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The Adola Fold and Thrust Belt, southern Ethiopia: a re-examination with implications for Pan-African evolution

Published online by Cambridge University Press:  01 May 2009

W. H. “Beraki ,
F. F. Bonavia ,
T. Getachew ,
R. Schmerold  and
T. Tarekegn
W. H. “Beraki
Affiliation:
Ethiopian Institute of Geological Surveys Training Project, UNDP ETH 86/034, P.O.BOX 5580, Addis Ababa, Ethiopia
F. F. Bonavia
Affiliation:
Cooperazione Italiana Universitaria, c/o Department of Geology, Addis Ababa University, Addis Ababa, Ethiopia
T. Getachew
Affiliation:
Ethiopian Institute of Geological Surveys Training Project, UNDP ETH 86/034, P.O.BOX 5580, Addis Ababa, Ethiopia
R. Schmerold
Affiliation:
Ethiopian Institute of Geological Surveys Training Project, UNDP ETH 86/034, P.O.BOX 5580, Addis Ababa, Ethiopia
T. Tarekegn
Affiliation:
Ethiopian Institute of Geological Surveys Training Project, UNDP ETH 86/034, P.O.BOX 5580, Addis Ababa, Ethiopia
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Abstract

The Adola Fold and Thrust Belt of Ethiopia is a late- Precambrian, north–south trending belt of volcanic-sedimentary and ophiolite–like units overlying ‘basement rocks’ (gneisses and granitic gneisses). Detailed structural analysis and data from microfabrics have documented two thrusting events (D1, D5) and three folding phases (F2, F3, F4). All deformations have affected both the rocks of the Adola Fold and Thrust Belt and the ‘older basement’. The structural history is recorded as follows: (1) formation of ductile shear zones (Dl); (2) progressive development of recumbent folds (F2); (3) a superimposed north-south trending, tight to isoclinal, upright penetrative folding phase (F3), which imparted the dominant structure of the region; (4) F3 was later gently affected, at right angles to F3, by the last folding event (F4). Metamorphic conditions during this deformational cycle reached highest greenschist to medium amphibolite facies conditions. Close to major thrust contacts imbrication produced metamorphic discontinuities. Marked retrograde metamorphism in narrow horizons indicates a continuation of minor movements along the major thrusts, postdating the metamorphic peak. Evidence of a second thrusting/faulting episode (D5) is only recorded at the mesoscale. This latter event was accompanied by very low to low grade metamorphic conditions. In accepting the previously reported age of 1030±40 Ma for the volcanic–sedimentary unit of the Adola Fold and Thrust Belt, and the interpretation of these units as an immature island arc, a possibly early Pan-African oceanic accretion is postulated.

Type
Articles
Information
Geological Magazine , Volume 126 , Issue 6 , November 1989 , pp. 647 - 657
Copyright
Copyright © Cambridge University Press 1989

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