Aeromagnetic Constraints on Structural Framework, Basement Configuration, and Thermal Regime across the Southwestern Nigeria Basement-Basin Transition

Abstract

This study applies an integrated aeromagnetic interpretation workflow to a contiguous dataset spanning the Precambrian Basement Complex of southwestern Nigeria and the adjacent south–south sedimentary province at the Niger Delta transition zone (6°00′–7°30′N; 5°00′–7°00′E). High-resolution airborne magnetic data acquired by NGSA/Fugro (2003–2009; 500 m line spacing; ~80 m terrain clearance; ~8 m along-track sampling) were corrected for diurnal variations and IGRF, gridded at 250 m, and processed using regional–residual separation, reduction-to-equator, first/second vertical derivatives, analytic signal, tilt derivative, and total horizontal gradient. Quantitatively, total magnetic intensity anomalies show a pronounced basement-to-basin transition, with values of ~70–119 nT over the northern crystalline domain and ~−10 to −58 nT over the southern sedimentary domain, defining a ~130 nT decrease over ~100 km. Residual anomalies range from approximately +66 nT to −104 nT, sharpening faulted basement blocks and contact relationships. Depth-to-source estimation using spectral analysis resolved shallow source depths of ~0.50-1.59 km and deeper source (basement/centroid) depths of ~2.99-8.27 km, with maximum deepening toward the basinward sector. Two-dimensional forward magnetic modelling (GM-SYS) across four profiles confirms fault-bounded basement relief, with basement depths varying from <1 km to >4 km and local vertical displacements exceeding ~2 km. Thermal modelling from spectral-derived Curie point depth indicates CPD values of ~6.10-18.05 km, corresponding to geothermal gradients of ~32.28-95.34 °C/km and estimated heat flow of ~80.69-238.36 mW/m². Spatially, high heat flow and high geothermal gradients coincide with shallow CPD zones, implying structurally influenced thermal anomalies across the basement–basin transition. The results demonstrate that inherited NE-SW and NW-SE structural fabrics persist across the province boundary and jointly control basement architecture and thermal variability, with implications for regional tectonic reconstruction and geothermal prospect screening.