Deformation and Metamorphic History of Basement Rocks from Blue Nile Gorge, Around Kuch Area, Western Ethiopian Shield

Atinkut Kelemu

dc.contributor.author	Atinkut Kelemu
dc.date.accessioned	2023-05-02T12:17:12Z
dc.date.available	2023-05-02T12:17:12Z
dc.date.issued	2022-03
dc.identifier.uri	http://ir.bdu.edu.et/handle/123456789/15231
dc.description.abstract	Deformation and metamorphic studies were carried out on the Blue Nile basement rocks near the Kuch area, western Ethiopian shield. The study aimed to investigate and reconstruct the deformation and metamorphic history of the area. Field investigations, petrographic analysis, structural analysis, and microstructural interpretations were used to characterize the different phases of deformations and to identify the nature of the metamorphism of the rocks in the area. The area is part of the western Ethiopian shield containing metamorphic rocks ranging from highgrade gneisses to migmatites, medium-grade schist to low-grade phyllites, and granitoid rocks. The analysis showed that the Blue-Nile basement rocks experienced at least four phases of deformation and two paths of metamorphism. The first phase of deformation (D1) was compressional stress that resulted from NW-directed shortening of the original formation forming strong S1foliation and associated F1 folds. The second phase of deformation (D2) is also compressional stress-directed NNW (clockwise shift of D1) that further shortens the D1 structures but not coaxial to D1, which resulted in further tightening of the F1 folds and shaping in different geometries. The third phase of deformation (D3) was a shear force that resulted in different types of strike-slip faults, shear zones, and having characteristic brittle-ductile nature. Different kinematic indicators suggest D3 deformation was a combined effect of both sinistral and dextral sense of shear. D3 is also manifested by the development of penetrative NE to NNE striking shear zone. The fourth phase of deformation (D4) was brittle deformation which might be due to the stabilizing of the area after the extrusion of post tectonic magmatic intrusions, erosion, and uplift. D4 resulted in large normal faults and smaller localized faults and fractures which were later filled by hydrothermal veins. Metamorphic mineral assemblages on metamorphic rocks of the area are characteristic green schist to upper amphibolite facies. The mineral assemblages of clinopyroxene, plagioclase, hornblende, and garnet are inferred to be formed at the highest grade metamorphic conditions (upper amphibolite facies) which is regarded as peak metamorphic path (M1) in association with D1/D2 event. The retrogressive metamorphic path (M2) was mainly responsible for the formation of chlorite, muscovite/sericite, and epidote minerals which are characteristic green schist facies and interpreted to be associated with the D3.	en_US
dc.language.iso	en	en_US
dc.subject	Petrology	en_US
dc.title	Deformation and Metamorphic History of Basement Rocks from Blue Nile Gorge, Around Kuch Area, Western Ethiopian Shield	en_US
dc.type	Thesis	en_US