Ferric iron in Al‐bearing post‐perovskite

Sinmyo, Ryosuke; Hirose, Kei; O’Neill, Hugh; Okunishi, Eiji

doi:10.1029/2006gl025858

Cited by 44 publications

(25 citation statements)

References 20 publications

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“…, consistent with previous observations (23,27), albeit with significantly lower Fe 3+ /ΣFe above 116 GPa (PPv stability field) than at lower pressure (Brg stability field). Ferric iron is therefore entirely contained in the silicate phase and doesn't exchange or partition between the silicate and Fp, whereas ferrous iron is distributed between both silicate and Fp through an Fe-Mg exchange reaction, The compositional effect on K eff is apparent in Fig.…”

Section: +supporting

confidence: 81%

Spin and valence dependence of iron partitioning in Earth’s deep mantle

Piet

Badro

Nabiei

et al. 2016

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

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We performed laser-heated diamond anvil cell experiments combined with state-of-the-art electron microanalysis (focused ion beam and aberration-corrected transmission electron microscopy) to study the distribution and valence of iron in Earth's lower mantle as a function of depth and composition. Our data reconcile the apparently discrepant existing dataset, by clarifying the effects of spin (high/low) and valence (ferrous/ferric) states on iron partitioning in the deep mantle. In aluminum-bearing compositions relevant to Earth's mantle, iron concentration in silicates drops above 70 GPa before increasing up to 110 GPa with a minimum at 85 GPa; it then dramatically drops in the postperovskite stability field above 116 GPa. This compositional variation should strengthen the lowermost mantle between 1,800 km depth and 2,000 km depth, and weaken it between 2,000 km depth and the D" layer. The succession of layers could dynamically decouple the mantle above 2,000 km from the lowermost mantle, and provide a rheological basis for the stabilization and nonentrainment of large low-shearvelocity provinces below that depth.iron partitioning | lower mantle | spin state | valence state | viscosity T he relative concentration (partitioning) of iron in minerals constituting mantle rocks is a critical parameter controlling their physical properties and, consequently, the dynamical properties of the mantle. In a pyrolitic mantle, the lower-mantle mineral phase assemblage consists of bridgmanite (Brg)-which transforms to postperovskite (PPv) at pressures higher than 110 GPa (1-4)-ferropericlase (Fp), and calcium silicate perovskite. Only Brg/PPv (hereafter referred to as "silicate" and abbreviated Sil) and Fp can accommodate significant amounts of iron in their structure (5). Density, elasticity, viscosity, and thermal or electrical conductivities, along with associated phase relations, melting temperatures, and relative melt/solid buoyancy, are all linked to the concentration, valence, and spin state of iron in lower-mantle minerals. The seismic observation of global-scale heterogeneities such as large low-shear-velocity provinces (LLSVPs) (6, 7), and that of experimental iron spin-pairing in mantle minerals at lower-mantle depths (8, 9), has fueled a number of investigations of iron partitioning in the lower mantle (10-22).Despite remarkable advances in experimental and analytical techniques in the last two decades (Supporting Information), stark discrepancies have been reported, depending on the composition of the starting material (San Carlos olivine vs. pyrolite) and differences in iron valence (Fe 2+ and Fe 3+ ). San Carlos olivine has a molar (Mg + Fe)/Si = 2 and contains only iron as Fe 2+, whereas pyrolite has a molar (Mg + Fe)/Si = 1.4, contains Ca and Al, and contains iron as Fe 2+ and Fe 3+ (23). Therefore, the parameters controlling iron partitioning in deep mantle conditions are complex (12), and hinder any attempts to infer largescale geophysical or geochemical consequences on the mantle.To disentangle vale...

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Section: +supporting

confidence: 81%

Spin and valence dependence of iron partitioning in Earth’s deep mantle

Piet

Badro

Nabiei

et al. 2016

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

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“…It has been proposed that the ultra-lowvelocity zones observed seismologically at the CMB (38) can be explained by Fe-enriched PPv (39). Furthermore, recent studies have shown enhancement in the concentration of Fe 3+ by Al in both mantle Pv and PPv (22,23). It is notable that the basaltic layer at the top of the subducting slab has a high concentration of Al and some seismic studies have suggested that the subducting slabs reach CMB (40).…”

Section: Resultsmentioning

confidence: 99%

“…It has recently been found that the PPv phase is stable at 2,000 K and 60 GPa with an Fe 2 O 3 stoichiometry (1). Furthermore, some studies suggested that a substantial amount of Fe in Mgsilicate Pv and PPv are Fe 3+ (Fe 3+ / Fe = 0.1 ∼ 0.7) at mantle P-T conditions due to crystal chemistry effects (22,23). Therefore, Fe 2 O 3 provides opportunities to understand the properties of Fe end-member PPv.…”

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confidence: 99%

Electronic and magnetic structures of the postperovskite-type Fe ₂ O ₃ and implications for planetary magnetic records and deep interiors

Shim

Bengtson

Morgan³

et al. 2009

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

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“…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. Experimental studies have demonstrated that ppv can take up much more iron than silicate perovskite (pv) (14,15), and the equation of state (EOS) and phase boundaries have been determined as a function of Fe 2þ content (16)(17)(18)(19). In Al-bearing ppv, the presence of Fe 3þ may also have a significant effect on the physical properties, phase boundaries and iron partitioning (20).…”

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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.

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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.

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Ferric iron in Al‐bearing post‐perovskite

Cited by 44 publications

References 20 publications

Spin and valence dependence of iron partitioning in Earth’s deep mantle

Spin and valence dependence of iron partitioning in Earth’s deep mantle

Electronic and magnetic structures of the postperovskite-type Fe ₂ O ₃ and implications for planetary magnetic records and deep interiors

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

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Ferric iron in Al‐bearing post‐perovskite

Cited by 44 publications

References 20 publications

Spin and valence dependence of iron partitioning in Earth’s deep mantle

Spin and valence dependence of iron partitioning in Earth’s deep mantle

Electronic and magnetic structures of the postperovskite-type Fe 2 O 3 and implications for planetary magnetic records and deep interiors

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

Contact Info

Product

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Electronic and magnetic structures of the postperovskite-type Fe ₂ O ₃ and implications for planetary magnetic records and deep interiors

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