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Strong clockwise block rotation of the Ali-Sabieh/Aïsha Block: evidence for opening of the Afar Depression by a ‘saloon-door’ mechanism

By
Tesfaye Kidane
Tesfaye Kidane
School of Earth Science, College of Natural Science, Addis Ababa University, PO Box 1176, Addis Ababa, Ethiopia
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Published:
January 01, 2016

Abstract

Palaeomagnetic investigations were carried out on tilted Jessoma sandstones in the Aïsha block. The average natural remanent magnetization intensity was 0.026A m−1 with good behaviour on demagnetization both by thermal and alternating fields. The normalized magnetization intensity decay curves indicated that fine-grained, Ti-poor titanomagnetites were the carriers of magnetization. A well-defined single-component magnetization with a poorly defined secondary component was found. The latter was removed at temperatures below 300°C or at 10 mT. After these steps, a straight-line segment directed towards the origin was identified, which was interpreted as the characteristic remanent magnetization. Site mean direction coordinates of Decg=227.8°, Incg=–33.9° (n=7, α95=2.8°, K=478) (in situ) and Decs=225.6°, Incs=0.4° (n=7, α95=2.8°, K=478) (tilt-corrected) were obtained. Corresponding mean virtual geomagnetic pole coordinates of Long=117.5° E, Latg=43.3° N (A95=3.2°, n=7) (in situ) and Lons=143.5° E, Lats=43.3° N (A95=2.8°, n=7) (tilt-corrected) were obtained. The corrected in situ mean pole position was compared with the African apparent polar wander path curve and a deposition age for the sandstone of 60±5 Ma was determined, which is consistent with previous reports. A vertical axis rotation (R±ΔR) of the Aïsha block of 29.1±4.06° was obtained, which is equivalent to an inferred 30° counterclockwise rotation of the Danakil block, in agreement with a ‘saloon-door’ mechanism for the opening of the Afar Depression.

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Contents

Geological Society, London, Special Publications

Magmatic Rifting and Active Volcanism

T. J. Wright
T. J. Wright
University of Leeds, UK
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A. Ayele
A. Ayele
Addis Ababa University, Ethiopia
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D. J. Ferguson
D. J. Ferguson
University of Leeds, UK
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T. Kidane
T. Kidane
Addis Ababa University, Ethiopia
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C. Vye-Brown
C. Vye-Brown
British Geological Survey, UK
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Geological Society of London
Volume
420
ISBN electronic:
9781862391345
Publication date:
January 01, 2016

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