Abstract
Results from magnetic field modelling of the Lower Benue Trough, West Africa revealed thick sedimentation with maximum values in the neigbourhood of 7,000m-10,000m. This is in contrast to the average value of 5000m suggested by earlier studies. The thick sedimentation represent thermal sag which is a regional post-rift subsidence associated with West and Central Africa rift systems. N-S, NNW-SSE and E-W structural fabrics interpreted from the transformed magnetic data bound the trough. The subsurface magnetic models also revealed extended graben structures that form the major depoceters that are segmented by intrarift horsts and average crustal thickness of 22km. The qualitative interpretation comprising, analytic signal, directional derivatives and wavelength filtering in frequency domain and subsurface magnetic modelling show that the rift architecture/geometry is controlled by high angle faults and some sinistral transtensional movements that are predominant in the Benue rift system. The low mean anisotropic susceptibility (kb = -6.7x10-4 SI) correlating with the directional horizontal derivative (dy) of the magnetic field conform with the sinistral movement in the trough indicating that magnetic anomalies align themselves along fractures/faults/shear zones owing to their variations in physical properties. The characteristics/patterns of the magnetic anomaly wavelength and inferred results from earlier studies on geophysical potential field methods, geological investigation and physical parameters (susceptibility and remanence) obtained from the subsurface magnetic modelling are pointers to non-magmatic origin of the Lower Benue Trough. The basement structuring, basin framework and predominance of anisotropic susceptibilities (ka, kb and kc) in three orthogonal directions and remanence suggest tectonic setting in the trough due to Early Cretaceous opening of the South Atlantic Ocean and interplate movement in Africa. The grabens, half grabens, faults and deep sedimentation (depocenters) interpreted from the magnetic data are hydrocarbon related structural features.
Highlights
The Benue Trough is one of the most important rift features in Africa and is believed to be formed by the rifting of the central West African basement during the Cretaceous
The qualitative interpretation comprising, analytic signal, directional derivatives and wavelength filtering in frequency domain and subsurface magnetic modelling show that the rift architecture/geometry is controlled by high angle faults and some sinistral transtensional movements that are predominant in the Benue rift system
3.1 Subsurface Magnetic Models Modelled cross-sections (Figures 8- 13) from the residual magnetic field show that the anomalies are both due to structural and lithological variations and there is a variation in extent and thickness of the depocenters between the profiles
Summary
Careful re-examination of geophysical evidence makes it quite clear that there are only three interconnected rifts in West Africa; the Lower Benue Rift which extends from the Gulf of Guinea to a triple junction near Chum and the Gongola and Yola Rifts which extend to the north and east, respectively from the Chum triple junction (Figure 2). These three rifts opened during the ealier part of the Mesozoic and were subsequently filled with Cretaceous sediments (Freeth, 1984). The trough development is attributed to major horizontal movements along a series NE-SW trending fractures accompanied by basement fragmentation, subsidence and rifting during Early Cretaceous opening of the South Atlantic Ocean (Grant, 1971; Akande, Abimbola & Erdtmamn, 1971)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
