And one of the largest countries on Earth, lying between the

Chronological summary

The geologic development may be summarized as follows. Archean rocks (those more than 2.5 billion years old) crop out within the two-thirds of Australia that lies west of the Tasman Line. Individual blocks of Archean rocks became embedded in Proterozoic fold belts (those from about 2.5 billion to 541 million years old) to form a mosaic. The lines of weakness within the mosaic later guided stresses that pulled the blocks apart or pushed them together. The Proterozoic fold belts that bounded the western and southern sides of the Archean Yilgarn block, for example, became the sites of the continental margin during seafloor spreading in the Mesozoic, and the fold belts of the Amadeus Transverse Zone in central Australia guided the overthrusting of blocks in the north over those in the south during the late Paleozoic.

Proterozoic Australia was part of the supercontinent of Gondwanaland, comprising India and the other southern continents, from about 750 million years ago. At the beginning of the Paleozoic, some 541 million years ago, pieces began to flake off the Australian portion of Gondwanaland when ocean basins opened around its periphery. Off the northwest, an ancient forebear of the Indian Ocean, called the Tethys, transferred continental terranes (fault-bounded fragments of the crust) from Gondwanaland to Asia; later generations of that ocean rifted material northward, including the biggest and latest terrane of India. Off the east, an ancient Pacific Ocean opened and closed in the first of a series of back-arc basins or marginal seas that persists to the present.

The structure of Australia was determined by the following: the processes that welded the Archean blocks and Proterozoic fold belts into a mosaic; the lithospheric plate processes that acted on that mosaic along lines of weakness to form ocean basins by spreading along the western and southern margins; and the processes that accompanied the convergence of the Pacific Plate, including alternating back-arc spreading and subduction that accreted the eastern third of Australia during the Phanerozoic. Australia ultimately became isolated from its Gondwanaland neighbours India and Antarctica by seafloor spreading. It was isolated from Lord Howe Rise/New Zealand by back-arc spreading that began in the Mesozoic. Today, Australia is drifting northward from Antarctica as a result of seafloor spreading in the southeast Indian Ocean and, consequently, is colliding with the westward-moving Pacific Plate to form the strike-slip ranges of New Guinea and the S-shaped fold of the Banda arcs.