Seismic evidence for a deep upper mantle thermal anomaly beneath east Africa
- 1Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA
- 2Department of Geological Sciences, University of South Carolina, Columbia, South Carolina 29208, USA
- 3Department of Geosciences, Texas Tech University, Lubbock, Texas 79409, USA
- 4Seismological Laboratory, California Institute of Technology, Pasadena, California 91125, USA
Abstract
Upper mantle seismic velocity variations beneath northern Tanzania coupled with the structure of the 410 and 660 km discontinuities reveal a 200–400-km-wide thermal anomaly extending into but not necessarily through the transition zone beneath the eastern branch of the East African rift system. This finding is not easily explained by small-scale mantle convection induced by passive stretching of the lithosphere or by a broad thermal upwelling extending from the lower mantle into the upper mantle, but it can be attributed to a mantle plume, provided that a plume head is present under the lithospheric keel of the Tanzania craton. A plume interpretation for the deep thermal anomaly is supported by evidence for mantle having the geochemical characteristics of a plume at >150 km depth beneath northern Tanzania.
Footnotes
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- Accepted April 18, 2000.
- Received December 27, 1999.
- Revision received April 14, 2000.
- Geological Society of America
