Tectonic mode switches at the Australian Mesoproterozoic Boundary - tectonic events at the same scale lengths as modern tectonic systems

Interpreted time scales for Proterozoic orogenic systems suggest they developed over 10's of million to 100 million years and imply, at a first order, a relatively consistent tectonic regime (ie. crustal shortening). These time scales conflict with modern tectonic systems where: (1) individual events occur over several million years; and (2) tectonic mode switches are common, especially at convergent margins. We detail geological observations, geochronology, and geophysical interpretations from the Gawler Craton and Mount Painter Inlier to illustrate rapid changes in tectonic regime at the Paleo-Mesoproteroic boundary of eastern and southern Australia. Our data suggest that crustal shortening associated with the Wartakan Orogeny (Gawler Craton) and the Olarian Orogeny (Curnamona Province) (ca 1611-1592 Ma) was followed by a switch to crustal extension, intense magmatic activity and crustal anatexis (ca 1595-1580 Ma), and uplift in the Gawler Craton. In the Mount Painter Inlier this extensional switch is recorded by ca 1592 Ma rapid clastic sedimentation with material derived from the Gawler Craton. These sedimentary rocks were subsequently buried to mid crustal levels and exhumed in approximately 5-10 million years during the Painter Orogeny. Shallow level magmatic rocks were then emplaced between ca 1575 Ma and 1552 Ma coincident with renewed metamorphism, which possibly correlated with the Kararan Orogeny identified in the northern Gawler Craton. We suggest that rapid tectonic mode switches were prevalent in the Proterozoic and, although these likely occurred on modern time-scales, are difficult to recognise due to poor preservation of different crustal levels and complex over prints.