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| Titel |
Flow, melt and fossil seismic anisotropy beneath Ethiopia |
| VerfasserIn |
James Hammond, J.-Michael Kendall, James Wookey, Graham Stuart, Derek Keir, Atalay Ayele |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250090004
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| Publikation (Nr.) |
 EGU/EGU2014-4216.pdf |
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| Zusammenfassung |
| Ethiopia is a region where continental rifting gives way to oceanic spreading. Yet the role that
pre-existing lithospheric structure, melt, mantle flow or active upwellings may play in this
process is debated. Measurements of seismic anisotropy are often used to attempt to
understand the contribution that these mechanisms may play. In this study we use new data in
Afar, Ethiopia along with legacy data across Ethiopia, Djibouti and Yemen to obtain
estimates of mantle anisotropy using SKS-wave splitting. We show that two layers of
anisotropy exist, and use shear-wave splitting tomography to invert for these. We
show that fossil anisotropy with fast directions oriented northeast-southwest may be
preserved in the lithosphere away from the rift. Beneath the Main Ethiopian Rift and
parts of Afar, anisotropy due aligned melt due to sharp changes in lithospheric
thickness dominate the shear-wave splitting signal in the mantle. Beneath Afar,
away from lithospheric topography, melt pockets associated with the crustal magma
storage dominate the signal and little anisotropy is seen in the uppermost mantle
suggesting melt retains no preferential alignment, possibly due to a lack of mantle
lithosphere. These results show the important role melt plays in weakening the
lithosphere and imply that as rifting evolves passive upwelling sustains extension. A
dominant northeast-southwest anisotropic fast direction is observed in a deeper layer
across all of Ethiopia. This suggests that a conduit like plume is absent beneath
Afar today, rather a broad flow from the southwest dominates in the upper mantle. |
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