HR: 0830h
AN: S51C-0057    [PDF]
TI: Hotspots and Superswell Beneath Africa Inferred From Surface Wave Anisotropic Tomography.
AU: Sebai, A
EM: sebai@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75005 France
AU: * Stutzmann, E
EM: stutz@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75005 France
AU: Montagner, J
EM: jpm@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75005 France
AB: In order to study the interaction at depth between hotspots and lithosphere we present a new anisotropic S-wave tomographic model of Africa which is derived from Rayleigh and Love wave phase velocity measurements. The strongest negative anomaly corresponds to the Afar plume which is presently the most active area of Africa. This slow anomaly, visible down to the deepest inverted depth (400km), is associated with azimuthal anisotropy that is weak right beneath the Afar and whose direction at further distances is diverging around the plume. This is consistent with active upwelling beneath the Afar. The smaller hotspots of Tibesti, Darfur, Hoggar and Mt Cameroon have appeared in regions that had been weakened by Late Jurassic-Early Cretaceous (145 Ma) rifting of West and Central Africa. They are associated with slow velocities down to about 200km. The smaller amplitude of these anomalies with respect to the Afar area and their limited depth extent may indicate that these hotspots have their origin in the uppermost boundary layer between asthenosphere and lithosphere. Nevertheless, there may be a complex relationship at depths shallower than 150km between these hotspots and the Afar. The superswell, located in the southern part of Africa is characterized by a broad area of positive velocity anomaly visible down to 300km depth. The base of Kalahari craton ($\sim 280 km$) is evidently characterized by an increase of azimuthal anisotropy. The direction of azimuthal axis is roughly North-South that rotates at the longitude of the Eastern rift to move around the Afar. This may suggest a feeding of Victoria and Afar hotspots from the deep South African superplume.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 9305 Africa
SC: Seismology [S]
MN: 2003 Fall Meeting