The nature of the southern West African craton lithosphere inferred from its electrical resistivity

The West-African craton is defined by a combination of Archean and Palaeoproterozoic rocks that stabilised at similar to 2 Ga towards the end of the Paleoproterozoic Eburnean Orogeny, and therefore may reflect the transition from Archean to modern tectonic processes. Exploring its present lithospheric architecture aids further understanding of not only the craton's stability through its history but also its formation. We investigate the lithospheric structure of the craton through analysing and modelling magnetotelluric (MT) data from a 500-km-long east-west profile in northern Ghana and southern Burkina Faso crossing part of the Baoule-Mossi Domain and reaching the Volta Basin in the south-eastern part of the craton. Although the MT stations are along a 2D profile, due to the complexity of the structures characterising the area, 3D resistivity modelling of the data is performed to obtain insights on the thermal signature and composition of the subcontinental lithosphere beneath the area. The thermal structure and water content estimates from different resistivity models highlight a strong dependence on the starting model in the 3D inversions, but still enable us to put constraints on the deep structure of the craton. The present-day thermal lithosphere-asthenosphere boundary (LAB) depth is estimated to be at least 250 km beneath the Baoule-Mossi domain. The area likely transitions from a cold and thick lithosphere with relatively low water content into thinner, more fertile lithosphere below the Volta Basin. Although the inferred amount of water could be explained by Paleoproterozoic subduction processes involved in the formation of the BaouleMossi domain, later enrichment of the lithosphere cannot be excluded

Automated summary

This study investigates the lithospheric structure of the West-African craton through analyzing and modeling magnetotelluric data, providing insights into the thermal signature and composition of the subcontinental lithosphere. The inferred deep structure suggests a present-day thermal lithosphere-asthenosphere boundary depth of at least 250 km below the Baoule-Mossi domain, with the lithosphere transitioning from cold and thick to thinner and more fertile below the Volta Basin. The amount of water in the lithosphere may be explained by Paleoproterozoic subduction processes, but later lithospheric enrichment cannot be ruled out.