Evidence from numerical modelling for 3D spreading of [001] screw dislocations in Mg<sub>2</sub>SiO<sub>4</sub>forsterite

Carrez, Philippe; Walker, Andrew; Metsue, Arnaud; Cordier, Patrick

doi:10.1080/14786430802363804

Cited by 25 publications

(26 citation statements)

References 45 publications

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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: 98%

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: 98%

Development of texture and seismic anisotropy during the onset of subduction

Leo

Walker

et al. 2014

Geochem Geophys Geosyst

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“…Influence of lattice friction and interactions with point defects on dislocation velocities are taken into account via the mobility laws defined for glide and climb. In olivine, dislocations exhibit marked crystallographic orientation; this reflects a high glide resistance, probably due to an extended core structure [31]. In high lattice resistance materials, it is commonly assumed that glide is controlled by a thermally activated kink-pair mechanism.…”

Section: Methodsmentioning

confidence: 99%

Modeling the creep properties of olivine by 2.5-dimensional dislocation dynamics simulations

et al. 2015

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In this work we performed 2.5-dimensional (2.5D) dislocation dynamics simulations coupling climb with the glide dislocation motion to model the creep behavior of olivine, one of the main component of the Earth's upper mantle. In particular, we present an application of this method to determine the creep strain rate in a material with high lattice resistance, such as olivine. We show that by including the climb mechanism we reach steady state creep conditions. Moreover, we find that a creep power law with a stress exponent close to 3 can be extracted from our simulations and we provide a model based on Orowan's law to predict the creep strain rates in the high temperature and low stress regime. The model presented is relevant to describe the plastic flow of olivine in the Earth's mantle deformation conditions and can be useful to derive the high temperature creep behavior of other materials.

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“…Experimental studies have reported Peierls stresses for olivine, ranging widely from as little as 3.8 GPa (Idrissi et al, 2016) to ~15 GPa (Demouchy et al, 2013), although typical values are in the range [5][6][7][8][9][10] GPa (e.g. Evans and Goetze, 1979;Kranjc et al, 2016;Proietti et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

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

Skelton

Walker

2019

Physics of the Earth and Planetary Interiors

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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, σ 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 Mg vacancies on the Peierls stresses of [100](010) and [001](010) dislocations in forsterite. Mg vacancies considerably reduce GSF energies and, consequently, σ p for dislocations gliding on (010) in olivine. The magnitude of this decrease depends strongly on dislocation and the type of the lattice site, with vacant M2 sites producing the largest reduction of σ p. The [001](010) slip system is found to be more sensitive than the [100](010) slip system to the presence of vacancies. Although, at ambient pressure, σ p is lower for [100](010) than [001](010) edge dislocations, dσ p /dP is greater for [100](010) dislocations, resulting in a change in the preferred slip system at 1.5 GPa. By preferentially lubricating [001](010) glide, Mg vacancies reduce the pressure at which this cross-over occurs. An M2 vacancy 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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Evidence from numerical modelling for 3D spreading of [001] screw dislocations in Mg₂SiO₄forsterite

Cited by 25 publications

References 45 publications

Development of texture and seismic anisotropy during the onset of subduction

Development of texture and seismic anisotropy during the onset of subduction

Modeling the creep properties of olivine by 2.5-dimensional dislocation dynamics simulations

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

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Evidence from numerical modelling for 3D spreading of [001] screw dislocations in Mg2SiO4forsterite

Cited by 25 publications

References 45 publications

Development of texture and seismic anisotropy during the onset of subduction

Development of texture and seismic anisotropy during the onset of subduction

Modeling the creep properties of olivine by 2.5-dimensional dislocation dynamics simulations

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

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Evidence from numerical modelling for 3D spreading of [001] screw dislocations in Mg₂SiO₄forsterite