Phase relations and equation-of-state of aluminous Mg-silicate perovskite and implications for Earth's lower mantle

Walter, Michael J.; Kubo, Atsushi; Yoshino, Takashi; Brodholt, John P.; Koga, Kenneth T.; Ohishi, Yasuo

doi:10.1016/j.epsl.2004.03.014

Cited by 74 publications

(96 citation statements)

References 46 publications

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“…Experimental evidence could be interpreted to confirm this dichotomy. Andrault et al [8] and Walter et al [14] have measured the compressibilities of a series of aluminous perovskites along the charge-coupled join, and observed only a mild effect on the bulk modulus generally consistent with theoretical calculations. Navrotsky et al [17] synthesized perovskites along the O-defect join, as well as other MgO-saturated perovskite compositions.…”

Section: Mgalo25 (O-defect Join)supporting

confidence: 53%

“…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: Introductioncontrasting

confidence: 40%

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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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Section: Mgalo25 (O-defect Join)supporting

confidence: 53%

Section: Introductioncontrasting

confidence: 40%

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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“…(Thomson et al 1996;Brodholt 2000;Caracas and Cohen 2005;Panero et al 2006). Experimental data are shown as red closed symbols Ito et al 1998;Kubo et al 2000;Walter et al 2004). Data set values are shown as purple closed symbols Lithgow-Bertelloni 2005, 2011;Holland et al 2013).…”

Section: Discussionmentioning

confidence: 99%

“…Data points are calculated from the experimentally derived 300 K equations of state of Du et al (2015), with isentropic bulk moduli calculated using the thermodynamic identity K S = K T (1 + T) and the thermal expansion and Grüneisen parameter taken from an ideal pyrope-grossular solution (the choice of model is unimportant at 300 K) The values MgSiO 3 provide a good fit to Fiquet et al (2000) and Murakami et al (2007). The (MgSi) 0.87 (FeSi) 0.13 O 3 , (MgSi) 0.75 (AlAl) 0.25 O 3 , and (MgSi) 0.9 (FeAl) 0.1 O 3 equations of state are fit to data from Wolf et al (2015), Walter et al (2004), and Kurnosov et al (2017), respectively (see text) and that excess non-configurational entropies tend to zero at low temperature. There are limitations to the elastic model.…”

Section: Discussionmentioning

confidence: 99%

“…6). Samples with similar bulk compositions produce estimates of bulk moduli spanning about 20 GPa (Daniel et al 2001(Daniel et al , 2004Walter et al 2004;Yagi et al 2004;Andrault et al 2007). This may be the result of high compressibility of defect-structured bridgmanite or sensitivity to deviatoric stress (Andrault et al 2007).…”

Section: The Bridgmanite Solid Solutionmentioning

confidence: 99%

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The elastic solid solution model for minerals at high pressures and temperatures

Myhill

2018

Contrib Mineral Petrol

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Non-ideality in mineral solid solutions affects their elastic and thermodynamic properties, their thermobaric stability, and the equilibrium phase relations in multiphase assemblages. At a given composition and state of order, non-ideality in minerals is typically modelled via excesses in Gibbs free energy which are either constant or linear with respect to pressure and temperature. This approach has been extremely successful when modelling near-ideal solutions. However, when the lattice parameters of the solution endmembers differ significantly, extrapolations of thermodynamic properties to high pressures using these models may result in significant errors. In this paper, I investigate the effect of parameterising solution models in terms of the Helmholtz free energy, treating volume (or lattice parameters) rather than pressure as an independent variable. This approach has been previously applied to models of order-disorder, but the implications for the thermodynamics and elasticity of solid solutions have not been fully explored. Solid solution models based on the Helmholtz free energy are intuitive at a microscopic level, as they automatically include the energetic contribution from elastic deformation of the endmember lattices. A chemical contribution must also be included in such models, which arises from atomic exchange within the solution. Derivations are provided for the thermodynamic properties of n-endmember solutions. Examples of the use of the elastic model are presented for the alkali halides, pyroxene, garnet, and bridgmanite solid solutions. Elastic theory provides insights into the microscopic origins of non-ideality in a range of solutions, and can make accurate predictions of excess enthalpies, entropies, and volumes as a function of volume and temperature. In solutions where experimental data are sparse or contradictory, the Helmholtz free energy approach can be used to assess the magnitude of excess properties and their variation as a function of pressure and temperature. The formulation is expected to be useful for geochemical and geophysical studies of the Earth and other planetary bodies.

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The thermal equation of state of (Mg, Fe)SiO₃bridgmanite (perovskite) and implications for lower mantle structures

et al. 2015

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The high‐pressure/high‐temperature equation of state (EOS) of synthetic 13% Fe‐bearing bridgmanite (Mg silicate perovskite) is measured using powder X‐ray diffraction in a laser‐heated diamond anvil cell with a quasi‐hydrostatic neon pressure medium. We compare these results, which are consistent with previous 300 K sound speed and compression studies, with a reanalysis of Fe‐free Mg end‐member data from Tange et al. (2012) to determine the effect of iron on bridgmanite's thermoelastic properties. EOS parameters are incorporated into an ideal lattice mixing model to probe the behavior of bridgmanite at deep mantle conditions. With this model, a nearly pure bridgmanite mantle composition is shown to be inconsistent with density and compressibility profiles of the lower mantle. We also explore the buoyant stability of bridgmanite over a range of temperatures and compositions expected for Large Low‐Shear Velocity Provinces, concluding that bridgmanite‐dominated thermochemical piles are more likely to be passive dense layers externally supported by convection, rather than internally supported metastable domes. The metastable dome scenario is estimated to have a relative likelihood of only 4–7%, given the narrow range of compositions and temperatures consistent with seismic constraints. If buoyantly supported, such structures could not have remained stable with greater thermal contrast early in Earth's history, ruling out formation scenarios involving a large concentration of heat producing elements.

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Phase relations and equation-of-state of aluminous Mg-silicate perovskite and implications for Earth's lower mantle

Cited by 74 publications

References 46 publications

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

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

The elastic solid solution model for minerals at high pressures and temperatures

The thermal equation of state of (Mg, Fe)SiO₃bridgmanite (perovskite) and implications for lower mantle structures

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Phase relations and equation-of-state of aluminous Mg-silicate perovskite and implications for Earth's lower mantle

Cited by 74 publications

References 46 publications

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

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

The elastic solid solution model for minerals at high pressures and temperatures

The thermal equation of state of (Mg, Fe)SiO3bridgmanite (perovskite) and implications for lower mantle structures

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The thermal equation of state of (Mg, Fe)SiO₃bridgmanite (perovskite) and implications for lower mantle structures