Structural interpretation in the Mount Woods Inlier

Abstract

The Mount Woods Inlier (MWI) is an Early to Mid-Proterozoic terrane represented by numerous small scattered outcrops of metasediments and granitoids, located approximately 100 km southeast of Coober Pedy, north-central South Australia. Field mapping of three outcrops reveal the following deformation history: 1. D1/M1 was a high T, low P event that produced an S1 foliation defined by sillimanite, cordierite+/-almandine garnet (Flint and Benbow, 1977). 2. D2 produced folding on scales from microscopic crenulations of S1 to macroscopic folding of metasedimentary units over tens of km. Steep fold axes and variations in fold orientations throughout the MWI appeal to fold interference (i.e. re-folding), which probably occurred during the subsequent D3 shearing event. 3. D3 was a shearing (+ folding) event that produced discreet zones (100's m long) and a large scale shear zone (>7 km) in the Spire Hills-Skylark Hills area. Kinematic indicators such as Type I S-C mylonite fabrics suggest movement was predominantly strike-slip. The discrete shear zones appear to be the result of strain caused by dextral movement on the large scale shear zone. Dating of a foliated granitoid interpreted as syn-D1/M1 at ~1700 Ma and a granite interpreted as post-D2 and pre- to early-D3 at ~1580 Ma has constrained the timing of tectonism to within these dates. This deformation is synchronous with D3 of the Kimban Orogeny, The Olarian Orogeny, the Ernabellan deformation of the Musgrave Block, D1 of the Peake-Denison Inlier and deformation and metamorphism in the Karari Fault Zone.