Upper Lithospheric Structure of the Middle Benue Trough, Nigeria, Derived from Analysis of Satellite Gravity Data

The middle Benue Trough is the central segment of the Benue Trough, an elongate northeast orientated intracratonic rift basin in Nigeria. This study provides new information on the morphology/geometry of the upper lithospheric structures (Moho, crystalline crust thickness and crustal stretching factor) and tectonics in the middle Benue Trough and adjacent basement complex regions by analysis and three-dimensional (3D) inverse modelling of satellite Bouguer gravity anomaly data. Results from 3D inverse modelling reveal Moho depths varying from c. 24 ± 2 to 32 ± 3 km and crystalline crustal thickness values ranging between c. 20 ± 2 and 32 ± 3 km. Shallow Moho and thin crust occur beneath the Trough axial region, whereas deep Moho and thick crust underlay the basement complex regions and the Trough northwestern region. It also shows the presence of a prominent northeast-southwest (NE-SW) orientated, shallow Moho structures (c. 24 ± 2 to 27 ± 3 km deep) and thin crust (c. 20 ± 2 to 26 ± 3 km thick) within the Trough axial region. Comparisons of Moho depths with topography and Bouguer gravity anomaly values using profiles highlight that the observed broad, longer-wavelength near-positive Bouguer gravity anomalies over the Trough axial region are strongly associated with elevated (shallow) Moho and isostatic effect of lower topography. Crustal stretching factor (â) values obtained across the area range between c. 1.03 and 1.59 with moderately high values (c. 1.25 – 1.59) occurring in the Trough axial region. The tectonic implication of the results is that the crust/lithosphere beneath middle Benue Trough has been strongly affected/modified by intense regional, extensional and/or wrench (strike-slip) tectonics associated with past rifting events