Analysis and interpretation of aeromagnetic data of the Eyasi basin and its adjacent areas

The Lake Eyasi Basin is among the rift basins that have developed along the eastern arm of the Cenozoic East African Rift System (EARS). Its structural features and distribution of sediment thickness were still debatable. The structural features were investigated using aeromagnetic data surveyed by Geo-survey international in l977-1980. Several filters were applied to these data using Oasis Montaj Software and the structures observed were delineated using analytic signal, vertical and horizontal derivatives and tilt derivative. The thickness distribution of sediments was revealed using Spectral analysis and Euler Deconvolution methods while the modelling of individual magnetic anomalies helped in setting up the basin configuration. Petrophysical properties were measured from fresh rocks samples using Risto 7 at Geological Survey Tanzania laboratory.The analysis of aeromagnetic data, revealed WNW trending lineament that begins at Basuto through Iramba plateau to Lake Kitangiri and the E-W trending lineament which bound Lake Kitangiri to its north. These lineaments control the spread of Lake Kitangiri between the two structures. A NW weak zone intruded by gabbroic bodies buried at shallow depths was observed, it starts at Basuto to Imalaseko magnetic bodies. The depth estimation results using 3D Euler Deconvolution in combination to the spectral analysis of aeromagnetic data revealed maximum of 5 km thick of sediment on south-western portion of Lake Eyasi and a 2.5 km thick of sediment to eastern part of the basin while part of Manonga and Wembere basin constitute thickness of 3.5 km and 3 km respectively. The bodies shown by profiles crossing the basin dip in such a way that they display a full graben behaviour. Petrophysical analysis of rocks and fieldwork recognized intrusive dykes and rocks of high magnetization which have ability to retain strong magnetization. The central part of the basin is deeper enough for hydrocarbon exploration because it exceeds 2.5 km depth that favour oil accumulation.