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The upper-mantle low-velocity anomaly beneath Ethiopia, Kenya, and Tanzania: Constraints on the origin of the African superswell in eastern Africa and plate versus plume models of mantle dynamics

By
Andrew A. Nyblade
Andrew A. Nyblade
Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA
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Published:
June 01, 2011

To further advance our understanding of the way in which a portion of the African superswell in eastern Africa formed, and also to draw attention to the importance of eastern Africa for the plume versus plate debate about mantle dynamics, upper-mantle structure beneath eastern Africa is reviewed by synthesizing published results from three types of analyses applied to broadband seismic data recorded in Tanzania, Kenya, and Ethiopia. (1) Joint inversions of receiver functions and surface wave dispersion measurements show that the lithospheric mantle of the Ethiopian Plateau has been significantly perturbed, much more so than the lithospheric mantle of the East African Plateau. (2) Body wave tomography reveals a broad (≥300 km wide) and deep (≥400 km) low-velocity anomaly beneath the Ethiopian Plateau and the eastern branch of the rift system in Kenya and Tanzania. (3) Receiver function stacks showing Ps conversions from the 410 km discontinuity beneath the eastern branch in Kenya and Tanzania reveal that this discontinuity is depressed by 20–40 km in the same location as the low-velocity anomaly. The coincidence of the depressed 410 km discontinuity and the low-velocity anomaly indicates that the low-velocity anomaly is caused primarily by temperatures several hundred degrees higher than ambient mantle temperatures. These findings cannot be explained easily by models invoking a plume head and tail, unless there are a sufficient number of plume tails presently under eastern Africa side-by-side to create a broad and deep thermal structure. These findings also cannot be easily explained by the plate model. In contrast, the breadth and depth of the upper-mantle thermal structure can be explained by the African superplume, which in some tomographic models extends into the upper mantle beneath eastern Africa. Consequently, a superplume origin for the anomalous topography of the African superswell in eastern Africa, in addition to the Cenozoic rifting and volcanism found there, is favored.

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GSA Special Papers

Volcanism and Evolution of the African Lithosphere

Luigi Beccaluva
Luigi Beccaluva
Dipartimento di Scienze della Terra, Università di Ferrara, Italy
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Gianluca Bianchini
Gianluca Bianchini
Dipartimento di Scienze della Terra, Università di Ferrara, Italy
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Marjorie Wilson
Marjorie Wilson
School of Earth & Environment, The University of Leeds, Leeds, UK
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Geological Society of America
Volume
478
ISBN print:
9780813724782
Publication date:
June 01, 2011

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