Shear deformation of bridgmanite and magnesiowüstite aggregates at lower mantle conditions

Girard, Jennifer; Amulele, George; Farla, Robert; Mohiuddin, A.; Karato, Shun‐ichiro

doi:10.1126/science.aad3113

Cited by 139 publications

(164 citation statements)

References 40 publications

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“…%; Irifune, 1994), dominates the viscosity of this region (Girard et al, 2016). Seismic observation suggests that some slabs stagnate at 600-1000 km depths (Fukao and Obayashi, 2013).…”

Section: Geochemical Implicationsmentioning

confidence: 90%

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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“…%; Irifune, 1994), dominates the viscosity of this region (Girard et al, 2016). Seismic observation suggests that some slabs stagnate at 600-1000 km depths (Fukao and Obayashi, 2013).…”

Section: Geochemical Implicationsmentioning

confidence: 90%

Rapid decrease of MgAlO2.5 component in bridgmanite with pressure

Liu¹,

Ishii²,

Katsura³

2017

Geochem. Persp. Let.

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“…Their Figure 9 shows that low-viscosity slabs can still displace the chemical piles laterally and lead to strong heterogeneity in the mantle. Another effect that may lead to shear localization near subducted slabs would be a strong viscosity contrast between lower mantle constituents, bridgmanite and magnesiowüstite (Girard et al, 2016), if, under the stronger stresses surrounding slabs, the weak phase gets connected, whereas elsewhere the strong phase is interconnected. But until now, no numerical models of the mantle exist that would show the characteristics proposed by Kevin.…”

Section: Geodynamic Modelsmentioning

confidence: 99%

Earth evolution and dynamics—a tribute to Kevin Burke

et al. 2016

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Kevin Burke's original and thought-provoking contributions have been published steadily for the past sixty years, and more than a decade ago he set out to resolve how plate tectonics and mantle plumes interact by proposing a simple conceptual model, which we will refer to as "the Burkian Earth". On the Burkian Earth, mantle plumes take us from the deepest mantle to sub-lithospheric depths, where partial melting occurs, and to the surface, where hotspot lavas erupt today, and where large igneous provinces and kimberlites have erupted episodically in the past. The arrival of a plume head contributes to continental break-up and punctuates plate tectonics by creating and modifying plate boundaries. Conversely, plate tectonics makes an essential contribution to the mantle through subduction. Slabs restore mass to the lowermost mantle and are the triggering mechanism for plumes that rise from the margins of large-scale low shear-wave velocity structures in the lowermost mantle, that Kevin christened TUZO and JASON. Situated just above the core-mantle boundary beneath Africa and the Pacific, these are two stable and antipodal thermochemical piles, which Kevin reasons represent the immediate after-effect of the moon-forming event and the final magma ocean crystallization.

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“…With the silicate phase being the dominant interconnected phase in the lower mantle, it should strongly influence transport properties (34)(35)(36) and, most notably, viscosity (37). Although there are no compositional-dependence deformation data on Brg, experiments on olivine (38) and Fp (39) have shown an inverse correlation between iron content and strength: Minerals with higher iron concentrations are softer.…”

Section: +mentioning

confidence: 99%

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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Shear deformation of bridgmanite and magnesiowüstite aggregates at lower mantle conditions

Cited by 139 publications

References 40 publications

Rapid decrease of MgAlO2.5 component in bridgmanite with pressure

Rapid decrease of MgAlO2.5 component in bridgmanite with pressure

Earth evolution and dynamics—a tribute to Kevin Burke

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

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