HR: 0800h
AN: S11B-0553    [Abstracts]
TI: Small Scale Heterogeneity in the Uppermost Mantle and the Dynamic Topography on the West Coast of Africa
AU: * Fishwick, S
EM: sf358@cam.ac.uk
AF: Bullard Laboratories, Department of Earth Sciences, University of Cambridge, Madingley Rise, Madingley Road, Cambridge, CB3 0EZ, United Kingdom
AU: * Fishwick, S
EM: sf358@cam.ac.uk
AF: now at, Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH, United Kingdom
AU: White, N
EM: nwhite@esc.cam.ac.uk
AF: Bullard Laboratories, Department of Earth Sciences, University of Cambridge, Madingley Rise, Madingley Road, Cambridge, CB3 0EZ, United Kingdom
AU: Al-Hajri, Y
AF: Bullard Laboratories, Department of Earth Sciences, University of Cambridge, Madingley Rise, Madingley Road, Cambridge, CB3 0EZ, United Kingdom
AB: Tomographic models provide a snapshot of the Earth's velocity structure, and, when combined with other geological and geophysical information we can begin to make further inferences on the dynamics of the system. In Africa, much of the focus has been on the large slow velocity anomaly (African superplume) in the lower mantle and its relationship with dynamic topography. A new surface wave tomographic model of the uppermost mantle beneath Africa is presented here, and discussed in relation to the topography. To improve the reliability of the tomography we use multiple path-specific starting models for the waveform inversion, rather than a starting model based on a global reference model. From the tomographic inversion, well recognised differences in velocity structure are observed between the cratonic regions and active areas such as Afar. There are also a number of smaller scale features within the model, and we investigate the relationship between the pattern of negative wavespeed anomalies and the uplift and possible mantle dynamics along the western coast of Africa. The results from the tomographic model are compared with estimates of uplift derived from seismic reflection profiles along the shelf of the West African Salt Basin, and also with long wavelength gravity anomalies. At the shallowest depths in the model, the areas of slowest seismic velocities show a good correlation with positive gravity anomalies, and with the areas of largest recent uplift. From the combination of results we can therefore infer that the slow wavespeeds are related to small-scale convection in the upper mantle which has given rise to localised uplift in the past 1My.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7218 Lithosphere (1236)
DE: 7270 Tomography (6982, 8180)
DE: 8121 Dynamics: convection currents, and mantle plumes
SC: Seismology [S]
MN: 2007 Fall Meeting