Integration of Magnetic, Gravity and Geologic Data in Mapping Geologic Structures: A Case Study of a Part of Lafiagi [Sheet 203], Southwestern Nigeria.

Abstract:

The geophysical study of a part of Lafiagi (Sheet 203) in the Nigerian topographical map was carried out. It was aimed at mapping the subsurface morphology so as to identify the tectonic features responsible for the structural setting and update the geological map of the area. This work involved the qualitative and quantitative analysis of aeromagnetic and pseudo-gravity data using the Oasis Montaj^TMsoftware.

Gravity and magnetic (GM) data have been widely used to interpret features in the Earth’s lithosphere. These data can be used to identify natural hazards, to explore for natural resources etc. The need to continue with and to step up efforts on the hydrocarbon exploration programmes in Nigeria's other sedimentary basins outside the Niger Delta as mitigating measure against agitation for resources control, dwindling national and global reserves etc has made gravity and magnetic surveys to become powerful tools for informing geoscientists about subsurface structures under thick sediments and in basement complex terrain.

The approaches 2-D Forward modeling and inversion and 3-D Euler inversion of the acquired aero-magnetic and pseudo-gravity data and geological information were employed in the interpretation works. The identified faults and lineament features obtained from geophysical data generally coincide with the river channels on the geologic map which indicate a structural control of the drainage system in the study area. The solutions obtained from standard 3D Euler Deconvolution (Figs. 1a and b) have shown that the structural indices of 2.0 (magnetics) and 1.1 (gravity) (i.e. pipe model), which is abundant in this area had been used worldwide in detecting Kimberlite pipes which is known to host large quantity of minerals (diamonds and garnet) and rocks (peridotite and xenoliths) while the structural indices of 2.0 (gravity) and 3.0 (magnetics) in the 3D Euler Deconvolution (i.e. the sphere model), which is also common in this area had been used worldwide in detecting tanks and drums. This perhaps explains while the study area is rich in economic minerals.