Theoretical and Experimental Contributions to Understanding Anomalous Magnetic Field Variations Over the West African Craton and Their Geodynamic Implications

The West African Craton, one of the world's most ancient and tectonically stable continental nuclei, exhibits regional anomalies in the geomagnetic field that carry information about deep crustal and upper mantle composition, thermal state, and ancient tectonic events including Pan-African collision zones and Mesozoic rifting systems represented by the Nigerian basement complex. This research makes original theoretical and experimental contributions to interpreting anomalous magnetic field variations over the Nigerian sector of the West African Craton. A new crustal magnetic field model for Nigeria is developed by synthesis of newly acquired ground total field magnetic surveys conducted across 18 transects covering all six geopolitical zones, with a compilation of previously published aeromagnetic survey data and satellite magnetic model residuals from the SWARM constellation. The theoretical component develops original formulations of the thermomagnetism and magnetoelastic stress contributions to depth-integrated crustal magnetization for Precambrian basement rocks characterized by measurements on sample suites from Plateau, Kebbi, and Anambra States. Spectral analysis methods including Parker's wavenumber domain inversion and matched filter depth separation are applied to derive the spatial distribution of magnetization sources at depths corresponding to mid-crust, lower crust, and sub-Moho levels. The research identifies for the first time a deep positive magnetic anomaly beneath the Bida Basin interpreted as a fragment of dense, highly magnetized lower crustal material emplaced during Neoproterozoic arc accretion. Original forward models of the source body geometry constrained jointly by magnetic, gravity, and seismic refraction data provide the first three-dimensional geodynamic reconstruction of this feature. Keywords: crustal magnetic anomaly, West African Craton, geodynamics, Nigeria, magnetization