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Tomographie anisotrope du manteau superieur sous la Corne de l'Afrique: Implications geodynamiques du point chaud de l'Afar

Abstract : In a geologically rich region of the African continent, we are attending to the birth of a new ocean. Indeed, since
nearly 30Ma, a mantle plume coming from a still undetermined depth, could have initiated the extension in the Horn of Africa. In order to define the role of the Afar Hotspot in the North Africa geodynamics, a tomographic study was carried out using fundamental mode of surface waves. The mean phase velocities along each great circle epicenter-station path are calculated using a new nonlinear inverse algorithm. The simultaneous inversion of Rayleigh and Love waves enable us to retrieve the perturbations of SV-waves velocities, the fast axis directions of azimuthal anisotropy and the radial anisotropy. The azimuthal anisotropy displays a complex pattern around the Afar Hotspot. This char
acteristic is more pronounced at shallow depth. The fast axis directions are in good agreement with the fast polariz
ation direction of the shear-wave splitting of previous studies. Fast velocities are attributed to the cratons down
to about 250km, a result also consistent with previous studies.
We observe a negative anomaly of strong amplitude below the Afar Hotspot. A second hotspot located on the East-Afric
an rift is also visible at great depths (300km). Contrary to the ethiopian rift and the Red sea, the Gulf of Aden is
associated with slow velocities only to 150km depth. The hotspots of North Africa seem to have a superficial signat
ure and could be a consequence of small-scale and edge-driven convection. The E-W heterogeneous structure, character
ized by a succession of positive and negative contrasts, supports this idea.
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Contributor : Deborah Sicilia <>
Submitted on : Monday, June 16, 2003 - 1:36:09 PM
Last modification on : Friday, March 27, 2020 - 4:05:13 AM
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Deborah Sicilia. Tomographie anisotrope du manteau superieur sous la Corne de l'Afrique: Implications geodynamiques du point chaud de l'Afar. Géologie appliquée. Institut de physique du globe de paris - IPGP, 2003. Français. ⟨tel-00003005⟩

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