Modelling the Witwatersrand basin: a window into neoarchaean-palaeoproterozoic crustal-scale tectonics

Abstract

The aim of this study was to investigate and evaluate the 3D structural architecture around the Vredefort dome in the Witwatersrand basin, in particular the unexposed southern portion. This was done in order to establish strato-tectonic relationships, first order deformation structures, and basement architecture. The outcomes provide a more detailed architecture around the central uplift that may be used in future work aimed at examining the nature of giant terrestrial impacts. In summary, the integration of borehole, surface mapping, and 2D reflection seismic data provides a well constrained 3D geological model of the dome, central uplift, and adjacent areas (covering approximately 11600 km2). Seven structural features are discussed from the 3D modelling results. These include, (1) a normal fault in the lower West Rand Group, (2) an undulate, normal faulted truncation plane, constrained as post-West Rand Group and pre or early-Central Rand Group, (3) a truncation plane and local enhanced uplift constrained as pre to syn-VCF, (4) a listric fault system, constrained as post-Klipriviersberg Group and syn-Platberg Group, (5) a truncation plane, constrained as syn-Black Reef Formation, (6) folds, including a large asymmetric, gentle anticline here named the Vaal Dam Anticline, constrained as post-Magaliesberg Formation and pre-Vredefort impact, and (7) a listric fault across the southeastern margin of the Vredefort dome, constrained as late to post-central uplift formation. The findings support previous work by Tinker et al. (2002), Ivanov (2005), Alexandre et al. (2006), Dankert and Hein (2010), Manzi et al. (2013), Jahn and Riller (2015), and Reimold and Hoffmann (2016). However the findings oppose various parts of previous work by Friese et al. (1995), Henkel and Reimold (1998), and Reimold and Koeberl (2014). A new term is also proposed for the periclinal folds located around the central uplift, i.e., impact-type curvature-accommodation folds. This study demonstrates the importance of integrating multiple sources of data into a single 3D spatial environment in order to better refine and distinguish impact-related deformation from the pre-existing basement architecture.