Cenozoic structural evolution of the Mount Lofty Ranges and Flinders Ranges, South Australia, constrained by analysis of deformation bands

Abstract

The presence of deformation bands in Upper Cretaceous–Pleistocene sediments of the St Vincent and Lake Eyre basins, South Australia supports the occurrence of intraplate normal and reverse faulting in this region throughout the Cenozoic. Current tectonic models for the development of this region lack structural evidence and underestimate the role and influence of extensional tectonics in the Cenozoic tectonic evolution of the Mount Lofty Ranges and Flinders Ranges. This lack of understanding has resulted in poor structural and chronological constraints of the regions paleostress models. For the first time, we use detailed mapping and structural analysis of deformation bands across different chronostratigraphic units to identify variations in paleostress. Deformation bands are discrete, measurable strain features that develop readily in clastic sedimentary rocks in response to regional stress. We present a comprehensive structural analysis of five study sites across six chronostratigraphic units adjacent to the Mount Lofty Ranges and Flinders Ranges. Here, we have recorded 737 cataclastic and dilation bands and 397 fractures adjacent to reactivated Cenozoic faults, which reveal step changes in structural sets, identifying temporal constraints for our paleostress model. Our analysis supports the notion of a regional late Miocene shift in the paleostress regime from N–S extension to N–S compression, followed by a rotation of the maximum horizontal stress (σ H ) from NW–SE to E–W. This coincides with a well-documented pulse of late Miocene–Pliocene compression and uplift observed throughout southeastern Australia. Our results indicate that deformation bands are a useful resource for constraining discrete changes in local stress regimes and enhance our understanding of dynamic intraplate strain accommodation within the Mount Lofty Ranges and Flinders Ranges. These have proven useful for hydrocarbon and mineral exploration in neighbouring Otway Basin and Gippsland Basin.