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The Mid-Miocene East African Plateau: a pre-rift topographic model inferred from the emplacement of the phonolitic Yatta lava flow, Kenya

By
Henry Wichura
Henry Wichura
Institut für Erd- und Umweltwissenschaften, Universität Potsdam, Karl-Liebknecht-Str. 24, D-14476 Potsdam, Germany
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Romain Bousquet
Romain Bousquet
Institut für Erd- und Umweltwissenschaften, Universität Potsdam, Karl-Liebknecht-Str. 24, D-14476 Potsdam, Germany
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Roland Oberhänsli
Roland Oberhänsli
Institut für Erd- und Umweltwissenschaften, Universität Potsdam, Karl-Liebknecht-Str. 24, D-14476 Potsdam, Germany
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Manfred R. Strecker
Manfred R. Strecker
Institut für Erd- und Umweltwissenschaften, Universität Potsdam, Karl-Liebknecht-Str. 24, D-14476 Potsdam, GermanyDFG Leibniz Center for Surface Process and Climate Studies, Universität Potsdam, Karl-Liebknecht-Str. 24, D-14476 Potsdam, Germany
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Martin H. Trauth
Martin H. Trauth
Institut für Erd- und Umweltwissenschaften, Universität Potsdam, Karl-Liebknecht-Str. 24, D-14476 Potsdam, Germany
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Published:
January 01, 2011

Abstract

High topography in the realm of the rifted East African Plateau is commonly explained by two different mechanisms: (1) rift-flank uplift resulting from mechanical and/or isostatic relaxation and (2) lithospheric uplift due to the impingement of a mantle plume. High topography in East Africa has far-reaching effects on atmospheric circulation systems and the amount and distribution of rainfall in this region. While the climatic and palaeoenvironmental influences of high topography in East Africa are widely accepted, the timing, the magnitude and this spatiotemporal characteristic of changes in topography have remained unclear. This dilemma stems from the lack of datable, geomorphically meaningful reference horizons that could unambiguously record surface uplift. Here, we report on the formation of high topography in East Africa prior to Cenozoic rifting. We infer topographic uplift of the East African Plateau based on the emplacement characteristics of the c. 300 km long and 13.5 Ma Yatta phonolitic lava flow along a former river valley that drained high topography, centred at the present-day rift. The lava flow followed an old riverbed that once routed runoff away from the eastern flank of the plateau. Using a compositional and temperature-dependent viscosity model with subsequent cooling and adjusting for the Yatta lava-flow dimensions and the covered palaeotopography (slope angle), we use the flow as a ‘palaeo-tiltmeter’. Based on these observations and our modelling results, we determine a palaeoslope of the Kenya dome of at least 0.2° prior to rifting and deduce a minimum plateau elevation of 1400 m. We propose that this high topography was caused by thermal expansion of the lithosphere interacting with a heat source generated by a mantle plume. Interestingly, the inferred Mid-Miocene uplift coincides with fundamental palaeoecological changes including the two-step expansion of grasslands in East Africa as well as important radiation and speciation events in tropical Africa.

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Geological Society, London, Special Publications

The Formation and Evolution of Africa: A Synopsis of 3.8 Ga of Earth History

D. J. J. Van Hinsbergen
D. J. J. Van Hinsbergen
University of Oslo, Norway
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S. J. H. Buiter
S. J. H. Buiter
Geological Survey of Norway
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T. H. Torsvik
T. H. Torsvik
University of Oslo
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C. Gaina
C. Gaina
Geological Survey of Norway
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S. J. Webb
S. J. Webb
University of the Witwatersrand, South Africa
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Geological Society of London
Volume
357
ISBN electronic:
9781862396050
Publication date:
January 01, 2011

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