Abstract
M.Sc.
The configuration of the supercontinent Rodinia, at the end of the
Mesoproterozoic to the beginning of the Neoproterozoic (1100-750 Ma), and its
subsequent break up into cratonic fragments that would later result in the formation of
Gondwana (Early Palaeozoic), is still not completely understood. This is largely due to
ambiguity surrounding relationships between cratons, craton evolution and timing of
significant tectonic or sedimentary events.
Particular to this study is the evolution and palaeogeographic history of the
Kalahari Craton and a comprehensive provenance analysis of Neoproterozoic to early
Palaeozoic clastic sedimentary rocks from the Kango Inlier (Saldania Belt, South Africa).
This includes the Cango Caves and Kansa Groups as well as the Schoemanspoort and the
adjacent Peninsula Formation (Table Mountain Group, Cape Supergroup). A well
established lithostratigraphy, in addition to recent establishment of age constraints by UPb
zircon dating and microfossil evidence, allowed for strategic sampling with the
objective of gaining insight to the crustal evolution of SW Gondwana.
In this study, a progression from immature, moderately altered rocks in the Cango
Caves Group (Upper Neoproterozoic) to mature, strongly altered rocks in the Lower
Palaeozoic Kansa Group and overlying formations is observed. Thus, rapid sedimentation
of the former is anticipated, while the subsequent formations developed at a passive/rifted
margin culminating in the laterally extensive deposition of the Peninsula Formation.
Ongoing extensional movement is evident due to chronologically deeper-water
facies and the progressive influence of a less fractionated component in the Cango Caves
Group, particularly in the Huis Rivier Formation. The association of these rocks with an
active margin is not certain since index trace element concentrations are too high for
typical arc terranes. Thus, the mixing of a younger (570-600 Ma) magmatic source (close
to an active margin) with mafic and felsic rocks of the older Mesoproterozoic Natal-
Namaqua Mobile Belt (NMB) is the most likely possibility. A maximum, pre-Cape
Granite age of 571 Ma can be assigned to the Huis Rivier Formation (Cango Caves
Group) by detrital zircon dating, and thus correlation with the Malmesbury Group can be
made. Ediacaran age zircons might be related to the active continental margin (Trans
Antarctic Orogen) surrounding southern Gondwana, but this is still hypothetical.
The post-Cape Granite Kansa Group and overlying Schoemanspoort Formation
were most likely deposited as basin infill subsequent to folding and transtensional
tectonics affecting the underlying Cango Caves Group. The Kansa Group may be
comparable with the Klipheuwel Formation (southwest South Africa) in terms of its
stratigraphic position beneath the Table Mountain Group.
Deposition of the Table Mountain Group is much younger than previously
believed in light of Ordovician zircon ages (471, 485, 499 Ma) obtained from the
underlying Kansa Group. However, the provenance of these thus far unheard of ages for
magmatic events in South Africa is a matter of contention. The proximal Ordovician
Ross-Delamerian Orogenic event in Antarctica is the most likely source.
Peninsula Formation deposition represents a cover sequence i.e. the culmination
of small isolated basins (e.g. the Kansa Group and lower Table Mountain Group) into a
larger, laterally extensive basin where reworking played a dominant role. This basin is
likely to be a rift-related. However, it is not clear which crustal entity rifted away from
vi
South Africa and if, during the Ordovician an, active continental margin further to the
south - bridging the South American Famatina Orogen with the Ross-Delamerian arc in
Antarctica - existed.
The Natal-Namaqua Mobile Belt appears to be the predominant source throughout
the succession as indicated by Nd-isotope data and zircon populations. This implies that
simple crustal recycling of Natal-Namaqua basement (or rocks with similar Nd-isotope
characteristics) led to the genesis of the magmatic material younger than 1 Ga, observed
in this study.