PART OF GONDWANA

During the Paleozoic, between 541 and 252 Ma, there was no Australia as it is known today. The present Australia was just a segment of eastern Gondwana embedded in continental crust of much larger extent within a single tectonic plate. Australia was continuous with Antarctica to the south and India to the west. Continental crust now embedded in Asia adjoined present Australia to the northwest. For most of the Cambrian the eastern Gondwanan margin that included Australia faced deep ocean built by seafloor spreading following the breakup of the supercontinent Rodinia, in the late Proterozoic (see Chapter 4). Contemporary research indicates that Tasmania was a separate microcontinent located in the ocean beyond Australia and independent in its history. In proto-Australia's northern part, stretching eastwards from the Kimberley region, within-plate, hotspot-related volcanism generated extensive basaltic fields.

However, in the late Cambrian, at about 500 Ma, the plate geometry changed. From that time onwards through the Paleozoic the ocean-facing part of eastern Gondwana, including the Australian segment, lay close to a convergent plate boundary, with the Paleo-Pacific Ocean floor being consumed by subduction (see Figure 5.1). As a consequence, eastern Australia was transformed into an active continental margin characterised by magmatism, the accumulation of very large-scale sedimentary systems and mountain building. Changing stress regimes along the margin reflected contrasting episodes of plate boundary advance characterised by crustal compression, widespread thickening and mountain building, and by plate boundary retreat characterised by crustal extension, widespread thinning and sedimentary basin formation (see Chapter 5).