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Investigations into the Tectonic Lineaments and Thermal Structure of Lake Magadi, Southern Kenya Rift using Integrated Geophysical Methods

Komolafe, Akinola Adesuji (2010) Investigations into the Tectonic Lineaments and Thermal Structure of Lake Magadi, Southern Kenya Rift using Integrated Geophysical Methods.

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Abstract:In this research, the tectonic lineaments and thermal structure around Lake Magadi, southern Kenya rift were investigated in order to explore its geothermal potential using integrated geophysical methods. Surface lineaments around this Lake and their influence on the hot springs manifestations along its margins have not been previously investigated. Also, depth to the heat source which could provide information on the thermal structure and geodynamic activities in the area has not been delineated using aeromagnetic data despite the vast expression of geothermal resources on the surface. The structural information of the area was derived from the enhanced AsterDEM and Aster images, supplemented by the existing lineaments map of the area. Five N-S Faults in the south of study area, within Magadi basin, close to the known hot springs were identified for ground investigation using combined Electrical Resistivity Tomography (ERT) and Ground Magnetic Survey. These were further probed to greater depths with aeromagnetic data using 2D Euler deconvolution. The heat source (Curie point) depth was delineated by analysing the aeromagnetic data using power spectral method. The subsurface constituents of the investigated structures revealed a funnel-shaped fluid-filled (mostly saline hydrothermal) zone with a relatively low resistivity values of less than 1Ωm, separated by resistive structures to the west and east, to a depth of 75m along the ERT profiles. The ERT shows an upward flow of saline hydrothermal fluid to the surface through the fault splays. The gradual downward increase in resistivity values within the ERT profiles show the salinity differences from the near surface to the subsurface. Ground magnetic profiles revealed subsurface faulting/tectonic activities up to a depth of 400m and the presence of fluid-filled zones within the basin which are marked by the absence of magnetic sources. These complimentary methods confirm the fluid-filled high micro crack porosity in the upper crust and also show that the N-S faults structures in the south of the lake serve as fluid conduits which support the upward flow of the hydrothermal fluid along its margin. A deeper investigation into the lineaments from the aeromagnetic data showed that the surface faults extend into a depth of 7.5 km in the subsurface. These faults are probably the parallel faults which bound the basin/graben to the west and to the east. The spectral analysis of the aeromagnetic data revealed the emplacement of Magadi Curie point (heat source) at the depth of 12.1km. This estimation is consistent with the existing crustal model proposed by other researchers. This depth marked the transition point between the ductile and brittle crust. The shallowness of this depth implies a high heat flow around Lake Magadi; this is supported by the surface manifestations of hot springs along its margins. The correlation of the heat source, subsurface tectonic activities and seismic hypocenters showed that the seismogenenic zone exist directly on top of the magma intrusion (heat source) and forms the commencement of geodynamic activities. Keywords: Lake Magadi,Curie Point, Electrical Resistivity Tomography, Ground Magnetic Survey, Aeromagnetic, AsterDEM, Seismogenic, Geothermal, geodynamics and Tectonics Lineaments
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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