Lyla Lindsey
Australia's geology includes virtually all known rock types, spanning a geological time period of over 3.8 billion years. The Pilbara region of Western Australia provides a diversity of Archaean to Proterozoic igneous rocks in a relatively compact area. Igneous rocks can also be found in the Gawler Craton, the Musgrave Block, the Arunta Block, and the Gascoyne Complex. In Victoria, the western plains are pockmarked by Australia's youngest volcanoes, while the eastern state has been pushed up to form the mountains of the Great Dividing Range.
| Characteristics | Values |
|---|---|
| Location | Western Australia, South Australia, New South Wales, Queensland, Victoria |
| Specific regions | Pilbara region, Gawler Craton, Willyama Block, Musgrave Block, Yilgarn Block, Arunta Block, Gascoyne Complex, Glengarry Basin, Bangemall Basin, Glenburgh terrane, Yarlarweelor Gneiss Complex, Padbury Basin, Amadeus Basin, Great Sandy Desert, Snowy Mountains, Eden, New England, Queensland, Western Victoria |
| Age | Igneous rocks in Australia span a geological time period of over 3.8 billion years, including some of the oldest rocks on Earth |
| Types of rocks | Felsic, intermediate, granitoid, volcanic, volcaniclastic, ironstone, chert, dolomite, shale, intrusive dolerite, granite, basalt, tuff, volcanic breccia, dacite, rhyodacite, rhyolite, andesite, gabbro, pegmatitic gabbro, adamellite, monzogranite, syenogranite, granodiorite, tonalite, granophyre, mafic, ultramafic, diorite, feldspar, quartz, hornblende, amphibole, pyroxene, olivine, biotite, plagioclase, mica, phlogopite, orthoclase, leucite, feldspathoid minerals, K-Ti-richterite, priderite, wadeite, jeppeite, leucite |
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What You'll Learn
Victoria's western plains and western Victoria
Igneous rocks are formed when magma cools and solidifies. Australia's geology includes virtually all known rock types, with some of the oldest rocks on Earth. The Archaean cratonic shields, Proterozoic fold belts and sedimentary basins, Phanerozoic sedimentary basins, and Phanerozoic metamorphic and igneous rocks are the four primary divisions of Australia's geology.
In Victoria, some areas are geologically younger due to volcanic activity that last erupted a few thousand years ago. The Gippsland, Bass, and Otway Basins in Victoria were formed when Australia began to separate from Antarctica in the Cretaceous period. The Bungle Bungle Range sandstone was formed in Western Australia from river sands.
The Gawler Craton and the Willyama Block, which are of Archaean to Proterozoic age, are two of the Australian continent's primary continental blocks. The Musgrave Block, which is made of granulite gneiss and igneous rocks, and the Arunta Block, which is made of amphibolite-grade metamorphic rocks and granites, are both flanked by several Proterozoic orogenic belts and sedimentary basins.
The Yilgarn Craton, which is still preserved today, is an example of the geological history of the Australian continent, which has been long and complex, stretching from the Archaean to the present. The assembly of the Archaean Yilgarn and Pilbara cratons of Australia was initiated during the first phases of the Glenburgh orogen. The Palaeoproterozoic in southeastern Australia is represented by the polydeformed high-grade gneiss terranes of the Willyama Supergroup, Olary Block, and Broken Hill Block in South Australia and New South Wales.
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Pilbara region, Western Australia
The Pilbara region of Western Australia is known for its diversity of Archaean to Proterozoic igneous rocks, spanning a geological time period of over 3.8 billion years. Covering an area of approximately 500 km by 500 km, the Pilbara region offers a unique opportunity to study the evolution of the Earth's crust and the processes that shaped our planet in the distant past.
The igneous rocks in the Pilbara region vary in age, type, and mode of occurrence, recording a southward crustal history of igneous activity, sedimentation, early life, tectonics, and metamorphism. The Archaean Pilbara Craton, one of the oldest and most stable parts of the continental lithosphere, consists of a granitoid-and-greenstone complex. The northern part of the Pilbara Craton includes well-preserved Archean granite-greenstone terranes, providing insights into the sources of felsic magmas and the growth and evolution of the continental crust.
In the central region, there are Proterozoic sequences of volcanic rock, volcaniclastic rock, ironstone, chert, dolomite, shale, and intrusive dolerite sills and cross-cutting dolerite dykes. The Fortescue, Hamersley, and Turee Creek basins in this area feature interbedded clastic or chemical sedimentary rocks and volcanic rocks, typically aged between 2.78 and 2.42 billion years old. The Fortescue Group, in particular, contains Archean mafic-ultramafic rock samples that represent repeated and long-lived volcanic activity.
To the south, the Proterozoic shale, dolomite, and chert sequences continue, with isolated granitic batholiths. The youngest rocks in the Pilbara region are approximately 1.7 billion years old, found in the Ashburton Basin and the surface region between the Fortescue and Hamersley basins. These igneous rocks in the Pilbara region include a range of rock types such as komatiite, basalt, tuff, volcanic breccia, dolerite, gabbro, granite, andesite, dacite, rhyolite, and various granitoids.
The Pilbara region's arid climate has resulted in excellent outcrop exposure, making it a globally unique potential Precambrian igneous-rock geopark. The geological significance of the region has led to proposals for its recognition as a geopark, highlighting its importance in understanding the early geological history of the Earth.
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Tasmania
The Precambrian rocks of Tasmania form several blocks. These include King Island, Rocky Cape in the North West, Dundas Element in the mid-west, Sheffield Element in the central north, Tyennan Element in the west-central and south-west, and the Adamsfield-Jubilee Element in the south-central to the south coast.
In the Permian period, conditions were again glacial, and the Tasmania basin formed, with low sea levels in the Triassic. The continental breakup occurred in the Cretaceous and Cenozoic periods, ultimately breaking Tasmania away from Antarctica.
Around Launceston, igneous rocks were intruded into Cenozoic sediments, forming dolerite and monzonite. During the Ice Age, there was an ice cap on the Central Plateau, which was around 65 km in diameter.
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Andesite and Rhyolite volcanoes in central NSW, the Snowy Mountains, Eden, New England, and Clermont, Queensland
Australia's geology includes virtually all known rock types, with a geological time period of over 3.8 billion years. The country's geology can be divided into several main sections: the Archaean cratonic shields, Proterozoic fold belts and sedimentary basins, Phanerozoic sedimentary basins, and Phanerozoic metamorphic and
Igneous rocks are formed when magma cools and solidifies. They can be divided into four groups based on how they were formed and what they are made of. Examples of igneous rocks include andesite and rhyolite. Andesite is a volcanic rock of intermediate composition, typically found between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture and is composed predominantly of sodium-rich plagioclase, pyroxene, or hornblende. Andesite lava has a viscosity similar to smooth peanut butter, resulting in explosive volcanism that forms tuffs and agglomerates.
Rhyolite is a volcanic rock characterised by its light colour, high silica content, and richness in potassium and sodium. Rhyolitic lavas are viscous and tend to form thick blocky lava flows or steep-sided piles of lava called lava domes. Rhyolite magmas tend to erupt explosively, producing abundant ash and pumice.
While I could not find specific information on andesite and rhyolite volcanoes in central NSW, the Snowy Mountains, Eden, New England, and Clermont, Queensland, Australia does have a history of volcanism. For example, the Glasshouse Mountains in Queensland are Tertiary examples of a chain of small volcanic plugs. Cretaceous volcanism also occurred in the offshore of Queensland, typified by the Whitsunday Islands.
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The Gawler Craton and Willyama Block
The Gawler Craton is an extensive region of Archaean to Mesoproterozoic crystalline basement underlying approximately 440,000 square kilometres of central South Australia. It is the oldest and largest geological province in the state, preserving a complex tectonic history spanning from around 3250 Ma to 1450 Ma. The Gawler Craton is a distinct physiographic province of the larger West Australian Shield division. It includes the smaller Stuart Range Basin and Pimba Platform physiographic sections. The southern boundary of the craton coincides with South Australia's coastline. The Palaeoproterozoic in southeastern Australia is represented by the polydeformed high-grade gneiss terranes of the Willyama Supergroup, Olary Block and Broken Hill Block, in South Australia and New South Wales.
The Gawler Craton's Mesoarchean history is dominated by felsic magmatism, while its Neoarchean to Paleoproterozoic history is marked by sedimentation and bimodal magmatism. The Mesoproterozoic history is characterised by bimodal magmatism. The oldest stratigraphic unit in the Gawler Craton is the Cooyerdoo Granite, exposed in northeast Eyre Peninsula. It is the product of the melting of pre-existing tonalite-trondhjemite-granodiorite (TTG) crust, and inherited zircons suggest that older crustal material up to around 3400 Ma may be present at depth. Gneisses with an older protolith of up to around 3250 Ma are also known in this area but have not been stratigraphically defined.
The Gawler Craton and the Willyama Block are flanked by several Proterozoic orogenic belts and sedimentary basins. The Gawler Craton is one of three main cratonic shields of recognised Archaean age within the Australian landmass, along with the Yilgarn and Pilbara cratons. The Australian landmass has been part of all major supercontinents, and its association with Gondwana is especially notable as important correlations have been made geologically with the African continental mass and Antarctica.
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Frequently asked questions
Igneous rocks can be found all over Australia, with the geology of the country including almost all known rock types.
The Pilbara region in Western Australia provides a diversity of Archaean to Proterozoic igneous rocks in a relatively compact area.
The youngest igneous rocks in Australia are those that erupted out of the country's youngest volcano, Mount Gambier in South Australia, 4,000 to 8,000 years ago.
Mantle xenoliths can be found in cooled lava in western Victoria.
Granite can be found in the Musgrave Block, the Arunta Block, and in the Pilbara region of Western Australia.
