume is associated with Cenozoic rifting and volcanism in West Antarctica, the existence of a plume remains conjectural. Here we use P wave receiver functions (PRFs) from the Antarctic POLENET array to estimate mantle transition zone thickness, which is sensitive to temperature perturbations, throughout previously unstudied parts of West Antarctica. We obtain over 8000 high-quality PRFs using an iterative, time domain deconvolution method filtered with a Gaussian width of 0.5 and 1.0, corresponding to frequencies less than 0.24 and 0.48 Hz, respectively. Single-station and common conversion point stacks, migrated to depth using the AK135 velocity model, indicate that mantle transition zone thickness throughout most of West Antarctica does not differ significantly from the global average, except in two locations; one small region exhibits a vertically thinned (210 6 15 km) transition zone beneath the Ruppert Coast of Marie Byrd Land and another laterally broader region shows slight, vertical thinning (225 6 25 km) beneath the Bentley Subglacial Trench. We also observe the 520 discontinuity and a prominent negative peak above the mantle transition zone throughout much of West Antarctica. These results suggest that the mantle transition zone may be hotter than average in two places, possibly due to upwelling from the lower mantle, but not broadly across West Antarctica. Furthermore, we propose that the transition zone may be hydrated due to >100 million years of subduction beneath the region during the early Mesozoic.

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Precise measurements of enthalpy of postspinel transition in Mg₂SiO₄ and application to the phase boundary calculation

2016

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Drop solution enthalpies (ΔH°d‐s) of Mg2SiO4 ringwoodite, Mg2SiO4 forsterite, perovskite‐type MgSiO3 (bridgmanite), and MgSiO3 enstatite were measured using a single batch of 2PbO · B2O3 solvent at 978 K. From the obtained ΔH°d‐s values of Mg2SiO4 ringwoodite, MgSiO3 bridgmanite, and MgO, an enthalpy of the postspinel phase transition, Mg2SiO4 ringwoodite = MgSiO3 bridgmanite + MgO, was determined to be 78.54 ± 2.28 kJ/mol. Thermodynamic calculations using the obtained phase transition enthalpy and available thermochemical and thermoelastic data provided the phase transition pressure of 23.1 ± 1.4 GPa at 298 K. This value is comparable to those at about 2000 K determined by previous experimental and theoretical studies, implying a considerably gentle Clapeyron slope. Thermodynamic calculations of the postspinel boundary at high temperatures in the anhydrous condition by changing thermochemical and thermoelastic parameters within the uncertainties suggested that the postspinel transition pressure of Mg2SiO4 at high temperature is lower than the pressure corresponding to the global average depth of the “660 km” seismic discontinuity in the Earth's mantle (~23.5 GPa) estimated from one‐dimensional reference Earth models and that a most likely Clapeyron slope is about −1 MPa/K. The postspinel transition in the hydrous condition with about 2 wt % H2O, which shows higher transition pressure and steeper Clapeyron slope than those in the anhydrous condition, gives a plausible explanation for seismic observations on the 660 km discontinuity, and therefore, hydrous mantle transition zone would be required.

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Low-temperature heat capacities, entropies and enthalpies of Mg2SiO4 polymorphs, and α−β−γ and post-spinel phase relations at high pressure

Cited by 83 publications

References 53 publications

First Principles Thermodynamics of Minerals at HP–HT Conditions: MgO as a Prototypical Material

First Principles Thermodynamics of Minerals at HP–HT Conditions: MgO as a Prototypical Material

The mantle transition zone beneath West Antarctica: Seismic evidence for hydration and thermal upwellings

Precise measurements of enthalpy of postspinel transition in Mg₂SiO₄ and application to the phase boundary calculation

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Low-temperature heat capacities, entropies and enthalpies of Mg2SiO4 polymorphs, and α−β−γ and post-spinel phase relations at high pressure

Cited by 83 publications

References 53 publications

First Principles Thermodynamics of Minerals at HP–HT Conditions: MgO as a Prototypical Material

First Principles Thermodynamics of Minerals at HP–HT Conditions: MgO as a Prototypical Material

The mantle transition zone beneath West Antarctica: Seismic evidence for hydration and thermal upwellings

Precise measurements of enthalpy of postspinel transition in Mg2SiO4 and application to the phase boundary calculation

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Precise measurements of enthalpy of postspinel transition in Mg₂SiO₄ and application to the phase boundary calculation