Probing the edge of the West African Craton: a first seismic glimpse from Niger

Constraints on crustal and mantle structure of the Eastern part of the West African Craton have to date been scarce. Here we present results of P receiver function and SK(K)S wave splitting analyses of data recorded at IMS array TORD in SW Niger. Despite lacking in lateral coverage, our measurements sharply constrain crustal thickness (∼41 km), VP /VS ratio (1.69±0.03), mantle transition zone (MTZ) thickness (∼247 km), and a mid-lithospheric discontinuity at ∼67 km depth. Splitting delay times are low with an average of 0.63±0.01 s. Fast directions follow the regional surface geological trend with an average of 57±1◦. We suggest that splitting is due to fossil anisotropic fabrics in the crust and lithosphere, incurred during the Paleoproterozoic Eburnean Orogeny, with possible contributions from the later Pan-African Orogeny and present-day mantle flow. The MTZ appears to be unperturbed, despite the proximity of the sampled region to the deep cratonic root.