The history and tectonic implications of the Redbank Thrust Zone, central Australia, based on structural, metamorphic and Rb‐Sr isotopic evidence

Abstract

The Redbank Thrust Zone in the Proterozoic Arunta Block is a complex thrust zone separating the Central and Southern Arunta Provinces, which differ in their lithology and seismic reflection image as well as structural, metamorphic and geochronological histories. New structural evidence and Rb‐Sr isotopic dating indicates that hydration, accompanying mylonitization during thrusting, occurred at 1500–1400 Ma and again between 400 and 350 Ma. The intervening period was characterized by overall crustal stability except for: (1) a tectonothermal event centred in the Southern Arunta Province, during which 1140 Ma pegmatite locally cuts the 1500–1400 Ma shear zones in the Central Arunta Province; (2) slow episodic intracratonic basin formation between 900 and 400 Ma. Insights into the tectonic significance of the 1500–1400 Ma megashearing can be gained by comparison with the 400–350 Ma thrusting event, which is better understood as it has not been overprinted by later events. Thrusting on the Redbank Thrust Zone at 400–350 Ma was part of widespread crustal shortening during the 400–300 Ma Alice Springs Orogeny inferred to result from propagation of large horizontal compressive stresses through the Australian plate and their focusing at a pre‐existing intracratonic province boundary. The megashearing at 1500–1400 Ma is analogous to that of thrusting at 400–350 Ma in that the older shears were of comparable dip, were subparallel in orientation to the younger thrusts and involved crustal shortening of similar horizontal and vertical magnitude. These relationships suggest that high compressive stresses were also focused at the same crustal boundary at 1500–1400 Ma when it was near the leading edge of the substantially cratonized North Australia Orogenic Province.