Neoproterozoic structures in the Mozambique Orogenic belt of southern Ethiopia

Abstract

This paper describes the complex arrangement of faults and dismembered ophiolites defined by geological mapping or interpreted from Landsat MSS imagery in the Mozambique Orogenic belt of southern Ethiopia. These rocks display the deep-rooted structures of collision zones. Metamorphic grade reached the amphibolite or locally the granulite facies; retrogression to greenschist facies occurs. In the description of the ophiolites, the problem of the location, orientation, and possible linkage of these masses is discussed; low- to high-angle fault (or shear-zone) orientations are presented. The faults were developed largely in a ductile regime and produced a wide range of mylonitic textures. The tectonic history started with a collision (Sabachian events > 826 Ma) followed by strike-slip faulting of basement rocks (a second orogeny <620,>530 Ma). These later events are expressed as: (i) early shears (Baragoian event, 620 Ma); (ii) late shears (Barsaloian event, 570 Ma) which trend north to northwest and have generally straight trends. The early and late shears formed upright folds, open and tight, respectively; (iii) in the southern region, northwest-trending reactivated shears produced gentle refolding and small-scale thrusting (Loldaikan-Kipsingian events 530 Ma). North- and northwest-trending shear zones (<620, > 530 Ma) are interpreted to be the reactivated surface expression of lateral and frontal ramps formed during the collision (> 826 Ma) between the Mozambique Orogenic belt/Arabian-Nubian shield and the old African continent.