Constraining the timing of deformation in the southwestern Central Zone of the Damara Belt, Namibia
L. Longridge, R. L. Gibson, J. A. Kinnaird, R. A. Armstrong, 2011. "Constraining the timing of deformation in the southwestern Central Zone of the Damara Belt, 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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Structural investigations and U–Pb sensitive high-resolution ion microprobe (SHRIMP) dating of rocks from the southwestern Central Zone of the Damara Belt, Namibia, reveal that a major SE-verging deformation event (D2) occurred at between 520 and 508 Ma. During D2, SE-verging simple shear and NE–SW pure shear extension in a constrictional stress field produced recumbent, south- to SE-verging, kilometre-scale folds and ductile shear zones, a NE–SW extensional lineation and conjugate shear bands, and was coeval with granitoid emplacement and high-grade metamorphism. The timing of this event is constrained by anatectic leucosomes in D2 shear zones (511±18 Ma) and extensional shear bands (508.4±8.7 Ma) as well as by syntectonic grey granites (520.4±4.2 Ma), and is similar to ages for high-grade metamorphism in the Central Zone. An upright folding event (D3) occurred at c. 508 Ma, resulting in the formation of basement-cored fold interference domes. The timing of deformation and metamorphism at 520–508 Ma in the mid-crustal SW Central Zone contrasts with ages of 560–540 Ma for shallow crustal NW-verging folding and thrusting elsewhere in the Central Zone that was concomitant with voluminous magmatism. This magmatism led to metamorphism and anatexis of the basement and the emplacement of anatectic red granites at 539±17 to 535.6±7.2 Ma, which contain 1013±21 Ma inherited zircons. The Central Zone therefore contains a record of crustal thickening, heating of the mid-crust, exhumation and orogen-parallel extension over the life of an orogen.
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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.