Structural sequence in the metamorphosed Precambrian Rocks of the Frankland and Wilmot Ranges, south-western Tasmania

Abstract

Four groups of deformational events are recognised in the low grade Precambrian quartzite and phyllite of the Frankland and Wilmot Ranges. The rocks generally show the presence of a penetrative D foliation with associated folding.D3 folds are the most pronounced structures occurring on all scales in all lithologies and control the present attitude of the earliest foliation. Steeply inclined foliations are the rule. D2 structures are variable; some inter-foliated quartzite/phyllite zones display strong F2 and S2 (a crenulations foliation) whereas these may be totally lacking in the same material, particularly to the south. The few mesoscopic F2 folds in zones of massive quartzite layers involve localised rotation of S1. D4 structures only occur on a minor scale with little cleavage development. All D1-4 structures have been rotated by a major wrench system thought to have operated during the Cambrian which accounts for the swing of the main quartzite ridges from N/S to E/W.