HR: 0800h
AN: S51E-1056    [Abstracts]
TI: Upper mantle and transition zone structure beneath Ethiopia: Regional evidence for the African Superplume
AU: * Benoit, M H
EM: mbenoit@erl.mit.edu
AF: Massachusetts Institute of Technology, Earth Resources Laboratory 42 Charleton St., Cambridge, MA 02142 United States
AU: Nyblade, A A
EM: andy@geosc.psu.edu
AF: Penn State, Department of Geosciences Deike Building, University Park, PA 16802 United States
AU: Pasyanos, M
EM: pasyanos1@llnl.gov
AF: Lawrence Livermore National Lab, Geophysics and Global Security Division P.O. Box 808 L-205, Livermore, CA 94551 United States
AU: Owens, T J
EM: owens@seis.sc.edu
AF: University of South Carolina, Department of Gological Sciences 701 Sumter St. Room EWSC 617, Columbia, SC 29201 United States
AB: Throughout much of the Cenozoic, Ethiopia has undergone extensive tectonism, including rifting, volcanism and uplift, and the origin of this tectonism remains enigmatic. While the cause of the tectonism has often been attributed to one or more mantle plumes, recent global tomographic studies suggest that the African Superplume, a broad, through-going mantle upwelling, may be related to the tectonism. To further understand the origin of the tectonism in Ethiopia, we employ a variety of methods, including an S wave travel time body wave tomography, receiver function analysis of the 410 and 660 km discontinuities, and surface wave tomography. Using data from the Ethiopia Broadband Seismic Experiment [2000-2002], we computed new S wave models of the upper mantle seismic velocity structure from 150 - 400 km depth. The S wave model revealed an elongated low wave speed region that is deep (> 300 km) and wide (> 500 km). The location of the low wave speed anomaly aligns with the Afar Depression and Main Ethiopian Rift in the uppermost mantle, but the center of the anomaly shifts to the west with depth. Results from receiver function stacking of the 410 and 660 km discontinuities show a shallow 660 beneath most of Ethiopia, implying that the low wave speed anomaly found in the S wave model likely extends to at least 660 km depth. This result suggests that the low velocity anomaly may be related to the African Superplume. A group velocity surface wave tomographic study of East Africa was also computed using data from permanent and temporary stations from Africa and Arabia. Results of this study reveal low Sn velocities beneath much of the region, and suggest that low elevations found in the region between the Ethiopian and East African Plateaus likely reflect an isostatic response to crustal thinning. If the crust in this region had not been thinned by approximately 10 - 15 km, then it is likely that the high elevation of the Ethiopian and East African Plateaus would be continuous and that these plateaus would not be viewed as separate, distinct regions of uplift. This finding further suggests that a large scale, buoyant feature, such as the African Superplume, exists in the mantle beneath the Ethiopia and East African Plateaus that contributes to the uplift of the region.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7218 Lithosphere (1236)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7270 Tomography (6982, 8180)
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
SC: Seismology [S]
MN: Fall Meeting 2005