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Tectonic evolution of the Central Steep Zone, Axum area, northern Ethiopia: inferences from magnetic and geochemical data

By
Helga De Wall
Helga De Wall
Geozentrum Nordbayern, Universitat Erlangen-Nürnberg, Schlossgarten 5, D-91054 Erlangen, Germany
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Carlo Dietl
Carlo Dietl
Institut für Geowissenschaften, Johann Wolfgang Goethe-Universität Frankfurt (Main)
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Olga Jungmann
Olga Jungmann
Institut für Geowissenschaften, Johann Wolfgang Goethe-Universität Frankfurt (Main)
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Ashenafi T. Tegene
Ashenafi T. Tegene
Geozentrum Nordbayern, Universitat Erlangen-Nürnberg, Schlossgarten 5, D-91054 Erlangen, Germany
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Manoj K. Pandit
Manoj K. Pandit
Department of Geology, University of Rajasthan, Jaipur – 302004, India
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Published:
January 01, 2011

Abstract

Northern Ethiopia is marked by a fanning system of thrust planes with NW-dipping structures in the east and southeast-dipping in the west. The central zone of this large-scale (200 km long) structure is formed by a c. 10 km wide zone of localized strain and amphibolites facies metamorphic conditions (680 °C and 3.4 kbar) referred to as the Central Steep Zone (CSZ). The CSZ comprises a mafic rock assemblage of amphibolite, serpentinite showing ocean-floor characteristics and calc-silicate schist. A monzonite intrusion in the central part of the CSZ post-dates the deformation and is related to partial melting of the mafic rocks. Magnetic fabric measurements reveal NE-trending (043°) steep foliations in the CSZ with vertical orientation of lineation, parallel to the axes of micro-folds. This high-strain zone is interpreted as central zone of a positive flower structure on the basis of simultaneous flattening and shear movement, typical for transpressive kinematics. The CSZ has a northern continuation into the Nafka terrane of Eritrea where it can be traced over a distance of 200 km. This high-strain belt forms a major structure in the context of Arabian–Nubian Shield (ANS) collision tectonics during the closure of the Mozambique Ocean and assembly of Gondwana.

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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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