Synchronous development of Type 2 and Type 3 fold interference patterns: evidence for recumbent sheath folds in the Allendale Area, Broken Hill, NSW, Australia

Synchronous development of Type 2 and Type 3 fold interference patterns occur in the poly-deformed Broken Hill Inlier. The interference patterns have resulted from the superposition of recumbent F2 folds and ∼N–S-oriented upright F3 folds. The synchronous development of Type 2 and Type 3 fold interference patterns is attributed to variation in the hinge of F2 folds by as much as 90°, suggesting the development of a regional-scale sheath-like fold geometry during D2. Overprinting relationships along the eastern limb of the Pap Synform suggests that it formed part of a recumbent fold hinge that was flattened during horizontal crustal shortening. This has resulted in the development of a modified Type 3 fold interference pattern. The results of this study show that the Type 2 and Type 3 fold interference patterns can develop during the same deformation event in an evolving orogen.