A Perovskitic Lower Mantle Inferred from High-pressure, High-temperature Sound Velocity Data

Murakami, Motohiko; Ohishi, Yasuo; Hirao, Naohisa; Hirose, Kei

doi:10.1007/s12594-012-0111-2

Cited by 59 publications

(121 citation statements)

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“…However, in most seismic tomography models, values of R S=P increase with depth and do not show a peak within mid-lower mantle depths (45,48). The present study suggests that the absence of a clear peak in R S=P or a peak above the 1,500-2,000-km depth interval could be used as an indirect argument in support of compositional heterogeneity, particularly a reduction in Fp abundance with depth (19). A peak at greater depths could be produced by a combination of factors, especially by a change in iron partitioning between MgPv and Fp throughout the spin crossover in Fp.…”

Section: Significancementioning

confidence: 48%

“…Most of its properties are affected by the spin crossover. In particular, thermodynamics (14) and thermal elastic properties (15)(16)(17)(18)(19)(20) are modified in unusual ways that can change profoundly our understanding of the Earth's mantle. However, this is a broad and smooth crossover that takes place throughout most of the lower mantle and might not produce obvious signatures in radial velocity or density profiles (20, 21) (see Figs.…”

mentioning

confidence: 99%

“…It has been challenging for both experiments (15)(16)(17)(18)(19) and theory (20) to reach a consensus on this topic. Measurements often seemed to include extrinsic effects, making it difficult to confirm the spin crossover signature by different techniques and across laboratories.…”

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confidence: 99%

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Spin crossover in ferropericlase and velocity heterogeneities in the lower mantle

Wentzcovitch

2014

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

109

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Deciphering the origin of seismic velocity heterogeneities in the mantle is crucial to understanding internal structures and processes at work in the Earth. The spin crossover in iron in ferropericlase (Fp), the second most abundant phase in the lower mantle, introduces unfamiliar effects on seismic velocities. Firstprinciples calculations indicate that anticorrelation between shear velocity (V S ) and bulk sound velocity (V φ ) in the mantle, usually interpreted as compositional heterogeneity, can also be produced in homogeneous aggregates containing Fp. The spin crossover also suppresses thermally induced heterogeneity in longitudinal velocity (V P ) at certain depths but not in V S . This effect is observed in tomography models at conditions where the spin crossover in Fp is expected in the lower mantle. In addition, the one-of-a-kind signature of this spin crossover in the R S/P (∂ ln V S =∂ ln V P ) heterogeneity ratio might be a useful fingerprint to detect the presence of Fp in the lower mantle.seismic tomography | lateral heterogeneity | elastic modulus | density functional theory | mantle plume F erropericlase (Fp) is believed to be the second most abundant phase in the lower mantle (1, 2). Since the discovery of the high-spin (HS) to low-spin (LS) crossover in iron in Fp (3), this phenomenon has been investigated extensively experimentally and theoretically (4-14). Most of its properties are affected by the spin crossover. In particular, thermodynamics (14) and thermal elastic properties (15)(16)(17)(18)(19)(20) are modified in unusual ways that can change profoundly our understanding of the Earth's mantle. However, this is a broad and smooth crossover that takes place throughout most of the lower mantle and might not produce obvious signatures in radial velocity or density profiles (20, 21) (see Figs. S1 and S2). Therefore, its effects on aggregates are more elusive and indirect. For instance, the associated density anomaly can invigorate convection, as demonstrated by geodynamics simulations in a homogeneous mantle (22)(23)(24). The bulk modulus anomaly may decrease creep activation parameters and lower mantle viscosity (10, 24, 25) promoting mantle homogenization in the spin crossover region (24), and anomalies in elastic coefficients can enhance anisotropy in the lower mantle (16). Less understood are its effects on seismic velocities produced by lateral temperature variations.The present analysis is based on our understanding of thermal elastic anomalies caused by the spin crossover. It has been challenging for both experiments (15-19) and theory (20) to reach a consensus on this topic. Measurements often seemed to include extrinsic effects, making it difficult to confirm the spin crossover signature by different techniques and across laboratories. A theoretical framework had to be developed to address these effects. However, an agreeable interpretation of data and results has emerged recently (20). With increasing pressure, nontrivial behavior is observed in all elastic coefficients, aggregate mo...

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Section: Significancementioning

confidence: 48%

mentioning

confidence: 99%

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Spin crossover in ferropericlase and velocity heterogeneities in the lower mantle

Wentzcovitch

2014

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

109

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“…Eqs. (3) and (4) Assuming an adiabatic temperature gradient in the lower mantle, rT depends on the geochemical model and mineralogical composition (Turcotte and Schbert, 1982;Matas et al, 2007;Murakami et al, 2012). BSE and LM, which imply different convection mechanisms, yield rT throughout the investigated P range as large as 0.3 and 0.5 K/km, respectively, in agreement with Ono (2008); therefore, the ensuing P-T relationships used in this study are: Table 3 for the calculations.…”

Section: Equilibrium Constant: Mswv Vs Mswamentioning

confidence: 99%

Lower mantle hydrogen partitioning between periclase and perovskite: A quantum chemical modelling

Merli

Bonadiman

Diella

et al. 2016

Geochimica et Cosmochimica Acta

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“…Murakami et al, 2012), for which application is limited to optically transparent specimens. Impulsive stimulated light scattering (ISLS) has been developed to enable measurements on metallic samples but is sensitive to surface properties, and data analysis is relatively complex (e.g.…”

Section: Experimental Techniques For Sound Velocity Determination Undmentioning

confidence: 99%

Sound velocity of hcp-Fe at high pressure: experimental constraints, extrapolations and comparison with seismic models

Antonangeli

Ohtani

2015

Prog. in Earth and Planet. Sci.

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Determining the sound velocity of iron under extreme thermodynamic conditions is essential for a proper interpretation of seismic observations of the Earth's core but is experimentally challenging. Here, we review techniques and methodologies used to measure sound velocities in metals at megabar pressures, with specific focus on the compressional sound velocity of hexagonal close-packed iron. A critical comparison of literature results, coherently analyzed using consistent metrology (pressure scale, equation of state), allows us to propose reference relations for the pressure and density dependence of the compressional velocity of hexagonal close-packed iron at ambient temperature. This provides a key base line upon which to add complexity, including high-temperature effects, pre-melting effects, effects of nickel and/or light element incorporation, necessary for an accurate comparison with seismic models, and ultimately to constrain Earth's inner core composition.

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A Perovskitic Lower Mantle Inferred from High-pressure, High-temperature Sound Velocity Data

Cited by 59 publications

References 0 publications

Spin crossover in ferropericlase and velocity heterogeneities in the lower mantle

Spin crossover in ferropericlase and velocity heterogeneities in the lower mantle

Lower mantle hydrogen partitioning between periclase and perovskite: A quantum chemical modelling

Sound velocity of hcp-Fe at high pressure: experimental constraints, extrapolations and comparison with seismic models

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