Magnetotelluric Sounding for Deep Crustal Structure Imaging in the Sahel Zone of Northern Nigeria

This study applies magnetotelluric sounding to image deep crustal structure in the Sahel zone of northern Nigeria, addressing a fundamental gap in knowledge of lithospheric architecture in this underexplored region. The Sahel zone of northern Nigeria spans the southern margin of the West African craton and the northern edges of the Chad and Sokoto sedimentary basins, representing a geologically complex transition zone whose deep structure controls basin architecture and potential resource endowment. MT profiling provides electrical resistivity information from the surface to depths of 50 to 200 kilometres depending on the period range, enabling characterisation of crustal and upper mantle conductors associated with major geological boundaries. This study acquires MT data at 22 stations along a 180-kilometre profile from Maiduguri through Potiskum to Damaturu. Broadband MT data are recorded using Phoenix MTU-5 instruments capturing periods of 0.001 to 10,000 seconds. Strike analysis, dimensionality assessment, and tensor decomposition precede 2D inversion using MARE2DEM finite element code. Tikhonov regularisation balances data fit and model smoothness. Findings reveal a major conductive zone below 40 kilometres depth beneath the Chad Basin that is consistent with a hot, partially molten lower crust. The base of the Precambrian basement appears as a sharp resistivity boundary at 4 to 7 kilometres depth, confirming sedimentary cover thickness estimates from potential field data. A mid-crustal conductor beneath the basin centre at 15 to 25 kilometres depth may indicate a Proterozoic suture zone with graphite-bearing metasediments. The study contributes the first MT-derived crustal model for this section of northern Nigeria.

Keywords: magnetotellurics, crustal structure, Sahel zone, northern Nigeria, deep electrical imaging.