Map of hotspots. The East Australia hotspot is marked 30 on map.View inside thecrater ofMount Schank from the rim
TheEast Australia hotspot (which is now believed by some scientists to represent multiple hotspots including a southwesternCosgrove hotspot) is a volcanic province in southeastAustralia which includes the Peak Range in centralQueensland, theMain Range on the Queensland-New South Wales border,Tweed Volcano in New South Wales, and theNewer Volcanics Province (NVP) inVictoria andSouth Australia. A number of the volcanoes in the province have erupted since Aboriginal settlement (46,000 BP). The most recent eruptions were about 5,600 years ago, and memories of them survive in Aboriginal folklore. These eruptions formed the volcanoesMount Schank andMount Gambier in the NVP. There have been no eruptions on the Australian mainland since European settlement.
The cause of volcanism in the area is uncertain. Theories typically fall into one of two categories: themantle plume theory and theplate theory. On the basis of the long duration of volcanic activity, its vast lateral extent,geochemistry of lavas, andseismic data, it has been proposed that the region is underlain by one or more deep mantle plumes which have forcedmagma up through points of weakness in theIndo-Australian Plate as it has moved northward over the source.[2][3][4][5]
The lack of clear age progression across the province and the orientation of the NVP, which is orthogonal to plate motion, are inconsistent with a single plume model.[1] Furthermore, seismic anomalies terminate at a depth of around 200 km, making the presence of a mantle plume unlikely.[6] However subsections of the province such as the bimodal Central Volcanoes have definite linear age progression on theHillsborourgh toBuckland lineament and theFraser toComboyne lineament.[7] Similarly theCenozoicleucitite volcanics of eastern Australia, some of which are under thicker continental crust than the coastal volcanics, are progressively younger towards the south, fromByrock in northern NSW toCosgrove in northern Victoria. This is now interpreted as theCrosgove hotspot and has been extended southward to theMacedon-Trentham central volcano and theNewer Volcanics Province lava field in Victoria.[7]
Various tectonic causes have been proposed. Some studies have argued that volcanic activity results from a combination of edge-driven convection (small-scale, shallowmantle convection caused by a change in lithospheric thickness at the continental margin where thick continentallithosphere meets thinner oceanic lithosphere) and decompression of the crust from normal faulting caused by plate stresses.[1][6] Another view is that extension from stresses brought about by changes in plate boundary configurations has caused severe lithospheric thinning resulting in decompression melting of theasthenosphere.[8] Both of these models invoke shallow processes closely related to the operation ofplate tectonics and so fall under the plate theory.[9][10] Other models combine both plume and plate-tectonic processes.[11][12][13] A 2022 synthesis, based on age and composition, suggests three different processes exist for the Cenozoic volcanoes found in eastern Australia and some are not hot spot volcanoes:[7]
Oceanic type, high volume, age-progressive volcanism from deep mantle plume(s)
Continental, age progressive volcanism some from the same plume(s) mixed with different melts
Continental, low volume, non-age-progressive volcanism related to passive melting.
^abcCas, R.A.F.; van Otterloo, J.; Blaikie, T.N.; van den Hove, J. (2017). "The dynamics of a very large intra-plate continental basaltic volcanic province, the Newer Volcanics Province, SE Australia, and implications for other provinces". In Németh, K.; Carrasco-Núñez, G.; Aranda-Gómez, J.J.; Smith, I.E.M. (eds.).Monogenetic volcanism. Geological Society, London, Special Publications, 446. Vol. 446. Geological Society of London. pp. 123–172.doi:10.1144/SP446.8.S2CID132586800.{{cite book}}:|journal= ignored (help)
^Sutherland, F.L. (1991). "Cainozoic volcanism, Eastern Australian: a predictive model on migration over multiple 'hotspot' magma sources". In DeDeckker, P.; Kershaw, A.P. (eds.).The Cainozoic in Australia: A re-appraisal of the evidence. Geological Society of Australia, Special Publications, 18. Geological Society of Australia. pp. 15–43.ISBN0-909869-76-6.
^Foulger, G.R. (2007). "The 'plate' model for the genesis of melting anomalies". In Foulger, G.R.; Jurdy, D.M. (eds.).Plates, plumes, and planetary processes: Geological Society of America Special Paper 430. The Geological Society of America. pp. 1–28.ISBN978-0813724300.
