Southern South Africa provides a unique setting to study the extension of a pre-existing compressional belt (negative structural inversion) because of the juxtaposition of excellent levels of pre-rift exposure, enabling basement structures to be determined, and high quality 2D seismic data, allowing the detailed temporal and spatial controls on rift system evolution to be established. Through the construction of five regional transects, orientated perpendicular to the Permian-Triassic Cape Fold Belt (CFB), an intimate link between compression and the subsequent Mesozoic extension can be established. A comparison between the CFB and other orogens suggests that it is atypical and it is proposed that the north of the foldbelt is controlled by low angle listric faults, while the centre and south are dominated by high angle planar faults. These faults have been reactivated during the subsequent extension. This model is supported by depth converted seismic sections that reveal listric normal faults that detach at a shallow crustal level in the north, while the south is dominated by a limited number of large, planar crustal scale normal faults. Comparison with both contractional and extensional reactivation (structural inversion and negative inversion respectively) models and examples supports the model. The high quality of the available 2D seismic data arrays have enabled a sequence level seismic stratigraphic framework to be established for the three offshore basins (Pletmos, Gamtoos, and Algoa). The integration of the three basins has revealed a generally uniform evolution that differs from previous studies. In particular, the formation of complex deformation features, previously considered to be of a compressional origin, are re-examined in light of detailed basin modelling. The dimension and evolution of the South African system are atypical when compared to other basins. The lengths of faults are at least 150 km with approximately 12 km of throw on the basin-bounding faults, which are significantly larger than most rift settings. There is also no evidence of along trend segmentation of the faults and extreme localisation of stress occurring from an early stage in the rift history. The results provide a critical test for existing models, which adequately account for normal fault evolution in homogeneous crust, to a region with a significant pre-existing, compressional fabric.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:660425 |
| Date | January 2002 |
| Creators | Paton, Douglas Alan |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/15594 |
Page generated in 0.0016 seconds