Reconstructing Deformation History By Using Microstructural and Petrographic Analysis of Sorobo, Konso Area, Southern Ethiopia

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Addis Ababa University


The deformation history of Sorobo, Konso area (southern Ethiopia) within the Mozambique Belt, is described using microstructural and petrographic analysis. The area is characterized by folds and metamorphic fabrics that trend between NNE and NNW and consist of high-grade, amphibolite- to granulite-facies rocks. It is affected by five deformational phases (D1 to D5) and two metamorphic events (M1 &M2). During shortening deformation events (D1 to D3) the development of gneissosity (D1), the formation of tight to isoclinal and recumbent folds(D2) and the superposition of secondary (upright) fold (D3) on earlier recumbent fold resulting in type-3 fold interference pattern are formed respectively. During fourth deformation phase (D4) most of the rock units of the area are affected by shearing or shows east and west vergence. From field observation and thin section analysis, the area is affected by both sinistral and a dextral sense of shearing but dextral shear-sense appears dominant. Brittle type of deformation phase (D5) was developed and resulting in different types of faults varies in orientation. Peak progressive metamorphism of the granulite facies (M1) and retrogression (M2) are also associated with the deformational phase. The breakdown of biotite to chlorite mineral and transformation of plagioclase to clay mineral by alteration, and the metamorphic mineral assemblage Hbl + Pl + Qtz +/- Cpx +/- Bt manifested a retrograde metamorphism (M2) and have attained upper amphibolite facies.



Microstructure, Deformation, Metamorphism, Progression, Retrogression