Characterization of Spectral Depth to Buried Magnetic Rocks over Part of Upper Benue Trough, Nigeria, Using Aeromagnetic Data

Abstract

A statistical method of analysis was employed in this study to determine the depths to recorded magnetic sources over part of Upper Benue Trough, Nigeria, using aeromagnetic data. The area lies between Latitudes 9o 00’ N to 10o 00’ N and Longitudes 11o 00’ E to 12o 00’ E and covered by four Index Map Sheets of Kaltungo (173), Guyuk (174), Lau (194) and Dong (195), of 1/2o x 1/2o each with total area of approximately 12,100 km2. The aim of this research is to determine the source(s) of magnetic anomalies over buried rocks and estimate the depths of their origin with a view of making informed suggestions as regards hydrocarbon perspectivity of the area. A total number of 1369 data points covering the entire study area, systematically acquired was obtained in soft copy from the Nigerian Geological Survey Agency of Nigeria, Abuja and used for this work. Oasis Montaj was used to carry out residual-regional anomaly separation based on First Order Polynomial Fitting. The depths to buried magnetic source rocks were then determined from the Slopes of the plots of logarithm of spectral energy against frequency using the Slope Plot Program. Results show that the high/strong magnetic anomalies are oriented northeast-southwest and flanked on the northwestern side by low and southeastern side by very low magnetic anomalies respectively. The magnetic anomalies also originated from two sources; the first (shallow source) from depths not exceeding 1.0 km and believed to be due to intrusive rock bodies in the basin while the second (deeper source) which originated from the magnetic basement lies at depth not greater than 3.25 km. the sedimentary cover in the area is generally thin and associated with many intrusive rock bodies.