Atomic-scale models of dislocation cores in minerals: progress and prospects

Walker, Andrew; Carrez, Philippe

doi:10.1180/minmag.2010.074.3.381

Cited by 25 publications

(22 citation statements)

References 177 publications

(271 reference statements)

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“…We demonstrate that this is achievable with the simplest of models—i.e., pure dry olivine deforming so as to generate an A‐type LPO in progressive simple shear—due to the combination of simple‐shear strain induced by trench‐parallel flow in the upper part of the subslab mantle, but also compression leading to trench‐parallel extension in the lower part. Furthermore, there is no need to invoke other mechanisms such as a pressure‐induced transition in the olivine slip systems to B‐type LPO [ Couvy et al ., ; Raterron et al ., ; Carrez et al ., ; Jung et al ., ; Raterron et al ., ; Walker et al ., ]. Faccenda and Capitanio [] have recently pointed out the importance of pure shear and extension in the development of trench‐parallel subslab seismic anisotropy.…”

Section: Discussionmentioning

confidence: 99%

Development of texture and seismic anisotropy during the onset of subduction

Leo

Walker

et al. 2014

Geochem Geophys Geosyst

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[1] How reliable are shear wave splitting measurements as a means of determining mantle flow direction? This remains a topic of debate, especially in the context of subduction. The answer hinges on whether our current understanding of mineral physics provides enough to accurately translate between seismic observations and mantle deformation. Here, we present an integrated model to simulate strainhistory-dependent texture development and estimate resulting shear wave splitting in subduction environments. We do this for a mantle flow model that, in its geometry, approximates the double-sided Molucca Sea subduction system in Eastern Indonesia. We test a single-sided and a double-sided subduction case. Results are compared to recent splitting measurements of this region by Di Leo et al. (2012a). The setting lends itself as a case study, because it is fairly young and, therefore, early textures from the slab's descent from the near surface to the bottom of the mantle transition zone-which we simulate in our models-have not yet been overprinted by subsequent continuous steady state flow. Second, it allows us to test the significance of the double-sided geometry, i.e., the need for a rear barrier to achieve trench-parallel subslab mantle flow. We demonstrate that although a barrier amplifies trenchparallel subslab anisotropy due to mantle flow, it is not necessary to produce trench-parallel fast directions per se. In a simple model of A-type olivine lattice-preferred orientation and one-sided subduction, trench-parallel fast directions are produced by a combination of simple shear and extension through compression and pure shear in the subslab mantle.

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Section: Discussionmentioning

confidence: 99%

Development of texture and seismic anisotropy during the onset of subduction

Leo

Walker

et al. 2014

Geochem Geophys Geosyst

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“…Even though the data for LPO experiments on lowermost mantle phases remain incomplete, it is observed that the contribution to any LPO-induced anisotropy is due to the ferropericlase and postperovskite, and bridgmanite when dominantly present in the D 00 layer [Mainprice et al, 2008]. In addition to the laboratory experiments on analog materials, primary principle calculations with the help of Peierls-Nabarro model [e.g., Devincre et al, 2001;Walker et al, 2010] are also utilized to investigate the deformation mechanisms (slip systems, which help to determine how the mineral aligns). The dominant slip system for pv is (100)[010], determined with the help of Peierl-Nabarro dislocation model [Mainprice et al, 2008], which agrees with the experimental results of Cordier et al [2004] and Merkel et al [2003] performed at pressures lower than the pressures at CMB.…”

Section: 1002/2016gc006604mentioning

confidence: 99%

Anisotropy in the lowermost mantle beneath the Indian Ocean Geoid Low from ScS splitting measurements

Rao

Kumar

Singh

2017

Geochem Geophys Geosyst

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The Indian Ocean Geoid Low (IOGL) to the south of Indian subcontinent is the world's largest geoid anomaly. In this study, we investigate the seismic anisotropy of the lowermost mantle beneath the IOGL by analyzing splitting of high‐quality ScS phases corrected for source and receiver side upper mantle anisotropy. Results reveal significant anisotropy ( ∼1.01%) in the D′′ layer. The observed fast axis polarization azimuths in the ray coordinate system indicate a TTI (transverse isotropy with a tilted axis of symmetry) style of anisotropy. Lattice Preferred Orientation (LPO) deformation of the palaeo‐subducted slabs experiencing high shear strain is a plausible explanation for the observed anisotropy beneath the IOGL.

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“…Devincre et al 2001;Walker et al 2010). These have also been applied to periclase ), perovskite (Cordier et al 2004;Mainprice et al 2008), and post-perovskite (Oganov et al 2005;Carrez et al 2007;Metsue et al 2009).…”

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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Atomic-scale models of dislocation cores in minerals: progress and prospects

Abstract: University of Bristol -Explore Bristol Research General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Keywords: computer modelling, dislocations, plasticity, core structure, deformation.

Cited by 25 publications

References 177 publications

Development of texture and seismic anisotropy during the onset of subduction

Development of texture and seismic anisotropy during the onset of subduction

Anisotropy in the lowermost mantle beneath the Indian Ocean Geoid Low from ScS splitting measurements

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

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