Geology of Australia
The geology of Australia records over 3.8 billion years of the Earth's history. Australia is a continent on the Indo-Australian Plate. It is immensely old, and has rocks of many different types.
Like its close neighbour, New Guinea, Australia was once part of the southern supercontinent of Gondwanaland. Geologically, they are on the same tectonic plate. When world sea levels were low, the two shared shorelines (which now lie 100 to 140 metres below sea level).[1] They combined with lands now under water,[2][3] sometimes known as Greater Australia.[4] The two huge countries became separated when the area now known as the Torres Strait flooded after the end of the last glacial period. Big as Australia is, it was much bigger in the past. The end of the last ice age saw sea levels rise, and the old connections were broken.
Blocks
changeThe main continental blocks of the Australian continent are;
- The Yilgarn Craton, of Archaean age. The Murchinson Province of the craton has the oldest dated meteorite impact crater: 2229 ± 5 mya.[5] (the Yarrabubba crater).
- The Pilbara Craton of Archaean to Proterozoic age
- The Gawler Craton and Willyama Block, of Archaean to Proterozoic age.
Around them are several Proterozoic volcanic belts and sedimentary basins. The cratons formed the greater Australian landmass in the late Archaean to mesoProterozoic, (~2400 mya to 1,600 mya).
- Musgrave Block of granulite gneiss and igneous rocks.
- The Arunta Block of amphibolite grade metamorphic rocks and granites.
- The Gascoyne Complex, Glengarry Basin, and Bangemall Basin sandwiched between the Yilgarn and Arunta Blocks.
The older, western, two-thirds of the continent is much thicker (over 200 km thick) than the eastern third (about 38 to 59 km thick). The continental crust is mainly made 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 7 km thick).
Meteorite craters
changeMany meteorite craters have been found in Australia, but few have yet been confirmed.
- Gosses Bluff crater (Tnorala) in southern Northern Territory. Confirmed, 22km diameter, 142.5 mya (Lower Cretaceous).
- Shoemaker crater (central Western Australia). Confirmed, 30km+, 1630 mya (Proterozoic).
- Wolf Creek crater (Western Australia). Confirmed, 875 m, Pleistocene, ~150 kya.
The Earth Impact Database lists 190 confirmed craters, of which Australia has 27. The largest is the Yarrabubba crater in mid Western Australia. Its estimated age is 2.229 billion years ago.[6][7] It is one of the oldest known impact structures on Earth.
References
change- ↑ "Big Bank Shoals of the Timor Sea: An environmental resource atlas". Australian Institute of Marine Science. 2001. Archived from the original on 2011-09-27. Retrieved 2006-08-28.
- ↑ Ballard, Chris (1993). "Stimulating minds to fantasy? A critical etymology for Sahul". Sahul in review: Pleistocene archaeology in Australia, New Guinea and island Melanesia. Canberra: Australian National University. ISBN 0-7315-1540-4.
- ↑ Allen, J. (1977). Golson, J.; Jones, R. (eds.). Sunda and Sahul: Prehistorical studies in Southeast Asia, Melanesia and Australia. London: Academic Press. ISBN 0-12-051250-5.
- ↑ Allen, Jim; Gosden, Chris; Jones, Rhys; White, J. Peter (1988). "Pleistocene dates for the human occupation of New Ireland, northern Melanesia". Nature. 331 (6158): 707–709. Bibcode:1988Natur.331..707A. doi:10.1038/331707a0. PMID 3125483. S2CID 6912997.
- ↑ Erickson, Timmons M.; Kirkland, Christopher L.; Timms, Nicholas E.; Cavosie, Aaron J.; Davison, Thomas M. (21 January 2020). "Precise radiometric age establishes Yarrabubba, Western Australia, as Earth's oldest recognised meteorite impact structure". Nature Communications. 11 (1): 300. Bibcode:2020NatCo..11..300E. doi:10.1038/s41467-019-13985-7. PMC 6974607. PMID 31964860.
- ↑ Macdonald F.A., Bunting J.A. & Cina S.E. 2003. Yarrabubba—a large, deeply eroded impact structure in the Yilgarn Craton, Western Australia. Earth and Planetary Science Letters 213, 235–247. Abstract
- ↑ Bunting J.A. & Macdonald F.A. 2004. The Yarrabubba structure, Western Australia—clues to identifying impact events in deeply eroded ancient cratons. Geological Society of Australia Abstracts 73, 227.