NEOPROTEROZOIC STRUCTURES IN THE MOZAMBIQUE OROGENIC BELT OF SOUTHERNETHIOPIA

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. Thes e rocks display the deep-rooted structures of collision zones. Metamor phic grade reached the amphibolite or locally the granulite facies; re trogression to greenschist facies occurs. In the description of the op hiolites, the problem of the location, orientation, and possible linka ge of these masses is discussed; low- to high-angle fault (or shear-zo ne) orientations are presented. The faults were developed largely in a ductile regime and produced a wide range of mylonitic textures. The t ectonic history started with a collision (Sabachian events > 826 Ma) f ollowed 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, 5 70 Ma ) which trend north to northwest and have generally straight trends. T he early and late shears formed upright folds, open and tight, respect ively; (iii) in the southern region, northwest-trending reactivated sh ears produced gentle refolding and small-scale thrusting (Loldaikan-Ki psingian events 530 Ma). North- and northwest-trending shear zones ( < 620, > 530 Ma) are interpreted to be the reactivated surface expressi on of lateral and frontal ramps formed during the collision (> 826 Ma) between the Mozambique Orogenic belt/Arabian-Nubian shield and the ol d African continent.