Three episodes of crustal development in the Rehoboth Province, Namibia
Valby Van Schijndel, David H. Cornell, K.-H. Hoffmann, Dirk Frei, 2011. "Three episodes of crustal development in the Rehoboth Province, Namibia", The Formation and Evolution of Africa: A Synopsis of 3.8 Ga of Earth History, D. J. J. Van Hinsbergen, S. J. H. Buiter, T. H. Torsvik, C. Gaina, S. J. Webb
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The African continental crust was assembled by a series of orogenies over a period of billions of years mainly in Precambrian times. Tracing the build-up history of this stable crust is not always straightforward due to multiphase deformation and regions with poor outcrop. Episodes of metamorphism and magmatism associated with multiple Wilson cycles are recorded in zircons, which found their way into sediments derived from the hinterland. Dating of zircon populations in detrital rocks can hence provide age spectra which reflect the metamorphic and magmatic events of the region. Microbeam dating of detrital zircon is used to characterize the crustal development history of the Rehoboth Province of southern Africa. We investigated a quartzite of the Late Palaeo-Early Mesoproterozoic Billstein Formation, formed in a continental basin, and a quartz-feldspar arenite layer of the late Mesoproterozoic Langberg Formation conglomerates, immature sediments formed within a felsic volcanic system (both close to Rehoboth Town). The combined data indicate three episodes of crustal evolution in the Rehoboth Province. The oldest phase is only documented in the Billstein quartzite by three 2.98–2.7 Ga Archaean zircons. A Palaeoproterozoic phase between 2.2 and 1.9 Ga is older than any known exposures of the Rehoboth Province. The Billstein quartzite shows a main peak at 1.87 Ga, corresponding to the 1863±10 Ma Elim Formation. The Langberg sample reflects magmatism related to the entire Namaqua–Natal Wilson cycle between c. 1.32 and 1.05 Ga. The absence of zircons of that age range in the Billstein quartzite indicates a pre-Namaqua age for the Billstein Formation. Our data shows that there were at least three episodes of crustal development at 2.98–2.7 Ga, 2.05–1.75 and 1.32–1.1 Ga. We have documented the existence of a previously unrecognized 2.98–2.7 Ga Archaean crustal component, which was probably exposed in the Rehoboth Province during the Palaeoproterozoic and thus indicates a much longer geological history for the Rehoboth Province than previously known.
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The African continent preserves a long geological record that covers almost 75% of Earth’s history. The Pan-Africanorogeny (c.600–500—Ma) brought together old continental kernels (West Africa, Congo, Kalahari and Tanzania) to form Gondwana and subsequently the supercontinent Pangaea by the late Palaeozoic. The break-up of Pangaea since the Jurassic and Cretaceous, primarily through opening of the Central Atlantic, Indian, and South Atlantic oceans, in combination with the complicated subduction history to the north, gradually shaped the African continent.
This volume contains 18 contributions that discuss the geology of Africa from the Archaean to the present day. It celebrates African geology in two ways: first, it highlights multidisciplinary Earth science research by viewing the formation and evolution of Africa from 18 different angles; second, it celebrates the work of Kevin Burke and Lewis Ashwal and portrays the wide range of interests and research angles that have characterized these two scientists throughout their careers, working in Africa, and studying African geology.