HR: 10:20h
AN: S51F-01 INVITED     [PDF]
TI: The Origin of the African Superswell
AU: * Nyblade, A A
EM: andy@geosc.psu.edu
AF: Penn State University, Department of Geosciences, University Park, PA 16802 United States
AB: The African Superswell is comprised of three contiguous regions of anomalous topography, the East African Plateau, the Southern African Plateau, and the southeastern Atlantic Ocean basin. The long wavelength anomalous topography and bathymetry associated with the African Superswell is about 500 m, and many shorter wavelength features are superimposed on this long wavelength swell. The anomalous topography in East Africa and the anomalous bathymetry in the southeastern Atlantic Ocean basin can be readily attributed to buoyant support from thermally perturbed upper mantle structure. A region of low seismic wave speeds has been imaged in the upper mantle beneath much of East Africa, providing strong evidence for thermally perturbed upper mantle structure. Numerous hotspots, manifest as seamount chains, ridges and rises, are found within the southeastern Atlantic Ocean basin, and provide evidence of lithospheric reheating. In addition, some global tomographic images show a broad region of low seismic wave speeds in the upper mantle beneath the southeastern Atlantic Ocean basin, consistent with the presence of thermally perturbed upper mantle structure. In contrast, the anomalous topography of the southern African Plateau cannot be easily explained by Cenozoic heating of the upper mantle and consequently, it is difficult to attribute uplift everywhere within the African Superswell to Cenozoic thermal modification of the upper mantle. Several other explanations for plateau uplift in southern Africa have been advanced, such as dynamic uplift induced by anomalous structure extending upward from the core mantle boundary under southern Africa, delayed phase changes within the upper mantle, dynamic rebound after slab detachment following the cessation of subduction below the Cape Fold Belt at the end of the Triassic, and the underplating of low-density melts to the underside of the lithosphere at the time of Karoo volcanism. To these, we add the possibility of long lasting plateau uplift caused by Mesozoic mantle plume activity. The uplift history of southern Africa is poorly understood and new constraints on the timing of uplift are needed to advance further our understanding of plateau uplift in southern Africa.
DE: 7205 Continental crust (1242)
DE: 7207 Core and mantle
DE: 7218 Lithosphere and upper mantle
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2003 Fall Meeting