Seismic anisotropy and geodynamics of the lithosphere–asthenosphere system

Plomerová, Jaroslava; Frederiksen, A. W.; Park, Jeffrey

doi:10.1016/j.tecto.2008.08.007

Cited by 6 publications

(5 citation statements)

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“…In such a case, the fast shear‐wave polarization directions and the high velocities retrieved from surface wave inversions would be parallel to the current plate motion and any regional variation would reflect deflections of the mantle flow (Bormann et al 1996). However, the fast shear‐wave polarization directions evaluated in central Fennoscandia (with the use of data from the SVEKALAPKO array and the SNSN) indicate distinct directional and geographical variations, which are not consistent with present day sub‐lithospheric mantle flow around the Fennoscandian root (Plomerová et al 2006, 2008; Vecsey et al 2007; Eken et al 2010). Due to the long history of the Precambrian lithosphere, which includes accretionary processes related to different phases of plate tectonics (Plomerová & Babuška 2010) one can expect complicated lithosphere–asthenosphere structures beneath regions which are now ‘intra‐plate’ areas, including Fennoscandia (Plomerová et al 2008).…”

Section: Discussionmentioning

confidence: 89%

“…The Shield possesses the characteristics of a continental lithosphere with a thick, undulated and sharply stepping lithospheric root—cratonic keel (Sandoval et al 2004; Babuška & Plomerová 2006; Olsson 2007; Plomerová et al 2002, 2008; Eken et al 2007, 2008). Traditionally, a sub‐lithospheric flow around this keel would be considered as an explanation for the mechanism of observed anisotropy (Wylegalla et al 1999; Pedersen et al 2006).…”

Section: Discussionmentioning

confidence: 99%

“…Previous analyses of P ‐wave traveltimes and shear‐wave splitting directionality indicate that the Precambrian mantle lithosphere of Fennoscandia can be mostly modelled by dipping foliations in the Proterozoic part and a plunging lineation in the Archean part (Plomerová et al 2001, 2006, 2008; Vecsey et al 2007; Eken et al 2010). Discrepancies between isotropic inversions of radial and tangential components (SV and SH) of direct shear waves at depths down to ∼150–200 km, which are depths corresponding to an estimate of the lithosphere–asthenosphere boundary (LAB, Plomerová et al 2008; Plomerová & Babuška 2010), have been attributed to the effect of large‐scale anisotropy in the mantle lithosphere (Eken et al 2008, 2010).…”

Section: Introductionmentioning

confidence: 99%

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Effects of seismic anisotropy on P-velocity tomography of the Baltic Shield

Eken

Plomerová²,

Vecsey³

et al. 2011

Geophysical Journal International

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A B S T R A C TWe investigate possible effects of neglecting seismic anisotropy on standard isotropic Pvelocity tomographic images of the upper mantle beneath the Baltic shield. Isotropic inversions of teleseismic P-and S-wave traveltimes exhibit alternating high-and low-velocity heterogeneities down to depths of over 400 km. Differences in tomographic inversions of SV -and SH-wave traveltimes are distinct down to depths of about 200 km and are associated with anisotropy of the lithospheric mantle. Anisotropic structures of the upper mantle affect both the P and S traveltimes, shear-wave splitting as well as the P polarization directions. Joint inversion for isotropic and anisotropic velocity perturbations is not feasible due to the limited 3-D ray coverage of available data. Therefore, we correct the input traveltimes for anisotropic contributions derived from independent analyses and then perform standard isotropic inversions. These corrections are derived either directly from directional deviations of P-wave propagation or are calculated in anisotropic models retrieved by joint inversions of bodywave anisotropic parameters (P-residual spheres and shear-wave splitting). These anisotropic models are also used to fit backazimuth variations of P-wave polarization directions. General features of tomographic images calculated from the original and the anisotropy-corrected data are similar. Amplitudes of the velocity perturbations decrease below ∼200 km depth, that is in the sub-lithospheric mantle. In general, large-scale anisotropy related to the fabrics of the continental mantle lithosphere can contaminate tomographic images in some parts of models and should not be ignored.

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Section: Discussionmentioning

confidence: 89%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effects of seismic anisotropy on P-velocity tomography of the Baltic Shield

Eken

Plomerová²,

Vecsey³

et al. 2011

Geophysical Journal International

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“…Anisotropy in the upper mantle may result from both past and current deformation. Past orogenic processes can imprint the lithospheric upper mantle with a crystallographic fabric that can remain stable after thermal relaxation, which is often called "frozen anisotropy" (e.g., Nicolas and Christensen, 1987;Vauchez and Nicolas, 1991;Ben Ismaïl and Mainprice, 1998;Savage, 1999;Fouch and Rondenay, 2006;Plomerová et al, 2008). Current deformation and fl ow of the asthenospheric mantle, which is related to plate motion, also causes olivine LPO.…”

Section: Introductionmentioning

confidence: 99%

Upper-mantle seismic anisotropy from SKS splitting in the South American stable platform: A test of asthenospheric flow models beneath the lithosphere

et al. 2011

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Upper-mantle seismic anisotropy has been extensively used to infer both present and past deformation processes at lithospheric and asthenospheric depths. Analysis of shear-wave splitting (mainly from core-refracted SKS phases) provides information regarding uppermantle anisotropy. We present average measurements of fast-polarization directions at 21 new sites in poorly sampled regions of intraplate South America, such as northern and northeastern Brazil. Despite sparse data coverage for the South American stable platform, consistent orientations are observed over hundreds of kilometers. Over most of the continent, the fast-polarization direction tends to be close to the absolute plate motion direction given by the hotspot reference model HS3-NUVEL-1A. A previous global comparison of the SKS fast-polarization directions with fl ow models of the upper mantle showed relatively poor correlation on the continents, which was interpreted as evidence for a large contribution of "frozen" anisotropy in the lithosphere. For the South American plate, our data indicate that one of the reasons for the poor correlation may have been the relatively coarse model of lithospheric thicknesses. We suggest that improved models of upper-mantle fl ow that are based on more detailed lithospheric thicknesses in South America may help to explain most of the observed anisotropy patterns.

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“…A anisotropia no manto superior pode ser resultado de uma deformação antiga ou de uma deformação atual, que esta em andamento. A deformação decorrente de um evento de orogênese passado produz uma trama no manto superior, que pode continuar estável após o relaxamento termal do orógeno, chamada comumente de anisotropia congelada (Ben Ismail & Mainprice, 1988;Founch & Rondenay, 2006;Nicolas & Christensen, 1987;Plomerová et al, 2008;Savage, 1999;Vauchez & Nicolas, 1991). A movimentação e deformação atual do manto astenosférico, relacionada com o movimento das placas tectônicas, também pode produzir uma orientação dos cristais de olivina.…”

Section: Introductionunclassified