http://ir.bdu.edu.et/handle/123456789/10833 2001-01-13T05:52:48Z 2001-01-13T05:52:48Z Atinkut Kelemu http://ir.bdu.edu.et/handle/123456789/15231 2023-05-02T12:17:12Z 2022-03-01T00:00:00Z

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

2022-03-01T00:00:00Z Zemenu Molla http://ir.bdu.edu.et/handle/123456789/15230 2023-05-02T12:16:07Z 2022-02-01T00:00:00Z

“Geology, Petrography and Geochemistry of Volcanic Rocks of Koma-Andabet Areas, North Western Ethiopian Large Igneous Province” Zemenu Molla This study is aimed to investigate the petrological, geological and geochemical characteristics of magmatic rocks in the study area. To achieve this objective, detailed field work, geological, lithostratigraphical, cross sectional mapping, petrographical and geochemical analyses of 15 and 10 samples respectively was done. The geology of the study area has been classified into five lithological units: Aphanitic and porphyritic basaltic rocks, Gabbroic rock units, felsic pyroclastic rocks and unwelded ignimbrites. The low Ti basalts of the study area display sub ophitic texture and together with the presence of glomerophyric aggregates of pyroxene and plagioclase minerals denote a tholeiitic tendency. The correlation of MgO and CaO is positive and is an indicative of co-fractionation of olivine and clinopyroxene. The chondrite normalized values of the REE pattern shows enrichment in LREE, (La/Yb)N of 9.4 to 18 than MREE ( La/Sm N =1.38-1.86) and HREE (Dy/Yb =1.39-1.72) and there is fractionation of these HREE and MREE. The Nb/U ratio of the study area largly ranged from 13.91 to 37.1, which is an indicator for the contamination nature of the outpouring magma from the source crustal materials. The Koma-Andabet magmatic suits have similar trace element patterns and trace element ratios as Zr/Nb (12.95-14.37), Zr/Ce (4.53-5.23) and Hf/La (0.26-0.33) indicating originated from the same magmatic source. The low CaO/Al2O3 ratio (0.50-0.80) and the relatively flat pattern of HREE ((Dy/Yb) =1.39-1.72) and the HREE value is above 10 times greater than the chondrite values is a clue for the source of the Koma-Andabet magmatic rocks to be spinel containing mantle rather than garnet sourced. N N

2022-02-01T00:00:00Z Bayelign Tewachew http://ir.bdu.edu.et/handle/123456789/15228 2023-05-02T07:53:59Z 2022-08-01T00:00:00Z

Petrology and Geochemistry of Volcanic Rocks at Mertule Maryam Area, Northwestern Ethiopian Plateau: Implications for Source Characterization” Bayelign Tewachew The study is conducted on the Mertule Maryam volcanic section which is located in the northwestern Ethiopian Plateau (EP). The aim of the study is to understand the petrogenesis of volcanic rocks based on their petrological and geochemical signatures. To achieve the aim of the study: geological mapping, petrographic and geochemical studies of the volcanic rocks by comparing and contrasting with the regional studied datasets have been conducted. As a result, the study area contains volcanic rocks varying in composition from basaltic rocks at the lower part through intermediate rocks (alkali feldspar-phyric trachyandesitic pyroclast and porphyritic trachyandesitic to phonolite) at the middle part to pyroxene-rich tephrite at the upper part. Petrographically, the texture of the basalts vary from aphyric through olivine-clinopyroxeneplagioclase-phyric to plagioclase-phyric up section. The texture of the intermediate rocks vary from alkali-feldspar-phyric to alkali-feldspar-hornblende-aegirine-phyric. On the other hand, the pyroxene-rich tephrites are characterized by having a texture varying from clinopyroxene-phyric to clinopyroxene-glomeroporphyritic up section. Based on geochemical analysis, the basalts are transitional; while the intermediate rocks and pyroxene-rich tephrites are alkaline in composition. Different degree of partial melting at different depths and in some cases crustal contamination were responsible for the compositional variation of the basaltic rocks; whereas both fractional crystallization and partial melting processes, without crustal contamination, were responsible for the compositional variation of the pyroxene-rich tephrites. The intermediate volcanic rocks were affected by assimilation fractional crystallization (AFC) process in their genesis. The basaltic and intermediate magmas were generated from spinel dominated amphibole-bearing spinel-garnet asthenospheric mantle sources with some interaction of the lithospheric and crustal materials. While the basanite magmas were generated from garnet dominated spinel-garnet asthenospheric mantle source.

2022-08-01T00:00:00Z Adem, Siham http://ir.bdu.edu.et/handle/123456789/15212 2023-04-06T12:00:24Z 2020-07-01T00:00:00Z

Petro genesis of Granitoid Rocks from Koch Area, North Western Ethiopia, Petro graphical and Geochemical Evidence Adem, Siham

2020-07-01T00:00:00Z