Geology of Australia

The geology of Australia is very special because it has almost every kind of rock you can think of. These rocks tell stories that go back more than 3.8 billion years—some of them are among the oldest on Earth! Australia is a large landmass, called a continent, that sits on the Indo-Australian plate. This makes Australia unique and full of amazing tales from the very start of Earth's history. Looking at these rocks helps us understand how our planet has changed over millions and millions of years.

Components

Australia's rocks can be divided into several main groups: very old Archaean cratonic shields, Proterozoic fold belts and sedimentary basins, Phanerozoic sedimentary basins, and Phanerozoic metamorphic and igneous rocks.

Australia began to form as its own continent after the breakup of Gondwana in the Permian. It split from Antarctica in the Cretaceous. The land we see today has a thick layer of rock, more than 200 kilometres thick in the west and about 100 kilometres thick in the east. The crust is mostly made of very old Archaean, Proterozoic, and some Palaeozoic rocks, with younger sedimentary layers on top. Wind and water slowly wear these layers away, forming sand dunes, special soil types, and temporary lakes.

Blocks

Australia's continent is made up of several large blocks of very old rocks. These include the Yilgarn craton, the Pilbara Craton, and the Gawler craton along with the Willyama Block. These blocks are surrounded by other rock formations and basins such as the Musgrave Block, the Arunta Block, and the Gascoyne Complex along with the Glengarry and Bangemall Basins.

Geologic history

The geologic history of Australia is very long, from the Archaean to today. Australia grew from west to east. Rocks from the Archaean are mostly in the west. Rocks from the Proterozoic are in the centre. Rocks from the Phanerozoic are in the east. Recent events include earthquakes, as Australia is far from plate boundaries.

Australia’s landmass was part of all major supercontinents, especially Gondwana. This helps scientists compare it with Africa and Antarctica. Australia separated from Antarctica beginning in the Permian and continuing through the Cretaceous.

There are three main very old areas called cratons in Australia: the Yilgarn, the Pilbara and the Gawler cratons. These cratons came together to form Australia from very early times up until around 1,600 million years ago.

The main way these cratons came together was through events like the Glenburgh Orogeny. This joined the Yilgarn and Pilbara cratons. Other events helped connect different parts of Australia.

In the Mesoproterozoic, very old rocks formed in Tasmania. During the Neoproterozoic, large areas of sediment built up in basins across central and southern Australia.

Paleozoic

The Paleozoic era in Australia was a time of big geological changes.

During the Cambrian period, deepwater sediments formed in places like Victoria and New South Wales, and big flood basalts erupted in Western Australia.

In the Ordovician period, mountains formed in New South Wales and deepwater sediments were in Victoria and eastern New South Wales.

During the Silurian period, much of western and central Australia was dry land, but there were rivers along the far west coast and volcanoes in the east.

The Devonian period had warm conditions with reefs in the Great Sandy Desert and the first known Australian land plant, Baragwanathia longifolia].

In the Carboniferous period, Australia moved into parts of what are now South America and New Zealand, forming high mountains that have since worn down. This time also had a big ice age that covered much of the continent in ice.

Mesozoic

The time from the Permian to the Triassic periods in Australia had big geological changes. Subduction zones formed along the east, part of the Hunter-Bowen Orogeny. This made arcs, zones, and basins.

In Western and Central Australia, mountains like the Petermann Ranges were worn down by ice. This made thick layers of marine and river deposits, including limestone with fossils. Australia began moving away from India and Africa, making rift basins and half-grabens in places like the Perth Basin. Oil formed in places such as the Swan Coastal Plain and Pilbara.

The Jurassic period in western Australia had a tropical climate. Australia moved away from Antarctica, forming basins in Victoria and offshore areas of South Australia and Western Australia. These basins have oil and gas. Coal basins formed in north central Queensland, and marine sediments built up in the Perth Basin.

The Cretaceous period saw Australia and Antarctica moving apart, with Tasmania breaking away. Volcanism happened off the coast of Queensland, making the Whitsunday Islands and coral platforms. Sedimentation continued in the Surat Basin and the Perth Basin.

Palaeocene to Recent

Tertiary

The Tertiary period ended most tectonic activity in Australia. There were a few examples of volcanic activity from this time. For example, the Glasshouse Mountains in Queensland are small volcanic hills. Near the coast of eastern Victoria, there is a deep underwater valley called the Bass Canyon. There are also very recent volcanic areas, such as the Newer Volcanics in South Australia and Victoria.