SOUTHWARD GROWTH OF AUSTRALIA IN THE PALAEO- AND MESOPROTEROZOIC - ACCRETIONARY MARGIN OF A PRE-RODINIAN SUPERCONTINENT?

Following a period of rapid continental amalgamation (ca 1.9-1.8 Ga) an ocean-continent convergent margin developed along the southern edge of the North Australian Craton and persisted until at least 1.6 Ga. The margin (incorporating an ~1500 km wide section of the overriding plate) was dominantly in extension with transient periods of shortening corresponding to accretion of the West Australian Craton (ca 1.80-1.79 Ga) and the Gawler Craton and its extensions in Antarctica (ca 1.74-1.71 Ga). The margin was characterised by sedimentary and magmatic reworking of Archaean and Palaeoproterozoic crust with a lesser component of juvenile material added by a comibination of mafic underplating (more distal to the margin) and arc-magmatism (more proximal to the margin). We propose that this was one of a number of long-lived external orogenic belts, including the Yavapai/Mazatzal, Transcandinavian and western Amazonides, that (inevitably?) developed on the margin of a Palaeo- to Mesoproterozoic supercontinent, the nucleus of which amalgamated between 1.9 and 1.8 Ga. These external belts are comparable to the long-lived accretionary margins of Gondwana in the Paleozoic or Eurasia in the Mesozoic. (Although the specific processes acting within the belts, for example the relative importance of continental reworking compared to the addition of juvenile material, may have varied through time.) If there was a pre-Rodinian supercontinent then external orogenic belts of this type are excellent pinning points upon which to reconstruct it because they should form a semi-continuous belt with consistent polarity - younging toward the paleo-ocean.