Upper mantle structure of southern Africa from Rayleigh wave tomography

Li, Aibing; Burke, Kevin

doi:10.1029/2006jb004321

Cited by 98 publications

(165 citation statements)

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“…Jun Korenaga is thanked for providing a preprint of a paper containing new analyses of olivine creep parameters. (Li and Burke, 2006) > 150 km (Chen et al, 2007) Consistent with 250 km (Bruneton et al, 2004a) S-Receiver function~ 250-300 km (Kumar et al, 2007) Magnetotelluric (MT) 230 km (Miensopust et al, 2006) 210 km at LdG 260 km average (Jones et al, 2003) 205 km at NAT (Jones, 1999) > 300 km (Korja, 2007) . The LAB may also correlate with a downward extinction of seismic anisotropy (e.g., Gaherty and Jordan, 1995) or a change in the direction of anisotropy (e.g., Debayle and Kennett, 2000a;2000b;Sebai et al, 2006).…”

Section: Discussionmentioning

confidence: 99%

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The elusive lithosphere–asthenosphere boundary (LAB) beneath cratons

Eaton

Darbyshire

Evans

et al. 2009

Lithos

393

288

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The lithosphere-asthenosphere boundary (LAB) is a first-order structural discontinuity that accommodates differential motion between tectonic plates and the underlying mantle. Although it is the most extensive type of plate boundary on the planet, its definitive detection, especially beneath cratons, is proving elusive. Different proxies are used to demarcate the LAB, depending on the nature of the measurement. Here we compare interpretations of the LAB beneath three The seismic LAB beneath cratons is typically regarded as the base of a high-velocity mantle lid, although some workers infer its location based on a distinct change in seismic anisotropy.Surface-wave inversion studies provide depth-constrained velocity models, but are relatively insensitive to the sharpness of the LAB. The S-receiver function method is a promising new seismic technique with complementary characteristics to surface-wave studies, since it is 2 sensitive to sharpness of the LAB but requires independent velocity information for accurate depth estimation. Magnetotelluric (MT) observations have, for many decades, imaged an "electrical asthenosphere" layer at depths beneath the continents consistent with seismic lowvelocity zones. This feature is most easily explained by the presence of a small amount of water in the asthenosphere, possibly inducing partial melt. Depth estimates based on various proxies considered here are similar, lending confidence that existing geophysical tools are effective for mapping the LAB beneath cratons.

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Section: Discussionmentioning

confidence: 99%

“…• absolute velocity variation with depth -taking a specific V s value instead of a percent velocity anomaly as a proxy (Li and Burke, 2006);…”

Section: Defining the Lab Using Surface-wave Observationsmentioning

confidence: 99%

The elusive lithosphere–asthenosphere boundary (LAB) beneath cratons

Eaton

Darbyshire

Evans

et al. 2009

Lithos

393

288

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“…5b). Most models do not fit neither our, nor the xenolith-based isotropic S wave velocity profiles of James et al (2004), but there is a fit with the DataX model of Larson et al (2006) and, in to lesser extent, with the model L&B06 of Li and Burke (2006). The QPM model of Qiu et al (1996) and the model of Hansen et al (2009) (H09) display a marked decrease of V s at 110-120 km that is not observed in the xenolith data.…”

Section: Comparison With Seismological Velocity Profiles and Tomograpmentioning

confidence: 90%

“…on top of a low velocity layer (Jordan, 1978;Priestley, 1999;James et al, 2001;Li and Burke, 2006;Priestley et al, 2006). Most body and surface wave tomography models indicate that this lid is 200-250 km thick beneath the Kaapvaal craton (James et al, 2001;Chevrot and Zhao, 2007;Fishwick, 2010).…”

Section: Baptiste and A Tommasi: Seismic Properties Of The Kaapvamentioning

confidence: 99%

Petrophysical constraints on the seismic properties of the Kaapvaal craton mantle root

Baptiste

Tommasi

2014

Solid Earth

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Abstract.We calculated the seismic properties of 47 mantle xenoliths from 9 kimberlitic pipes in the Kaapvaal craton based on their modal composition, the crystal-preferred orientations (CPO) of olivine, ortho-and clinopyroxene, and garnet, the Fe content of olivine, and the pressures and temperatures at which the rocks were equilibrated. These data allow constraining the variation of seismic anisotropy and velocities within the cratonic mantle. The fastest P and S 2 wave propagation directions and the polarization of fast split shear waves (S 1 ) are always subparallel to olivine [100] axes of maximum concentration, which marks the lineation (fossil flow direction). Seismic anisotropy is higher for high olivine contents and stronger CPO. Maximum P wave azimuthal anisotropy (AV p ) ranges between 2.5 and 10.2 % and the maximum S wave polarization anisotropy (AV s ), between 2.7 and 8 %. Changes in olivine CPO symmetry result in minor variations in the seismic anisotropy patterns, mainly in the apparent isotropy directions for shear wave splitting. Seismic properties averaged over 20 km-thick depth sections are, therefore, very homogeneous. Based on these data, we predict the anisotropy that would be measured by SKS, Rayleigh (S V ) and Love (S H ) waves for five endmember orientations of the foliation and lineation. Comparison to seismic anisotropy data from the Kaapvaal shows that the coherent fast directions, but low delay times imaged by SKS studies, and the low azimuthal anisotropy with with the horizontally polarized S waves (S H ) faster than the vertically polarized S wave (S V ) measured using surface waves are best explained by homogeneously dipping (45 • ) foliations and lineations in the cratonic mantle lithosphere. Laterally or vertically varying foliation and lineation orientations with a dominantly NW-SE trend might also explain the low measured anisotropies, but this model should also result in backazimuthal variability of the SKS splitting data, not reported in the seismological data. The strong compositional heterogeneity of the Kaapvaal peridotite xenoliths results in up to 3 % variation in density and in up to 2.3 % variation of V p , V s , and V p /V s ratio. Fe depletion by melt extraction increases V p and V s , but decreases the V p /V s ratio and density. Orthopyroxene enrichment due to metasomatism decreases the density and V p , strongly reducing the V p /V s ratio. Garnet enrichment, which was also attributed to metasomatism, increases the density, and in a lesser extent V p and the V p /V s ratio. Comparison of density and seismic velocity profiles calculated using the xenoliths' compositions and equilibration conditions to seismological data in the Kaapvaal highlights that (i) the thickness of the craton is underestimated in some seismic studies and reaches at least 180 km, (ii) the deep sheared peridotites represent very local modifications caused and oversampled by kimberlites, and (iii) seismological models probably underestimate the compositional heterogeneity in the Kaapvaal man...

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“…In general, shear-wave velocity structure can provide better rheological images than that of the P-wave tomography, and surface-wave phase velocity is sensitive to the variation of shear-wave velocity, thus, surface-wave tomography is one of the most important tools to understand the rheological and tectonic structures in the crust and the upper mantle (Li and Burke 2006;Jia and Zhang 2008;Ding et al 2008;Jobert et al 1985;Toksoz and Anderson 1966;Kanamori 1970;Forsyth 1975;Zhang and Lay 1996;Zhang and Ma 1997). A number of studies have resolved the crustal and upper-mantle velocity structures using longperiod surface-wave data Yanovskaya and Kozhevnikov 2003;Huang et al 2003;He et al 2002He et al , 2009).…”

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confidence: 99%