Lithological and Structural Characterization of parts of the Lower Benue Trough, Southeast Nigeria, Using Radiometric and Aeromagnetic Data

Background and Objective: Geophysical signatures depend on lithology and structural properties. Evaluation and interpretation of radiometric and aeromagnetic data acquired over parts of Lower Benue Trough were done to characterize lithologies and structure. Materials and Methods: The airborne geophysical data was acquired along a series of NW-SE flight lines (perpendicular to regional trend) at 500 m line spacing and 80 m terrain altitude, with tie lines at about 2 km intervals and sampling interval of 1.0 s and 0.1 s for radiometric and aeromagnetic data, respectively. Data processing was done and key images of classified ternary map residual magnetic intensity and tilt derivatives maps were produced. Results: Qualitative analysis of produced maps integrated with geologic map of the study area showed that the outcrop of different rock formations presented peculiar magnetic and radiometric signatures/ratios such as Odukpani Formation and crystalline rocks (relatively high K and magnetic intensity), the Oban Massif facies (K = Th), Asu River group (K = Th = U around the central areas and K>U&Th towards the southwest), Ezeaku Formation (U>Th&K), Awgu and Nkporo (high U and K, respectively) and Mamu and Ajali Formations (relatively high Th and U=Th, respectively). Structural lineaments extracted from tilt derivative map showed fractures with major, intermediate and minor trends in the NE-SW, NW-SE and NNW-SSE, & E-W, respectively. Stress-strain relationships suggest that fractures with NNW-SSE, E-W; NE-SW and NW-SE trends represent pre-folding (pre-Santonian), syn-folding (Santonian) and post-folding (Post-Santonian) fracture systems, respectively. Conclusion: These results show that lithology and structural features can be mapped from geophysical data.