The deformation of the Cape Fold Belt has been attributed to repeated structural reactivation of a mega-detachment from the late Proterozoic to the Mesozoic (650-65 Ma). Through the integration of onshore cross-sections with observations from the offshore Mesozoic extensional system this study evaluates the applicability of the mega-detachment model.
Regional scale cross-sections through the Permian-Triassic Cape Fold Belt reveal that it comprises two main structural domains: a northern domain dominated by northward verging and asymmetric folds; and a southern domain comprising a series of approximately 8 km wavelength box folds. The genesis of these box folds is attributed to motion on underlying high angle (> 45 degrees) reverse faults. This variation between north and south in the fold belt is reflected by a similar variation in extensional geometry of the Mesozoic normal faults, as revealed by subsurface data. The normal faults demonstrate a progressive increase in dip from 24 in the north to 60 in the south.
Features commonly attributed to thin- and thick-skinned tectonic models are observed in both domains, therefore it is not appropriate to describe the observed deformation as one of the two end members. In addition, the structures are inferred to have undergone at least two stages of inversion, irrespective of dip. This is not predicted by either end-member model. (c) 2006 Elsevier Ltd. All rights reserved.
DP was funded by a Natural Environment Research Council (NERC) Industrial CASE studentship with partners CASP, and CASP are also thanked for covering the cost of fieldwork. DP would like to thank Peter McFadzean for his assistance in the field. We also gratefully acknowledge Petroleum Agency South Africa for access to 2D seismic and well data and in particular David Broad and Ian McLachlan for facilitating data release and support of the project. Two anonymous reviewers are thanked for their constructive comments and helpful reviews. We are very grateful to Midland Valley for providing the 2D Move software license. The University of Edinburgh's seismic interpretation facilities, using Schlumberger GeoQuest IESX software, were funded by the Centre for Marine and Petroleum Technology, Esso, Norsk Hydro and Shell. Computing support was provided by James Jarvis and Chris Place.
- thin-skinned tectonics
- thick-skinned tectonics
- fault reactivation
- structural inversion South Africa
- Cape fold belt
- fault propagation folds
- balanced cross sections
- Karoo basin