Efficacy of the post-perovskite phase as an explanation for lowermost-mantle seismic properties

Wookey, James; Stackhouse, Stephen; Kendall, J.‐M.; Brodholt, John P.; Price, G. D.

doi:10.1038/nature04345

Cited by 192 publications

(165 citation statements)

References 28 publications

Supporting

Mentioning

138

Contrasting

Unclassified

Order By: Relevance

“…The presence of a dominantly postperovskite D´´ layer is therefore consistent with regional variations in lower-mantle shear-wave anisotropy (see e.g. Hernlund et al, 2005;Wookey et al 2005).…”

Section: Introductionsupporting

confidence: 59%

Thermal expansion of CaIrO3 determined by X-ray powder diffraction

Lindsay-Scott

Wood

Dobson

2007

Physics of the Earth and Planetary Interiors

View full text Add to dashboard Cite

show abstract

Section: Introductionsupporting

confidence: 59%

Thermal expansion of CaIrO3 determined by X-ray powder diffraction

Lindsay-Scott

Wood

Dobson

2007

Physics of the Earth and Planetary Interiors

View full text Add to dashboard Cite

show abstract

“…In this region of the planet, anomalous features have been documented by seismology, including the ultralow velocity zones (ULVZ) which have been attributed to partial melt, chemical and thermal heterogeneities (3,4). Numerous studies of pure Mg (or Mg-rich) ppv have been undertaken to interpret these unusual seismic signatures (2,(5)(6)(7)(8)(9)(10)(11)(12)(13). Iron is likely to be an important component in ppv, and its incorporation in silicate ppv has been found to have a considerable influence on the properties of the phase.…”

mentioning

confidence: 99%

Crystal structures of (Mg _{1-
x} ,Fe _x )SiO ₃ postperovskite at high pressures

Yamanaka

Hirose

Mao

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

X-ray diffraction experiments on postperovskite (ppv) with compositions (Mg 0.9 Fe 0.1 )SiO 3 and (Mg 0.6 Fe 0.4 )SiO 3 at Earth core-mantle boundary pressures reveal different crystal structures. The former adopts the CaIrO 3 -type structure with space group Cmcm , whereas the latter crystallizes in a structure with the Pmcm ( Pmma ) space group. The latter has a significantly higher density ( ρ = 6.119(1) g/cm 3 ) than the former ( ρ = 5.694(8) g/cm 3 ) due to both the larger amount of iron and the smaller ionic radius of Fe 2+ as a result of an electronic spin transition observed by X-ray emission spectroscopy (XES). The smaller ionic radius for low-spin compared to high-spin Fe 2+ also leads to an ordered cation distribution in the M1 and M2 crystallographic sites of the higher density ppv structure. Rietveld structure refinement indicates that approximately 70% of the total Fe 2+ in that phase occupies the M2 site. XES results indicate a loss of 70% of the unpaired electronic spins consistent with a low spin M2 site and high spin M1 site. First-principles calculations of the magnetic ordering confirm that Pmcm with a two-site model is energetically more favorable at high pressure, and predict that the ordered structure is anisotropic in its electrical and elastic properties. These results suggest that interpretations of seismic structure in the deep mantle need to treat a broader range of mineral structures than previously considered.

show abstract

“…A lthough the postperovskite (pPv) phase transition in MgSiO 3 (1-3) is suggested to be strongly related to the deep-mantle DЉ seismic discontinuity (4)(5)(6), phase relations in more realistic chemical compositions, containing particularly aluminum and iron, are needed for further detailed investigations of this region. High-pressure experiments (7,8) demonstrated that magnesium silicate perovskite (Pv) is the major host of aluminum over the entire pressure (P) and temperature (T) range of the lower mantle, possessing Ϸ5 mol% of Al 2 O 3 in pyrolite and Ϸ20 mol% in MORB.…”

mentioning

confidence: 99%

Postperovskite phase equilibria in the MgSiO ₃ –Al ₂ O ₃ system

Tsuchiya

2008

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

We investigate high-P,T phase equilibria of the MgSiO3-Al2O3 system by means of the density functional ab initio computation methods with multiconfiguration sampling. Being different from earlier studies based on the static substitution properties with no consideration of Rh2O3(II) phase, present calculations demonstrate that (i) dissolving Al2O3 tends to decrease the postperovskite transition pressure of MgSiO3 but the effect is not significant (Ϸ-0.2 GPa/mol% Al2O3); (ii) Al2O3 produces the narrow perovskite؉postperovskite coexisting P,T area (Ϸ1 GPa) for the pyrolitic concentration (xAl2O3 Ϸ6 mol%), which is sufficiently responsible to the deep-mantle D؆ seismic discontinuity; (iii) the transition would be smeared (Ϸ4 GPa) for the basaltic Al-rich composition (xAl2O3 Ϸ20 mol%), which is still seismically visible unless iron has significant effects; and last (iv) the perovskite structure spontaneously changes to the Rh2O3(II) with increasing the Al concentration involving small displacements of the Mg-site cations.ab initio density functional method ͉ Earth's lower mantle ͉ DЉ seismic discontinuity ͉ solid-solution thermodynamics ͉ Rh2O3(II) structure A lthough the postperovskite (pPv) phase transition in MgSiO 3 (1-3) is suggested to be strongly related to the deep-mantle DЉ seismic discontinuity (4-6), phase relations in more realistic chemical compositions, containing particularly aluminum and iron, are needed for further detailed investigations of this region. High-pressure experiments (7, 8) demonstrated that magnesium silicate perovskite (Pv) is the major host of aluminum over the entire pressure (P) and temperature (T) range of the lower mantle, possessing Ϸ5 mol% of Al 2 O 3 in pyrolite and Ϸ20 mol% in MORB. The pPv phase transition of aluminous silicate has therefore been studied extensively both theoretically and experimentally (9-13) along with the effects of Al on the elastic properties of ). An ab initio study (9) showed that the Al incorporation into Mg-Pv drastically increases the pPv transition pressure and also enhances the PvϩpPv coexistence region, which reaches Ͼ10 GPa even for 5 mol% Al 2 O 3 . Also, a laser-heated diamond-anvil-cell experiment of pyrope composition (25 mol% Al 2 O 3 ) (11) proposed a similar phase diagram with wide PvϩpPv coexisting pressure ranges of 20-30 GPa, although their estimations of transition width were quite rough. Similar broadening of the transition width is also reported for the iron-bearing systems (17, 18), although their transition pressures are still highly contradictory. These gradual phase changes through such huge divariant loops suggest the pPv transition fails to explain the sharp seismic discontinuity as observed at the top of DЉ (9, 11). However, the ultrahigh-P,T experiments of multicomponent phase equilibria currently usually involve significant uncertainties in controlling homogeneous P,T conditions and reaction kinetics. In this study, we reinvestigate the aluminum-bearing Pv system theoretically for the first step of better understanding the ...

show abstract

Efficacy of the post-perovskite phase as an explanation for lowermost-mantle seismic properties

Cited by 192 publications

References 28 publications

Thermal expansion of CaIrO3 determined by X-ray powder diffraction

Thermal expansion of CaIrO3 determined by X-ray powder diffraction

Crystal structures of (Mg _{1-
x} ,Fe _x )SiO ₃ postperovskite at high pressures

Postperovskite phase equilibria in the MgSiO ₃ –Al ₂ O ₃ system

Contact Info

Product

Resources

About

Efficacy of the post-perovskite phase as an explanation for lowermost-mantle seismic properties

Cited by 192 publications

References 28 publications

Thermal expansion of CaIrO3 determined by X-ray powder diffraction

Thermal expansion of CaIrO3 determined by X-ray powder diffraction

Crystal structures of (Mg 1- x ,Fe x )SiO 3 postperovskite at high pressures

Postperovskite phase equilibria in the MgSiO 3 –Al 2 O 3 system

Contact Info

Product

Resources

About

Crystal structures of (Mg _{1-
x} ,Fe _x )SiO ₃ postperovskite at high pressures

Postperovskite phase equilibria in the MgSiO ₃ –Al ₂ O ₃ system