Spectral analysis of aeromagnetic data over parts of Southwestern Nigeria

Abstract

This study endeavors to assess spectral depths, explore Basement structure variability, and deduce geothermal heat distribution by determining Curie point depth (Zb) through aeromagnetic data analysis across 14 sheets in Southwestern Nigeria. The depths to the shallow magnetic source (Zt) range from 0.14286 km to 1.02632 km, indicating sediment thickness, with the deepest point situated in the Northwestern region and progressively shallower towards the central and Southern portions of the study area. Depths to the deeper magnetic source (Z0) span from 1.08333 km in the North-central part to 3.23529 km in the Southwestern part. The primary sources of the first layer (Zt) depth are intrusions/outcropping Basement rocks, while the second layer (Z0) results from the intrusion of magnetic rocks into the basement, intra-Basement fissures, and deeper magma intrusions below the bedrock. Curie point depth ranges from 1.87380 km to 6.25629 km, with the North-central region exhibiting the shallowest depths, followed by the Northeast, Northwest, and Southeast. Shallow Curie point depth is attributed to magma upwelling and magmatic intrusion in highly fractured quartzite units and older granite units, while deeper Curie point in the Southwestern part may result from isostatic compensation/recovery. Given that Curie point depths are shallower than 10 km, the study area holds geothermal resource potential, particularly in the North-central region. The correlation between estimated spectral depths from aeromagnetic data and observed geothermal signatures in the study area promises to be advantageous in the pursuit of alternative energy generation, potentially mitigating the effects of global warming.

Geothermal resource potentials estimation from the interpretation of aeromagnetic data over parts of Southwestern Nigeria

“…The above result agrees with the conclusion by Ref. [14] that sedimentary rocks have rather low magnetic intensity, the observed intensity over them is largely due to igneous or metamorphic basement rocks or sedimentary rocks with banded iron formations. Studies in recent past [23,24,[30][31][32] have shown that depth to the magnetic sources are largely dependent on the geological composition of the subsurface.…”

“…where negative magnetic anomalies were recorded (sedimentary basin area), probably because of the presence of schist. The closures of magnetic low are mostly in areas with thick sedimentary cover whereas closures of the magnetic high are probably due to shallow basements, due to thin sedimentary cover or basic intrusion into the igneous and metamorphic basement rocks [14].…”

“…The survey also included 135 degrees for Flight Line Trend and 225 degrees for Tie Line Trend, as well as 80 meters for Sensor Mean Terrain Clearance, recorded at 0.05 seconds interval. For this study, fourteen (14) and Okowu (Sheet No. 297) were used.…”

“…The radial spectrum's logarithmic plot would result in a straight line with a slope (m) of (-2z). The ensemble's mean depth of burial hence becomes [14]:…”

“…The study area is located between latitudes 6 • 23 ′ and 7 • 38 ′ and longitudes 3 • 53 ′ and 5 • 8 ′ . The region is underlain by two geologic units (Figure 1); the Basement Complex Rocks (about 90%) and the Sedimentary Basins located in the coastal areas and the ensuing river tributaries around Lagos state and parts of Ondo state [14,15]. The basement complex of Southwestern Nigeria originated from the Pan African orogenic belt, located between the west African/Congo Cratons and towards the South of Tuareg Shields [16], and it is largely made up of three rock units; the migmatite and gneiss controlled (Liberian to Pan-African age), the schists (metasediments) with quartzites and other minor lithologies structuring a long, narrow, north-south trends, and lastly the intrusive granitic rocks, otherwise referred to as Older Granites (Late Precambrian to Early Palaeozoic age) and lastly, the Jurassic Younger Granites [17].…”