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Thermochemical structure and evolution of cratonic lithosphere in central and southern Africa

Abstract

The thermochemical structure of the subcontinental mantle holds information on its origin and evolution that can inform energy and mineral exploration strategies, natural hazard mitigation and evolutionary models of Earth. However, imaging the fine-scale thermochemical structure of continental lithosphere remains a major challenge. Here we combine multiple land and satellite datasets via thermodynamically constrained inversions to obtain a high-resolution thermochemical model of central and southern Africa. Results reveal diverse structures and compositions for cratons, indicating distinct evolutions and responses to geodynamic processes. While much of the Kaapvaal lithosphere retained its cratonic features, the western Angolan–Kasai Shield and the Rehoboth Block have lost their cratonic keels. The lithosphere of the Congo Craton has been affected by metasomatism, increasing its density and inducing its conspicuous low-topography, geoid and magnetic anomalies. Our results reconcile mantle structure with the causes and location of volcanism within and around the Tanzanian Craton, whereas the absence of volcanism towards the north is due to local asthenospheric downwellings, not to a previously proposed lithospheric root connecting with the Congo Craton. Our study offers improved integration of mantle structure, magmatism and the evolution and destruction of cratonic lithosphere, and lays the groundwork for future lithospheric evolutionary models and exploration frameworks for Earth and other terrestrial planets.

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Fig. 1: Tectonic and thermochemical structures in central and southern Africa.
Fig. 2: Three-dimensional renderings of the thermal structure beneath the study area.
Fig. 3: Hot-spot tracks and location of kimberlitic and carbonatitic volcanism superimposed on lithospheric structure.

Data availability

The data that support the findings of this study are available from the community data repository Figshare at https://doi.org/10.6084/m9.figshare.19322180.

Code availability

The codes used to perform the inversions are available from the corresponding author upon request or via https://www.juanafonso.com/.

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Acknowledgements

We thank S. Lebedev for valuable suggestions. We also acknowledge the AfricaArray programme and all its members. W.B.-M. and J.C.A. acknowledge funding from ARC Grant DP160103502, ARC CE110001017, ARC Linkage Grant LP170100233 and Macquarie University DVCR co-funding scheme. This is contribution 1681 from the ARC Centre of Excellence for Core to Crust Fluid Systems (www.ccfs.mq.edu.au) and 1480 in the GEMOC Key Centre (http://www.gemoc.mq.edu.au).

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Authors

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J.C.A., N.J., A.M. and W.B.-M. conceived the project. W.B.-M., J.C.A., F.S. and I.F. performed the inversions and processed all datasets and results. All authors analysed the results and contributed to writing the manuscript.

Corresponding author

Correspondence to Juan C. Afonso.

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The authors declare no competing interests.

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Nature Geoscience thanks Sergei Lebedev, Atalay Ayele and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: Rebecca Neely, in collaboration with the Nature Geoscience team.

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Supplementary information

Supplementary Information

Supplementary Text, Discussion and Figs. 1–29.

Supplementary Video 1

Supplementary video S1 is a video displaying a sequence of 2,500 random realizations of LAB depth from the full posterior distribution at a nominal resolution of 2° × 2°.

Supplementary Video 2

Supplementary video S2 is a video displaying a sequence of 2,500 random realizations of average lithospheric Mg# from the full posterior distribution at a nominal resolution of 2° × 2°.

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Afonso, J.C., Ben-Mansour, W., O’Reilly, S.Y. et al. Thermochemical structure and evolution of cratonic lithosphere in central and southern Africa. Nat. Geosci. 15, 405–410 (2022). https://doi.org/10.1038/s41561-022-00929-y

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