Journal ArticleDOI
Deformation in the lowermost mantle beneath Australia from observations and models of seismic anisotropy
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In this paper, the authors examined seismic anisotropy in the lowermost mantle beneath Australia, bounded by the African and Pacific Large Low Shear Velocity Provinces, and applied a forward modeling strategy to understand which anisotropic scenarios are consistent with the observations.Abstract:
Observations of seismic anisotropy near the core-mantle boundary may yield constraints on patterns of lowermost mantle flow. We examine seismic anisotropy in the lowermost mantle beneath Australia, bounded by the African and Pacific Large Low Shear Velocity Provinces. We combined measurements of differential splitting of SKS-SKKS and S-ScS phases sampling our study region over a range of azimuths, using data from ten long-running seismic stations. Observations reveal complex and laterally heterogeneous anisotropy in the lowermost mantle. We identified two sub-regions for which we have robust measurements of D”-associated splitting for a range of ray propagation directions, and applied a forward modeling strategy to understand which anisotropic scenarios are consistent with the observations. We tested a variety of elastic tensors and orientations, including single-crystal elasticity of lowermost mantle minerals (bridgmanite, post-perovskite, and ferropericlase), tensors based on texture modeling in post-perovskite aggregates, elasticity predicted from deformation experiments on polycrystalline MgO aggregates, and tensors that approximate the shape preferred orientation of partial melt. We find that post-perovskite scenarios are more consistently able to reproduce the observations. Beneath New Zealand, the observations suggest a nearly horizontal [100] axis orientation with an azimuth that agrees well with the horizontal flow direction predicted by previous mantle flow models. Our modeling results further suggest dominant slip on the (010) plane in post-perovskite aggregates provide a good fit to the data but the solution is non-unique. Our results have implications for the mechanisms of deformation and anisotropy in the lowermost mantle and for the patterns of mantle flow.read more
Citations
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The effect of temperature on the seismic anisotropy of the perovskite and post-perovskite polymorphs of MgSiO 3
TL;DR: In this article, the seismic anisotropy of MgSiO3 perovskite is significantly temperature dependent, and it is shown that the direction of greatest shear wave splitting changes from [001] at 0 K to [010] at 3500 K.
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Deformation of Earth Materials - An Introduction to the Rheology of Solid Earth
TL;DR: In this paper, the deformation of Earth materials is presented in a systematic way covering elastic, anelastic and viscous deformation, and discussion on relevant debates are also included to bring readers a full picture of science in this interdisciplinary area.
Journal ArticleDOI
Lowermost Mantle Anisotropy Beneath Africa From Differential SKS‐SKKS Shear‐Wave Splitting
TL;DR: In this article, the authors investigate seismic anisotropy in the lowermost mantle in the vicinity of the African large low shear velocity province (LLSVP) using observations of differential SKS-SKKS shear wave splitting.
Journal ArticleDOI
Constraining lowermost mantle anisotropy with body waves: a synthetic modelling study
TL;DR: In this paper, a forward modeling approach was used to determine the combination of body wave phases (e.g., SKS, SKKS, ScS, SdS and PdP reflections off the D\" discontinuity) that are required to uniquely constrain a mechanism for D\" anisotropy.
References
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Free software helps map and display data
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Constraints on seismic velocities in the Earth from traveltimes
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Shear wave splitting and subcontinental mantle deformation
Paul G. Silver,W. Winston Chan +1 more
TL;DR: In this article, the authors consider three hypotheses concerning the origin of the continental anisotropy: (1) strain associated with absolute plate motion, as in the oceanic upper mantle, (2) crustal stress, and (3) the past and present internal deformation of the subcontinental upper mantle by tectonic episodes.
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Post-Perovskite Phase Transition in MgSiO3
TL;DR: Results demonstrate that MgSiO3 perovskite transforms to a new high-pressure form with stacked SiO6-octahedral sheet structure above 125 gigapascals and 2500 kelvin (2700-kilometer depth near the base of the mantle) with an increase in density of 1.0 to 1.2%.