Delineating the Lineaments within the Major Structures around Eastern Part of the Lower Benue Trough from 2009 Aeromagnetic Data

Abstract

Magnetic susceptibility in the area ranged from -689 nT to 613 nT, positive magnetic anomalies were observed at the Northern end of the area above Kwalla and Wamba in Plateau and Nassarawa States,respectively However susceptibility ware generally low below Wamba down to Akira and Katsina-Ala in Benue State. The IGRF filtered residual data for the study area was reduced to the pole (RTP) before being subjected to Vertical Derivative, Source Parameter Imaging and CET grid analysis. All these were aimed at estimating depth to magnetic rocks and delineate the lineaments within the area. The first vertical derivative that sharpens the edges of the anomalies reveals that the Northern part of the study area consist of basement rock outcrops with various degrees ofdeformations as seen from the distortion to the magnetic signatures which represents the Granite Gneiss at Kwalla and the Migmatite Gneiss at Wamba. Similar features were obtained around Akwana, Gboko and Katsina-Ala which depicts weathered porphyritic homblede Granite. Depth to magnetic rocks estimates within the study area is generally shallow though some noticeable depths in the range 3 –3.5 kilometers were obtained around Akira just above river Benue and below Akwana on latitude 7º30ʹN. The phase symmetry from CET grid analysis, mapped the geologic boundaries which equally coincided with ridges within the area as thick pink bands enclosing major magnetic highs, these features are predominant within the outcrop basement rocks. Valleys were observed within regions of long wavelength anomalies which could be found from the 1VD map around Makurdi, Lafia and Akira. Lineament map obtained from CET shows linear structures that trend in the NW-SE and E-W directions these could be interpreted as veins that are host for minerals within the area, they are predominant around Kwalla in Plateau State and Wamba in Nassarawa State and also in Katsina-Ala and Gboko in Benue State.