Second vertical derivatives and trend surface analysis of the aeromagnetic data over part of the Benin Basin, Nigeria

Abstract

The Benin basin has been interpreted as a rift basin bounded by two trans-oceanic fracture zones: the Romanche Fracture Zone to the west and Chain Fracture Zone to the east. These paleo-structures trend approximately in the NE-SW direction. Linear features identified in the study area have principal trend directions in the NE-SW and N-S, and to a lesser extent E-W and NW-SE directions. The E-W structures are localized in their occurrence and are revealed around Akure area while the N-S fractures which are revealed in part of the study area especially around the Ilesha – Ife axis are marked by considerable shearing and brecciations. The N-S fractures are gravity induced while the conjugate northeasterly and northwesterly sets which were products of transcurrent movements are characterized by wide zones of cataclastic deformation. The NE-SW is indeed well developed in the study area and has been interpreted as an important zone of tectonic activity which tends to suggest that they are deep seated. Finally, the distribution of mafic and felsic rock forming minerals were correlated to the positive and negative second vertical derivative anomalies around Ilesha area. These minerals are believed to be the by-products of the re-activation of the trans-oceanic fracture zones that also acted as conduits for the primary mineralization.