Olivine crystals align during diffusion creep of Earth’s upper mantle

Miyazaki, T.; Sueyoshi, Kenta; Hiraga, Takehiko

doi:10.1038/nature12570

Cited by 144 publications

(217 citation statements)

References 42 publications

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“…Recrystalization could further reduce the anisotropy. These mechanisms are generally not thought to affect the anisotropic patterns, although recent experiments suggest CPO from diffusion creep in olivine is possible (Miyazaki et al 2013). Both the overestimation of anisotropic strength in our models and the underestimation in observations are additional arguments for the anisotropy in the pPv B model to be unrealistically weak.…”

Section: Limitations Of These Modelsmentioning

confidence: 65%

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: Limitations Of These Modelsmentioning

confidence: 65%

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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“…linear-viscous (newtonian) creep has also been experimentally observed in anorthite and forsterite aggregates (Gómez Barreiro et al, 2007;Miyazaki et al, 2013); the mechanism responsible for such LPO formation, likely 'diffusion related' although still unclear, is not accounted for in the present model. Along the same line, diffusion creep in two phase aggregates shows some quite odd behaviors, as predicted by early modeling (Wheeler, 1992) and recently observed in experimentally deformed harzburgite (Sundberg and Cooper, 2008); such behaviors cannot be described in the framework of the present modeling.…”

Section: Specifics Of the Present Second-order (So) Modelmentioning

confidence: 79%

Multiscale modeling of upper mantle plasticity: From single-crystal rheology to multiphase aggregate deformation

Raterron

Detrez

Castelnau

et al. 2014

Physics of the Earth and Planetary Interiors

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is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. We report a first application of an improved second-order (SO) viscoplastic self-consistent model for multiphase aggregates, applied to an olivine + diopside aggregate as analogue for a dry upper mantle peridotite deformed at 10 À15 s À1 shear strain rate along a 20-Ma ocean geotherm. Beside known dislocation slip systems, this SO-model version accounts for an isotropic relaxation mechanism representing 'diffusionrelated' creep mechanisms in olivine. Slip-system critical resolved shear stress (CRSS) are evaluated in both phases -as functions of P, T, oxygen fugacity (fO 2 ) and strain rate -from previously reported experimental data obtained on single crystals and first-principle calculations coupled with the Peierls-Nabarro model for crystal plasticity; and the isotropic-mechanism dependence on T and P matches that of Si selfdiffusion in olivine, while its relative activity is constrained by reported data. The model reproduces well the olivine and diopside lattice preferred orientations (LPO) produced experimentally and observed in naturally deformed rocks, as well as observed sensitivities of multiphase aggregate strength to the volume fraction of the hard phase (here diopside). It shows a significant weakening of olivine LPO with increasing depth, which results from the combined effects of the P-induced

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“…It has also been suggested that a distinct LPO may form in olivine when it is deformed via diffusion creep (Miyazaki et al 2013). Similarly, a transition to a grain boundary sliding deformation mechanism may explain the presence of the B-type deformation fabric, rather than water-induced changes to the relative strengths of olivine slip systems.…”

Section: Discussionmentioning

confidence: 99%

Lubrication of dislocation glide in forsterite by Mg vacancies: insights from Peierls-Nabarro modeling

Skelton¹,

Walker²

2018

Preprint

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Dislocation glide is an important contributor to the rheology of olivine under conditions of high stress and low to moderate temperature, such as occur in mantle wedges. Interactions between point defects and dislocation core may alter the Peierls stress,  p , and has been suggested that vacancy-related defects may selectively enhance glide on certain slip systems, changing the olivine deformation fabric.In this study, the Peierls-Nabarro model, parameterized by generalized stacking fault (GSF) energies calculated atomistically using empirical interatomic potentials, is used to determine the effect of bare concentration at the glide plane of 0.125 defects/site is sufficient to reduce cross-over to 0.7 GPa. This may account for the existence of the B-type olivine deformation fabric in the corners of mantle wedges.

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Olivine crystals align during diffusion creep of Earth’s upper mantle

Cited by 144 publications

References 42 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

Multiscale modeling of upper mantle plasticity: From single-crystal rheology to multiphase aggregate deformation

Lubrication of dislocation glide in forsterite by Mg vacancies: insights from Peierls-Nabarro modeling

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