The Red Rock Fault zone (northeast New South Wales): kinematics, timing of deformation and relationships to the New England oroclines

Abstract

The formation of the northern part of the New England oroclines has previously been linked to dextral strike-slip faulting, but hitherto no concrete evidence has been shown to support this suggestion. We studied an exposure of a fault zone in the Red Rock headland, northeastern New South Wales, and we present here structural observations from the fault zone complemented by geochronological constraints on the timing of faulting and geochemical data that inform us on the nature of the co-seismic fluids. Our observations show evidence for dextral strike-slip faulting, with a reverse kinematic component, along a subvertical fault plane oriented NNE–SSW. Rb–Sr and 40Ar/39Ar ages from fault gouge samples indicate that brittle faulting occurred at 286.5 ± 1.5 Ma with possible reactivations at 267.0 ± 9.6 Ma and 264 ± 11 Ma. Oxygen and hydrogen stable isotope geochemistry indicates that the fluids that circulated in the fault zone were associated with a deep crustal source. Based on these results, we conclude that the Red Rock Fault zone is likely an exposed segment of a larger fault system, that was active at 288–285 Ma (Early Permian). The timing of faulting was contemporaneous with the development of the New England oroclines, raising the possibility that oroclinal bending was accompanied by strike-slip faulting. Whether faulting was associated with local deformation at the limb of the Coffs Harbour Orocline, or with a larger-scale wrench tectonic zone remains unresolved.