Indo-Australian Plate
Overview
 
The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia
Australia (continent)
Australia is the world's smallest continent, comprising the mainland of Australia and proximate islands including Tasmania, New Guinea, the Aru Islands and Raja Ampat Islands...

 and surrounding ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

, and extends northwest to include the Indian subcontinent
Indian subcontinent
The Indian subcontinent, also Indian Subcontinent, Indo-Pak Subcontinent or South Asian Subcontinent is a region of the Asian continent on the Indian tectonic plate from the Hindu Kush or Hindu Koh, Himalayas and including the Kuen Lun and Karakoram ranges, forming a land mass which extends...

 and adjacent waters. Recent studies suggest that the Indo-Australian Plate may be in the process of breaking up into two separate plates due primarily to stresses induced by the collision of the Indo-Australian Plate with Eurasia along the Himalayas. The two protoplates or subplates are generally referred to as the Indian Plate and the Australian Plate.
Depositional age of the Mount Barren Group on the southern margin of the Yilgarn Craton
Yilgarn craton
The Yilgarn Craton is a large craton which constitutes the bulk of the Western Australian land mass. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts...

 and zircon
Zircon
Zircon is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4. A common empirical formula showing some of the range of substitution in zircon is 1–x4x–y...

 provenance analysis support the hypothesis that collisions between the Pilbara–Yilgarn
Yilgarn craton
The Yilgarn Craton is a large craton which constitutes the bulk of the Western Australian land mass. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts...

 and Yilgarn
Yilgarn craton
The Yilgarn Craton is a large craton which constitutes the bulk of the Western Australian land mass. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts...

–Gawler Craton
Craton
A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...

s assembled a proto-Australian continent approximately 1696±7 Ma (Dawson et al.
Encyclopedia
The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia
Australia (continent)
Australia is the world's smallest continent, comprising the mainland of Australia and proximate islands including Tasmania, New Guinea, the Aru Islands and Raja Ampat Islands...

 and surrounding ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

, and extends northwest to include the Indian subcontinent
Indian subcontinent
The Indian subcontinent, also Indian Subcontinent, Indo-Pak Subcontinent or South Asian Subcontinent is a region of the Asian continent on the Indian tectonic plate from the Hindu Kush or Hindu Koh, Himalayas and including the Kuen Lun and Karakoram ranges, forming a land mass which extends...

 and adjacent waters. Recent studies suggest that the Indo-Australian Plate may be in the process of breaking up into two separate plates due primarily to stresses induced by the collision of the Indo-Australian Plate with Eurasia along the Himalayas. The two protoplates or subplates are generally referred to as the Indian Plate and the Australian Plate.

Origins

Depositional age of the Mount Barren Group on the southern margin of the Yilgarn Craton
Yilgarn craton
The Yilgarn Craton is a large craton which constitutes the bulk of the Western Australian land mass. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts...

 and zircon
Zircon
Zircon is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4. A common empirical formula showing some of the range of substitution in zircon is 1–x4x–y...

 provenance analysis support the hypothesis that collisions between the Pilbara–Yilgarn
Yilgarn craton
The Yilgarn Craton is a large craton which constitutes the bulk of the Western Australian land mass. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts...

 and Yilgarn
Yilgarn craton
The Yilgarn Craton is a large craton which constitutes the bulk of the Western Australian land mass. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts...

–Gawler Craton
Craton
A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...

s assembled a proto-Australian continent approximately 1696±7 Ma (Dawson et al. 2002).

Geographical extent

The Indian subcontinent
Indian subcontinent
The Indian subcontinent, also Indian Subcontinent, Indo-Pak Subcontinent or South Asian Subcontinent is a region of the Asian continent on the Indian tectonic plate from the Hindu Kush or Hindu Koh, Himalayas and including the Kuen Lun and Karakoram ranges, forming a land mass which extends...

, Meganesia
Australia (continent)
Australia is the world's smallest continent, comprising the mainland of Australia and proximate islands including Tasmania, New Guinea, the Aru Islands and Raja Ampat Islands...

 (Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, New Guinea
New Guinea
New Guinea is the world's second largest island, after Greenland, covering a land area of 786,000 km2. Located in the southwest Pacific Ocean, it lies geographically to the east of the Malay Archipelago, with which it is sometimes included as part of a greater Indo-Australian Archipelago...

, and Tasmania
Tasmania
Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...

), New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

, and New Caledonia
New Caledonia
New Caledonia is a special collectivity of France located in the southwest Pacific Ocean, east of Australia and about from Metropolitan France. The archipelago, part of the Melanesia subregion, includes the main island of Grande Terre, the Loyalty Islands, the Belep archipelago, the Isle of...

 are all fragments of the ancient supercontinent of Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...

. Seafloor spreading
Seafloor spreading
Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. Seafloor spreading helps explain continental drift in the theory of plate tectonics....

 separated these land masses from one another, but as the spreading centers became inactive they fused into a single plate.

Recent GPS measurement in Australia confirms the plate's velocity of 67 mm/yr at 35 degrees east of north . Note also the same directions and velocities for points at Auckland
Auckland
The Auckland metropolitan area , in the North Island of New Zealand, is the largest and most populous urban area in the country with residents, percent of the country's population. Auckland also has the largest Polynesian population of any city in the world...

, Christmas Island
Christmas Island
The Territory of Christmas Island is a territory of Australia in the Indian Ocean. It is located northwest of the Western Australian city of Perth, south of the Indonesian capital, Jakarta, and ENE of the Cocos Islands....

 and southern India. The slight change in direction at Auckland is presumably due to a slight buckling of the plate there, where it is being compressed by the Pacific Plate
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....

.

The southeasterly side is a complex but generally convergent boundary
Convergent boundary
In plate tectonics, a convergent boundary, also known as a destructive plate boundary , is an actively deforming region where two tectonic plates or fragments of lithosphere move toward one another and collide...

 with the Pacific Plate. The Pacific Plate subducting under the Australian Plate forms the Tonga
Tonga Trench
The Tonga Trench is located in the South Pacific Ocean and is deep at its deepest point, known as the Horizon Deep.The Tonga Trench is a convergent plate boundary. The trench lies at the northern end of the Kermadec-Tonga Subduction Zone, an active subduction zone where the Pacific Plate is being...

 and Kermadec Trench
Kermadec Trench
The Kermadec trench is one of Earth's deepest oceanic trenches, reaching a depth of . Formed by the subduction of the Pacific Plate under the Indo-Australian Plate, it runs over a thousand kilometres parallel with and to the east of the Kermadec Ridge and island arc, from near the northeastern tip...

es, and the parallel Tonga
Tonga
Tonga, officially the Kingdom of Tonga , is a state and an archipelago in the South Pacific Ocean, comprising 176 islands scattered over of ocean in the South Pacific...

 and Kermadec
Kermadec Islands
The Kermadec Islands are a subtropical island arc in the South Pacific Ocean northeast of New Zealand's North Island, and a similar distance southwest of Tonga...

 island arc
Island arc
An island arc is a type of archipelago composed of a chain of volcanoes which alignment is arc-shaped, and which are situated parallel and close to a boundary between two converging tectonic plates....

s. It has also uplifted the eastern parts of New Zealand's North Island
North Island
The North Island is one of the two main islands of New Zealand, separated from the much less populous South Island by Cook Strait. The island is in area, making it the world's 14th-largest island...

.

The continent of Zealandia
Zealandia (continent)
Zealandia , also known as Tasmantis or the New Zealand continent, is a nearly submerged continental fragment that sank after breaking away from Australia 60–85 million years ago, having separated from Antarctica between 85 and 130 million years ago...

, which separated from Australia 85 million years ago and stretches from New Caledonia
New Caledonia
New Caledonia is a special collectivity of France located in the southwest Pacific Ocean, east of Australia and about from Metropolitan France. The archipelago, part of the Melanesia subregion, includes the main island of Grande Terre, the Loyalty Islands, the Belep archipelago, the Isle of...

 in the north to New Zealand's subantarctic islands
New Zealand sub-antarctic islands
The five southernmost groups of the New Zealand Outlying Islands form the New Zealand Sub-Antarctic islands. These islands are collectively designated as an UNESCO World Heritage Site....

 in the south, is now being torn apart along the transform boundary marked by the Alpine Fault
Alpine Fault
The Alpine Fault is a geological fault, more specifically known as a right-lateral strike-slip fault, that runs almost the entire length of New Zealand's South Island. It forms a transform boundary between the Pacific Plate and the Indo-Australian Plate. Earthquakes along the fault, and the...

.

South of New Zealand the boundary becomes a transitional transform-convergent boundary, the Macquarie Fault Zone
Macquarie Fault Zone
The Macquarie Fault Zone is a major right lateral-moving transform fault along the seafloor of the south Pacific Ocean which runs from New Zealand southwestward to the Macquarie Triple Junction...

, where the Australian Plate is beginning to subduct under the Pacific Plate along the Puysegur Trench
Puysegur trench
The deep Puysegur Trench is a deep cleft in the floor of the south Tasman Sea formed by the subduction of the Indo-Australian Plate under the Pacific Plate to the south of New Zealand. Immediately to its east lies a ridge, a northern extension of the Macquarie Ridge, which separates the Puysegur...

. Extending southwest of this trench is the Macquarie Ridge.

The southerly side is a divergent boundary
Divergent boundary
In plate tectonics, a divergent boundary or divergent plate boundary is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent boundaries within continents initially produce rifts which produce rift valleys...

 with the Antarctic Plate
Antarctic Plate
The Antarctic Plate is a tectonic plate covering the continent of Antarctica and extending outward under the surrounding oceans. The Antarctic Plate has a boundary with the Nazca Plate, the South American Plate, the African Plate, the Indo-Australian Plate, the Scotia Plate and a divergent boundary...

 called the Southeast Indian Ridge
Southeast Indian Ridge
The Southeast Indian Ridge is a divergent tectonic plate boundary located along the seafloor of the southern Indian Ocean. It separates the Indo-Australian Plate to the north from the Antarctic Plate to the south...

 (SEIR). The westerly side is a transform boundary with the Arabian Plate
Arabian Plate
The Arabian Plate is one of three tectonic plates which have been moving northward over millions of years and colliding with the Eurasian Plate...

 called the Owen Fracture Zone
Owen Fracture Zone
The Owen Fracture Zone is a transform fault which runs along the eastern boundary of the Arabian Plate, separating it from the Indo-Australian Plate for most of its length, and from the African Plate for a much shorter distance...

, and a divergent boundary with the African Plate
African Plate
The African Plate is a tectonic plate which includes the continent of Africa, as well as oceanic crust which lies between the continent and various surrounding ocean ridges.-Boundaries:...

 called the Central Indian Ridge
Central Indian Ridge
The Central Indian Ridge is a divergent tectonic plate boundary between the African Plate and the Indo-Australian Plate, traversing the western regions of the Indian Ocean...

 (CIR). The northerly side of the Indo-Australian Plate is a convergent boundary with the Eurasian Plate
Eurasian Plate
The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...

 forming the Himalaya and Hindu Kush
Hindu Kush
The Hindu Kush is an mountain range that stretches between central Afghanistan and northern Pakistan. The highest point in the Hindu Kush is Tirich Mir in the Chitral region of Khyber-Pakhtunkhwa, Pakistan.It is the westernmost extension of the Pamir Mountains, the Karakoram Range, and is a...

 mountain
Mountain
Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...

s.

The northeast side of the Indo-Australian plate forms a subducting boundary with the Eurasian plate on the borders of the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...

 from Bangladesh
Bangladesh
Bangladesh , officially the People's Republic of Bangladesh is a sovereign state located in South Asia. It is bordered by India on all sides except for a small border with Burma to the far southeast and by the Bay of Bengal to the south...

, to Myanmar
Myanmar
Burma , officially the Republic of the Union of Myanmar , is a country in Southeast Asia. Burma is bordered by China on the northeast, Laos on the east, Thailand on the southeast, Bangladesh on the west, India on the northwest, the Bay of Bengal to the southwest, and the Andaman Sea on the south....

 (formerly Burma) to the south-west of Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...

n islands of Sumatra
Sumatra
Sumatra is an island in western Indonesia, westernmost of the Sunda Islands. It is the largest island entirely in Indonesia , and the sixth largest island in the world at 473,481 km2 with a population of 50,365,538...

 and Borneo
Borneo
Borneo is the third largest island in the world and is located north of Java Island, Indonesia, at the geographic centre of Maritime Southeast Asia....

.

The subducting boundary through Indonesia is not parallel to the biogeographical
Biogeography
Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...

 Wallace line
Wallace Line
The Wallace Line separates the ecozones of Asia and Wallacea, a transitional zone between Asia and Australia. West of the line are found organisms related to Asiatic species; to the east, a mixture of species of Asian and Australian origin is present...

 that separates the indigenous fauna of Asia from that of Australasia
Australasia
Australasia is a region of Oceania comprising Australia, New Zealand, the island of New Guinea, and neighbouring islands in the Pacific Ocean. The term was coined by Charles de Brosses in Histoire des navigations aux terres australes...

: the Eastern islands of Indonesia lie mainly on the Eurasian Plate
Eurasian Plate
The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...

, but have Australasian-related fauna and flora.
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