Geology and geochemistry of volcanic rocks of Kulf Amba area, North Wollo, Northwestern Ethiopian Plateau

Dejen Teka

dc.contributor.author	Dejen Teka
dc.date.accessioned	2021-02-24T09:13:52Z
dc.date.available	2021-02-24T09:13:52Z
dc.date.issued	2021-02-24
dc.identifier.uri	http://ir.bdu.edu.et/handle/123456789/11952
dc.description.abstract	The Kulf Amba area is situated in the Northwestern Ethiopian plateau. Most studies in the plateau volcanic rocks have been carried out at a regional scale and focused on basalt and very little are known about the petrogenetic relationship of both the mafic and felsic volcanic rocks. Thus, the main objective of this research study is to determine the geology and geochemical characteristics of Oligocene volcanic rocks of the Kulf Amba area. Field investigation, petrographic description and geochemical study have been used to attain the objectives. The main volcanic products identified in the study area are basalt, volcanic glass, rhyolitic ignimbrite, rhyolite and tuff. The basalts are characterized by aphanitic, porphyritic and Glomirophyric texture with phenocrysts of olivine, clinopyroxene, Ca-rich plagioclase and Fe-Ti oxide whereas, the felsic rocks are characterized by phyric, porphyritic and glassy texture with phenocryst assemblage of alkali feldspar, quartz and Fe-Ti oxides. The geochemical analysis indicates the Kulf Amba volcanic rocks are bimodal in composition, with the absence of intermediate rocks. The mafic rocks are transitional to tholeiitic ultra titaniferous (HT2) basalt with major and trace element concentration nearly similar to Northwestern Ethiopian high-Ti (HT2) basalts but, the felsic rocks are dominantly peralkaline comendite with minor pantellerite. The chondrite normalized rare earth element (REE) patterns of the mafic rocks show enriched LREE and depleted HREE without Eu negative anomaly, indicating little or absence of plagioclase fractionation but, the felsic rocks show enriched LREE and flat HREE with variable negative Eu anomaly, indicating fractionation of plagioclase during their evolutions. More or less constant ratios of Zr/Hf (37.53-45.08) and Nb/Ta (17.29-23.67) in both mafic and felsic rocks suggest fractional crystallization is a dominant process with little crustal contamination. Primitive-mantle normalized multi-element diagrams of the mafic rocks are characterized by depletion of HREE and enrichment of LREE, indicating the presence of garnet in the source and modeled results for melting using Sm/Yb vs. La/Sm indicates a low degree of partial melting of a source with garnet. Further, the primitive mantle normalized multi-element variation patterns of the mafic volcanic rocks display a negative anomaly of K, indicating the presence of phlogopite in the mantle source and considered as an indicator for mixing of different mantle sources for their genesis and the basalts are formed in the within plate tectonic setting. Key words: Fractional crystallization, Crustal contamination, Petrogenesis, Bimodal volcanism	en_US
dc.language.iso	en	en_US
dc.subject	Petrology	en_US
dc.title	Geology and geochemistry of volcanic rocks of Kulf Amba area, North Wollo, Northwestern Ethiopian Plateau	en_US
dc.type	Thesis	en_US