The energetics of aluminum solubility into MgSiO3 perovskite at lower mantle conditions

Akber-Knutson, S.; Bukowinski, M. S. T.

doi:10.1016/s0012-821x(04)00065-2

Cited by 34 publications

(31 citation statements)

References 28 publications

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“…S3 in SI Text) indicate that at 300 K, 92% of the ideal value is achieved, and at 1,000 K 99% is achieved. This implies that the entropy of mixing is very close to the ideal value under the temperature condition relevant to the Earth's deep mantle (Ϸ2,500 K) and are consistent with previous findings from classical simulations for Pv (25). This analysis suggests the present cell sampling is sufficient to capture the statistical properties of cation distributions under high pressure, although the CDoSs are still not completely smooth (Fig.…”

Section: Resultssupporting

confidence: 89%

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

Tsuchiya

2008

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

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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 ...

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Section: Resultssupporting

confidence: 89%

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

Tsuchiya

2008

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

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“…Theoretical calculations show that these two substitution mechanisms will have distinctly different effects on the compressibility of perovskite [9], [10] and [12].…”

Section: Mgalo25 (O-defect Join)mentioning

confidence: 99%

“…This state of affairs has created a flurry of activity, both experimental and theoretical, to understand how aluminum substitutes into the perovskite structure, and how that substitution affects the compressibility [7], [8], [9], [10], [11], [12], [13], [14], [15] and [16]. Although results from these studies are not in uniform agreement, it has emerged that the substitution mechanism is likely to control the compressibility.…”

Section: Introductionmentioning

confidence: 99%

Subsolidus phase relations and perovskite compressibility in the system MgO–AlO1.5–SiO2 with implications for Earth's lower mantle

Walter¹,

Trønnes²,

Armstrong³

et al. 2006

Earth and Planetary Science Letters

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Experimentally determined phase relations in the system MgO-AlO1.5-SiO2 at pressures relevant to the upper part of the lower mantle indicate that Mgsilicate perovskite incorporates aluminum into its structure almost exclusively by a charge-coupled reaction. MgSiO3-rich bulk compositions along the joins showing unusually compressive aluminous perovskite. The maximum solubility of alumina in perovskite is ∼25 mol% along the MgSiO3-AlO1.5 join within the ternary MAS-system (i.e. pyrope composition), and the join is apparently binary.Although primitive mantle peridotite compositions are MgO-saturated and fall nearly on the oxygen vacancy join, alumina substitution into perovskite is expected to occur primarily by charge-coupled substitution throughout the lower mantle. The compressibility of aluminous perovskite in primitive mantle is expected to be only a few percent lower than for end member MgSiO3 perovskite.

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“…Earlier theoretical calculations investigated whether oxygen vacancies exist in bridgmanite (Brodholt, 2000;Yamamoto et al;Akber-Knutson and Bukowinski, 2004). Brodholt (2000) suggested that oxygen-vacancy substitution should dominate at pressures only up to 30 GPa.…”

Section: Introductionmentioning

confidence: 99%

“…Yamamoto et al (2003) argued oxygen-vacancy substitution should be unfavourable in the entire lower mantle. Furthermore, energetic calculations by Akber- Knutson and Bukowinski (2004) suggested that oxygen-vacancy substitution could only account for 3-4 % and less than 1 % of Al substitutions in the shallower and deeper parts of the lower mantle, respectively.…”

Section: Introductionmentioning

confidence: 99%

Rapid decrease of MgAlO2.5 component in bridgmanite with pressure

Liu¹,

Ishii²,

Katsura³

2017

Geochem. Persp. Let.

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The solubility of the MgAlO 2.5 component in bridgmanite was measured at pressures of 27, 35 and 40 GPa and a temperature of 2000 o K using an ultra-high pressure multi-anvil press. Compositional analysis of recovered samples demonstrated that the MgAlO 2.5 component decreases with increasing pressure, and approaches virtually zero at 40 GPa. Above this pressure, the MgAlO 2.5 component, i.e. the oxygen-vacancy substitution, becomes negligible, and Al is incorporated in bridgmanite by the charge-coupled substitution only. These results are supported by the volume change associated with the change from the oxygen-vacancy substitution to charge-coupled substitution. The present result may explain the seismically observed slab stagnation in the mid-lower mantle. Although bridgmanite has been put forward as a potential host for water and argon in the lower mantle by trapping them in oxygen vacancies, such capabilities will rapidly decrease with depth and be lost in regions deeper than 1000 km.

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The energetics of aluminum solubility into MgSiO3 perovskite at lower mantle conditions

Cited by 34 publications

References 28 publications

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

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

Subsolidus phase relations and perovskite compressibility in the system MgO–AlO1.5–SiO2 with implications for Earth's lower mantle

Rapid decrease of MgAlO2.5 component in bridgmanite with pressure

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The energetics of aluminum solubility into MgSiO3 perovskite at lower mantle conditions

Cited by 34 publications

References 28 publications

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

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

Subsolidus phase relations and perovskite compressibility in the system MgO–AlO1.5–SiO2 with implications for Earth's lower mantle

Rapid decrease of MgAlO2.5 component in bridgmanite with pressure

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

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