The Australian plate is or was a major
tectonic plate
Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...
in the
eastern and, largely,
southern hemispheres. Originally a part of the ancient continent of
Gondwana
Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...
, Australia remained connected to
India
India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
and
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
until approximately when India broke away and began moving north. Australia and Antarctica had begun rifting by
and completely separated a while after this, some believing as recently as ,
but most accepting presently that this had occurred by .
The Australian plate later fused with the adjacent
Indian plate
The Indian plate (or India plate) is or was a minor tectonic plate straddling the equator in the Eastern Hemisphere. Originally a part of the ancient continent of Gondwana, the Indian plate broke away from the other fragments of Gondwana an ...
beneath the
Indian Ocean
The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...
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.
[ The Australian plate includes the continent of ]Australia
Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
, including Tasmania
Tasmania (; palawa kani: ''Lutruwita'') is an island States and territories of Australia, state of Australia. It is located to the south of the Mainland Australia, Australian mainland, and is separated from it by the Bass Strait. The sta ...
, as well as portions of New Guinea
New Guinea (; Hiri Motu: ''Niu Gini''; , fossilized , also known as Papua or historically ) is the List of islands by area, world's second-largest island, with an area of . Located in Melanesia in the southwestern Pacific Ocean, the island is ...
, New Zealand and the Indian Ocean
The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...
basin.
Scope
The continental crust of this plate covers the whole of Australia, the Gulf of Carpentaria
The Gulf of Carpentaria is a sea off the northern coast of Australia. It is enclosed on three sides by northern Australia and bounded on the north by the eastern Arafura Sea, which separates Australia and New Guinea. The northern boundary ...
, southern New Guinea
New Guinea (; Hiri Motu: ''Niu Gini''; , fossilized , also known as Papua or historically ) is the List of islands by area, world's second-largest island, with an area of . Located in Melanesia in the southwestern Pacific Ocean, the island is ...
, the Arafura Sea, the Coral Sea
The Coral Sea () is a marginal sea of the Pacific Ocean, South Pacific off the northeast coast of Australia, and classified as an Interim Biogeographic Regionalisation for Australia, interim Australian bioregion. The Coral Sea extends down t ...
. The continental crust also includes northwestern New Zealand, New Caledonia
New Caledonia ( ; ) is a group of islands in the southwest Pacific Ocean, southwest of Vanuatu and east of Australia. Located from Metropolitan France, it forms a Overseas France#Sui generis collectivity, ''sui generis'' collectivity of t ...
and Fiji
Fiji, officially the Republic of Fiji, is an island country in Melanesia, part of Oceania in the South Pacific Ocean. It lies about north-northeast of New Zealand. Fiji consists of an archipelago of more than 330 islands—of which about ...
. The oceanic crust includes the southeast Indian Ocean
The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...
, the Tasman Sea
The Tasman Sea is a marginal sea of the South Pacific Ocean, situated between Australia and New Zealand. It measures about across and about from north to south. The sea was named after the Dutch explorer Abel Janszoon Tasman, who in 1642 wa ...
, and the Timor Sea
The Timor Sea (, , or ) is a relatively shallow sea in the Indian Ocean bounded to the north by the island of Timor with Timor-Leste to the north, Indonesia to the northwest, Arafura Sea to the east, and to the south by Australia. The Sunda Tr ...
. 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
The Indian plate (or India plate) is or was a minor tectonic plate straddling the equator in the Eastern Hemisphere. Originally a part of the ancient continent of Gondwana, the Indian plate broke away from the other fragments of Gondwana an ...
. 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, and Macquarie microplates.
Geography
The northeasterly side is a complex but generally convergent boundary
A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a ...
with the Pacific plate. The Pacific plate is subducting under the Australian plate, which forms the Tonga
Tonga, officially the Kingdom of Tonga, is an island country in Polynesia, part of Oceania. The country has 171 islands, of which 45 are inhabited. Its total surface area is about , scattered over in the southern Pacific Ocean. accordin ...
and Kermadec Trenches, and the parallel Tonga
Tonga, officially the Kingdom of Tonga, is an island country in Polynesia, part of Oceania. The country has 171 islands, of which 45 are inhabited. Its total surface area is about , scattered over in the southern Pacific Ocean. accordin ...
and Kermadec island arc
Island arcs are long archipelago, chains of active volcanoes with intense earthquake, seismic activity found along convergent boundary, convergent plate tectonics, tectonic plate boundaries. Most island arcs originate on oceanic crust and have re ...
s. It has also uplifted the eastern parts of New Zealand's North Island
The North Island ( , 'the fish of Māui', historically New Ulster) is one of the two main islands of New Zealand, islands of New Zealand, separated from the larger but less populous South Island by Cook Strait. With an area of , it is the List ...
.
The continent of Zealandia
Zealandia (pronounced ), also known as (Māori language, Māori) or Tasmantis (from Tasman Sea), is an almost entirely submerged continent, submerged mass of continental crust in Oceania that subsided after breaking away from Gondwana 83� ...
, which separated from Australia and stretches from New Caledonia
New Caledonia ( ; ) is a group of islands in the southwest Pacific Ocean, southwest of Vanuatu and east of Australia. Located from Metropolitan France, it forms a Overseas France#Sui generis collectivity, ''sui generis'' collectivity of t ...
in the north to 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
In plate tectonics, a divergent boundary or divergent plate boundary (also known as a constructive boundary or an extensional boundary) is a linear feature that exists between two List of tectonic plates, tectonic plates that are moving away fr ...
with the Antarctic plate called the Southeast Indian Ridge (SEIR).
The subducting boundary through Indonesia is not parallel to the biogeographical Wallace line
The Wallace Line or Wallace's Line is a faunal boundary line drawn in 1859 by the British naturalist Alfred Russel Wallace and named by the English biologist Thomas Henry Huxley.
It separates the biogeographic realms of Asia and 'Wallacea', a ...
that separates the indigenous fauna of Asia from that of Australasia
Australasia is a subregion of Oceania, comprising Australia, New Zealand (overlapping with Polynesia), and sometimes including New Guinea and surrounding islands (overlapping with Melanesia). The term is used in a number of different context ...
. The eastern islands of Indonesia lie mainly on the Eurasian plate, but have Australasian-related fauna and flora. Southeasterly lies the Sunda Shelf
Geology, Geologically, the Sunda Shelf () is a south-eastern extension of the continental shelf of Mainland Southeast Asia. Major landmasses on the shelf include the Indonesia, Indonesian islands of Bali, Borneo, Java, Madura Island, Madura, an ...
.
To the east of Indonesia there appears to be under the Indian Ocean
The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...
a deformation zone between the Indian and Australian plates with both earthquake and 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. This zone is along the northern Ninety East Ridge 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. There is also deformation in an approximately zone north of the Southeast Indian Ridge between the Australian plate and the proposed Capricorn plate.
Origins
It is known that the Eastern Pilbara Craton within present day Western Australia
Western Australia (WA) is the westernmost state of Australia. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Aust ...
, contains some of the oldest surface rocks on earth being pristine crust up to 3.8 billion
Billion is a word for a large number, and it has two distinct definitions:
* 1,000,000,000, i.e. one thousand million, or (ten to the ninth power), as defined on the short scale. This is now the most common sense of the word in all varieties of ...
years ago. Accordingly, the Pilbara Craton continues to be studied for clues as to the commencement and subsequent course of plate tectonics
Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...
.
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
The Pilbara () is a large, dry, sparsely populated regions of Western Australia, region in the north of Western Australia. It is known for its Indigenous Australians, Aboriginal people; wealth disparity; its ancient landscapes; the prevailing r ...
– Yilgarn and Yilgarn– Gawler Craton
A craton ( , , or ; from "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and rifting of contine ...
s assembled a proto-Australian continent approximately (Dawson et al. 2002).
Australia and East Antarctica were merged with Gondwana
Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...
between 570 and starting in the Ediacaran
The Ediacaran ( ) is a geological period of the Neoproterozoic geologic era, Era that spans 96 million years from the end of the Cryogenian Period at 635 Million years ago, Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last ...
(South African Kuunga Orogeny).
As a separate plate, the Australian plate came into being on the breakup of Gondwana
Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...
with final separation from what is now the Antarctic plate and Zealandia
Zealandia (pronounced ), also known as (Māori language, Māori) or Tasmantis (from Tasman Sea), is an almost entirely submerged continent, submerged mass of continental crust in Oceania that subsided after breaking away from Gondwana 83� ...
starting in the Early Cretaceous
The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...
between about and finishing in the Cenomanian
The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...
at about . 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
Tasmania (; palawa kani: ''Lutruwita'') is an island States and territories of Australia, state of Australia. It is located to the south of the Mainland Australia, Australian mainland, and is separated from it by the Bass Strait. The sta ...
by 60 million years ago although some had argued historically that this was as recent as 45 million years ago.
Speed
The Australian plate, which Australia is on, is moving faster than other plates. The Australian plate is moving about 6.9 cm (2.7 inches) a year in a northward direction and with a small clockwise rotation. The Global Positioning System
The Global Positioning System (GPS) is a satellite-based hyperbolic navigation system owned by the United States Space Force and operated by Mission Delta 31. It is one of the global navigation satellite systems (GNSS) that provide ge ...
must be updated due to the movement, as some locations move faster.
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.
In terms of the middle of India and Australia landmasses, with Australia as the point of reference, presently Australia is moving northward at per year with respect to India 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.
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 per year ± per year at the Java Trench decreasing to ± per year at the southern Sumatra Trench.
The eastern collision with the Pacific plate has increasing displacement rates towards the north from a low of less than per year at the southern end of the Macquarie fault zone, where there is the major plate triple junction with the Pacific and Antarctic plates. 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 near eastern Papua New Guinea. This has resulted in shear complexities, resolved by the formation of multiple microplates and convergence velocity that varies between where the Solomon Sea plate subducts under the South Bismarck plate and Pacific plate at the New Britain subduction zone. 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
The New Hebrides Trench (perhaps better termed the South New Hebrides Trench) is an oceanic trench which is over deep in the Southern Pacific Ocean. It lies to the northeast of New Caledonia and the Loyalty Islands, to the southwest of Vanuatu ...
of the Vanuatu subduction zone under the New Hebrides plate. As we go south the convergence rate falls from north of the Torres Islands to in the central section of the trench, to rise again to in the south.
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
A transform fault or transform boundary, is a fault (geology), fault along a plate boundary where the motion (physics), motion is predominantly Horizontal plane, horizontal. It ends abruptly where it connects to another plate boundary, either an ...
s of the Hunter fracture zone to Fiji
Fiji, officially the Republic of Fiji, is an island country in Melanesia, part of Oceania in the South Pacific Ocean. It lies about north-northeast of New Zealand. Fiji consists of an archipelago of more than 330 islands—of which about ...
. 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 plates. To the west of Fiji the Australian plate interacts in the spreading centre of the Lau Basin
The Lau Basin is a back-arc basin (also addressed as "interarc basin") at the Australian-Pacific plate boundary. It is formed by the Pacific plate subducting under the Australian plate. The Tonga-Kermadec Ridge, a frontal arc, and the Lau-Colvill ...
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 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 per year in the north and per year in the south.
At the central Alpine Fault in New Zealand
New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
the subduction component of the Pacific plate moving westward is about per year. The Australian plate then to the south starts subducting under the Pacific plate at a rate of at the Puysegur Trench, 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.
Data from the long Southeast Indian Ridge only became available after about 1985 and this gives a fairly consistent spreading rate between the Antarctic
The Antarctic (, ; commonly ) is the polar regions of Earth, polar region of Earth that surrounds the South Pole, lying within the Antarctic Circle. It is antipodes, diametrically opposite of the Arctic region around the North Pole.
The Antar ...
and Australian plates of per year at a heading of 80° (slightly north of due east, at the Amsterdam transform fault to the south western side of Australian plate), per year with heading 120° (southeast) and per year near the Macquarie triple junction which is the south eastern side of the Australian plate.
The Capricorn plate at the western side of the Australian plate is moving at per year ± per year with heading 45° (northwest) relative to the Australia plate.
See also
* List of earthquakes in Australia
This is a list of significant earthquakes recorded in Australia and its territories. The currency used is the Australian dollar (A$) unless noted otherwise.
List of earthquakes
Other earthquakes
*Broome, Western Australia, Broome, 16 August 1 ...
* 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
*
* Indo-Australian plate
* Indian plate
The Indian plate (or India plate) is or was a minor tectonic plate straddling the equator in the Eastern Hemisphere. Originally a part of the ancient continent of Gondwana, the Indian plate broke away from the other fragments of Gondwana an ...
References
{{Tectonic plates
Tectonic plates
Natural history of Oceania
Plates
Plates