A Dissertation Submitted to the Faculty of Science, University of the Witwatersrand,
Johannesburg, in Fulfilment of the Requirements of the Degree of Doctor of
Philosophy. / The Gariep Belt is an arcuate north-south trending tectonic unit extending ;along the
western coast of southern Namibia and northwestern South Africa. It forms part of the
Pan-African Damara Oragert, which consists of a north-south trending coastal branch
(Kaoko and Gariep Belts) and an east-west trending inland branch. The Gariep Belt
is subdivided into an eastern parautochthonous passive continental margin on the
western edge of the Kalahari Craton, the Port Nolloth Zone, and a western
allochthonous ophiolitic terrane, the Marmora Superterrane, thrusted on the Port
Nolloth Zone.
The sedimentary evolution of the Gariep Belt was initiated with the deposition of
sediments of the Rosh Pinah Formation into fluvial, alluvial and lacustrine depositional
systems, which are associated with bimodal volcanic activity and related Zn-Pb-Cu-Ag-
(+Ba) sulphide mineralization. The overlying mixed continental/shallow marine
deposits of the Gumchavib Formation are overlain by the carbonate dominated
Pickelhaube Formation, which was deposited in shallow marine to pelagic depositional
settings. The Rosh Pinah, Gumchavib and lower Pickelhaube Formations are intruded
by basic volcanic sills of the "Gannakouriep dyke swarm", The conformably overlying
Obib Peak Formation was deposited into a fluvial/alluvial palaeoenvlronrnent, The
Numees Formation unconformably overlies the underlying stratigraphic units and
consists predominantly of glaciomarine massive diamictites and occasionally
interbedded iron formations, which are occasionally interbedded with interglacial
sediments and volcanics.
The regional structural pattern is characterized by three phases of deformation. The
earliest deformational event, D1, comprises intrafolial small scale recumbent and
isoclinal F1 folds, a penetratlve beddlnq-subparatel 81 cleavage and a preferred
elongation of boulders, pebbles, grains and minerals (11). Associated with D1 are
bedding-subparallel thrust faults. The D2 deformational phase is characterized by small
to large scale, north to northwest trending F2 folds with a generally easterly vergence,
which can change into a westerly direction due to backfolding. The F2 folds are
associated with a penetrative axial planar S2 cleavage. Thrusting continued during the
D2 deformational phase. The latest deformational event, D3, is characterized by small
to large scale open F3 folds with southerly to south-westerly trending fold axes. The
metamorphic evolution of the Gariep Belt during the Damara Orogeny was associated
with barrovtan-type metamorphism with a geothermal gradient of about 20oC/km,
reaching greenschist to lower amphibolite facies metamorphism.
The sedimentological and structural features are explained in a tectono-sedimentery
model, which started with rift initiation during the deposition of Rosh Plnah Formation
lithologies along old tectonic weakness zones of Middle Proterozoic age at about
780Ma. Supercontinenta! breakup is documented by the initial transgression of
Gumchavib Formation sediments and the continuous trensgression of the Pickelhaube
Formation, which is related to thermal subsidence after the initiation of oceanic
spreading of the Adamastor Ocean. Renewed rifting and/or glacial outwash heralding'
the advance of the Numees glaciation and associated seale': :'changes may be
responsible for the sudden break in marine sedimentation during the deposition of the
Ohio Peak Formation. The Numees glaciation is probably contemporaneous with the
670Ma old Varangian glacial and the Rapitan glacial episodes and provides a minimum
age for the deposition of Gariep Group lithologies. Rifting and spreading was followed
by the closure of the Adamastor Ocean, associated with. a southeastward directed
subduction. of oceanic crust under the Kalahari Craton and was accompanied by
intense southeastward and subsequently eastward directed tectonic transport during
01 and D2. During D3, a late Sinistral movement developed along tre defined fault
zones in the late stages of the Adamastor Orogeny.Metamorphic ages from the Nama
and Vanrhynsdorp Groups indicate that that the tectonic evolution of the Gariep Belt only
ceased at about 500Ma. / Andrew Chakane 2018
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/25466 |
| Date | January 1994 |
| Creators | Jasper, Marold Jens Uwe |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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