Thermal structure of the lithosphere across Africa and its controls on the generation of carbonated igneous rocks and primary mineral deposits

Understanding how deep lithospheric processes govern the formation and distribution of critical raw materials is essential for supporting the energy transition. Carbonated mantle-derived magmas, particularly carbonatites, are the primary hosts of rare earth elements (REE) and critical metals such as Nb and Ta. Yet, the subsurface conditions that control their generation and emplacement remain unclear and are debated. Here, we present a continent-scale study linking lithospheric thermal structure, carbonated rocks, and primary mineral deposits across Africa.

We integrate state-of-the-art seismic tomography models with thermodynamic inversion (Lebedev et al. 2024; Xu et al. 2025) to construct a high-resolution (1° × 1°) temperature model of the African lithosphere and upper mantle down to 400 km depth. The map of the lithosphere–asthenosphere boundary (LAB), defined by the 1290 °C isotherm, reveals the regional-scale structure of thick cratonic roots and lithospheric thinning beneath areas of rifting and basaltic volcanism.

Comparisons with extensive compilations of mantle-derived igneous rocks reveal a systematic relationship between the lithospheric thickness and magma composition: basalt (66.1 ± 21.27 km), nephelinite and melilitite (97.1 ± 33.00 km), carbonatite (126.2 ± 43.36 km) and kimberlite (184.4 ± 44.90 km; both diamondiferous and barren). The new thermal model and the lithospheric thickness-magmatism relationship also provide insights into the distribution of primary mineral deposits. The known REE and critical metal (i.e. Nb, Ta) deposits in Africa are found to have similar LAB depths (120.9 ± 42.42, 123.6 ± 30.75 km, respectively) to that of locations with carbonatites. LAB depth of known diamond mines (192.0 ± 42.67 km) is similar to that of kimberlites in general.

The consistency between the average mantle geotherms for each rock type and the lab-measured pressure-temperature (P-T) conditions of carbonated peridotite melt generation confirms and cross-validates the models of mantle temperature and those of the origin of the magmatism (e.g., Gibson et al. 2024). Our results highlight the role of the lithospheric thermal architecture in controlling deep carbonated fluid–melt systems and associated critical raw materials, providing a geophysically grounded framework for targeting future exploration.

References

Gibson, S., McKenzie, D. and Lebedev, S., 2024. The distribution and generation of carbonatites. Geology, 52(9), 667-671.

Lebedev, S., Fullea, J., Xu, Y. and Bonadio, R., 2024. Seismic thermography. Bulletin of the Seismological Society of America, 114(3), 1227-1242.

Xu, Y., Lebedev, S. and Fullea, J., 2025. Average physical structure of cratonic lithosphere, from thermodynamic inversion of global surface-wave data. Mineralogy and Petrology, 119,  811–822.