Qualitative interpretation of high resolution aeromagnetic data of abeokuta metropolis for geological characterisation

Abstract

Qualitative interpretation of aeromagnetic maps involves the visual inspection and pattern analyses of produced maps to identify potential geological structures in the magnetic field by processing the dataset to characterize the Earth's magnetic variations and map subsurface geological structure which is important to tackle the challenges of resource management, environmental assessment and infrastructure design in the study area. This technique has been employed to a part of Abeokuta metropolis of Ogun state, Southwestern Nigeria, using high resolution aeromagnetic dataset acquired from the Nigerian Geological Survey Agency (NGSA). Pre-processing analyses such as data transformation, map re-projection and power spectrum plot were performed on the dataset to minimize noises and remove unwanted variations. The application of Reduction to Magnetic Equator (RTE) filter was to remove asymmetries in the data and position the peaks of magnetic anomalies over their sources while the Gaussian (low pass) filter was aimed at improving the signal-to-noise ratio. Low magnetic zones indicated by blue colours from the total magnetic fields possibly reveal the sedimentary intrusions into the area, intermediate magnetic regions having green, yellow and red colourations suggest transition zones and the Northeastern portion of the maps indicated with pink colours correlate to the core basement regions. Derivative filters are applied as enhancement techniques to accentuate the inferred linear subsurface structures interpreted as cracks, fractures, lineaments, etc. These structures are predicted mineral entrapments or fault lines whose NE-SW orientation conforms to the Pan African Orogeny and they can aid environmental assessments generally.