HR: 09:15h
AN: T21C-06    [Abstracts]
TI: The African Lithosphere
AU: * Priestley, K
EM: keith@esc.cam.ac.uk
AF: Bullard Laboratories, University of Cambridge, Madingley Rise, Madingley Road, Cambridge, CB3 0EZ, United Kingdom
AU: Debayle, E
AF: EOST, IPG, Strasbourg, Universite Louis Pasteur, 5 rue Rene Descartes, Strasbourg, 67084, France
AU: McKenzie, D
EM: mckenzie@esc.cam.ac.uk
AF: Bullard Laboratories, University of Cambridge, Madingley Rise, Madingley Road, Cambridge, CB3 0EZ, United Kingdom
AU: Pilidou, S
EM: s_pilidou@yahoo.co.uk
AF: Bullard Laboratories, University of Cambridge, Madingley Rise, Madingley Road, Cambridge, CB3 0EZ, United Kingdom
AU: Pilidou, S
EM: s_pilidou@yahoo.co.uk
AF: Cyprus Geological Survey, 1415, Lefkosia, na, Cyprus
AB: There have been a number of prior, large scale surface wave studies of Africa, the majority of which rely on fundamental mode observations. In this study we use a large data set of multi-mode surface waves recorded over epicentral distances most of which are shorter than 6000 km, to investigate the Sv wave speed heterogeneity of the upper mantle beneath Africa. The inclusion of the higher mode data allow us to build an upper mantle model for the African plate with a horizontal resolution of a few hundred kilometers and a vertical resolution of a few tens of kilometers extending to about 400 km depth. Our tomographic images of the upper mantle beneath Africa displays significant shear velocity features, much of which correlate with surface geology. High velocity mantle persists beneath the West African and Congo cratons to 225-250 km depth, but the high velocity root beneath Kalahari Craton extends to only about 175 km depth. Low velocity upper mantle underlies the Pan- African terranes of Africa with the exception of the Damara mobile belt separating the Congo and Kalahari Cratons. The Damara mobile belt is underlain by a thick high velocity upper mantle lid which is indistinguishable from that beneath the Congo Craton to the north and the Kalahari Craton to the south. Low velocity upper mantle underlie the Hoggar, Tebesti and Darfur volcanic areas of northern Africa, and very low velocities underlie the Afar region to at least 400 km depth. We use the relationship between shear velocity and temperature of Priestley & McKenzie (2006) to derive a model for the African thermal lithosphere. Two types of lithosphere underlie Africa. Thick lithosphere underlies most of western Africa and all of southern Africa; in the latter the extent of the thick lithosphere is significantly different from the distribution of Archean crust mapped at the surface. Thick lithosphere forms one continuous structure beneath the Congo and Kalahari Cratons. Other than the Pan-African Damara mobile belt, the only Pan-African terrane of Africa free of recent (<30 Ma) volcanism, all of the Pan- African is underlain by lithosphere whose thickness is too thin to be resolved by our current surface wave analysis.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7218 Lithosphere (1236)
DE: 8103 Continental cratons
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting