Evaluation Of The Magnetic Basement Depth Over Parts Of Middle Benue Trough Nigeria By Empirical Depth Rule Based On Slope Techniques Using The HRAM
Nwosu O.B, Onuba L.N
Key words: Middle Benue Trough, Magnetic anomaly, high resolution aeromagnetic data (HRAM), magnetic basement depth, Maximum slope technique, half slope technique, high frequency and low frequency anomaly source.
Abstract: The new High resolution aeromagnetic data (HRAM) of parts of the middle Benue trough Nigeria have been interpreted to determine the magnetic basement depth and appraise its hydrocarbon accumulation potential through the empirical depth rule methods employing the maximum and half slope techniques. The regional field was modeled with a first order polynomial and the residual field regarded as an error between the model and the data using the polifit program. The residual data was contoured into a map and the preliminary qualitative analysis on it revealed areas of low frequency anomaly probably related to deep seated bodies which are areas of thicker sediment; and areas of high frequency anomaly for shallow seated bodies. Then profiles were then taken along these most prominent anomaly closures of the map and labeled profile OO', NN', WW',BB' and AA' respectively for the purpose of depth determination. The Maximum slope techniques employed using an empirical constant of 1.82 estimated an average depth of 3.66km for the deep magnetic basement and an average of 0.80km for the shallow depth. The half slope technique also employed using an empirical constant of 0.63 estimated an average depth of 3.74km for the deep magnetic source. The results obtained with this method compares favorably with that obtained through spectra analysis for the area. Predominant NE-SWtrend in the orientation of the magnetic contour closures were equally found within the study area which is an attribute of the Pan - African Orogeny trends. The significance of this result is that, this study area with an average depth to basement of 3.70km and the oldest geological formation being marine sediment of Albian age, may be promising for hydrocarbon accumulation if other conditions are met.
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