Plume, Lithospheric Interaction and Small-scale Convection Beneath Africa from Anisotropic Tomography and Geochemical Data <p> HR: <span class="hr"> 13:55h<br></span> AN: <span class="an"> S52G-02 <a href="../absbook/fm03-S52G.pdf">[PDF]</a><br></span> TI: <span class="ti"> Plume, Lithospheric Interaction and Small-scale Convection Beneath Africa from Anisotropic Tomography and Geochemical Data <br></span> AU: <span class="au"> * Montagner, J <br></span> EM: <span class="em"> jpm@ipgp.jussieu.fr<br></span> AF: <span class="af"> Dept. Seismology, Institut de Physique du Globe, 4 Place Jussieu, Paris cedex 05, 75252 France <br></span> AU: <span class="au"> Marty, B <br></span> AF: <span class="af"> CRPG-CNRS, rue Notre-Dame des pauvres, BP20, Vandreuves-les-Nancy, 54501 France <br></span> AU: <span class="au"> Cara, M <br></span> AF: <span class="af"> EOST-IPGS, Universite Louis Pasteur, 5 rue Descartes, Strasbourg, 67084 France <br></span> AU: <span class="au"> Sicilia, D <br></span> AF: <span class="af"> Dept. Seismology, Institut de Physique du Globe, 4 Place Jussieu, Paris cedex 05, 75252 France <br></span> AU: <span class="au"> Debayle, E <br></span> AF: <span class="af"> EOST-IPGS, Universite Louis Pasteur, 5 rue Descartes, Strasbourg, 67084 France <br></span> AU: <span class="au"> Leveque, J <br></span> AF: <span class="af"> EOST-IPGS, Universite Louis Pasteur, 5 rue Descartes, Strasbourg, 67084 France <br></span> AU: <span class="au"> Lepine, J <br></span> AF: <span class="af"> Dept. Seismology, Institut de Physique du Globe, 4 Place Jussieu, Paris cedex 05, 75252 France <br></span> AB: <span class="ab"> A high resolution three-dimensional tomographic model beneath Africa has been derived by using seismic data provided by the French seismic experiment named "Horn of Africa" complemented by permanent (GEOSCOPE and IRIS networks) and temporary experiments in this region. By simultaneously inverting for seismic velocity and anisotropy of the upper 400km of the mantle, two kinds of mantle plumes are revealed. The first one, the Afar plume is coming from deeper than 400km (at least from the transition zone), and the second kind of plume is the consequence of the complex interaction between the asthenospheric mantle flow, the plume head and the lithosphere. If anisotropy direction is considered as a good marker of convective flow in the upper mantle, the flow in the asthenosphere (100-300km) is to first order, close to the almost South-North plate motion of the African plate except around the Afar hotspot where it is diverted and gives rise to secondary convection in the East-west direction with a wavelength around 1000-1500km. This small-scale convection can explain the existence of the Darfur, Tibesti, Hoggar and Cameroon hotspots and their geochemical signature different from the Afar hotspot. The origin of this second kind of hotspot is then confined to the asthenospheric upper mantle in the space left between african cratons. <br></span> DE: <span class="de"> 7218 Lithosphere and upper mantle<br></span> DE: <span class="de"> 7255 Surface waves and free oscillations<br></span> DE: <span class="de"> 8121 Dynamics, convection currents and mantle plumes<br></span> DE: <span class="de"> 8180 Tomography<br></span> DE: <span class="de"> 9305 Africa<br></span> SC: <span class="sc"> Seismology [S]<br></span> MN: <span class="mn"> 2003 Fall Meeting<br></span></p></body></html>