Geology of Australia

Lying on the Indo-Australian Plate, the mainland of Australia is the lowest and most primordial landmass on Earth with a relatively stable geological history. The landmass includes virtually all known rock types and from all geological time periods spanning over 3.8 billion years of the Earth's history. The Pilbara Craton is one of only two pristine Archaean 3.6–2.7 Ga (billion years ago) crusts identified on the Earth.

Having been part of all major supercontinents, the Australian continent began to form after the breakup of Gondwana in the Permian, with the separation of the continental landmass from the African continent and Indian subcontinent. It separated from Antarctica over a prolonged period beginning in the Permian and continuing through to the Cretaceous. When the last glacial period ended in about 10,000 BC, rising sea levels formed Bass Strait, separating Tasmania from the mainland. Then between about 8,000 and 6,500 BC, the lowlands in the north were flooded by the sea, separating New Guinea, the Aru Islands, and the mainland of Australia. The Australian continent is moving toward Eurasia at the rate of 6 to 7 centimetres a year.

Basic geological regions of Australia, by age.

The Australian mainland's continental crust, excluding the thinned margins, has an average thickness of 38 km, with a range in thickness from 24 km to 59 km. Australia's geology can be divided into several main sections, showcasing that the continent grew from west to east: the Archaean cratonic shields found mostly in the west, Proterozoic fold belts in the centre and Phanerozoic sedimentary basins, metamorphic and igneous rocks in the east.

The Australian mainland and Tasmania are situated in the middle of the tectonic plate and have no active volcanoes, but due to passing over the East Australia hotspot, recent volcanism has occurred during the Holocene, in the Newer Volcanics Province of western Victoria and southeastern South Australia. Volcanism also occurs in the island of New Guinea (considered geologically as part of the Australian continent), and in the Australian external territory of Heard Island and McDonald Islands. Seismic activity in the Australian mainland and Tasmania is also low, with the greatest number of fatalities having occurred in the 1989 Newcastle earthquake.