Abstract
D.Phil. (Geology)
The structural history and mechanisms of bedding-parallel
faulting associated with the Ventersdorp Contact Reef (VCR) on the
Kloof Gold Mine are discussed. Pre-VCR deformation is determined
by folding of the Booysens Shale Formation and the Turffontein
Subgroup. Extension of Ventersdorp age (± 2700 Ma) probably took
place by the simultaneous operation of normal, strike-slip and
oblique slip faults (mixed-mode extension). Because the strikeslip
and oblique-slip faults were extensional, they could be
utilised as conduits for dykes, forming "Fault and Dyke Zones".
Northwestward directed thrusting, which postdates the normal
faulting, resulted in positive inversion. The thrust faults have a
ramp-flat symmetry with ramps forming in the VCR horizon and the
overlying Alberton Formation and flats forming in the underlying
Booysens Shale Formation and along the contact between the VCR and
the Alberton Formation. The thrust faults follow complex
deformation paths, indicated by out-of-sequence thrusting,
simultaneous folding and thrusting, underthrusting and compressed
boudins. Hanging-wall ripouts, which can be related to this thrust
event, are introduced as a shear sense indicator. No northwestward
verging thrust faults of post-Transvaal age (post 2430 Ma) could
be identified, indicating that this compressional event occurred
prior to the deposition of the Black Reef Quartzite Formation.
The minimum amount of shortening due to northwestward directed
thrusting was estimated as 37 % with the help of restored
sections. However, due to the out-of-sequence propagation of
thrust faults, a control of the strain estimation was possible and
true shortening probably exceeded the calculated amount of
shortening considerably. The restoration of sections with out-of sequence
thrusts is discussed in detail. Sheath fold-like
structures in pseudotachylyte can be related to northwestward
directed thrusting and are introduced as a new shear sense
indicator.