Gravity Studies of the Crustal Structures Beneath the Northern Main Ethiopian Rift and the Adjoining Eastern Plateau

Kassa, Fithat Habteweld (2014) Gravity Studies of the Crustal Structures Beneath the Northern Main Ethiopian Rift and the Adjoining Eastern Plateau. Masters thesis, Addis Ababa University.

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Abstract

The Main Ethiopian Rift (MER) constitutes the northern most part of the East African Rift System (EARS), connecting the EARS with the Afar triple junction and is an area characterised by active extensional tectonics and associated volcanic activities. Structurally the area is generally characterised by intense quaternary faulting and fracturing. This geophysical investigation comprises of the gravity method of prospecting, carried out in the Northern Main Ethiopian Rift. The method implemented is useful in locating dense intrusion and rift structures like horst and graben. The total gravity data employed in this study were 1230 observation points.The magmatic NMER is believed to represent the transitional stage from continental to oceanic crust. This is due to oceanic crust is denser than that of continental crust. The crust along the NMER shows such kinds of charactersics. The result are presented qualitative and quantitatively in the form of anomaly plots and modeled sections respectively to outline the magmatic segments and the structure beneath them. The resulting Bouguer gravity map is seen to be dominated by a regional gravity anomaly that increases in amplitude from SW to NE direction of the study area. This increment in Bouguer anomaly value might be due to crustal thining towards in the southern Afar. While the residual gravity anomaly shows shallow features and indicates gravity maxima over the volcanic centers that occur within the study area. The quantitative interpretation is based on 2.5D modeling technique, which is constrained with seismic refraction result and stratigraphy of the area. The result reveals a possible subsurface crustal structures and density distribution beneath the rift. The gravity maxima occurring over the magmatic segments were modeled as dense bodies caused by intrusion into the upper crust. The resulting model suggest that beneath the profiles magma emplacement into the upper crust ( or magmatic segment) exist in the form of 15 – 18 km wide with a top at 8 km depth extending to 16 km at the Precambrian basement. The magmatic segements are formed when a magma comes from the upper mantle intrude faults and fractures along the centeral rift. These intrusive igneous bodies are mafic or gabbro in composition and has a possible density values of 2.8 – 3 g/cc.

Item Type:	Thesis (Masters)
Subjects:	Q Science > Q Science (General) Q Science > QE Geology
Divisions:	Africana
Depositing User:	Selom Ghislain
Date Deposited:	31 Oct 2018 10:01
Last Modified:	31 Oct 2018 10:01
URI:	http://thesisbank.jhia.ac.ke/id/eprint/7209

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