Title:
Sedimentary basinal responses to a Late Precambrian Wilson Cycle: the Damara Orogen and Nama Foreland, Namibia
Publication Year:
1991
Abstract:
In the Damara Orogen sedimentary basinal responses are important in recording the evolution of the fold belt. Here we integrate sedimentological patterns and tectonics to characterise the basin development of both the pre- to syn-orogenic Damara Sequence and the syn- to post-orogenic Nama Group. The evolution of an entire Late Proterozoic Wilson Cycle involved initial rifting, with the opening of two oceanic arms through convergence to collision and foreland basin development. Rift initiation (stage 1) took place along old tectonic weaknesses and extensional rift basins (stage 2) were filled by continental sediments and alkaline/bimodal volcanics. Two oceanic openings occurred: (i) the Adamastor Ocean (stage 3) produced a break-up unconformity and eastward transgression over the Kalahari and Congo Cratons; and (ii) the Khomas Sea gulf subsequently developed betwen the two cratons (stage 4) and is associated with break-up unconformities, and ultimately the development of mature shleves (stage 5). In the latter opening, we envisage an anticlockwise rotation of the Kalahari Craton with respect to the Congo Craton. During convergence the closing Khomas Sea produced an accretionary prism/arc/retro-arc system (stage 6) and the first deformation phase in the Southern Zone. The Khomas Orogeny records the collision between the Kalahari and Congo Cratons (stage 7) including the obduction of oceanic elements onto the Kalahari Craton foreland, and caused the second and third deformation phases in the Southern Zone and first and second deformation phases in the Central Zone. A peripheral foreland basin and peripheral bulge on the Kalahari Craton resulted, which respectively contained and affected the marine and fluvial Nama Group sedimentation. A complementary hinterland basin accepted Mulden Group sediments on the Congo Craton. Ultimately the collision of the South American continent with the newly reconstituted African foreland (stage 8) caused the Adamastor Orogeny and produced a peripheral foreland basin. This basin was divided into two parts by the extant Khomas mountain belt. This event resulted in a dominant westerly source for the fluvial Fish River Subgroup and exclusion of previous marine conditions. We distinguish for the first time, the temporal separation of the Khomas and Khomas and Adamstor Orogenesis. The Khomas Orogeny involved the subduction of hot young oceanic crust associated with the relatively short residence time of the Khomas Sea, and can be dated at just before the Precambrian-Cambrian boundary. In contrast, the Adamastor Ocean had a residence time of about 200 M.a. Convergence therefore involved the subduction of cooled oceanic crust and incorporation of exotic terranes. Collision was associated with relatively major translation of tectonostratigraphic units. The Adamastor Orogeny occurred close to 500 M.a.
Publication Title:
Journal of African Earth Sciences (and the Middle East)
Volume:
13
Issue:
1
Pages:
141-156
Item Type:
Journal Article
Language:
en

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