Timing of Mesoproterozoic tectonic activity in the northwestern Gawler Craton constrained by 40Ar/39Ar geochronology

An array of northeast-trending shear zones in the north-west Gawler Craton of South Australia has been implicated in widely disparate Proterozoic continental reconstructions. These shear zones are interpreted to have formed in response to sinistral transpression, and dissect the north-west Gawler Craton into several geological domains, each with contrasting metamorphic histories. New 40Ar/39Ar data provide age constraints for movement along these shear zones, and are interpreted to indicate that the Karari, Tallacootra and Coorabie Shear Zones were last active at ∼1450 Ma. Despite distinct differences in metamorphic grade, the various geological domains bounded by shear zones exhibit evidence for commonality in event histories prior to deformation at ∼1450 Ma, albeit at different crustal levels. This is interpreted to indicate that deformation at ∼1450 Ma was responsible for reshuffling of crustal blocks that were already adjacent, rather than amalgamation of exotic terranes. The new data also provide additional evidence for a widespread metamorphic and deformational event at ∼1530–1550 Ma across the north-western Gawler Craton. The timing of deformation at ∼1450 is ∼100 Ma younger than suggested in several published tectonic reconstructions and, importantly, is also significantly older than Grenvillian-age tectonism in adjacent provinces to the west and north.