THE GEOLOGICAL EVOLUTION OF THE ADOLA PRECAMBRIAN GREENSTONE-BELT, SOUTHERN ETHIOPIA

The repeatedly deformed and metamorphosed Adola Precambrian Greenstone Belt of Southern Ethiopia which is well known for its gold potential has been studied with its bounding gneisses. Mapping at a scale of 1:50,000 supported by petrographic studies revealed crustal or lithospheric extension resulted in formation of a continental basin(s) which became filled with voluminous mantle derived mafic-ultramafic, minor felsic rocks and associated sediments. Four deformation events have been recognized. The first generation structures (D1) are, largely related to thrust tectonics that resulted in a palm tree or flower structure. The second generation structures (D2) which are dominated by N-S trending upright sub-horizontal F2 folds and relatively late ductile transcurrent shear zones were accompanied by amphibolite facies metamorphism (M2). The third generation structures (D3) are E-W and produced curviplanar swings on pre-existing structures. The latest (D4) structures are represented by N-S/ENE-WSW trending sinistral transcurrent shear zones and associated vertical folds. Genesis of gold in the region appeared to associate grossly with the regional transcurrent shear movements that bound the greenstone belt.