Damon Mcknight
Australia is a continent situated on the Indo-Australian plate, and its geology includes almost all known rock types, spanning over 3.8 billion years. The country is home to some of the world's oldest geological features, with the oldest known rocks dating back more than 3 billion years. The geology of Australia can be divided into several sections, including Archaean cratonic shields, Proterozoic fold belts, Phanerozoic sedimentary basins, and Phanerozoic metamorphic and igneous rocks. The country's landscape has been shaped by various geological events, including the assembly of cratonic blocks, volcanic activity, erosion, and the formation of mineral deposits. These rocks have contributed to Australia's economy, society, and cultural significance, offering insights into the Earth's ancient history.
| Characteristics | Values |
|---|---|
| Geology | Virtually all known rock types, spanning a geological time period of over 3.8 billion years, including some of the oldest rocks on earth |
| Rock types | Sandstone, limestone, granite, gneiss, dolomite, basalt, banded iron formation, conglomerate |
| Notable rock formations | Uluru, Kata Tjuta, Wave Rock, Devils Marbles, Remarkable Rocks, Twelve Apostles, Pinnacles |
| Economic significance | Iron ore, gold, lead, zinc, silver, copper, uranium, gas |
| Cultural significance | Rock art by First Nations Australians, sacred sites for Aboriginal people |
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What You'll Learn
- Australia's geology includes rock types like Archaean cratonic shields, Proterozoic fold belts, and sedimentary basins
- Sydney's iconic landscapes are shaped by Hawkesbury Sandstone, which also preserves indigenous engravings
- Victoria's western plains feature Australia's youngest volcanoes, while the east has the Great Dividing Range mountains
- Banded iron formations in Western Australia are layered sedimentary rocks, hosting iron ore
- Victoria's volcanoes were formed from magma, tearing and transporting chunks of the surrounding mantle rock
Australia's geology includes rock types like Archaean cratonic shields, Proterozoic fold belts, and sedimentary basins
Australia's geology includes virtually all known rock types, spanning a geological time period of over 3.8 billion years, with some of the oldest rocks on Earth. The country's geology can be divided into several main sections, including Archaean cratonic shields, Proterozoic fold belts, and sedimentary basins.
The Archaean cratonic shields are composed of ancient, crystalline igneous and metamorphic rocks formed during the Precambrian era, over 2.5 billion years ago. These rocks are found in the western and central parts of the continent, including the Gawler craton and the Yilgarn and Pilbara cratons in Western Australia. The Gawler craton is flanked by Proterozoic orogenic belts, including the Musgrave Block and the Arunta Block. The Yilgarn and Pilbara cratons were assembled during the Glenburgh orogeny, which also exposed the Yarlarweelor Gneiss Complex. The Pilbara Craton also features banded iron formations, which are layered sedimentary rocks mainly comprised of chert and iron oxide, and are the main host of iron ore.
The Proterozoic fold belts, on the other hand, are found in southeastern Australia, represented by the polydeformed high-grade gneiss terranes of the Willyama Supergroup, Olary Block, and Broken Hill Block. These rocks record a period of widespread platform cover sedimentation and extensive phosphorite deposition in the deeper seabeds. The Palaeoproterozoic in the north of Australia includes the Mount Isa Block and complex fold-thrust belts.
Sedimentary basins are also a significant feature of Australia's geology. A thin veneer of Phanerozoic sedimentary basins covers much of the Australian landmass. These basins are undergoing erosion by aeolian and fluvial processes, forming sand dunes, laterite and saprolite profiles, and playa lakes. The Castlemaine Basin in Victoria, for example, hosts rich gold deposits that were formed as the sediments were folded and metamorphosed.
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Sydney's iconic landscapes are shaped by Hawkesbury Sandstone, which also preserves indigenous engravings
Australia's geology includes virtually all known rock types, spanning a geological time period of over 3.8 billion years, including some of the oldest rocks on Earth. The country's present-day environment, economy, and society have all been shaped by key geological events of the last 4 billion years.
Sydney, the harbourside capital of New South Wales, is a city founded and excavated in sandstone, partly built with sandstone materials, and set in a sandstone-dominated landscape. Sandstone is the principal rock type in the Sydney Basin, making up more than half of the sedimentary sequence, and the most prominent formation is called the Hawkesbury Sandstone. This rock type forms prominent cliffs along the northern beaches of Sydney and shapes the city's iconic landscapes.
Hawkesbury Sandstone is a quartz-rich sedimentary rock named after the Hawkesbury River north of Sydney, where this sandstone is particularly common. It forms the bedrock for much of the region of Sydney, Australia, and its durable quality is the reason many Aboriginal rock carvings and drawings in the area still exist. The soft sandstone is relatively easy to carve but also weathers easily, requiring generations of First Nations artists to maintain and refresh the engravings. These rock art sites are significant to First Nations people, providing important links to their past and their living culture.
Sydney's sandstone buildings, such as Sydney Hospital, the Queen Victoria Building, Sydney Town Hall, the Australian Museum, St. Mary's Cathedral, and the Art Gallery of New South Wales, are described by architects as "wonderful". Sandstone has also provided much of Sydney's 19th-century water supply, and it is used as a contemporary building material in major constructions and restorations.
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Victoria's western plains feature Australia's youngest volcanoes, while the east has the Great Dividing Range mountains
Australia's geology includes almost all known rock types, spanning over 3.8 billion years of geological history. The continent is situated on the Indo-Australian plate, and its geology can be divided into several sections: Archaean cratonic shields, Proterozoic fold belts and sedimentary basins, Phanerozoic sedimentary basins, and Phanerozoic metamorphic and igneous rocks.
Victoria's western plains feature Australia's youngest volcanoes. The Newer Volcanics Province, stretching from Melbourne in the east to Mount Gambier in the west, is home to over 400 volcanoes. The majority of these produced extensive lava flows, particularly in the Western Plains district of Victoria. The most recent eruption in this province was around 4,000 to 5,000 years ago, making it one of the youngest volcanic regions in Australia. Mount Gambier, which last erupted 5,000 years ago, is considered Australia's youngest volcano. It produced eruption plumes of about 10 km in height and a large volume of magma over a short period.
The western plains of Victoria are dotted with small hills and circular lakes, which are remnants of these geologically young volcanoes. Mount Elephant, a 240-metre-tall conical breached scoria cone, is the tallest scoria cone in this region. The Budj Bim Cultural Landscape, a World Heritage Site in western Victoria, is another notable volcanic feature. It is home to the world's oldest known aquaculture system, built by the Gunditjmara people over 6,000 years ago near the Budj Bim volcano.
In contrast to the western plains, Victoria's east features the Great Dividing Range mountains. This mountain range is part of the Proterozoic fold belts that make up a significant portion of Australia's geology. The Great Dividing Range extends from northern Queensland, through New South Wales, and into Victoria, forming the eastern highlands. While not as prominent as the western volcanoes, this mountain range contributes to the varied topography of Victoria.
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Banded iron formations in Western Australia are layered sedimentary rocks, hosting iron ore
Australia's geology includes rock types that span a geological time period of over 3.8 billion years. The country's landmass is composed of a thick subcontinental lithosphere, with the western two-thirds being over 200 kilometres thick and the younger eastern third being 100 kilometres thick. The continental crust is primarily composed of Archaean, Proterozoic, and some Palaeozoic granites and gneisses.
Banded iron formations (BIFs) are layered sedimentary rocks that consist of alternating layers of iron oxides and iron-poor chert. They are typically several hundred meters in thickness and extend for several hundred kilometers. BIFs are extremely hard, tough, and dense, making them highly resistant to erosion. They are found in all states of Australia, with Western Australia accounting for 90% of the country's iron ore. The banded iron formations of the Hamersley Province in the Pilbara region of Western Australia are the thickest and most extensive rocks of this type globally.
The formation of BIFs is associated with the oxygenation of the Earth's oceans. They are thought to have formed in seawater due to the production of oxygen by photosynthetic cyanobacteria. The oxygen combined with dissolved iron in the oceans to create insoluble iron oxides, which precipitated and formed layers on the ocean floor. These layers, or bands, consist of iron-rich and silica-rich sediments, creating bands of light and dark.
The iron-rich sediments of BIFs are granular to oolitic, forming discrete grains about a millimeter in diameter. They lack microbanding in their chert mesobands and exhibit more irregular mesobanding, with indications of ripples and other sedimentary structures. These features suggest a higher-energy depositional environment, such as shallower water disturbed by wave motions.
The Pilbara region, where BIFs are found, also contains fossilized remnants of marine communities called stromatolites, built up by cyanobacteria. These early photosynthetic organisms contributed to the formation of iron-rich sediments, which now provide a significant portion of Australia's export income.
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Victoria's volcanoes were formed from magma, tearing and transporting chunks of the surrounding mantle rock
Australia is not typically known as a "land of volcanoes", but the country does have many dormant and extinct volcanoes that run up its east coast. Victoria's volcanoes, in particular, were formed from magma, tearing and transporting chunks of the surrounding mantle rock.
Volcanoes are most commonly found at geologically active boundaries, specifically at divergent and convergent plate boundaries. At these sites, tectonic plates move apart from each other, and magma continuously moves up from the mantle into the boundary, building new plate material on both sides of the plate boundary. As the denser plate edge moves downward, the pressure and temperature surrounding it increase, causing changes to the plate that melt the mantle above. The melted rock then rises through the plate, sometimes reaching the surface in the form of a volcano.
The process of magma formation is crucial to understanding the geology and morphology of the mantle. The presence of magma is due to differences in temperature, pressure, and structural formations in the mantle and crust. Magma forms when rock melts due to lower melting points in areas of lower pressure. This reduction in overlying pressure, or decompression, allows the mantle rock to melt.
Volcanoes are connected to a reservoir of molten rock, called a magma chamber, below the Earth's surface. The molten material is called magma when it is underground and lava when it is on the surface. Over millions of years, the rising magma can create a series of volcanoes known as a volcanic arc.
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Frequently asked questions
The oldest known rocks in Australia date from more than 3 billion years ago, with rare zircon crystals dating back 4.4 billion years. The zircons are thought to have evolved shortly after the formation of the planet.
The geology of Australia includes almost all known rock types, spanning over 3.8 billion years of geological time. The country's rock types include granite, gneiss, sandstone, limestone, and basalt.
Australia has some of the world's most recognisable rock formations, including Uluru, Kata Tjuta, Wave Rock, the Pinnacles, and the Devils Marbles. Uluru, formerly known as Ayers Rock, is a massive sandstone rock laid down in an inland sea around 500 million years ago. Kata Tjuta, or The Olgas, is a group of 36 domed conglomerate rock formations, which are culturally significant to Aboriginal people. Wave Rock, located in Western Australia, is a granite formation shaped like a giant ocean wave, standing at 15 metres high and stretching 110 metres long.
