Subduction,mega-shear systems and Late Palaeozoic basin development in the African segment of Gondwana |
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| Authors: | Johan N J Visser Hermann E Praekelt |
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| Institution: | (1) Department of Geology, University of the Orange Free State, P.O. Box 339, ZA-9300 Bloemfontein, South Africa, ZA |
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| Abstract: | Basins within the African sector of Gondwana contain a Late Palaeozoic to Early Mesozoic Gondwana sequence unconformably
overlying Precambrian basement in the interior and mid-Palaeozoic strata along the palaeo-Pacific margin. Small sea-board
Pacific basins form an exception in having a Carboniferous to Early Permian fill overlying Devonian metasediments and intrusives.
The Late Palaeozoic geographic and tectonic changes in the region followed four well-defined consecutive events which can
also be traced outside the study area. During the Late Devonian to Early Carboniferous period (up to 330 Ma) accretion of
microplates along the Patagonian margin of Gondwana resulted in the evolution of the Pacific basins. Thermal uplift of the
Gondwana crust and extensive erosion causing a break in the stratigraphic record characterised the period between 300 and
330 Ma. At the end of this period the Gondwana Ice Sheet was well established over the uplands. The period 260–300 Ma evidenced
the release of the Gondwana heat and thermal subsidence caused widespread basin formation. Late Carboniferous transpressive
strike-slip basins (e.g. Sierra Australes/Colorado, Karoo-Falklands, Ellsworth-Central Transantarctic Mountains) in which
thick glacial deposits accumulated, formed inboard of the palaeo-Pacific margin. In the continental interior the formation
of Zambesi-type rift and extensional strike-slip basins were controlled by large mega-shear systems, whereas rare intracratonic
thermal subsidence basins formed locally. In the Late Permian the tectonic regime changed to compressional largely due to
northwest-directed subduction along the palaeo-Pacific margin. The orogenic cycle between 240 and 260 Ma resulted in the formation
of the Gondwana fold belt and overall north–south crustal shortening with strike-slip motions and regional uplift within the
interior. The Gondwana fold belt developed along a probable weak crustal zone wedged in between the cratons and an overthickened
marginal crustal belt subject to dextral transpressive motions. Associated with the orogenic cycle was the formation of mega-shear
systems one of which (Falklands-East Africa-Tethys shear) split the supercontinent in the Permo-Triassic into a West and an
East Gondwana. By a slight clockwise rotation of East Gondwana a supradetachment basin formed along the Tethyan margin and
northward displacement of Madagascar, West Falkland and the Gondwana fold belt occurred relative to a southward motion of
Africa.
Received: 2 October 1995 / Accepted: 28 May 1996 |
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| Keywords: | African basins Madagascar Falkland Islands Gondwana tectonics Late Palaeozoic geography Palaeo-Pacific margin |
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