Timing of Slaty Cleavage During Folding of Precambrian Rocks, Northwest Tasmania

Abstract

Detailed analysis of folds and cleavage in five small areas in the Precambrian Burnie Quartzite and Slate near Sulphur Creek, in northwest Tasmania, reveals that slary cleavage can be interpreted as an essentially planar structure initiated in a short interval during protracted folding. Cleavage initiated late during folding appears to be largely superimposed on fold profiles, and where rotation of early folds occurs during folding, cleavage may cut across the profile from one limb to the other. Cleavage initiated partway through folding is refracted in sandy beds forming cleavage fans. The largest cleavage-fan angles develop in folds where cleavage is initiated early in folding. Geometrical relations show that, for the area as a whole, either the onset of folding or the initiation of slaty cleavage was diachronous.