Sedimentation and Tectonics of the Khomas Hochland Accretionary Prism, along a Late Proterozoic Continental Margin, Damara Sequence, Central Namibia
- L. E. Frostick3 and
- R. J. Steel4
Published Online: 16 APR 2009
Copyright © 1993 The International Association of Sedimentologists
Tectonic Controls and Signatures in Sedimentary Successions
How to Cite
Kukla, P. A. and Stanistreet, I. G. (1994) Sedimentation and Tectonics of the Khomas Hochland Accretionary Prism, along a Late Proterozoic Continental Margin, Damara Sequence, Central Namibia, in Tectonic Controls and Signatures in Sedimentary Successions (eds L. E. Frostick and R. J. Steel), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304053.ch24
- Published Online: 16 APR 2009
- Published Print: 28 FEB 1994
Print ISBN: 9780632037452
Online ISBN: 9781444304053
- sedimentation and tectonics of Khomos Hochland accretionary prism, Namibia;
- tectono sedimentary evolution of active continental margins;
- geological setting and rock relationships of southern Damara Orogen;
- submarine fan sedimentation;
- facies sequences and sedimentary cycles;
- matchless amphibolite;
- Khomos Hochland accretionary prism
The Khomas Trough in central Namibia is one of the basins that was filled during sedimentation of the Late Proterozoic Damara Sequence (750–570 Ma). The basin that was filled by a thick sequence, now preserved as metagreywackes and pelites of the Kuiseb Formation, which were subsequently multiply deformed and thrusted during the Damaran Orogeny (570–450 Ma). Minor lithologies included are graphite schists, calc-silicates and scapolite schists. The intercalated Matchless Amphibolite contains tholeiitic metavolcanic rocks, including pillow lavas and breccias, as well as ultramafic lithologies, metagabbroic lenses, graphite schists, cherts, and a marble unit. Large exotic blocks of serpentinite were tectonically emplaced into the thrust pile.
Original sedimentary structures, the vertical facies distribution of progradational and retrogradtional cycles, and the lateral extent of major sedimentary units indicate that major parts of the sedimentary sequence have been deposited as an elongate deep-sea trench fan. The regional structural pattern is characterized by several phases of coaxial deformation with folds verging consistently to the southeast. The structural regime is markedly heterogeneous and is associated with thrusting which developed elongate thrust slices traceable laterally for at least 150 km. The thermal evolution comprises a prolonged amphibolite-facies metamorphism with the peak occurring late in the deformational history. These features are explained in a tectono-sedimentary model which involves the evolution of a Late Proterozoic accretionary prism, named the Khomas Hochland accretionary prism, within a convergent continental margin setting.
Rift initiation took place along old tectonic weakness zones between the Congo and Kalahari Cratons. This was followed by the opening of the Khomas Sea and the development of mature oceanic shelves on the two adjacent cratons. Regional geological constraints indicate that the Khomas Sea opened as a relatively small, gulf-type oceanic basin. A passive continental margin was maintained on the southern craton during closure of the Khomas Sea, which occurred at a northwest dipping subduction zone along the northern Andean-type active margin. Submarine fan sediments of the elongate trench, some pelagic sediments and pillow lavas of the oceanic crustal sequence were scraped off during accretionary prism evolution. Ultimately continental collision resulted in: (1) obduction of the accretionary prism onto the Kalahari Craton, involving the emplacement of serpentinite pods together with basement slices; (2) strong southeast vergent folding and thrusting; (3) extensive shortening; (4) prograde regional metamorphism through crustal thickening; and (5) widespread granitic plutonism.