Average orogenic strain rates may be calculated when it is possible to date mica cleavage or syndeformational veins and estimate finite strain. Deformation of accretionary-style thrust sheets in the western Lachlan Orogen occurred by chevron folding and faulting over an eastward propagating décollement. Based on ⁴⁰Ar/³⁹Ar dates of white micas, which grew below the closure temperature, this deformation started ca. 457 Ma in the west and ended ca. 378 Ma in the east, with apparent “pulses” of deformation ca. 440, 420, and 388 Ma. The ⁴⁰Ar/³⁹Ar data from thrust sheets in the Bendigo structural...