Seismic anisotropy in the mantle transition zone induced by shear deformation of wadsleyite

Kawazoe, Takaaki; Ohuchi, Tomohiro; Nishihara, Yu; Nishiyama, Norimasa; Fujino, Kiyoshi; Irifune, Tetsuo

doi:10.1016/j.pepi.2012.12.005

Cited by 50 publications

(54 citation statements)

References 28 publications

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“…LPO of wadsleyite and/or ringwoodite could indeed explain the observed signal in the upper and lower transition zone, respectively, as they have been shown to be intrinsically anisotropic. Wadsleyite single crystal anisotropy is about 14% (Zha et al, 1997), and recent modeling showed that a polycrystal of pyrolytic composition at MTZ conditions can have ∼ 1% seismic anisotropy (Tommasi et al, 2004;Kawazoe et al, 2013), compatible with our model. The intrinsic elastic anisotropy of ringwoodite is more ambiguous.…”

Section: Discussionsupporting

confidence: 88%

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Seismic anisotropy changes across upper mantle phase transitions

Yuan¹,

Beghein²

2013

Earth and Planetary Science Letters

149

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The mantle transition zone is believed to play an important role in the thermochemical evolution of our planet and in its deep water cycle. Constraining mantle flow at these depths can help elucidate its nature and better understand mantle dynamics and the history of plate tectonics. Seismic anisotropy, i.e. the directional dependence of seismic wave velocity, provides us with the most direct constraints on mantle deformation. Its detection below ∼250 km depth is challenging, and it is often assumed that the deep upper mantle is seismically isotropic due to a change in mantle deformation mechanism.Here, we present a global model of azimuthal anisotropy for the top 1000 km of the mantle. We used a dataset composed of fundamental and higher mode Rayleigh wave phase velocity maps, which provides resolution of azimuthal anisotropy to much greater depths than in previous studies. Our model unravels the presence of significant anisotropy in the transition zone, challenging common views of mantle deformation mechanisms, and reveals a striking correlation between changes in anisotropy amplitudes and in the fast * Corresponding author with the idea that the transition zone acts as a water filter.

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Section: Discussionsupporting

confidence: 88%

“…with V SV > V SH in horizontal flow and with V SH > V SV in vertical flow (Kawazoe et al, 2013). Based on results by Visser et al (2008b) this would translate into horizontal shear, but using other models (Montagner and Kennett, 1996;Beghein et al, 2006;Panning and Romanowicz, 2006) this would result in vertical shear instead.…”

Section: Discussionmentioning

confidence: 96%

Seismic anisotropy changes across upper mantle phase transitions

Yuan¹,

Beghein²

2013

Earth and Planetary Science Letters

149

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“…All allow the controlled deformation of millimeter size samples. The D-DIA is designed for deformation at constant pressure, both compressional and extensional, at strain rates between 10 −3 and 10 −7 /s and, currently, up to 18 GPa and 1900 K [238]. The DT-Cup allows for controlled deformation in axial geometry with experiments at about 20 GPa at 300 K and 10 GPa at 1100 K [237].…”

Section: Experimental Devicesmentioning

confidence: 99%

Dislocations and Plastic Deformation in MgO Crystals: A Review

et al. 2018

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This review paper focuses on dislocations and plastic deformation in magnesium oxide crystals. MgO is an archetype ionic ceramic with refractory properties which is of interest in several fields of applications such as ceramic materials fabrication, nano-scale engineering and Earth sciences. In its bulk single crystal shape, MgO can deform up to few percent plastic strain due to dislocation plasticity processes that strongly depend on external parameters such as pressure, temperature, strain rate, or crystal size. This review describes how a combined approach of macro-mechanical tests, multi-scale modeling, nano-mechanical tests, and high pressure experiments and simulations have progressively helped to improve our understanding of MgO mechanical behavior and elementary dislocation-based processes under stress.

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“…Even the spherically averaged component of radial anisotropy is of marginal significance in this depth range, as may be understood by comparing several radial profiles of spherically averaged radial anisotropy presented in Figure 8 of Visser et al (2008) and Figure 11 of Panning et al (2010). Kawazoe et al (2013) made a high pressure/ temperature deformation experiment of wadsleyte, a major constituent mineral in the transition zone, to show that if the transition zone is dominated by horizontal shear flow, one would expect a spherically averaged radial anisotropy such that V SH < V SV (horizontally polarized S waves are slower than vertically polarized S waves).…”

Section: Seismic Anisotropymentioning

confidence: 99%