Geology of Australia

The geology of Australia is very special because it includes almost every kind of rock you can imagine, covering more than 3.8 billion years of history. Some of the rocks here are among the oldest on our whole planet! Australia is a big landmass, called a continent, that sits on something called the Indo-Australian plate. This makes the land of Australia unique and full of amazing stories from the very beginning of Earth's history. Studying these rocks helps us learn about how our planet has changed and grown over millions and millions of years.

Components

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

Australia started to form as its own continent after the breakup of Gondwana in the Permian. It separated from Antarctica in the Cretaceous. The landmass 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 mainly made of very old Archaean, Proterozoic, and some Palaeozoic rocks, with younger sedimentary layers on top. These layers are slowly being worn away by wind and water, creating 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 made of strong and changed rocks, the Arunta Block with its special types of rocks, and the Gascoyne Complex along with the Glengarry and Bangemall Basins.

Geologic history

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

Australia’s landmass was part of all major supercontinents, especially Gondwana, which 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 were put 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, which 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 great geological change. 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, mountain-building events created serpentinite belts in New South Wales and deepwater sediments in Victoria and eastern New South Wales.

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

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

In the Carboniferous period, Australia collided with parts of what are now South America and New Zealand, forming high mountains that have since eroded. This time also saw a major ice age that covered much of the continent in ice.

Mesozoic

The time from the Permian to the Triassic periods in Australia was marked by important geological changes. Subduction zones formed along the eastern edge of the landmass, part of an event called the Hunter-Bowen Orogeny. This event included the formation of arcs, subduction zones, and sedimentary basins.

In Western and Central Australia, large mountain ranges like the Petermann Ranges were worn down by glacial activity. This created thick layers of marine and river deposits, including fossil-rich limestone. During this time, Australia began to drift away from India and Africa, forming rift basins and half-grabens in areas like the Perth Basin. Oil formed in places such as the Swan Coastal Plain and Pilbara due to conditions in rift valley lakes.

The Jurassic period in western Australia had a tropical climate, shown by weathering patterns still seen today in the Yilgarn craton. Australia started moving away from Antarctica, forming basins in Victoria and offshore areas of South Australia and Western Australia. These basins hold important oil and gas deposits. Coal-bearing basins formed in north central Queensland, and marine sediments continued to build up in the Perth Basin.

The Cretaceous period saw Australia and Antarctica continuing to separate, with Tasmania breaking away. Volcanism occurred off the coast of Queensland, leading to the formation of the Whitsunday Islands and coral platforms. Sedimentation continued in the Surat Basin and the Perth Basin.

Palaeocene to Recent

Tertiary

The Tertiary period marked the end of most tectonic activity in Australia. There are a few examples of volcanic activity from this time. For example, the Glasshouse Mountains in Queensland are small volcanic hills that get younger as you move south. Near the coast of eastern Victoria, there is a deep underwater valley called the Bass Canyon, which may have formed as far back as the Eocene period. There are also very recent volcanic areas, such as the Newer Volcanics in South Australia and Victoria, which include ancient lava flows and volcanic craters known as maars.