Mantle Anisotropy in NW Namibia From XKS Splitting: Effects of Asthenospheric Flow, Lithospheric Structures, and Magmatic Underplating

komeazi, Abolfazl; Kaviani, Ayoub; Rümpker, Georg

doi:10.1029/2022gl102119

Cited by 5 publications

(7 citation statements)

References 66 publications

(100 reference statements)

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“…(2009) with additional results from Komeazi et al. (2023) and Ebinger et al. (2024), gridded in 0.5° bins, on the global tectonic map of Hasterok et al.…”

Section: Resultsmentioning

confidence: 99%

“…(b) Overview of existing azimuthal anisotropy measurements for the same region. Station-averaged teleseismic shear-wave splitting measurements from the updated compilation of Wüstefeld et al (2009), with additional data from Qaysi et al (2018), Komeazi et al (2023), and Ebinger et al (2024), are plotted in pink. The orientation and strength of anisotropy at 150 km depth from the anisotropic global surface wave tomography model 3D2018_08Sv (Debayle et al, 2016) is represented by the black bars.…”

Section: Introductionmentioning

confidence: 99%

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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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“…(2009) with additional results from Komeazi et al. (2023) and Ebinger et al. (2024), gridded in 0.5° bins, on the global tectonic map of Hasterok et al.…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Merry,

Eakin

2024

Geochem Geophys Geosyst

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“…To assess whether more than one anisotropic layer contributes to the observed shear wave splitting parameters, modeling the observations using two anisotropic layers was attempted. Because the back azimuthal data coverage for most stations is insufficient to constrain a two-layer model, we combined measurements from stations within the same terrane, including individual measurements from previous studies (e.g., Komeazi et al, 2023;Yu et al, 2015) (Figure S6 in Supporting Information S1). Individual "good" and "fair" quality non-null measurements for stations within a terrane (Figure S6 in Supporting Information S1) were stacked in bins covering a maximum range of 5-6°with respect to back azimuth and epicentral distance using the method of Wolfe and Earth and Space Science 10.1029/2023EA003469 Silver (1998), as implemented in StackSplit (Grund, 2017), yielding a single splitting measurement (ϕ and δt) for each bin.…”

Section: Methodsmentioning

confidence: 99%

“…Their results show a strong NE ϕ orientation, which they attributed to APM. Komeazi et al (2023) reported shear wave splitting measurements for stations in NW Namibia, attributing an observed NE ϕ direction to a combination of fossil anisotropy in the lithospheric mantle and anisotropy in the asthenosphere resulting from APM.…”

Section: Introductionmentioning

confidence: 99%

“…Here, we report new shear wave splitting measurements for 88 seismic stations in Namibia, Botswana, South Africa and Mozambique (Figure 1; Figure S1 in Supporting Information ), greatly expanding the data set of ϕ and δt measurements for southern Africa. We combine our new measurements with 167 existing measurements (Barruol & Ben Ismail, 2001; Fouch, Silver, et al., 2004; Helffrich et al., 1994; Komeazi et al., 2023; Silver & Chan, 1991; Silver et al., 2001; Vinnik et al., 1992, 1996; Yu et al., 2015), and use the ensemble of measurements to (a) characterize the anisotropic structure of the upper mantle across southern Africa and (b) examine geodynamic processes that may have created anisotropic fabrics within the upper mantle.…”

Section: Introductionmentioning

confidence: 99%

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Coherent Seismic Anisotropy Pattern Across Southern Africa Revealed by Shear Wave Splitting Measurements

Andriampenomanana,

Nyblade,

Durrheim

et al. 2024

Earth and Space Science

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We report new PKS, SKS, and SKKS splitting measurements for 88 seismic stations in Namibia, Botswana, South Africa, and Mozambique. When combined with measurements from previous studies, the ensemble of measurements shows a fairly uniform NNE to NE (∼41° on average) fast‐polarization direction (ϕ) and delay time (δt) (∼0.7 s on average) across the entire southern African subcontinent. It is difficult to attribute the NNE‐NE ϕ direction to just one source of anisotropy either within the lithospheric or sublithospheric mantle. We instead propose the observed anisotropy pattern could result from a combination of several sources that together give rise to a pervasive NNE‐NE ϕ direction; (a) fossil anisotropy in the lithospheric mantle resulting from the Neoproterozoic collision of the Congo and Kalahari cratons to form the Damara Belt, (b) movement of the African plate over the asthenosphere, and (c) flow in the upper mantle induced by the African Superplume. In addition, a contribution from anisotropy in the lowermost mantle in the vicinity of the African large low shear velocity province cannot be ruled out.

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Discriminating Lithospheric and Asthenospheric Anisotropy Beneath Northern Oman: Sharp Contrast Observed at the Semail Gap Fault Zone

Komeazi,

Kaviani,

Rümpker

et al. 2024

JGR Solid Earth

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To gain a deeper understanding of the extensive and varied lithospheric deformations beneath northern Oman, we examine seismic anisotropy in this region using splitting analysis of teleseismic shear wave data. Our study utilizes data from a dense network consisting of 13 permanent and 45 temporary seismic stations, which were operational for approximately 2.5 years starting from October 2013. By examining the azimuthal distribution of shear wave splitting (SWS) parameters, we were able to divide the study area into three sub‐regions. The stations located to the west of the Hawasina window exhibit relatively azimuthally invariant SWS parameters suggesting a single anisotropic layer. On the other hand, most of the stations located in the central and eastern regions display variations versus back‐azimuth, indicating the potential presence of depth‐dependent anisotropy. The General NW‐SE trend of the Fast Polarization Directions (FPDs) of the one‐layer anisotropy in the west and FPDs of the upper layers in the east is concordant with the strike of the structures resulting from the collision between the continental and oceanic plates. A clear contrast in SWS parameters is observed in the Semail Gap Fault Zone (SGFZ), suggesting that the SGFZ can be a lithospheric‐scale structure that hampers the intrusion of mafic magma from the southeast. Furthermore, the FPDs of the lower layer in the east exhibit an NE‐SW trend, which may be indicative of the large‐scale mantle flow resulting from the present‐day plate motion.

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Mantle Anisotropy in NW Namibia From XKS Splitting: Effects of Asthenospheric Flow, Lithospheric Structures, and Magmatic Underplating

Cited by 5 publications

References 66 publications

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

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

Coherent Seismic Anisotropy Pattern Across Southern Africa Revealed by Shear Wave Splitting Measurements

Discriminating Lithospheric and Asthenospheric Anisotropy Beneath Northern Oman: Sharp Contrast Observed at the Semail Gap Fault Zone

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