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The relations between felsic and mafic volcanic rocks in continental flood basalts of Ethiopia: implication for the thermal weakening of the crust

By
Dereje Ayalew
Dereje Ayalew
Department of Earth Sciences, School of Earth and Planetary Sciences, Addis Ababa University, PO Box 729/1033, Addis Ababa, Ethiopia (e-mail: dereayal@geol.aau.edu.et)
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Published:
January 01, 2011

Abstract

Sr and Nd isotopic compositions are presented for a Miocene bimodal basalt–rhyolite suite from north Shewa, central Ethiopian plateau. Whole-rock Rb–Sr isochron of the rhyolites yields an age of 20.7±2.4 Ma, marking the onset of volcanism in central Ethiopia c. 20 Ma, 10 Ma after initial magmatism in the northern Ethiopian plateau. Initial 87Sr/86Sr ratios slightly vary in the basalts as well as in the rhyolites, ranging from 0.70440 to 0.70641 and from 0.70563 to 0.70658, respectively. Initial 143Nd/144Nd ratios show significant variations in the basalts (0.51248–0.51274), but remain nearly constant in the rhyolites (0.51273–0.51278). The Sr and Nd isotopic ratios of the basalts are interpreted to reflect their derivation from Afar plume contaminated by crustal materials (up to 15% contamination). The rhyolites evolved dominantly by fractional crystallization of mantle-derived basaltic magmas similar in composition to the exposed flood basalts.

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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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