Online Journal of Earth Sciences

Year: 2007
Volume: 1
Issue: 1
Page No. 24 - 42

Geology and Tectonic Evolution of the Pan-African Tulu Dimtu Belt, Western Ethiopia

Authors : Tadesse Alemu and Tsegaye Abebe

Abstract: The Tulu Dimtu Belt (TDB) is a NNE-SSW trending litho-tectonic unit, which forms the southwestern and wider branch of the predominantly low-grade volcano-sedimentary terrane of the Pan-African Arabian-Nubian Shield (ANS) and occupies a key position in understanding the geodynamic evolution of the East African Orogen (EAO). The belt can be traced for the entire length of the Precambrian basement of western Ethiopian and appears to continue to the proposed Barka ophiolitic suture in Eritrea and the Sudan. It is characterized by a variety of lithological units, including gneisses, metamorphosed volcanic, volcaniclastic and sedimentary successions with associated mafic-ultramafic rocks of probable ophiolitic origin and granitoid intrusives. The rocks in the belt are divided into five informal litho-tectonostratigraphic units separated from each other by tectonic discontinuities. From east to west these are. High-grade (amphibolite facies) gneiss and migmatites, Sayi Chenga Group, comprising metavolcanics, mainly basic and associated metasediments, Tulu Dimtu Complex, composed of mafic and ultramafic rocks and associated volcano-sedimentary rocks of probable ophiolitic association, 2 Chochi Domain, characterized by medium to high-grade supracrustal gneiss and schist and Katta Domain, characterized by low-grade metavolcano-sedimentary and associated intrusive rocks. The TDB represents a zone of shortening and is one of the best examples of a polydeformed northwest-verging fold-and-thrust belt in the ANS. Early Deformation (D1) is a progressive shortening, which resulted in the development of northwest-verging thrusts and associated recumbent, tight to isoclinal folds with subhorizontal axes and shallowly SE-dipping and NNE-SSW trending axial planar foliations (S1). The asymmetry of D1 structures indicates an oblique (top to the northwest) sense of movement. This phase of deformation might be related the closure of the oceanic basin which resulted in the northwestward obduction of the Tulu Dimtu ophiolites. D2 deformation resulted in steepening of D1 structures into upright folds. D3 deformation represents extensive shortening, which culminated in the formation of major NW-trending sinistral strike-slip faults/shear zones and minor N and NNE-trending sinistral/dextral strike-slip faults/shear zones that are superimposed at high angle to the D1 and D2 structures. The relationships between D1, D2 and D3 is consistent with development of the TDB during a period of oblique collision in response to a NW-SE compressional stress that induced sinistral transpression.

How to cite this article:

Tadesse Alemu and Tsegaye Abebe , 2007. Geology and Tectonic Evolution of the Pan-African Tulu Dimtu Belt, Western Ethiopia . Online Journal of Earth Sciences, 1: 24-42.

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