[S-MP25] Supercontinents and Crustal Evolution

[SMP25-P02] Proterozoic crustal evolution in southern Africa: implications for episodic thermal events related to intracratonic orogeny

*Toshiaki Tsunogae¹, Prince Mandingaisa², Yuji Wakita², So Wakabayashi², Yukiyasu Tsutsumi³ (1.Faculty of Life and Environmental Sciences, University of Tsukuba, 2.Degree Program in Geosciences, University of Tsukuba, 3.National Museum of Nature and Science)

Keywords:High-grade metamorphism, Geochronology, Southern Africa, Intracratonic orogeny, Supercontinent

The basement rocks in southern Africa are composed of Archean cratons (e.g., Zimbabwe, Kaapvaal, Congo, and Tanzania Cratons) and orogenic belts dissecting them. The orogenic belts are traditionally classified into four units based on their ages; ca. 2.7–2.6 Ga Limpopo Complex, ca. 2.0–1.9 Ga Magondi and Ubendian Belts, ca. 1.1–1.0 Ga Kibaran–Irumide and Namaqua–Natal Belts, and ca. 650–550 Ma Pan-African orogeny (e.g., Mozambique, Zambezi, and Damara Belts). Previous studies suggest that most of them were formed by continent-continent collisional events related to the assembly of supercontinents. However, detailed petrological and geochronological investigations on some of the orogenic belts indicate that southern Africa was not formed by the four continent-continent collisional events, but multiple thermal events probably took place even in a single orogenic belt. For example, the 2.7–2.6 Ga Limpopo Complex, which sutures the Kaapvaal Craton to the south and the Zimbabwe Craton to the north was locally overprinted by 2.0 Ga granulite-facies event (e.g., Jacket et al., 1997; Basupi et al., 2022). Similar ca. 2.0 Ga event was also found from the southernmost part of the Zimbabwe Craton adjacent to the Limpopo Complex (Tsunogae and Belyanin, 2020). The ca. 2.0 Ga Magondi Belt was affected by the ca. 1.2-1.1 Ga low-pressure amphibolite facies metamorphism (Mandingaisa et al., 2022), whereas ca. 2.0 Ga Ubendian Belt was overprinted by Pan-African (ca. 560-540 Ma) high-pressure metamorphism. The ages of the second thermal events that affected the belts are also consistent with the timing of global supercontinent amalgamation, therefore we infer intracratonic reworking affected most of the Neoarchean to Mesoproterozoic orogenies in southern Africa.

References

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Mandingaisa, P., Tsunogae, T., Uthup, S., Basupi, T.O., Meck, M.L., Tsutsumi, Y., 2022. Latest Mesoproterozoic (ca. 1.2–1.1 Ga) amphibolite-facies metamorphism from the Dete-Kamativi Inlier, NW Zimbabwe: Implications for a Rodinia-related intracratonic orogen in Southern Africa. Precambrian Research 376, Article No. 106688, 1-20.
Tsunogae, T., Belyanin, G.A., 2020. P-Tand Ar-Ar age constraints on low- to high-grade metabasites from the Buhwa Greenstone Belt, southern Africa: Implications for Neoarchean to Paleoproterozoic thermal evolution along the Limpopo Complex-Zimbabwe Craton boundary. Journal of African Earth Sciences, 162, Article 103722, 1-17