Early Palaeozoic subduction in the southeastern Lachlan Fold Belt, Batemans Bay, New South Wales

Abstract

The southeastern Lachlan Fold Belt at Batemans Bay on the New South Wales south coast is an accretionary complex with a prolonged deformation history. Early features include synsedimentary folds, mélange, disaggregated bedding and faults. Fabrics within the clast-in-matrix mélange and mudstone match those found in cores from the lower slopes of modern accretionary prisms. At the toe of the accretionary prism, the contact between the craton-derived Adaminaby Group and ocean floor deposits of the Wagonga Group is conformable. As subduction continued, the early structures were overprinted by (D₁) deformation that produced meridional north – south-trending, tight to isoclinal folds (F₁) and associated axial-plane cleavage (S₁). This west-dipping subduction occurred in the Late Ordovician/Early Silurian but probably began much earlier. A younger regional deformation (D₂) resulted in north – south-trending, open to tight folds (F₂), slightly oblique to F₁, and an axial-surface cleavage (S₂).

Key words:

• accretion
• Adaminaby Group
• Batemans Bay
• Lachlan Fold Belt
• mélange
• subduction
• thrust faults
• Wagonga Group

Acknowledgements

This work was carried out as part of a continuing PhD program at the University of Newcastle. I thank Robin Offler who provided very useful comments on early versions of the manuscript and also thank the referees, Chris Fergusson, Dick Glen and Evan Leitch, who provided constructive criticism that improved the final manuscript.