1.8-1.5 GA ACCRETIONARY TECTONICS ALONG THE SOUTHERN MARGIN OF THE AUSTRALIAN CONTINENT: IMPLICATIONS FOR PALAEOPROTEROZOIC PLATE RECONSTRUCTIONS OF AUSTRALIA AND LAURENTIA

The tectonic evolution of the Australian continent during the interval ca 1.8-1.5 Ga was largely controlled by southward continental growth associated with episodic accretion of small-scale continental fragments onto the southern margin of the North and West Australian Cratons. The record of this accretion is recorded in the ca 1.79-1.78 Yamba Event, ca 1.74-1.70 Ga Kimban/Strangeways events, ca 1.65-1.64 Ma Leibig/Early Kararan events, and the ca 1.57-1.54 Ga Late Kararan Event. In between these events were episodes of magmatism typical of modern plate margins at ca 1.78 Ga, 1.69-1.67 Ga, and ca 1.62 Ga, which formed in the overriding plate of a north-dipping subduction zone. Intracontinental basins in the overriding plate also record the distal effects of the accretion, resulting in basin reactivation and the transient basin inversion events. Reconstructions of Australia and Laurentia during the Early Proterozoic have relied on correlating a number of tectonic elements of similar ages between the two continents. For example, the Kimban and Kararan orogenies preserved on the margin of the Gawler Craton appear to correlate with the Yavapai and Mazatzal orogenies respectively. The Early Proterozoic basins of the North Australia Craton may have correlative basins in the Wernecke Mountains and throughout Colorado and Arizona. This coincident evolution strongly supports the notion that the two continents may have been fellow travellers between ca 1.80-1.66 Ga. However, following this time there tectonic histories appear to diverge. For example, the Australian continent records a major basin forming event termed the Isa Superbasin (1.67-160 Ga), which appears to be absent from the geological record in Laurentia. Moreover, a large felsic igneous province evolved throughout the Gawler Craton and the Curnamona Province in response to the interaction between a plume and the plate margin at ca 1.59-1.58 Ga. Magmatism of this age is rare in Laurentia. The divergence in the tectonic evolution after ca 1.66 Ga may indicate that an ocean had formed between the continents by this time.