Strong inheritance of texture between perovskite and post-perovskite in the D′′ layer

Dobson, David P.; Miyajima, Nobuyosihi; Nestola, Fabrizio; Alvaro, Matteo; Casati, Nicola; Liebske, Christian; Wood, Ian G.; Walker, Andrew

doi:10.1038/ngeo1844

Cited by 41 publications

(50 citation statements)

References 24 publications

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“…As the study of Walker et al (2011) also mentions, depending on the Clapeyron slope of the perovskite to post-perovskite transition, post-perovskite might not be present in these warmer regions. A recent study shows that the resulting inherited anisotropic signature in perovskite after converting back from post-perovskite would be consistent with seismic observations (Dobson et al 2013). Without thermochemical piles or lateral variations in phase, a global correlation might not be appropriate.…”

Section: Presence Of Post-perovskitementioning

confidence: 69%

“…We simplify our model by not accounting for the perovskite to post-perovskite transition specifically. When this phase transition occurs texture could be inherited, as shown for the post-perovskite to perovskite transition (Dobson et al 2013). Away from the transition, this inherited texture would be overridden due to the strong deformation as the slab hits the CMB.…”

Section: Limitations Of These Modelsmentioning

confidence: 99%

“…In the warmer regions, the D transition of perovskite to post-perovskite occurs at pressures below the core-mantle boundary, explaining the absence of substantial anisotropy in some areas [e.g. beneath the Atlantic, Garnero et al (2004)] , and an V SV > V SH signature of radial anistropy in others (Kawai & Geller 2010;Dobson et al 2013). Recently, experiments have shown that the occurrence of the post-perovskite transition at mantle pressures depends not only on temperature, but also on composition (Catalli et al 2009;Grocholski et al 2012).…”

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confidence: 99%

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Synthetic seismic anisotropy models within a slab impinging on the core–mantle boundary

Cottaar

McNamara

et al. 2014

Geophysical Journal International

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S U M M A R YThe lowermost few hundreds of kilometres of the Earth's mantle are elastically anisotropic; seismic velocities vary with direction of propagation and polarization. Observations of strong seismic anisotropy correlate with regions where subducted slab material is expected. In this study, we evaluate the hypothesis that crystal preferred orientation (CPO) in a slab, as it impinges on the core-mantle boundary, is the cause of the observed anisotropy. Next, we determine if fast polarization directions seen by shear waves can be mapped to directions of geodynamic flow. This approach is similar to our previous study performed for a 2-D geodynamic model. In this study, we employ a 3-D geodynamic model with temperaturedependent viscosity and kinematic velocity boundary conditions defined at the surface of the Earth to create a broad downwelling slab. Tracers track the deformation that we assume to be accommodated by dislocation creep. We evaluate the models for the presence of perovskite or post-perovskite and for different main slip systems along which dislocation creep may occur in post-perovskite [(100),(010) and (001)]-resulting in four different mineralogical models of CPO. Combining the crystal pole orientations with single crystal elastic constants results in seismically distinguishable models of seismic anisotropy. The models are evaluated against published seismic observations by analysing different anisotropic components: the radial anisotropy, the splitting for (sub-)vertical phases (i.e. azimuthal anisotropy), and the splitting for subhorizontal phases. The patterns in radial anisotropy confirm our earlier results in 2-D. Observations of radial anisotropy and splitting in subhorizontal phases are mostly consistent with our models of post-perovskite with (010)-slip and (001)-slip. Our model of (001)-slip predicts stronger splitting than for (010)-slip for horizontally propagating phases in all directions. The strongest seismic anisotropy in this model occurs where the slab impinges on the core-mantle boundary. The azimuthal anisotropy pattern for (001)-slip shows fast axis directions at the edges of the slab (sub-)parallel to flow directions, suggesting horizontal flows may be mapped out in the lowermost mantle using seismic observations.

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Section: Presence Of Post-perovskitementioning

confidence: 69%

Section: Limitations Of These Modelsmentioning

confidence: 99%

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confidence: 99%

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Synthetic seismic anisotropy models within a slab impinging on the core–mantle boundary

Cottaar

McNamara

et al. 2014

Geophysical Journal International

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“…This transition from the Pv Pbnm structure to the PPv Cmcm structure has been studied on the analog system NaNiF 3 [40]. Each Pv grain transforms to two PPv orientations, keeping the c-axis unchanged (Fig.…”

Section: Accounting For Phase Transitionsmentioning

confidence: 99%

“…for Pv [32,33], PPv [23][24][25], Ca-Pv [34], ferropericlase [35][36][37][38]. Additional information may be obtained from low-pressure analogs, although bonding characteristics are dierent [39,40], and from atomic force calculations over a wide range of pressure-temperature conditions [41][42][43][44]. Slip systems used in the simulations are shown in Table 1.…”

Section: Deformation Mechanismsmentioning

confidence: 99%

A Refined Approach to Model Anisotropy in the Lowermost Mantle

Chandler

Yuan

et al. 2018

IOP Conf. Ser.: Mater. Sci. Eng.

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Abstract.Seismic anisotropy in the lowermost mantle has been attributed to texture development during mantle convection. This study models texture evolution in a subducting slab impinging on the core-mantle boundary. Using a 3-dimensional geodynamic model with tracers recording the deformation history, a visco-plastic self-consistent (VPSC) model for polycrystal deformation, and relying on experimentally determined slip systems, aggregate grains with volume fractions of 60% orthorhombic silicate perovskite (MgSiO 3), 20% cubic calcium perovskite (CaSiO3), and 20% cubic ferropericlase ((Mg,Fe)O) were deformed plastically and developed crystal preferred orientation. Forward and reverse perovskite (Pv)-postperovskite (PPv) phase transitions were included by allowing for likely orientation variant selections. Grain orientations, P (compression) and S (shear) wave velocity pole gures were calculated for each phase as well as the aggregate. The results show that dominant (001) slip on PPv can produce strong texture and shear wave anisotropy of 0.01-3.07% with V S H >VSV which agrees with seismological observations in selected areas of the D layer.

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Rheology of Mg₂GeO₄ olivine and spinel harzburgite: Implications for Earth's mantle transition zone

Shi

Zhang

Xia

et al. 2015

Geophysical Research Letters

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Geophysical modeling requires an upper mantle low‐viscosity zone (LVZ); recent results suggest that the LVZ could be within the mantle transition zone (MTZ) or above it, depending on boundary conditions. The rheology of the olivine‐dominated uppermost mantle is well constrained experimentally but not the MTZ. Here we report first‐time measurement of the rheology of Mg2GeO4 spinel (analogue of ringwoodite, the dominant mineral of the lower MTZ) in the dislocation creep regime and compare it with that of Mg2GeO4 olivine. In both cases, we incorporate 15–20% pyroxene, the second most abundant mineral in the upper mantle to provide a realistic comparison of rock rheologies. Under similar conditions, spinel‐dominated material is about twice as strong as olivine‐dominated material. Our results suggest that unless H2O weakening of ringwoodite or phase‐transformation‐induced grain size reduction occurs in the lower MTZ, it will be more viscous than above the 410 km discontinuity.

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Strong inheritance of texture between perovskite and post-perovskite in the D′′ layer

Abstract: however, it is difficult to explain all of the observed seismic anisotropy in D'' using a single deformation mechanism in post--perovskite. Here we show that strong texture inheritance is possible during

Cited by 41 publications

References 24 publications

Synthetic seismic anisotropy models within a slab impinging on the core–mantle boundary

Synthetic seismic anisotropy models within a slab impinging on the core–mantle boundary

A Refined Approach to Model Anisotropy in the Lowermost Mantle

Rheology of Mg₂GeO₄ olivine and spinel harzburgite: Implications for Earth's mantle transition zone

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Strong inheritance of texture between perovskite and post-perovskite in the D′′ layer

Abstract: however, it is difficult to explain all of the observed seismic anisotropy in D'' using a single deformation mechanism in post--perovskite. Here we show that strong texture inheritance is possible during

Cited by 41 publications

References 24 publications

Synthetic seismic anisotropy models within a slab impinging on the core–mantle boundary

Synthetic seismic anisotropy models within a slab impinging on the core–mantle boundary

A Refined Approach to Model Anisotropy in the Lowermost Mantle

Rheology of Mg2GeO4 olivine and spinel harzburgite: Implications for Earth's mantle transition zone

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Product

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Rheology of Mg₂GeO₄ olivine and spinel harzburgite: Implications for Earth's mantle transition zone