INTERPRETATIONS OF THE SHORT WAVE-LENGTH AEROMAGNETIC ANOMALIES IN THE CHUNGOWA DEPRESSION, CHAD BASIN, NIGERIA

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Date
1999-07
Authors
ABUBAKR, SANUSI YUSUFU
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Abstract
ABSTRACT Aero magnetic data over the Chungowa Depression, Chad Basin, Nigeria has been studied in this work. The area is bounded between Longitudes 11 ° 30" E and 13°00"Eand Latitudes 12° 00" N and 12° 30" N. The Aeromagnetic maps supplied by the National Geological Survey, Kaduna, were digitized along the N - S flight lines at intervals of 0.5 Km to recover the original aeromagnetic data. The aeromagnetic data was then continued upward using a fortran computer program to 2.0 Km above the flight elevation to determine the regional field. The residual field of interest was then obtained by subtracting the determined regional field from the total field. Qualitative interpretation of the aeromagnetic field revealed that the study area is characterized by both high and low gradient anomalies trending mostly along the EW and ENE directions with few anomalies along the N - S direction. Two lineaments and three extended gradients were also observed in the Study area. The graphical techniques of Pal (1985) and Stanley (1977) were used to interpret the short wavelength anomalies of interest. The 2 - D interpretation based on the Pal's (1985) method shows that these anomalies were caused by intrusives lying predominantly between the depths of 0.011 Km and 1.29 Km with the shallow depths probably caused by shallow bodies which could be lava flows. The interpretation also suggested three set of ranges of the magnetic susceptibility contrasts associated with the igneous intrusions based on which the intrusions were thought to be granites, basalts and acidic rocks. On the other hand interpretations based on the Stanley's (1977) method suggested that the short wavelength anomalies of interest were caused by igneous intrusions lying predominantly between 0.148 Km and 1.18 Km. The interpretation also suggested three set of ranges for the susceptibility contrasts associated with the igneous intrusions based on which the intrusions were thought to be basalts, granites and acidic rocks. Some of the modeled bodies were found to lie at shallow depths which could be lava flows. The presence of the lava flows and the basaltic intrusions suggests a rift origin for the basin through which the rocks ascended as a result of volcanism.
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INTERPRETATIONS, SHORT, WAVE-LENGTH, AEROMAGNETIC, ANOMALIES, CHUNGOWA, DEPRESSION, CHAD BASIN, NIGERIA
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