In situ observation of texture development in olivine, ringwoodite, magnesiowüstite and silicate perovskite at high pressure

Wenk, H. R.; Lonardeli, I.; Pehl, J.; Devine, James M.; Prakapenka, Vitali; Shen, Guoyin; Mao, Ho‐kwang

doi:10.1016/j.epsl.2004.07.033

Cited by 81 publications

(67 citation statements)

References 56 publications

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“…However, samples containing <25% NaCl instead acquire weak maxima at {112} and {101}. A similar texture was observed for ferropericlase in bridgmanite-ferropericlase assemblages deformed in the DAC and was attributed to heterogeneous deformation (Wenk et al, 2004;Miyagi and Wenk, 2016). Weak ferropericlase textures were also observed by Wang et al (2013).…”

Section: Texturesupporting

confidence: 54%

“…For example, a (001) transformation texture was observed in bridgmanite just after conversion from enstatite that remained up to 56 GPa (Miyagi and Wenk, 2016). Wenk et al (2004) and Miyagi and Wenk (2016) both saw a (100) transformation texture in bridgmanite immediately after converting from olivine or ringwoodite to bridgmanite + ferropericlase. Yet Wenk et al (2004) found a subsequent weak {012} deformation texture while Miyagi and Wenk (2016) saw a (001) deformation texture at lower pressure followed by a (100) maximum at pressure >55 GPa.…”

Section: Texturementioning

confidence: 99%

“…Of the studies mentioned above, only Wang et al (2013) looked at CPO and found CaGeO 3 developed similar CPO whether deformed as a single phase or along with 28% volume MgO while MgO developed weak CPO. Wenk et al (2004) and Miyagi and Wenk (2016) deformed ferropericlase-bridgmanite aggregates to 50 GPa and 61 GPa, respectively, in a diamond anvil cell (DAC) and found that ferropericlase developed a weak, irregular texture when deformed with bridgmanite, and that bridgmanite texture changed depending on the starting material and/or the presence of ferropericlase. Microstructures in the DAC experiments were unknown but assumed to have ferropericlase not interconnected based on earlier studies (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Two-phase deformation of lower mantle mineral analogs

Kaercher

Miyagi

Kanitpanyacharoen

et al. 2016

Earth and Planetary Science Letters

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Editor: J. BrodholtKeywords: crystallographic preferred orientation seismic anisotropy two-phase deformation lower mantle rheology 3D X-ray microtomographyThe lower mantle is estimated to be composed of mostly bridgmanite and a smaller percentage of ferropericlase, yet very little information exists for two-phase deformation of these minerals. To better understand the rheology and active deformation mechanisms of these lower mantle minerals, especially dislocation slip and the development of crystallographic preferred orientation (CPO), we deformed mineral analogs neighborite (NaMgF 3 , iso-structural with bridgmanite) and halite (NaCl, isostructural with ferropericlase) together in the deformation-DIA at the Advanced Photon Source up to 51% axial shortening. Development of CPO was recorded in situ with X-ray diffraction, and information on microstructural evolution was collected using X-ray microtomography. Results show that when present in as little as 15% volume, the weak phase (NaCl) controls the deformation. Compared to single phase NaMgF 3 samples, samples with just 15% volume NaCl show a reduction of CPO in NaMgF 3 and weakening of the aggregate. Microtomography shows both NaMgF 3 and NaCl form highly interconnected networks of grains. Polycrystal plasticity simulations were carried out to gain insight into slip activity, CPO evolution, and strain and stress partitioning between phases for different synthetic two-phase microstructures. The results suggest that ferropericlase may control deformation in the lower mantle and reduce CPO in bridgmanite, which implies a less viscous lower mantle and helps to explain why the lower mantle is fairly isotropic.

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Section: Texturesupporting

confidence: 54%

Section: Texturementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Two-phase deformation of lower mantle mineral analogs

Kaercher

Miyagi

Kanitpanyacharoen

et al. 2016

Earth and Planetary Science Letters

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“…Calculations by Carrez et al (2009) show that the {100} planes become more active at higher pressures. For orthorhombic perovskite, slip dominates on the (001) plane, but also occurs on (100) and (010) planes (Wenk et al 2004). Calculations show (100)[010] as the most active slip system across all pressures (Mainprice et al 2008).…”

Section: Deformation Mechanismsmentioning

confidence: 99%

“…Slip systems are inferred by comparing experimental CPOs with textures obtained by VPSC simulations, assuming different slip system activities. Such experiments have been applied to periclase (Stretton et al 2001;Merkel et al 2002;Yamazaki & Karato 2002;Long et al 2006;Lin et al 2009), perovskite (Karato et al 1995;Wenk et al 2004) and post-perovskite (Merkel et al 2006(Merkel et al , 2007Miyagi et al 2009;Walte et al 2009;Hirose et al 2010;Miyagi et al 2010;Okada et al 2010;Nisr et al 2012).…”

Section: Deformation Mechanismsmentioning

confidence: 99%

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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Mid-mantle anisotropy in subduction zones and deep water transport

Nowacki

Kendall

Wookey

et al. 2015

Geochem. Geophys. Geosyst.

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The Earth's transition zone has until recently been assumed to be seismically isotropic. Increasingly, however, evidence suggests that ordering of material over seismic wavelengths occurs there, but it is unclear what causes this. We use the method of source-side shear wave splitting to examine the anisotropy surrounding earthquakes deeper than 200 km in slabs around the globe. We find significant amounts of splitting ( 2.4 s), confirming that the transition zone is anisotropic here. However, there is no decrease in the amount of splitting with depth, as would be the case for a metastable tongue of olivine which thins with depth, suggesting this is not the cause. The amount of splitting does not appear to be consistent with processes in the ambient mantle, such as lattice-preferred orientation development in wadsleyite, ringwoodite, or MgSiO 3 -perovskite. We invert for the orientation of several mechanisms-subject to uncertainties in mineralogy and deformation-and the best fit is given by updip flattening in a style of anisotropy common to hydrous phases and layered inclusions. We suggest that highly anisotropic hydrous phases or hydrated layering is a likely cause of anisotropy within the slab, implying significant water transport from the surface down to at least 660 km depth.

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In situ observation of texture development in olivine, ringwoodite, magnesiowüstite and silicate perovskite at high pressure

Cited by 81 publications

References 56 publications

Two-phase deformation of lower mantle mineral analogs

Two-phase deformation of lower mantle mineral analogs

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

Mid-mantle anisotropy in subduction zones and deep water transport

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