Equation of state of Al‐bearing perovskite to lower mantle pressure conditions

Daniel, Isabelle; Cardon, Hervé; Fiquet, G.; Guyot, F.; Mezouard, Mohamed

doi:10.1029/2001gl013011

Cited by 41 publications

(40 citation statements)

References 23 publications

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“…Observations from four experimental studies indicate that values for the bulk modulus of MgSiO3 perovskite typically used in mineralogic models, about 260 GPa, may be considerably too high [4], [5], [6] and [7]. These studies indicate that even the small amount of Al2O3 in a pyrolite mantle, about 5 mol%, can cause about a 10% reduction in the bulk modulus when substituted into perovskite.…”

Section: Introductionmentioning

confidence: 94%

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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: Introductionmentioning

confidence: 94%

“…6 are changes in relative volume for a set of unusually compressive aluminous perovskites [4], [6] and [7]. These perovskites have ambient unit cell volumes that are consistent with charge-coupled substitution.…”

Section: Unit Cell Volumes Of Perovskite At Ambient Conditions Vmentioning

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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“…We further simplify the pyroxene compositions by assuming that they contain no aluminum. The majorite equilibrium composition is calculated using the further constraint that the molar Al/Si ratio is 0.4 (from experimental results of Bertka and Fei [1997] Daniel et al 2001). …”

Section: Assumptions About Petrologymentioning

confidence: 99%

Magma ocean fractional crystallization and cumulate overturn in terrestrial planets: Implications for Mars

Elkins-Tanton

Parmentier

Hess

2003

Meteorit & Planetary Scien

234

229

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Abstract-Crystallization of a magma ocean on a large terrestrial planet that is significantly melted by the energy of accretion may lead to an unstable cumulate density stratification, which may overturn to a stable configuration. Overturn of the initially unstable stratification may produce an early basaltic crust and differentiated mantle reservoirs. Such a stable compositional stratification can have important implications for the planet's subsequent evolution by delaying or suppressing thermal convection and by influencing the distribution of radiogenic heat sources. We use simple models for fractional crystallization of a martian magma ocean, and calculate the densities of the resulting cumulates. While the simple models presented do not include all relevant physical processes, they are able to describe to first order a number of aspects of martian evolution. The models describe the creation of magma source regions that differentiated early in the history of Mars, and present the possibility of an early, brief magnetic field initiated by cold overturned cumulates falling to the coremantle boundary. In a model that includes the density inversion at about 7.5 GPa, where olivine and pyroxene float in the remaining magma ocean liquids while garnet sinks, cumulate overturn sequesters alumina in the deep martian interior. The ages and compositions of source regions are consistent with SNC meteorite data.

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“…The isothermal bulk modulus of MgSiO 3 and (Mg,Fe)SiO 3 perovskites have been established to generally fall within the range 250 260 GPa by numerous laboratories (e.g., Funamori et al, 1996;Fiquet et al, 1998;Fiquet et al, 2000;Sinogeikin et al, 2004); however measurements on perovskite compositions incorporating Al (hence stabilising some of the iron, if present, as Fe 3+ ) show dramatically different results, but with a large variation in observed behaviour. Some high pressure measurements show a 5 10% decrease in bulk modulus (Zhang and Weidner, 1999;Kubo et al, 2000;Daniel et al, 2001;Yagi et al, 2004), some show an increase in bulk modulus Ono et al, 2004) and some show no change (Yagi et al, 2004;Jackson et al, 2004). Incorporation of oxygen vacancies according to Equation 5 is predicted to decrease the bulk modulus (Brodholt, 2000;Ross et al, 2002); hence variations in oxygen vacancy concentrations and/or ordering could influence the behaviour, as well as differences in the trivalent cation substitution mechanism, partial amorphisation following sample synthesis, or as yet unidentified factors Ono et al, 2004;Yagi et al, 2004).…”

Section: +mentioning

confidence: 99%

Microscopic properties to macroscopic behaviour: The influence of iron electronic state

McCammon

2006

Journal of Mineralogical and Petrological Sciences

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Iron is the only major element in the Earth with multiple electronic configurations (oxidation and spin state). In the upper mantle and transition zone iron is predominantly Fe 2+ , but the small amount of Fe 3+ that is present significantly affects properties that are sensitive to defect chemistry, including electrical conductivity, diffusivity and hydrogen solubility. Fe 3+ also determines the oxygen fugacity, where the upper mantle is relatively oxidised due to the high Fe 3+ /ΣFe ratio in spinel, even though the overall Fe 3+ concentration in the upper mantle is low due to its concentration in modally minor phases. The transition zone contains a similar amount of Fe 3+ , but its distribution among all the major phases results in a significantly lower oxygen fugacity, near metal saturation. In the lower mantle the transition to (Mg,Fe)(Si,Al)O 3 perovskite involves the creation of significant Fe 3+(approximately 50% of available iron), even at reducing conditions, which is likely balanced in the bulk lower mantle by disproportionation of Fe 2+ to form Fe 3+ and metallic iron, and potentially in subducting slabs through reduction of oxidised species in the slab. The nature of Fe 3+ charge balance in (Mg,Fe)(Si,Al)O 3 perovskite largely determines the influence on physical and chemical properties, where electrical conductivity is enhanced, diffusivity is reduced, and elasticity and hydrogen solubility vary depending on the substitution mechanism. If Fe 2+ is more stable in the post perovskite phase relative to (Mg,Fe)(Si,Al)O 3 perovskite as suggested by experiments, both Fe 3+ /ΣFe and the nature of its influence on physical and chemical properties may be different in the post perovskite phase. The influence of spin crossover on mantle properties remains unclear. Recent models show that the growth of an (Mg,Fe)(Si,Al)O 3 perovskite rich lower mantle during core formation would progressively oxidise the mantle to present levels as a portion of the disproportionated iron rich metal phase became incorporated into the core, and the increase in oxygen fugacity during the later stages of Earth accretion would alter the partitioning behaviour of elements between mantle and core, resolving puzzles such as the siderophile element anomaly and the discrepancy between U-Pb and Hf-W systematics in the early Earth. Redox reactions involved in the movement of material across the lower mantle boundary could be related to the formation of deep diamonds, and potentially the rise of atmospheric oxygen through a mantle avalanche in the late Archean that disturbed the balance of volatile element cycles.

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Equation of state of Al‐bearing perovskite to lower mantle pressure conditions

Abstract: Abstract.A12Oa is estimated to total 4 to 5 mol% in all mantle compositional models, and is believed to be incorporated into (Mg,Fe)SiOs-perovskite at lower mantle con-

Cited by 41 publications

References 23 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

Magma ocean fractional crystallization and cumulate overturn in terrestrial planets: Implications for Mars

Microscopic properties to macroscopic behaviour: The influence of iron electronic state

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