HR: 10:40h
AN: S51F-02 INVITED     [PDF]
TI: The "African Anomaly"
AU: * Wen, L
EM: Lianxing.Wen@sunysb.edu
AF: State University of New York at Stony Brook, Dept. of Geosciences, Stony Brook, NY 11794 United States
AU: Wang, Y
EM: biphor@mantle.geo.sunysb.edu
AF: State University of New York at Stony Brook, Dept. of Geosciences, Stony Brook, NY 11794 United States
AB: Seismic results have consistently shown a significant low-velocity anomaly in the lower mantle beneath Africa. This "African anomaly" has a broad base near the core-mantle boundary, extending from the south Atlantic ocean to the Indian ocean, with steeply dipping edges, rapidly varying thicknesses (0-300 km) and geometries, and anomalously low shear wave velocities decreasing from -2% at 300 km above the core-mantle boundary to -9% to -12% at the core-mantle boundary. The base exhibits a L-shape changing from north-south orientation in the south Atlantic ocean to east-west direction in the Indian ocean, and occupies an area of about 1.7 $\times$ $10^{7} km^{2}$ and a volume of at least 4.6 $\times 10^{9} km^{3}$. The "African anomaly" extends about at least 1300 km above the core-mantle boundary beneath southern Africa. It appears that its edges dip toward its center in the lower mantle. The structural features and velocity characteristics of the basal layer unambiguously suggest that the base is compositionally distinct. The seismic characteristics associated with the basal layer can be best explained by partial melt driven by a compositional change produced early in the Earth's history. The geometry of the African anomaly in the lower mantle suggests that the portion in the lower mantle may have a same origin as its base. A dense "African anomaly" is also not inconsistent with the surface uplift and geoid, even if we assume the surface uplift is caused by the "African anomaly". In this presentation, we present seismic and geodynamical modeling results associated with the "African anomaly" and discuss their implications to the origin of the "African anomaly".
UR: http://geophysics.geo.sunysb.edu/wen/
DE: 1010 Chemical evolution
DE: 7205 Continental crust (1242)
DE: 7218 Lithosphere and upper mantle
DE: 8109 Continental tectonics--extensional (0905)
DE: 9305 Africa
SC: Seismology [S]
MN: 2003 Fall Meeting