An estimate of depths to the bottom of magnetic sources (DBMS) in the upper part of Sokoto Basin, northwest Nigeria has been made from the modified centroid method based on a fractal source distribution of magnetic sources and spectral analysis of aeromagnetic data. DBMS is used as an estimate of the Curie-point depth and hence a proxy for temperature at depth. Aeromagnetic maps covering an area bounded by latitudes 12.5 degrees N and 13.5 degrees N and longitudes 4.0 degrees E and 6.0 degrees E were digitized at an equal spacing of 1 km. Six profiles were subsequently mapped out on the magnetic data covering different geological parts for the purpose of spectral centroid analysis. The result shows that the DBMS varies between 11.37 km and 28.18 km. Consequently, geothermal gradient varies between 20.58 degrees C/km and 51.02 degrees C/km, while the ensuing heat flows vary between 51.45 mW/m(2) and 127.55 mW/m(2). The thermal structure of the earth's crust is one of the main parameters controlling geodynamic processes. This study is crucial for quantitative understanding of the geo-processes and rheological/rock-physics parameters in the study area. (C) 2014 Elsevier Ltd. All rights reserved.