View source for Australian plate

{{Short description|Major tectonic plate}}
{{Infobox tectonic plate
| image = File:AustralianPlate.png
| type = [[List of tectonic plates#Major plates|Major]]
| area = {{convert|47000000|km2|sqmi|abbr=on}}<ref>{{cite web |url=http://geology.about.com/library/bl/blplate_size_table.htm |title=Sizes of Tectonic or Lithospheric Plates |publisher=Geology.about.com |date=2014-03-05 |access-date=2015-12-25 |archive-date=2016-06-05 |archive-url=https://web.archive.org/web/20160605161523/http://geology.about.com/library/bl/blplate_size_table.htm |url-status=dead }}</ref>
| move_direction = northeast
| move_speed = 62–70 mm/year
| geo_features = Australia, [[New Guinea]], New Zealand, [[Indian Ocean]]
}}

The '''Australian plate''' is or was a major [[tectonic plate]] in the [[Eastern Hemisphere]] and, largely, [[Southern Hemisphere]]. Originally a part of the ancient continent of [[Gondwana]], Australia remained connected to [[Indian plate|India]] and [[Antarctic plate|Antarctica]] until approximately {{Mya|100}} when India broke away and began moving north. Australia and Antarctica had begun rifting by {{Mya|96}}<ref name="McLoughlin2001">{{Cite journal | last = McLoughlin | first = S. | title = The breakup history of Gondwana and its impact on pre-Cenozoic floristic provincialism | year = 2001 | journal = Australian Journal of Botany | volume = 49 | issue = 3 | pages = 271–300| url = https://www.researchgate.net/publication/216695699 | access-date = 21 May 2023 | doi = 10.1071/BT00023 }}</ref> and completely separated a while after this, some believing as recently as {{Mya|45}},<ref name="NewLook">{{cite web|url=https://www.livescience.com/37991-gondwana-breakup-detailed.html |title=New Look at Gondwana's Breakup |publisher=Livescience.com |date=2013-07-05 |access-date=2015-12-25}}</ref> but most accepting presently that this had occurred by {{Mya|60}}.<ref name="ODSN">{{cite web|url=https://www.odsn.de/odsn/services/paleomap/paleomap.html |access-date=2023-05-24 |title=ODSN Plate Tectonic Reconstruction Service }}</ref>

The Australian plate later fused with the adjacent [[Indian plate]] beneath the [[Indian Ocean]] to form a single [[Indo-Australian plate]]. However, recent studies suggest that the two plates may have once again split apart and have been separate plates for at least 3 million years.<ref name=Stein2002/> The Australian plate includes the continent of [[Australia (continent)|Australia]], including [[Tasmania]], as well as portions of [[New Guinea]], New Zealand and the [[Indian Ocean]] basin.

== Scope ==
The continental crust of this plate covers the whole of Australia, the [[Gulf of Carpentaria]], southern [[New Guinea]], the [[Arafura Sea]], the [[Coral Sea]]. The continental crust also includes northwestern New Zealand, [[New Caledonia]] and [[Fiji]]. The oceanic crust includes the southeast [[Indian Ocean]], the [[Tasman Sea]], and the [[Timor Sea]]. The Australian plate is bordered (clockwise) by the [[Eurasian plate]], the [[Philippine plate]], the [[Pacific plate]], the [[Antarctic plate]], the [[African plate]] and the [[Indian plate]]. It is however known from movement studies that this definition of the Australian plate is 20% less accurate than one that assumes independently moving [[Capricorn plate|Capricorn]], and [[Macquarie triple junction|Macquarie]] microplates.<ref name="DeMets2010">{{cite journal|last1=DeMets |first1=C |last2= Gordon |first2=RG |last3= Argus |first3=DF |title= Geologically current plate motions |journal= Geophysical Journal International |year=2010 |volume=181 |issue=1|pages=1–80|doi=10.1111/j.1365-246X.2009.04491.x |bibcode=2010GeoJI.181....1D |doi-access=free }}</ref>

== Geography ==
The northeasterly side is a complex but generally [[convergent boundary]] with the [[Pacific plate]]. The Pacific plate is subducting under the Australian plate, which forms the [[Tonga Trench|Tonga]] and [[Kermadec Trench]]es, and the parallel [[Tonga]] and [[Kermadec Islands|Kermadec]] [[island arc]]s. It has also uplifted the eastern parts of New Zealand's [[North Island]].

The continent of [[Zealandia (continent)|Zealandia]], which separated from Australia {{Mya|85}} and stretches from [[New Caledonia]] in the north to [[New Zealand Subantarctic Islands|New Zealand's subantarctic islands]] in the south, is now being torn apart along the [[transform boundary]] marked by the [[Alpine Fault]].

South of New Zealand the boundary becomes a transitional transform-convergent boundary, the [[Macquarie fault zone]], where the Australian plate is beginning to subduct under the Pacific plate along the [[Puysegur Trench]]. Extending southwest of this trench is the [[Macquarie Ridge]].

The southerly side is a [[divergent boundary]] with the [[Antarctic plate]] called the [[Southeast Indian Ridge]] (SEIR).

The subducting boundary through Indonesia is not parallel to the [[biogeography|biogeographical]] [[Wallace line]] that separates the indigenous fauna of Asia from that of [[Australasia]]. The eastern islands of Indonesia lie mainly on the [[Eurasian plate]], but have Australasian-related fauna and flora. Southeasterly lies the [[Sunda Shelf]].

To the east of Indonesia there appears to be under the [[Indian Ocean]] a deformation zone between the Indian and Australian plates with both earthquake and [[Satellite navigation|global satellite navigation system]] data indicating that India and Australia are not moving on the same vectors northward and have started a process of again separating.<ref name=Stein2002>{{cite book|chapter-url=https://www.earth.northwestern.edu/public/emile/PDF/EAO147.pdf |chapter=The January 26, 2001 Bhuj Earthquake and the Diffuse Western Boundary of the Indian Plate |last1=Stein|first1=Seth |title=Plate Boundary Zones |pages=243–254 |first2=Giovanni|last2=Sella |first3=Emile A.|last3=Okai |publisher=American Geophysical Union |date=2002 |doi=10.1029/GD030p0243 |access-date=26 December 2015|series=Geodynamics Series |isbn=9781118670446 }}</ref><ref name="Delescluse2007">{{cite journal|first1=Matthias |last1=Delescluse |first2=Nicolas |last2=Chamot-Rooke|title= Instantaneous deformation and kinematics of the India–Australia plate|journal= Geophysical Journal International |volume=168 |issue=2 |year=2007 |pages=818–842|doi=10.1111/j.1365-246X.2006.03181.x |bibcode=2007GeoJI.168..818D |s2cid=52998637 |doi-access=free }}</ref><ref name="Delescluse2012">{{cite journal |title=April 2012 intra-oceanic seismicity off Sumatra boosted by the Banda-Aceh megathrust |first1=Matthias|last1=Delescluse |first2=Nicolas|last2=Chamot-Rooke |first3=Rodolphe|last3=Cattin |first4=Luce|last4=Fleitout |first5=Olga|last5=Trubienko |first6=Christophe|last6=Vigny |date=26 September 2012 |journal=Nature |volume=490|issue=7419|pages=240–4 |doi=10.1038/nature11520|pmid=23023134 |bibcode=2012Natur.490..240D |s2cid=205230868}}</ref><ref name="Yue2012">{{cite journal|last1=Yue |first1= H. |last2= Lay |first2= T. |last3= Koper |first3= K. |title= En échelon and orthogonal fault ruptures of the 11 April 2012 great intraplate earthquakes. |journal= Nature |volume=490 |pages= 245–249 |year=2012 |issue= 7419 |doi=10.1038/nature11492 |pmid= 23023129 |bibcode= 2012Natur.490..245Y |s2cid= 4375902 }}</ref> This zone is along the northern [[Ninety East Ridge]]<ref name="Delescluse2007"/> which implies this area presently is weaker tectonically than the area where originally the Indian and Australian plates merged which is believed to have been further to the north west.<ref name="Delescluse2012"/> There is also deformation in an approximately {{convert|1200|km|abbr=on}} zone north of the Southeast Indian Ridge between the Australian plate and the proposed [[Capricorn plate]].<ref name="DeMets2010"/>

== Origins ==
{{main|Gondwana}}
It is known that the [[Eastern Pilbara craton|Eastern Pilbara Craton]] within present day [[Western Australia]], contains some of the oldest surface rocks on earth being pristine crust up to 3.8 [[1,000,000,000|billion]] years ago.<ref name="Hick2012">{{cite journal|last1=Hickman and Van Kranendonk|first1=Arthur and Martin|title=Early Earth evolution: evidence from the 3.5–1.8 Ga geological history of the Pilbara region of Western Australia |journal= Episodes|date=2012 |volume=35|issue=1|pages=283–297|doi=10.18814/epiiugs/2012/v35i1/028|url=http://aca.unsw.edu.au/sites/default/files/publications/Pilbara_Episodes_2012.pdf|doi-access=free}}</ref> Accordingly, the [[Pilbara craton|Pilbara Craton]] continues to be studied for clues as to the commencement and subsequent course of [[plate tectonics]].

Depositional age of the Mount Barren Group on the southern margin of the [[Yilgarn craton]] and [[zircon]] provenance analysis support the hypothesis that collisions between the [[Pilbara craton|Pilbara]]–[[Yilgarn craton|Yilgarn]] and [[Yilgarn craton|Yilgarn]]–[[Gawler]] [[Craton]]s assembled a proto-Australian continent approximately {{Mya|1696}} (Dawson et al. 2002).<ref name=Dawson>{{cite journal |last1=Dawson |first1=Galvin C. |last2=Krapež |first2=Bryan |last3=Fletcher |first3=Ian R. |last4=McNaughton |first4=Neal J. |last5=Rasmussen |first5=Birger |year=2002 |title=Did late Palaeoproterozoic assembly of proto-Australia involve collision between the Pilbara, Yilgarn and Gawler Cratons? Geochronological evidence from the Mount Barren Group in the Albany–Fraser Orogen of Western Australia |journal=[[Precambrian Research]] |volume=118 |issue=3–4 |pages=195–220 |doi=10.1016/S0301-9268(02)00110-9|bibcode=2002PreR..118..195D |issn=0301-9268 }}</ref>

Australia and East Antarctica were merged with [[Gondwana]] between 570 and {{mya|530}} starting in the [[Ediacaran]] (South African [[Kuunga Orogeny]]).<ref name="Meert2003">{{Cite journal| last = Meert | first = J. G.| title = A synopsis of events related to the assembly of eastern Gondwana| year = 2003 | journal = Tectonophysics | volume = 362 | issue = 1 | pages = 1–40| url = https://www.researchgate.net/publication/222404779| doi = 10.1016/S0040-1951(02)00629-7 | bibcode = 2003Tectp.362....1M }}</ref>

As a separate plate, the Australian plate came into being on the breakup of [[Gondwana]] with final separation from what is now the Antarctic plate and [[Zealandia]] starting in the [[Early Cretaceous]] between about {{Mya|132}} and finishing in the [[Cenomanian]] at about {{Mya|96}}.<ref name="McLoughlin2001"/> The separation continued with various authors modelling full separation time based on sea levels and/or biological separation. A currently widely used reference model for plate movement has total separation of [[Tasmania]] by 60 million years ago<ref name="ODSN"/> although some had argued historically that this was as recent as 45 million years ago.<ref name="NewLook"/>

== Speed ==
[[File:Global plate motion 2008-04-17.jpg|thumb|Global plate tectonic movement as measured by [[Global Positioning System|GPS]] devices.]] 
The Australian plate, which Australia is on, is moving faster than other plates. The Australian plate is moving about 6.9&nbsp;cm (2.7 inches) a year in a northward direction and with a small clockwise rotation. The [[Global Positioning System]] must be updated due to the movement, as some locations move faster.<ref>{{Cite web |last=Howard |first=Brian Clark |date=September 23, 2016 |title=Australia Is Drifting So Fast GPS Can't Keep Up |url=https://www.nationalgeographic.com/science/article/australia-moves-gps-coordinates-adjusted-continental-drift |url-status=live |archive-url=https://web.archive.org/web/20210227064836/https://www.nationalgeographic.com/science/article/australia-moves-gps-coordinates-adjusted-continental-drift |archive-date=Feb 27, 2021 |website=National Geographic}}</ref><ref>"[https://www.nytimes.com/2016/09/24/world/what-in-the-world/australia-continental-drift-location-gps.html Australia Is Not as Down Under as Everyone Thinks It Is]" by Michelle Innis, September 23, 2016, ''NY Times''.</ref><ref>{{cite report|url =https://un-ggim-ap.org/sites/default/files/media/working-groups/WG1/APREF/Report%20on%20the%20Asia%20Pacific%20Reference%20Frame%20%28APREF%29%20Project_2019.pdf|access-date=24 August 2024|title=Report on the Asia Pacific Reference Frame (APREF) Project. Record 2019/17.|year=2019|publisher=Geoscience Australia|first1 =G.|last1 =Hu|first2 =M.|last2 =Jia|first3 =J.|last3 =Dawson|issn=2201-702X|isbn =978-1-925848-54-0|location =Canberra|doi =10.11636/Record.2019.017|pages= 1–42}}</ref>

Technically movement is a vector and requires to be related to something. Much of the work involved in determining these plate vectors involves assurance that the points of reference are representative of the plates they are on, as distortion will be likely in areas of tectonic activity. Further assumptions such as there are only 8 plates were made in earlier modelling when as many as 52 may exist, with independent movement, although fair accuracy for larger plate movement can be obtained if only 25 are modelled.<ref name="DeMets2010"/>

In terms of the middle of India and Australia landmasses, with Australia as the point of reference, presently Australia is moving northward at {{convert|3|cm|in|abbr=on}} per year with respect to India<ref name="Delescluse2007"/> consistent with a zone of deformation between the two plates as commented upon earlier. This zone of deformation may actually presently involve some of India.<ref name="Delescluse2012"/>

The northwards collision of the Australian plate with the [[Sunda plate]] (Sundaland plate, previously classified as part of [[Eurasian plate]]) has a maximum convergence velocity of {{convert|7.3|cm|in|abbr=on}} per year ± {{convert|0.8|cm|in|abbr=on}} per year at the [[Java Trench]] decreasing to {{convert|6.0|cm|in|abbr=on}} ± {{convert|0.04|cm|in|abbr=on}} per year at the southern [[Sumatra Trench]].<ref name="DeMets2010"/>

The eastern collision with the Pacific plate has increasing displacement rates towards the north from a low of less than {{convert|0.2|cm|in|abbr=on}} per year at the southern end of the Macquarie fault zone,<ref name="DeMets2010"/> where there is the major plate [[Macquarie triple junction|triple junction]] with the Pacific and [[Antarctic plate]]s. Due to vector complexities at the north eastern end of this collision, which includes several spreading centres, it is perhaps simplest to state that the average displacement rate to the north is about half that of the collision with the Sunda plate, but this would not explain some of the largest and most destructive recent earthquakes and eruptions on the face of the planet.

There is oblique convergence of what are now the Pacific and Australian plates at about {{convert|11|cm/year|abbr=on}} near eastern Papua New Guinea.<ref>{{cite journal|first1=A. |last1=Vishiti|first2= S. |last2=Petersen|first3= C.E. |last3=Suh|first4= C.W. |last4=Devey| title=Texture, mineralogy and geochemistry of hydrothermally altered submarine volcanics recovered southeast of Cheshire Seamount, western Woodlark Basin| journal=Marine Geology| volume=347|year=2014 | pages=69–84|issn=0025-3227 |doi=10.1016/j.margeo.2013.11.002 |bibcode=2014MGeol.347...69V |url=https://www.sciencedirect.com/science/article/pii/S002532271300234X|url-access=subscription}}</ref> This has resulted in shear complexities, resolved by the formation of multiple microplates and convergence velocity that varies between {{convert|2|-|48|cm/year|abbr=on}} where the [[Solomon Sea plate]] subducts under the [[South Bismarck plate]] and Pacific plate at the [[New Britain subduction zone]].<ref>{{cite journal| last1=Li| first1=M| last2=Huang| first2=S| last3=Hao| first3=T| last4=Dong| first4=M| last5=Xu| first5=Y| last6=Zhang| first6=J| last7=He| first7=Q| last8=Fang| first8=G| title=Neogene subduction initiation models in the western Pacific and analysis of subduction zone parameters| journal=Science China Earth Sciences| year=2023| volume=66| issue=3| pages=472–91| doi=10.1007/s11430-022-1065-1| bibcode=2023ScChD..66..472L}}</ref> To the south of this there is sea floor spreading between the Australian plate and the [[Woodlark plate]] in the [[Woodlark Basin]] while the subduction of the oceanic crust of the Australian plate occurs to the south east in the [[New Hebrides Trench]] of the [[Vanuatu subduction zone]] under the [[New Hebrides plate]]. As we go south the convergence rate falls from {{convert|17|cm/year|abbr=on}} north of the [[Torres Islands]] to {{convert|4|cm/year|abbr=on}} in the central section of the trench, to rise again to {{convert|12|cm/year|abbr=on}} in the south.<ref>{{cite journal|last1=Roger|first1= J|last2=Pelletier|first2= B|last3=Gusman|first3= A|last4=Power|first4=W|last5=Wang|first5= X|last6= Burbidge|first6= D|last7= Duphil|first7= M|title=Potential tsunami hazard of the southern Vanuatu subduction zone: tectonics, case study of the Matthew Island tsunami of 10 February 2021 and implication in regional hazard assessment|journal=Natural Hazards and Earth System Sciences| volume=23| year=2023| issue=2| pages=393–414|doi=10.5194/nhess-23-393-2023|url=https://nhess.copernicus.org/articles/23/393/2023/nhess-23-393-2023.html|doi-access=free|bibcode= 2023NHESS..23..393R}}</ref>

Very active spreading then resumes in the [[North Fiji Basin]] where the edge of the Australian plate makes a transition in a bend up towards the north-east via the [[transform fault]]s of the [[Hunter fracture zone]] to [[Fiji]]. The Australian plate interacts at the southern and south-eastern border of the North Fiji Basin with the microplates of the New Hebrides already mentioned, as well as with the [[Conway Reef plate]] and the [[Balmoral Reef plate]]s. To the west of Fiji the Australian plate interacts in the spreading centre of the [[Lau Basin]] with the [[Niuafo'ou plate]] and the clockwise rotating [[Tonga plate]] under which the Pacific plate is subducting in the [[Kermadec-Tonga subduction zone]]. The back arc spreading in the Lau Basin continues almost due south in the line of interaction between the Australian and Tonga plates to the [[Kermadec plate]] and on to New Zealand where direct interaction resumes with the Pacific plate south of the [[Taupō Volcanic Zone]] and such direct interaction continues into the Macquarie fault zone to the south of New Zealand. There is up to {{convert|9.6|cm|abbr=on}} per year motion accommodated with complex rotational components in the collision dynamics between the north eastern Australian plate and the rotating [[Tonga plate]], the long thin [[Kermadec plate]] and the south western aspects of the Pacific plate. The Pacific plate east to west convergence rates along the subduction systems with the Kermadec plate, which are perhaps simpler to state, are among the fastest on Earth, being {{Convert|8|cm|abbr=on}} per year in the north and {{Convert|4.5|cm|abbr=on}} per year in the south.<ref name="Stratford2015">{{Cite journal| last1 = Stratford | first1 = W.| last2 = Peirce | first2 = C.| last3 = Paulatto | first3 = M.| last4 = Funnell | first4 = M.| last5 = Watts | first5 = A. B.| last6 = Grevemeyer | first6 = I.| last7 = Bassett | first7 = D.| title = Seismic velocity structure and deformation due to the collision of the Louisville Ridge with the Tonga-Kermadec Trench| year = 2015 | journal = Geophysical Journal International | volume = 200 | issue = 3 | pages = 1503–1522| url = https://oceanrep.geomar.de/id/eprint/28167/1/Stratford%20et.al.pdf | access-date = 21 May 2023| doi = 10.1093/gji/ggu475 | doi-access = free }}</ref>

At the central [[Alpine Fault]] in [[New Zealand]] the subduction component of the Pacific plate moving westward is about {{convert|3.9|cm|in|abbr=on}} per year.<ref>{{Cite book|url=https://books.google.com/books?id=LIgbjgEACAAJ&q=a+continent+on+the+move|title=A Continent on the Move: New Zealand Geoscience Revealed|last=Graham|first=I. J.|date=2015|publisher=Geoscience Society of New Zealand|isbn=9781877480478}}</ref> The Australian plate then to the south starts subducting under the Pacific plate at a rate of {{convert|3.6|cm/year|abbr=on}} at the [[Puysegur Trench]],<ref name="DeMets2010"/> which ends in the south as a long series of transform faults between the two plates called the Macquarie Ridge Complex, commencing with the McDougall fault zone and ending with the Macquarie fault zone. The south western portion of the zone has the Pacific plate interacting with an area of the Australian plate that the latest tectonic models suggest is still independent from when it first achieved independent rotation to the then Indo-Australian plate several million years ago, the Macquarie microplate.<ref name=Choi2017>{{cite journal|last1=Choi |first1=H|last2= Kim |first2=SS|last3= Dyment |first3=J.|last4=Granot |first4=R|last5=Park |first5=SH|last6= Hong |first6=JK |title=The kinematic evolution of the Macquarie Plate: A case study for the fragmentation of oceanic lithosphere. |journal=Earth and Planetary Science Letters|year= 2017 |volume=478 |pages=132–42|doi=10.1016/j.epsl.2017.08.035 |bibcode=2017E&PSL.478..132C|url=https://repository.kopri.re.kr/bitstream/201206/6256/1/414436.pdf }}</ref><ref name=Gasperini2023>{{cite journal| last1=Gasperini| first1=L| last2=Ligi| first2=M| last3=Accettella| first3=D| last4=Bosman| first4=A| last5=Cuffaro| first5=M| last6=Lodolo| first6=E| last7=Martorelli| first7=E| last8=Muccini| first8=F| last9=Palmiotto| first9=C| last10=Polonia| first10=A| title=Late Miocene to recent tectonic evolution of the Macquarie Triple Junction| journal=Geology| date=1 February 2023| volume=51 |issue=2|pages=146–50| doi=10.1130/G50556.1| doi-access=free| bibcode=2023Geo....51..146G}}</ref>

Data from the {{convert|11800|km|abbr=on}} long Southeast Indian Ridge only became available after about 1985 and this gives a fairly consistent spreading rate between the [[Antarctic plate|Antarctic]] and Australian plates of {{convert|6|cm|abbr=on}} per year at a [[Heading (navigation)|heading]] of 80° (slightly north of due east, at the Amsterdam transform fault to the south western side of Australian plate), {{convert|7|cm|abbr=on}} per year with heading 120° (southeast) and {{convert|6.6|cm|abbr=on}} per year near the Macquarie triple junction which is the south eastern side of the Australian plate.<ref name="DeMets2010"/>

The Capricorn plate at the western side of the Australian plate is moving at {{convert|1.9|mm|abbr=on}} per year ± {{convert|0.5|mm|abbr=on}} per year with heading 45° (northwest) relative to the Australia plate.<ref name="DeMets2010"/>

==See also==
* [[List of earthquakes in Australia]]
* [[List of earthquakes in India]]
* [[List of earthquakes in Indonesia]]
* [[List of earthquakes in New Zealand]]
* [[List of earthquakes in Papua New Guinea]]
* [[List of earthquakes in Samoa]]
* [[List of earthquakes in Tonga]]
* [[List of earthquakes in Vanuatu]]
* {{annotated link|Sunda plate}}
* [[Indo-Australian plate]]
* [[Indian plate]]

==References==
{{reflist}}

{{Tectonic plates}}

[[Category:Tectonic plates]]
[[Category:Natural history of Oceania]]
[[Category:Geology of the Indian Ocean|Plates]]
[[Category:Geology of Australia|Plates]]