Австралия геологиясының шолуы

Overview of the geology of Australia

The geology of Australia 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. Australia is a continent situated on the Indo Australian Plate.

Australia'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. Australia as a separate continent began to form after the breakup of Gondwana in the Permian, with the separation of the continental landmass from the African continent and Indian subcontinent. Australia rifted from Antarctica in the Cretaceous. The current Australian continental mass is composed of a thick subcontinental lithosphere, over thick in the western two thirds and thick in the younger eastern third. The Australian continental crust, excluding the thinned margins, has an average thickness of , with a range in thickness from
The continental crust is composed primarily of Archaean, Proterozoic and some Palaeozoic granites and gneisses. A thin veneer of mainly Phanerozoic sedimentary basins cover much of the Australian landmass (these are up to thick). These in turn are currently undergoing erosion by a combination of aeolian and fluvial processes, forming extensive sand dune systems, deep and prolonged development of laterite and saprolite profiles, and development of playa lakes, salt lakes and ephemeral drainage.

The geologic history of the Australian continental mass is extremely prolonged and involved, continuing from the Archaean to the recent. In a gross pattern, continental Australia grew from west to east, with Archean rocks mostly in the west, Proterozoic rocks in the centre, and Phanerozoic rocks in the east. Recent geologic events are confined to intraplate earthquakes, as the continent of Australia sits distant from the plate boundary. The Australian continent evolved in five broad but distinct time periods, namely: 3800–2100 Ma, 2100–1300 Ma, 1300–600 Ma, 600–160 Ma and 160 Ma to the present. The first period saw the growth of nuclei about which cratonic elements grew, whereas the latter four periods involved the amalgamation and dispersal of Nuna, Rodinia and Pangea, respectively.

The Australian landmass has been part of all major supercontinents, but its association with Gondwana is especially notable as important correlations have been made geologically with the African continental mass and Antarctica. Australia separated from Antarctica over a prolonged period beginning in the Permian and continuing through to the Cretaceous (84 Ma). Continental Australia is unique among the continents in that the measured stress field is not parallel to the present day north northeast directed plate motion. Most of the stress state in continental Australia is controlled by compression originating from the three main collision boundaries located in New Zealand, Indonesia and New Guinea, and the Himalaya (transmitted through the Indian and Capricorn plates). South of latitude −30°, the stress trajectories are oriented east–west to northwest–southeast. North of this latitude, the stress trajectories are closer to the present day plate motion, being oriented east northeast–west southwest to northeast–southwest. Notably, the main stress trajectories diverge most markedly from one another in north–central New South Wales (east southeast to north northeast), although the area is not known historically for earthquake activity. Young mountain building (< 5 Ma) in the Flinders Ranges of South Australia is driven from plate convergence at the boundary in New Zealand. Australia is currently moving toward Eurasia at the rate of 6–7 centimetres a year.

The assembly of the Archaean Yilgarn and Pilbara cratons of Australia was initiated at ~2200 Ma during the first phases of the Glenburgh orogen. The last stages of the 2770–2300 Ma Hamersley Basin on the southern margin of the Pilbara Craton are Palaeoproterozoic and record the last stable submarine fluviatile environments between the two cratons prior to the rifting, contraction and assembly of the intracratonic ~1800 Ma Ashburton and Blair basins, the 1600–1070 Ma Edmund and Collier basins, the 1840–1620 Ma northern Gascoyne Complex, the 2000–1780 Ma Glenburgh Terrane in the southern Gascoyne Complex and the Errabiddy Shear Zone at the northwestern margin of the Yilgarn Craton. Between approximately 2000–1800 Ma, on the northern margin of the Yilgarn Craton, the c. 2000 Ma Narracoota Volcanics of the Bryah Basin formed in a transverse back arc rift sag basin during collision. Culmination of the cratonic collision resulted in the foreland sedimentary Padbury Basin. To the east the Yerrida and Eerarheedy Basins were passive margins along the Yilgarn's northern margin. The c. 1830 Ma Capricorn Orogeny in this section of the Pilbara Yilgarn boundary resulted in deformation of the Bryah Padbury Basin and the western fringe of the Yerrida Basin, along with flood basalts. The Yapungku Orogeny (~1790 Ma) formed the Stanley Fold Belt on the northern margin of the Eerarheedy Basin, via assembly of the Archaean Proterozoic fold belts of Northern Australia.

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 Palaeoproterozoic in the north of Australia is represented mostly by the Mount Isa Block and complex fold thrust belts. These rocks, aside from suffering intense deformation, record a period of widespread platform cover sedimentation, ensialic rift sag sedimentation including widespread dolomite platform cover, and extensive phosphorite deposition in the deeper sea beds.

Widespread deposition occurred in the Centralian Superbasin and Adelaide Geosyncline (Adelaide Rift Complex) during the Neoproterozoic. The Petermann Orogeny caused extensive uplift, mountain building and basin fragmentation in central Australia at the close of the Neoproterozoic.

During the Silurian Period most of the Australian continent in the west and centre was dry land. However, from Geraldton north to Exmouth Gulf along the far Western Australian coast a fluvial sediment basin existed. Near Kalbarri on the Murchison River the footprints of a giant water scorpion were found on land, the first animal to walk on the Australian continent. A gulf linked to the sea existed under what is now the Great Sandy Desert. Meanwhile, in the east there were volcanic arcs in New England, also west of Townsville and Cairns, and in NSW and Victoria and the Australian Capital Territory. Deep water sediments formed in the Cowra, Tumut and Hillend Troughs. The Yass Molong rise was a row of volcanoes. Granite intrusions formed in New South Wales and Victoria from 435 to 425 Mya, with the Bega batholith as young as 400 Mya. In NSW granites the distinction between I type and S type granites was discovered.

The initial rifting of Australia and Antarctica in the Jurassic continued through the Cretaceous, with offshore development of a mid ocean ridge seafloor spreading centre. Tasmania was rifted off during this stage. Cretaceous volcanism in the offshore of Queensland was related to a minor episode of arc formation, typified by the Whitsunday Islands, followed by development of offshore coral platforms, passive margin basins and far field volcanism throughout the quiet Hunter Bowen orogenic belt. Cretaceous sedimentation continued in the Surat Basin. Some small Cretaceous volcanism was present at the edges of basement highs in the Great Artesian Basin, resulting in some sparse volcanic plugs today. Cretaceous sedimentation continued in the Perth Basin.

The Tertiary saw the majority of Australian tectonism cease. Sparse examples of intraplate volcanism exist, for instance the Glasshouse Mountains in Queensland, which are Tertiary examples of a chain of small volcanic plugs which decrease in age to the south, where they result in ~10,000 year old maar volcanoes and basalts of the Newer Volcanics in South Australia and Victoria.