Thermal evolution of the Redbank thrust system, central Australia: Geochronological and phase‐equilibrium constraints

Abstract

We constrain the thermal history of the Redbank thrust in central Australia by reviewing and substantially expanding on a small set of thermobarometric and field data, 40Ar/39Ar hornblende and biotite ages as well as chemical Th‐U‐Pb monazite and xenotime ages. Metamorphic PT data indicate peak conditions between 620°C and 800°C and between ∼6 and 8 kbar within the thrust system. For at least 50 km north of the thrust system (hanging wall) peak metamorphic conditions are fairly uniformly around ∼850°C and 10 kbar. The geochronological data are interpreted to indicate that these PT conditions were reached around 1780 Ma (Strangways Orogeny) north of the Redbank thrust zone and between around 1680 and ∼1600 (Argilke and Chewings tectonic events). Major cooling below or reheating up to 500°C of the entire region occurred around 1140 Ma (Teapot event). However, initial 40Ar/39Ar ages of biotites within and north of the thrust zone define the initiation of (re)activation along the Redbank thrust around 420 Ma. In combination we interpret the data to indicate exhumation of the thrust system from near 20 km to the surface between 420 Ma and 320 Ma. Recent authors have shown that exhumation processes like that described for the Redbank thrust here may have a substantial influence on the occurrence of intraplate orogeny by truncating a highly radioactive upper crust. Thus, our data may help to constrain the nature of intraplate orogeny in central Australia.