INTEGRATED LANDSAT-ETM+ AND AEROMAGNETIC STUDY FOR ENHANCED STRUCTURAL AND GEOTHERMAL INTERPRETATION: CASE STUDY OF PART OF CALABAR FLANK, NIGERIA

ABSTRACT

An integrated structural interpretation of part of the Calabar Flank and environs was carried out using high resolution aeromagnetic (HRAM) and Landsat-ETM+ data to study magnetic basement depth, structure and tectonics of the study area. It is believed that result of this study will help in making far reaching inferences of the hydrocarbon and geothermal potentials of the study area. Several image processing and analytical techniques were applied to both the aeromagnetic and Landsat-ETM+ data to improve the data quality and resolution. Regional – residual separation was carried out on the aeromagnetic data using polynomial regression analysis.The acquired residual data were then used for more detailed interpretation of the HRAM data. The study revealed several linear features with structural trends in the NE-SW, ENE-WSW and N-S directions, with the NE-SW been dominant. These paleo-structures are believed to have played essential roles in the geodynamic and tectonic evolution of the study area. Similarly, several circular clusters of magnetic anomaly closures observed in the NE-SW section of the study area were interpreted as lithological variations of mafic-ultramafic inclusions. The positive and negative second derivative anomalies correlated with the presence and distribution of mafic and felsic rock forming minerals within the study area.Spectral inversion was carried out using the residual data to estimate the Curie point depth, heat flow and geothermal gradient in the study area. Results of the 2-D spectral analysis revealed a two layer depth model with the depth to shallower magnetic source bodies (d1) varying from 0.0345 km to 2.7798 km, with an average depth of 1.365425 km, while the depth to the deeper magnetic source bodies (d2), varies from 0.7012 km – 6.7893 km, with an average depth of 3.403056 km. Structural analysis of these shallow anomalies using 3-D Euler deconvolution with structural index values ranging from 0-3, revealed three main structural models which include spheres, pipes/cylinders, and sills/dikes. These shallower sources are probably due to intra-basement features within the basement and magnetized bodies which intruded into the sedimentary cover. Heat flow estimated from spectral inversion revealed three main geo-thermally active areas which include Afikpo, Ugep and Uwet, with heat flow values of 64.71 mW/m , 66.23 mW/m and 64.87 mW/m respectively. These areas are therefore recommended for further geothermal exploration. Finally, the average sedimentary thickness of 2.660 km derived from this study is interpreted as unfavorable for hydrocarbon generation, as it suggests possible over cooking kerogen in the study area.

Keywords: Magnetic anomaly, Curie point, Thermal gradient, Heat flow, Lineament, Calabar Flank.