Deformation character and palaeo-fluid flow across a wrench fault within a Palaeozoic subduction–accretion system: Waratah Fault Zone, southeastern Australia

Mélange formation, cataclasis, meso- to micro-scale faulting, and veining reflect faulting processes within turbidite and limestone sequences juxtaposed along a steeply dipping, sinistral wrench-fault zone in the Lachlan Orogen, southeastern Australia. Fault damage occurs across a zone up to 600 m wide. Effects of faulting in the turbidites are shown by a 100–150 m wide zone of scaly mudstone-matrix mélange, mud-injection `dykesʹ and veinlets, and refolding of mélange fabrics, with minor subsidiary brittle-faulting and cataclasis extending up to 500 m from the major fault plane. Veining and cataclastic zones occur in the limestone and are most pronounced up to 100 m from the main brittle fault. Fluid inclusion data from quartz and calcite veins suggest faulting took place at temperatures between 160 and 200°C, whereas folding is inferred to have taken place at temperatures above 300°C. Fluid-assisted, fault zone `weakeningʹ mechanisms (pressure solution/solution transfer) were active over the whole fault zone. Veining, characteristic of fluid-assisted fault zone `strengtheningʹ processes (i.e. rock-mass cementation), is confined to the limestone sequence. Here, calcite precipation led to fault rocks with lower porosity and permeability than in the turbidite sequence. Overprinting between different veins and fractures, and zonation in vein cement suggest cyclic deformation and fluid flow. The repeated change between brittle fracturing and veining/cementation led to a combined conduit–barrier system in the limestone sequence, whereas the mélange zone in the turbidites acted as a fluid conduit only.