[S-MP25] Supercontinents and Crustal Evolution

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

*角替 敏昭¹、Mandingaisa Prince²、和気田 裕司²、若林 奏²、堤 之恭³ (1.筑波大学生命環境系、2.筑波大学地球科学学位プログラム、3.国立科学博物館)

キーワード：高度変成作用、地球年代学、南部アフリカ、クラトン内造山運動、超大陸

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

Basupi, T.O., Tsunogae, T., Tsutsumi, Y., 2022. Petrology and geochronology of sapphirine-bearing granulites from the Limpopo Complex in eastern Botswana: Implications for Paleoproterozoic long-lived high-pressure/ultrahigh-temperature metamorphism and rapid exhumation. Geological Journal, 57, 4194-4215.
Jaeckel, P., Kröner, A., Kamo, S.L., Brandl, G., Wendt, J.I., 1997. Late Archaean to early Proterozoic granitoid magmatism and high-grade metamorphism in the central Limpopo belt, South Africa. Journal of the Geological Society 154, 25-44.
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