Terra Australis Orogen

The Terra Australis Orogen (TAO) was a long-lived, active continental margin that formed along the southern edge of the supercontinents Rodinia and later Pannotia (also known as Greater Gondwana) from the late Neoproterozoic into the Paleozoic. This accretionary orogen extended roughly 18,000 km (11,000 mi) and, in the ancient paleogeographic frame, included regions that today make up the Andean margin of South America, the South African Cape, West Antarctica, Victoria Land in East Antarctica, Eastern Australia, Tasmania, and New Zealand. The orogen’s development began with the breakup of Rodinia at the end of the Neoproterozoic and the opening of the paleo-Pacific Ocean, Panthalassa. It eventually gave way to the Gondwanide orogeny during the assembly of Pangea in the middle Paleozoic.

The TAO originated in the Neoproterozoic and Paleozoic, with its activity declining in the late Paleozoic as Pangea came together. Unlike many orogens, it did not end through a continental collision; instead, it was succeeded by the Gondwanide orogeny. Spanning about 18,000 km (11,000 mi) in length and up to 1,600 km (990 mi) in width, it ranks among Earth’s longest and most enduring active continental margins, active from the breakup of Rodinia onward. Its evolution involved alternating phases of extensional back-arcs and compressional events, the latter occurring when the subducting oceanic plate became lodged in Gondwana’s margin. As Gondwana assembled during the early Paleozoic Pan-African orogenies, the TAO propagated along the supercontinent’s southern (modern coordinates) Proto-Pacific/Iapetus margin. Orogenic activity ceased around 300 to 230 Ma with the Gondwanide orogeny. This and younger orogens now cover most of the TAO’s outboard edge, while its inboard margin is largely buried under younger sediments and ice, though it remains exposed in Australia along the Torrens Hinge Line or Delamarian orogeny. One end of the TAO consisted of a series of terranes (Avalonia–Carolina–Cadomia) that rifted from western Gondwana and later attached to Laurentia in the late Paleozoic; its other end likely extended past Australia into New Guinea. In 1937, Alexander du Toit proposed the Samfrau Orogeny as evidence for Gondwana, a concept that includes orogenies of West Gondwana and events now considered separate, but excludes those of East Gondwana.