Complex seismic anisotropy in Madagascar revealed by shear-wave splitting measurements

Ramirez, C.; Nyblade, A.; Wysession, M. E.; Pratt, Martin; Andriampenomanana, Fenitra; Rakotondraibe, Tsiriandrimanana

doi:10.1093/gji/ggy367

Cited by 7 publications

(36 citation statements)

References 38 publications

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“…The good fit (20° misfit, Table ) of the observations with the mantle wind from Behn et al () suggests that the mantle wind from the African Superplume can generate the observed anisotropy in northern Madagascar. This interpretation is consistent with Ramirez et al ().…”

Section: Discussionsupporting

confidence: 93%

“…Comparison of synthetic splitting (white bars) derived from lithosphere‐mantle wind interactions models with SKS splitting measurement bars colored according to angular misfit (0–90°; Ramirez et al, ; Reiss et al, ) (a) for Behn et al () global mantle flow and (b) for (Forte et al, ) global mantle flow. Gray wedges represent confidence interval associated with the synthetic splitting.…”

Section: Resultsmentioning

confidence: 99%

“…In contrast, they attribute the SW‐NE oriented observations to asthenospheric flow induced by absolute plate motion. Ramirez et al () suggest that asthenospheric upwelling related to the African superplume explains the homogeneous pattern of seismic anisotropy in northern Madagascar (Figure , red bars), but they suggest the complex pattern of anisotropy in central Madagascar is due to asthenospheric upwelling driven by delamination of the Malagasy lithosphere. Ramirez et al () also suggest that, since the observed anisotropy cannot be attributed to a single process such as absolute plate motion, the most likely source of the anisotropy is strain‐induced LPO due to small‐scale convective flow, which is poorly understood beneath Madagascar and surroundings.…”

Section: Introductionmentioning

confidence: 99%

“…SKS splitting measurements across Madagascar. Red bars are splitting measurements from Ramirez et al (). Yellow bars are splitting measurements (Reiss et al, ) from the SELASOMA profile (black dashed line).…”

Section: Introductionmentioning

confidence: 99%

“…Reiss et al () produced the first SKS splitting observations along the SELASOMA seismic profile (SEismological signatures in the Lithosphere/Asthenosphere System Of Southern Madagascar) that spans southern Madagascar in a NE‐SW orientation, while Ramirez et al () provided additional SKS splitting measurements across the entire continental island (Figure ). Azimuthal seismic anisotropy across Madagascar is quite complex.…”

Section: Introductionmentioning

confidence: 99%

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Numerical Modeling of Mantle Flow Beneath Madagascar to Constrain Upper Mantle Rheology Beneath Continental Regions

et al. 2020

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Over the past few decades, azimuthal seismic anisotropy measurements have been widely used proxy to study past and present‐day deformation of the lithosphere and to characterize convection in the mantle. Beneath continental regions, distinguishing between shallow and deep sources of anisotropy remains difficult due to poor depth constraints of measurements and a lack of regional‐scale geodynamic modeling. Here, we constrain the sources of seismic anisotropy beneath Madagascar where a complex pattern cannot be explained by a single process such as absolute plate motion, global mantle flow, or geology. We test the hypotheses that either Edge‐Driven Convection (EDC) or mantle flow derived from mantle wind interactions with lithospheric topography is the dominant source of anisotropy beneath Madagascar. We, therefore, simulate two sets of mantle convection models using regional‐scale 3‐D computational modeling. We then calculate Lattice Preferred Orientation that develops along pathlines of the mantle flow models and use them to calculate synthetic splitting parameters. Comparison of predicted with observed seismic anisotropy shows a good fit in northern and southern Madagascar for the EDC model, but the mantle wind case only fits well in northern Madagascar. This result suggests the dominant control of the measured anisotropy may be from EDC, but the role of localized fossil anisotropy in narrow shear zones cannot be ruled out in southern Madagascar. Our results suggest that the asthenosphere beneath northern and southern Madagascar is dominated by dislocation creep. Dislocation creep rheology may be dominant in the upper asthenosphere beneath other regions of continental lithosphere.

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Section: Discussionsupporting

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Numerical Modeling of Mantle Flow Beneath Madagascar to Constrain Upper Mantle Rheology Beneath Continental Regions

et al. 2020

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Geophysical evidences for large-scale mullion-type structures at the mantle–crust interface in southern Madagascar: implications for Neoproterozoic orogeny

Martelat

Cardon

Lardeaux

et al. 2020

Int J Earth Sci (Geol Rundsch)

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Insights on the African Upper Mantle From Quasi‐Love Wave Scattering

Merry,

Eakin

2024

Geochem Geophys Geosyst

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The African upper mantle is diverse, featuring several cratonic roots, active and magmatic continental rifting, abundant intra‐plate volcanism, and several oceanic hotspots offshore. Relatively small‐scale mantle convection processes, some possibly related to lithospheric thickness variations, have been proposed to account for patterns of volcanism and topography. A key constraint on such features and processes can be found via seismic anisotropy, but limited coverage of seismograph stations across the continent has resulted in sparse observations. Quasi‐Love waves, produced by scattering of Love to Rayleigh energy at lateral gradients in upper mantle seismic anisotropy, can provide information about seismic anisotropy well away from seismograph stations. We catalog 525 observations of Quasi‐Love waves across the region and back‐project to scattering points, revealing locations of lateral gradients in upper mantle seismic anisotropy. Quasi‐Love wave scattering occurs at craton edges, likely due to the contrast between lithospheric and asthenospheric anisotropy, and close to ancient orogenic belts, indicating changes in fossilized lithospheric anisotropy from past collisional events. Scattering surrounding the proposed Al‐Kufrah cratonic remnant in north‐east Africa supports its existence as cratonic lithosphere. Scattering also occurs below thin lithosphere, suggesting deviations in asthenospheric flow patterns (such as localized upwellings), notably beneath the East African Rift, oceanic hotspot tracks, and the Cameroon Volcanic Line. Quasi‐Love scattering is abundant in the Indian Ocean and beneath Madagascar, consistent with small‐scale dynamic processes in the asthenosphere that likely relate to the complex rifting history of this ocean basin and the dispersed micro‐continents within.

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Complex seismic anisotropy in Madagascar revealed by shear-wave splitting measurements

Cited by 7 publications

References 38 publications

Numerical Modeling of Mantle Flow Beneath Madagascar to Constrain Upper Mantle Rheology Beneath Continental Regions

Numerical Modeling of Mantle Flow Beneath Madagascar to Constrain Upper Mantle Rheology Beneath Continental Regions

Geophysical evidences for large-scale mullion-type structures at the mantle–crust interface in southern Madagascar: implications for Neoproterozoic orogeny

Insights on the African Upper Mantle From Quasi‐Love Wave Scattering

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