Electrical conductivity of mantle in the North Central region of Nigeria

• Sq current was used to study mantle electrical conductivity profile in Nigeria.
• Results compared with conductivity profiles from other regions and continents.
• Some evidence of discontinuities were observed.
• Conductivity (σ) profile of this study agrees with other σ profiles in West Africa.
• 900–1100 km discontinuity is close to 920-km discontinuity by Kawakatsu and Niu (1994).

The mantle electrical conductivity profile of the North Central region of Nigeria was determined using the quiet day ionospheric current variations (Sq). The employed magnetic averaged hourly data were obtained from Magnetic Data Acquisition System (MAGDAS) ground based observatories at two Nigerian stations located at Ilorin (8°30′N, 4°33′E) and Abuja (8°59′N, 7°23′E) for the year 2009 and 2010. The magnetometer data from Pankshin (9°20′N, 9°27′E) and Katsina-Ala (7°10′N, 9°17′E) for the same years were equally employed. The separation of both the internal and external field contributions to the Sq variations was successfully carried out employing spherical harmonic analysis (SHA). Transfer function was performed in computing the conductivity–depth profile for North Central region of Nigeria from the paired external and internal coefficients of the SHA. The conductivity value of approximately 0.039 S/m was estimated at a depth of 100 km which rose gradually to 0.087 S/m at 207 km depth and 0.142 S/m at 367 km (close to the base of upper mantle). Subsequently, the conductivity profile continued rising to a value of 0.144 S/m at 442 km, 0.164 S/m at 653 km and 0.174 S/m at 710 km. Finally, value of approximately 0.195 S/m at a depth of 881 km and 0.240 S/m at 1100 km depth were recorded at the lower mantle with no indication of leveling off. Some evidence of discontinuities near 100–214 km, 214–420 km, 420–640 km, 640–900 km and 900–1100 km were clearly obvious. The sharp increase in conductivity from about 100 km depth to 230 km was interpreted to correspond to the global seismic low velocity zone – the asthenosphere.