GRAVITY AND MAGNETIC TECHNIQUES FOR THE DELINEATION OF SUBTERRANEAN STRUCTURAL FEATURES OF THE BASEMENT COMPLEX, IMO RIVER BASIN, SOUTHEASTERN NIGERIA.

Abstract

Gravity and magnetic techniques were applied to delineate the subterranean structural features of the basement complex of the Imo River Basin situated in the southeastern part of Nigeria, aimed at evaluating the subsurface tectonic pattern of the basement rocks. The gravity and aeromagnetic methods of exploration give an effective presentation of the subterranean structures. The corrected gravity data is represented by Bouguer anomaly map. The aeromagnetic data was corrected and represented by total aeromagnetic intensity map and then reduced to the north magnetic pole. The filtering techniques were applied to the corrected gravity and aeromagnetic maps to acquire the residual component produced by local structures and anomalies bodies. The combination of radially power spectrum was applied on both gravity and magnetic to estimate the depths of the deep and shallow sources. The equivalent depths of the isolated short wavelength anomalies are 500 m and 400 m, and the depths of the long wavelength anomalies are 2.8 km and 3.8 km for the gravity and magnetic data, respectively. The Euler deconvolution and 3-D modeling were applied to gravity and magnetic data. The 3-D Euler deconvolution is used not only to delineate major subterranean structures but also to figure out the structural indices of them as well as the mean depth of the gravity and magnetic sources. The computed structural indices show that the study area is mainly affected by contacts/thin sheet and the estimated depth of gravity and magnetic sources ranged between 500 m and 2000 m, also the 3-D Euler deconvolution showed that the area was affected by different fault trends such as E-W, NW-SE, and NE-SW trends. The results of     3-D gravity and magnetic interpretation revealed that the depth of basement was ranging from 2590 m to 3010 m. The main tectonic deformations of the area of study have NE-SW, NW-SE, and E-W trends. The obtained result from this geophysical examination could contribute for the understanding of the subterranean structural settings and the basement relief and tectonics of the Imo River Basin.