Geology of australia

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Geological overview of Australia by rock age

The Geology of Australia includes the appearance of almost all known rocks of all geological periods a period of more than 3.8 billion years of Earth's history .

Geological overview

Australia can be geologically divided into several main regions: the archaic shields , the Proterozoic fold belts and sedimentary basins, and the Phanerozoic sedimentary basins with their metamorphic and igneous rocks .

Today's Australian land mass has a thick crust : the thickness of the lithosphere under Australia is up to 150 km, of which about 70 km is continental crust . This is mainly made up of archaic, Proterozoic and some Paleozoic granites and gneisses . Only a thin veil of Phanerozoic deposits covers the ancient rocks of the Australian craton .

The erosion transmits these rocks in a continuous process from and generated by aeolian and fluviatile operations extensive dune systems , salt pan deposits and loose rock . Profound weathering leads to the formation of thick lateritic and saprolithic soil profiles .

Cratonic areas

The great kratonic blocks of the Australian continent are mainly in the west. these are

These Cratonic blocks are bordered by several Proterozoic mountain belts and sedimentary basins, mainly

Plate tectonic situation

Seismicity of Australia 1990–2000. The relative calm of Australia in contrast to the surrounding plate boundaries can be clearly seen. Source: USGS

The continent of Australia lies on the Australian Plate , which is surrounded on all sides by oceanic crust except for its northern edge .

The Australian plate was part of all supercontinents throughout Earth's history . Important for the research, especially the relationship of the Australian plate to was Gondwana , the southern part of the supercontinent Pangea , because of the agreement of many geological units and the geological development in Australia, Africa , South America and Antarctica had Alfred Wegener 's theory of continental drift derived.

The formation of Australia as a separate continent began in the Permian after the collapse of Gondwana, when it broke away from Africa and India together with Antarctica . After the separation from Gondwana, the separation from Antarctica took place over a longer period of time, and Antarctica did not completely separate from Australia until the Jura . The initial rift began on the edge of the southern Australian basin and also resulted in the separation of Tasmania from Australia.

Today, the Australian plate moves about five centimeters a year in a northerly direction towards Eurasia . Its northern edge has therefore already entered into a collision with the Sunda Arc and Papua New Guinea , and the outermost Australian shelf is subducted under the group of island arcs . Tensions from this continent-island arc collision, which is still in its early stages, are already building up in the interior of Australia, they are expressed in earthquakes and the beginning of thrusts as far as the Flinders Ranges , that is, far to the south of the continent.

Geological history

The geological history covers extremely large periods of time in large areas of the Australian continental mass.

Archean

In the Archean, the three great cratons of Australia were formed, their history is very complicated and took a long time to complete. At the beginning of the Archean and in the early Mesoproterozoic, the cratons were united in a series of mountain formations ( orogenes ) between 2400 and 1600 mya ( million years ago , million years ago today, 2.4 to 1.6 gigajyears, Ga) to form a continuous land mass . The Capricorn orogeny was responsible, among other things, for the union of the Yilgarn kratons with the Pilbara kratons to form the land mass that today forms Western Australia. From this orogeny affected rocks are in Bangemall Basin, in the Gascoyne Complex and in the basins of Glengarry, Yerrida and Padbury minded . The connection between the Yilgarn and Gawler kratons is not known as it is covered by the younger, Proterozoic-Paleozoic Officer and Amadeus basins . Possibly these unknown Proterozoic fold belts are similar to the Albany Complex and the Musgrave Block in southern Western Australia.

Paleoproterozoic

Western Australia

On the southern edge of the Pilbara craton in the Paleoproterozoic about 2.77 to 2.3 billion years ago (2.77 - 2.3 gig years ago, Ga) in the Hamersley Basin with river and sea deposits, the last evidence of an environment unaffected by mountain formations was deposited between the Pilbara Kraton and the Yilgarn Kraton.

The union of the two cratons began about 2.2 billion years ago in the Capricorn orogeny. In this long-lasting unification process, several sedimentary basins were created: the Ashburton and Blair basins (~ 1.8 Ga) formed inside the cratons, the Edmund and Collier basins (1.6 to 1.07 Ga), the northern one Gascoyne Complex (1.84-1.62 Ga), the Glenburgh Terrane (2-1.78 Ga) and the Errabiddy Shear Zone on the northwestern edge of the Yilgarn Craton.

Between about 2 and 1.8 Ga collision of the Yilgarn Craton was formed in the course on the northern edge a back-arc basin , the Bryah Basin , whose volcanic deposits that Narracoota volcanics , with an age of 1.89 Ga dated could be . The basins in the east (Yerrida and Eerarheedy basins) formed as sedimentary basins on the passive continental margin in the north of the Yilgarn craton. The climax of the collision between the two cratons led to the deformation of the Bryah and Padbury basins in the foreland of the mountains, and the western edge of the Yerrida basin was also included. There was an outflow of flood basalts . The Eerarheedy Basin was during the more recent Yapungku orogeny verfaltet , in the archaic-Proterozoic fold belt of northern Australia have been welded together.

Eastern Australia

The Palaeoproterozoic in southeastern Australia is represented by the multiple deformed, highly metamorphic gneiss areas of the Willyama Supergroup , the Olary Block and the Broken Hill Block in South Australia and New South Wales . In Northern Australia, the Paleoproterozoic occurs primarily in the Mount Isa Block and intricate fold-and-thrust belts. These rocks bear witness not only to intensive deformation, but also to widespread deposition in rift valleys of the continental crust, the development of dolomitic carbonate platforms and the formation of phosphorous deep-sea sediments.

Mesoproterozoic

Mesoproterozoic rocks form the oldest formations in Tasmania, they occur on King Island and in the Tyennan Block .

Neoproterozoic

During the Neoproterozoic , the Giles Complex , a series of mafic to ultramafic intrusions in the Musgrave Block dated to about 1.08 Ga, formed. Old storage tunnels are also widespread in the Bangemall Basin and in the Glenayle area, as well as in the Magmatic Greater Warukurna region ( Warukurna Large Igneous Province ).

Paleozoic

Cambrian

The Stavely zone in Victoria forms a terran that consists of boninitic to MOR basalts , a connection with the boninites of the volcanic series of Mount Read in northern Tasmania is assumed. In New South Wales and Victoria, the Adaminaby layers, deposited in deep water, are common. The Lachlan fold belt contains ophiolite episodes, classified in the Cambrian , and which were autopsied during the Ordovician Lachlan orogeny .

In Central Australia, the Petermann orogenesis occurred in the Cambrian . From the ascending mountain ranges, a mighty, intra-continental succession of fluvial sediments poured into the interior of the central Australian land mass. Marginal platforms and marginal basins on a passive continental margin in South Australia had formed in the foreland of the Delamerican orogeny . At this time, marginal basins and marginal platforms began to form in Western Australia. The flood basalts of the Antrim Plateau , which cover an area of ​​more than 12,000 km², form a supraregional reference horizon in Western Australia .

Ordoviz

In the Ordovician , the Lachlan fold belt was formed during the Lachlan orogeny, which has an alpinotype tectonics and led to the formation of the great serpentinite belt of western New South Wales. As part of this orogeny, the flysch and molasses sediments, which are now preserved in the slate belts of Victoria and eastern New South Wales, were attached.

In Victoria, in the transition from Cambrian to Ordovician, turbidite sediments of deep water were deposited, namely the St. Arnaud Group and the Castlemaine Group , which are now exposed in the Stawell and Bendigo zones . In the middle Ordovician, the Sunbury group was deposited, which is now open in the Melbourne zone . At the same time, the Bendoc group was deposited, and the Molong volcanic arch was formed, an arch formed from calcareous-alkaline magmas , which is related to the deposit of the turbidites of the Kiandra group .

Silurian

During the Silurian era , the west and center of the Australian continent was dry land. However, between Geraldton and the Exmouth Gulf on the extreme coast of Western Australia, there was a sedimentary basin in which the debris from rivers collected. In Kalbarri on the Murchison River , the footprints were of a great Seeskorpions found, the order was one of the first animals that entered the Australian country. At that time, under today's Great Sand Desert, there was a gulf that was connected to the open sea.

Deep-sea sediments have been deposited in the area of ​​the Cowra , Tumut and Hill End Basins . There were volcanic arcs in the east: in New England , in the west of Townsville and Cairns , in New South Wales and Victoria, at Yass and Molong, and in the Australian Capital Territory . In New South Wales and Victoria there was also an intrusion of granites between 435 and 425 mya , which was followed by the Bega batholith about 400 million years ago. On the granites of New South Wales, the difference between the I-type granites (melted from igneous rocks, English igneous rocks ) and S-type granites (melted from sedimentary rocks, English sedimentary rocks ) was determined for the first time.

Devon

Australia had a warm climate during the Devonian . Most of Central and Western Australia was land, in the area of ​​the Great Sand Desert there was a large sea ​​bay in which coral reefs grew. The Calliope Arch ran from north of Rockhampton to south of Grafton . The sandstones that make up the Western Australian Bungle Bungle Ranges were formed from river sands .

In an area that is now in the sea off the east coast of Australia, a chain of volcanic mountains was eroded, releasing sediments into a basin in parts of what is now the east coast. Here came sand and limestone for deposition. In central New South Wales, in the Snowy Mountains , in Eden , New England and near Clermont emerged andesitic and rhyolitic volcanics. Baragwanathia longifolia , a plant from the class of club moss plants , was the first land plant in Australia to appear at this time. The interior of the continent drained a large river system that flowed to the east at Parkes .

The east coast was covered by the tabberabberan orogeny at around 385-380 mya , which compressed and folded Tasmania, Victoria, and southern New South Wales in an east-west direction. Between 377 and 352 mya, northern New South Wales and Queensland were also narrowed.

At Mackay and western New England the Connors and Baldwin arcs formed . Granites also appeared in the Devonian.

Carbon

In the Carboniferous the collision with parts of South America unfolded the Eastern Highlands , their counterparts are now in the Sierras de Córdoba and New Zealand . A special feature of the carbon are the references to a great ice age that took place at that time , which covered more than half of the Australian continent. Remnants of this Karoo Ice Age , which lasted in the late Carboniferous and into the Permian, can be found not only in glacial sediments, but also in fossil gelisol formations, soil formations of an arctic climate that can be found today, for example, in the Hunter River basin.

Mesozoic

Permo Triassic

The Permian and Triassic in Australia are dominated by the subduction zones of the Hunter-Bowen orogeny on the eastern edge of the continent. During this orogeny, a larger arch of the island was accreted and a back arc basin formed. The process dragged on for a long time: it began in the late Carboniferous and lasted into the Middle Triassic. Its end is dated from 229 to 225 mya.

In Western and Central Australia, the then extensive mountain ranges such as the Petermann Ranges were eroded by the permocarbonic glaciation, so that mighty marine to fluvial glacial tillites formed, and fossil-rich limestones and extensive platform sediments formed. The rifting of the Australian Plate of India and Africa began in the Permian, triggering the formation of a long-standing rift basin, the Perth Basin . In the Swan Coastal Plain ( Swan Coastal Plain ) and Pilbara was oil during this rifting, possibly in an oxygen-depleted grave breach basin that with today's Lake Tanganyika can be compared.

law

In western Australia there was a tropical savannah that partially merged into jungle during the Jura . This is evidenced by the deep tropical weathering of the regolith in the Yilgarn Kraton, which can still be seen today. Australia broke away from Antarctica in the Jurassic, forming the Gippsland , Bass and Otway Basins in Victoria and the Shelf Basins off the coast of South and Western Australia. In all of these basins there are large deposits of oil and natural gas today . Coal was formed in sedimentary basins of north central Queensland and the deposits of a shallow epicontinental sea covered most of central Australia. Lowering of the passive continental margin and ocean transgressions covered the Perth Basin. Sediments were poured into the basin from the land, including the Jurassic Cattamarra coal layers.

chalk

The drifting apart of Australia and Antarctica, which began in the Jurassic, continued in the Cretaceous , and a fully developed mid-ocean ridge formed in the sea as a splitting axis . Tasmania also broke away from Australia in this process. The lateral shifts between Antarctica and Australia during the Cretaceous led to the formation of the Stirling Range . These were the last mountain-building processes in Australia.

Cretaceous volcanism off the coast of Queensland is evidence of a brief episode in which an island arc was formed (today for example in the Whitsunday Islands ). This was followed by the development of a carbonate platform, the formation of sedimentary basins on a passive continental margin, and volcanism in the otherwise calm Hunter-Bowen mountain belt. Scattered evidence of volcanism can also be found in the form of volcanic sticks on the edge of the Great Artesian Basin .

Cretaceous deposits are also known from the Surat Basin , and sedimentation continued in the Perth Basin.

Cenozoic

Tertiary and Quaternary

In tertiary almost all tectonic events in Australia found its end. A few examples of continental volcanism can be found in the Glasshouse Mountains in Queensland. Here, small volcanic stocks form a series of volcanic buildings, the age of which decreases from north to south to end in the Quaternary , approximately 10,000 year old maars and basalt casts of the Newer Volcanics Province of Victoria.

Individual evidence

  1. ↑ F. Pirajno, SA Occhipinti, CP Swager: Geology and tectonic evolution of the Palaeoproterozoic Bryah, Padbury and Yerrida basins, Western Australia: implications for the history of the south-central Capricorn orogen . In: Precambrian Research . tape 90 , 1998, pp. 119-140 , doi : 10.1016 / S0301-9268 (98) 00045-X .
  2. ^ A b David Johnson: Geology of Australia. Cambridge University Press, 2004

literature

  • David Johnson: Geology of Australia. Cambridge University Press, 2004. limited preview in Google Book search

Web links

Geology of australia

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