Thesis Open Access
GEZAHEGN ABIY WORKNEH
Tarekegn Tadesse (PhD)
The Weyto area lies within the Southwestern Ethiopian shield. Field geological mapping at scale of 1:50,000 and augmented with petrographic analysis, digital elevation model and google earth images are used to study the lithological distribution, deformation history and metamorphic features of the area covering 90 km2 around Weyto town. The result of the data shows that the area is covered by high-grade Precambrian metamorphic rocks, with minor Cenozoic volcanic rock and rift basin filling unconsolidated sediments. The area has experienced four phases of Precambrian ductile deformations (D1-D4) and a Cenozoic brittle deformation (D5). The first two deformational phases (D1 and D2) are progressive shortening deformation and produced major N-S trending composite regional foliations. The metamorphic minerals defining the S2 fabric are characteristic of upper amphibolite facies and suggest that peak metamorphism (M1) has attained during the D2 event. D3 is characterized by northsouth sinistral shearing produces north-south tight drag-folds with S3 shear fabrics defined by retrograde metamorphic minerals of upper greenschist facies (M2). D4 deformation locally produces a weak east-west trending open upright folds (F4) with no recorded axial planar fabric. D5 deformation is associated with the extensional deformation which produced the East African Rift System. It is characterized by northsouth trending normal faults and joints in the study area and produced a series of grabens and horsts; here termed the Buraele Graben, the Weyto Graben and the Guyle Horst. The faults have varied magnitude of throws along the strike of individual faults. The down throw reaches up to 600m when the fault plane is parallel to the Precambrian ductile structure and minimal when the faults dip opposite to the Precambrian structures indicative of the control of Tertiary rift faulting by the Precambrian structural grain.
STRUCTURE AND METAMORPHIC ANALYSIS OF WEYTO AREA, SOUTHWESTERN ETHIOPIA.pdf