A NOTE ON FOLDING MECHANISMS IN THE CAPE FOLD BELT, SOUTH AFRICA

Abstract

The relationship between folding and faulting in the Cape Fold Belt has been raised as an enigma. The mineral deformation mechanisms accommodating folding are integral to the relation between faults and folds. Here I discuss field and microstructural observations of folded rocks from the Laingsburg region in the Western Cape, and the underlying mineral deformation mechanisms accommodating strain in these rocks. In competent units, deformation was dominantly accomplished by flexural slip faulting and jointing; in relatively incompetent layers macroscale flow was accommodated by dissolution-precipitation creep and distributed cataclasis. Combined with previous studies suggesting deformation occurred at lowermost greenschist facies temperatures, these observations indicate that folding in the Cape Fold Belt occurred at temperatures and pressures within the normally frictional regime. Folding and thrust fault development therefore generally occurred concurrently, and partitioning between localised and distributed deformation was governed by factors such as fluid pressure conditions, strain rate, and relative viscosity.