The Indo-Australian Plate is or was a major tectonic plate. It is in the process of separation into three plates, and may be currently separated into more than one plate. It contains the continent of Australia, its surrounding ocean and extends north-west to include the Indian subcontinent and the adjacent waters.
It was formed by the fusion of the then Indian and the then Australian plates approximately 43 million years ago. [1] The fusion happened when the mid-ocean ridge in the Indian Ocean, which separated the two plates, ceased spreading. [2]
Australia-New Guinea (Mainland Australia, New Guinea, and Tasmania), the Indian subcontinent, and Zealandia (New Caledonia, New Zealand, and Norfolk Island) are all fragments of the ancient supercontinent of Gondwana. As the ocean floor broke apart, these land masses fragmented from one another, and for a time these centers were thought to be dormant and fused into a single plate. However, research in the early 21st century indicates plate separation of the Indo-Australian Plate may have already occurred. [3] [4] [5] [6]
The eastern side of the plate is the convergent boundary with the Pacific Plate. The Pacific Plate sinks below the Australian plate and forms the Kermadec Trench and the island arcs of Tonga and Kermadec. New Zealand is situated along the southeastern boundary of the plate, which with New Caledonia makes up the southern and northern ends of the ancient landmass of Zealandia, which separated from Australia 85 million years ago. The central part of Zealandia sank under the sea.
The southern margin of the plate forms a divergent boundary with the Antarctic Plate. The western side is subdivided by the Indian Plate that borders the Arabian Plate to the north and the African Plate to the south. The northern margin of the Indian Plate forms a convergent boundary with the Eurasian Plate, which constitutes the active orogenic process of the Himalayas and the Hindukush mountains.
The northeast side of the Australian Plate forms a subduction boundary with the Eurasian Plate in the Indian Ocean between the borders of Bangladesh and Burma and to the southwest of the Indonesian islands of Sumatra and Borneo. Along the northern Ninety East Ridge under the Indian Ocean there appears to be a weakness zone where the Indian and Australian plates are going different ways. [4] [6] The subsidence boundary through Indonesia is reflected in the Wallace line.
The eastern part (Australian Plate) is moving northward at the rate of 5.6 cm (2.2 in) per year while the western part (Indian Plate) is moving only at the rate of 3.7 cm (1.5 in) per year due to the impediment of the Himalayas. In terms of the middle of India and Australia's landmasses, Australia is moving northward at 3 cm (1.2 in) per year relative to India. [4] This differential movement has resulted in the compression of the former plate near its centre at Sumatra and the division into the separate Indian and Australian plates again. [7] [6]
A third plate, known as the Capricorn Plate, may also be separating off the western side of the Indian Plate as part of the continued breakup of the Indo-Australian Plate. [8]
There is good evidence that the Indo-Australian Plate is in the process of separation into new plates. [9] : 4648 Recent studies, and evidence from seismic events such as the 2012 Indian Ocean earthquakes, suggest that the Indo-Australian Plate may have already broken up into two or three separate plates due primarily to stresses induced by the collision of the Indo-Australian Plate with Eurasia along what later became the Himalayas, [10] [11] and that the Indian Plate and Australian Plate may have been separate for at least 3 million years ago. [3]
Contemporary models suggest at present there is 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. [4] [6] In due course, some expect a well defined localized boundary to reform between the Indian and Australian plates. [5] Studies show the Ninetyeast Ridge has active faulting along its whole length so that while the simplest explanation is that the Indian and Australian plates have already separated here, it remains possible that only the Capricorn Plate has separated from them. [9] : 4667
The Eurasian Plate is a tectonic plate that 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 eastern Siberia. It also includes oceanic crust extending westward to the Mid-Atlantic Ridge and northward to the Gakkel Ridge.
The Tonga Trench is an oceanic trench located in the southwestern Pacific Ocean. It is the deepest trench in the Southern hemisphere and the second deepest on Earth after the Mariana Trench. The fastest plate-tectonic velocity on Earth is occurring at this location, as the Pacific Plate is being subducted westward in the trench.
The Anatolian Sub-Plate is a continental tectonic plate that is separated from the Eurasian plate and the Arabian plate by the North Anatolian Fault and the East Anatolian Fault respectively. Most of the country of Turkey is located on the Anatolian plate. Most significant earthquakes in the region have historically occurred along the northern fault, such as the 1939 Erzincan earthquake. The devastating 2023 Turkey–Syria earthquake occurred along the active East Anatolian fault at a strike slip fault where the Arabian plate is sliding past the Anatolian plate horizontally.
The Australian Plate is a major tectonic plate in the eastern and, largely, southern hemispheres. Originally a part of the ancient continent of Gondwana, Australia remained connected to India and Antarctica until approximately 100 million years ago when India broke away and began moving north. Australia and Antarctica had begun rifting by 96 million years ago and completely separated a while after this, some believing as recently as 45 million years ago, but most accepting presently that this had occurred by 60 million years ago.
The Burma Plate is a minor tectonic plate or microplate located in Southeast Asia, sometimes considered a part of the larger Eurasian Plate. The Andaman Islands, Nicobar Islands, and northwestern Sumatra are located on the plate. This island arc separates the Andaman Sea from the main Indian Ocean to the west.
The Sunda Plate is a minor tectonic plate straddling the Equator in the Eastern Hemisphere on which the majority of Southeast Asia is located.
The Indonesian island of Sumatra is located in a highly seismic area of the world. In addition to the subduction zone off the west coast of the island, Sumatra also has a large strike-slip fault, the Great Sumatran Fault also known as Semangko Fault, running the entire length of the island. This fault zone accommodates most of the strike-slip motion associated with the oblique convergence between the Indo-Australian and Eurasian plates. The fault ends in the north just below the city of Banda Aceh, which was devastated in the 2004 Indian Ocean earthquake. After the December 2004 earthquake, pressure on the Great Sumatran Fault has increased tremendously, especially in the north.
The Owen Fracture Zone (OFZ), though misnamed as a fracture zone, is a transform fault in the northwest Indian Ocean that separates the Arabian and African Plates from the Indian Plate. Extending north-northeast from where the Carlsberg Ridge meets the Sheba ridge in the south to the Makran Subduction Zone in the north, it represents the port side of the northward motion of the Indian subcontinent during the Late Cretaceous–Palaeogene break-up of Gondwana. Slip along the Owen Fracture Zone is occurring at 2 mm (0.079 in)/yr, the slowest rate on Earth, which means the Arabian Plate moves northward faster than the Indian Plate.
The Ninety East Ridge is a mid-ocean ridge on the Indian Ocean floor named for its near-parallel strike along the 90th meridian at the center of the Eastern Hemisphere. It is approximately 5,000 kilometres (3,100 mi) in length and can be traced topographically from the Bay of Bengal southward towards the Southeast Indian Ridge (SEIR), though the feature continues to the north where it is hidden beneath the sediments of the Bengal Fan. The ridge extends between latitudes 31°S and 9°N and has an average width of 200 km (120 mi).
The Macquarie Triple Junction is a geologically active tectonic boundary located at 61°30′S161°0′E at which the historic Indo-Australian Plate, Pacific Plate, and Antarctic Plate collide and interact. The term Triple Junction is given to particular tectonic boundaries at which three separate tectonic plates meet at a specific, singular location. The Macquarie Triple Junction is located on the seafloor of the southern region of the Pacific Ocean, just south of New Zealand. This tectonic boundary was named in respect to the nearby Macquarie Island, which is located southeast of New Zealand.
The Kermadec-Tonga subduction zone is a convergent plate boundary that stretches from the North Island of New Zealand northward. The formation of the Kermadec and Tonga Plates started about 4–5 million years ago. Today, the eastern boundary of the Tonga Plate is one of the fastest subduction zones, with a rate up to 24 cm/year (9.4 in/year). The trench formed between the Kermadec-Tonga and Pacific Plates is also home to the second deepest trench in the world, at about 10,800 m, as well as the longest chain of submerged volcanoes.
The 1,600 kilometres (990 mi) long 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 towards the Macquarie Triple Junction. It is also the tectonic plate boundary between the Australian Plate to the northwest and the Pacific Plate to the southeast. As such it is a region of high seismic activity and recorded the largest strike-slip event on record up to 23 May 1989, of at least Mw8.0
Zealandia, also known as Te Riu-a-Māui (Māori) or Tasmantis, is an almost entirely submerged mass of continental crust in Oceania that subsided after breaking away from Gondwana 83–79 million years ago. It has been described variously as a submerged continent, continental fragment, and microcontinent. The name and concept for Zealandia was proposed by Bruce Luyendyk in 1995, and satellite imagery shows it to be almost the size of Australia. A 2021 study suggests Zealandia is over a billion years old, about twice as old as geologists previously thought.
The Kermadec Plate is a long and narrow tectonic plate located west of the Kermadec Trench in the south Pacific Ocean. Also included on this tectonic plate is a small portion of the North Island of New Zealand and the Kermadec Islands. It is separated from the Australian Plate by a long divergent boundary which forms a back-arc basin. This area is highly prone to earthquakes and tsunamis.
The Sunda megathrust is a fault that extends approximately 5,500 km (3300 mi) from Myanmar (Burma) in the north, running along the southwestern side of Sumatra, to the south of Java and Bali before terminating near Australia. It is a megathrust, located at a convergent plate boundary where it forms the interface between the overriding Eurasian plate and the subducting Indo-Australian plate. It is one of the most seismogenic structures on Earth, being responsible for many great and giant earthquakes, including the 2004 Indian Ocean earthquake and tsunami that killed over 227,000 people. The Sunda megathrust can be divided into the Andaman Megathrust, Sumatra(n) Megathrust and Java(n) Megathrust. The Bali-Sumbawa segment is much less active and therefore does not have the "megathrust" term associated with it.
The 2012 Indian Ocean earthquakes were magnitude 8.6 and 8.2 Mw undersea earthquakes that struck near the Indonesian province of Aceh on 11 April at 15:38 local time. Initially, authorities feared that the initial earthquake would cause a tsunami and warnings were issued across the Indian Ocean; however, these warnings were subsequently cancelled. These were unusually strong intraplate earthquakes and the largest strike-slip earthquake ever recorded.
The Sumatra Trench is a part of the Sunda Trench or Java Trench. The Sunda subduction zone is located in the east part of Indian Ocean, and is about 300 km (190 mi) from the southwest coast of Sumatra and Java islands. It extends over 5,000 km (3,100 mi) long, starting from Myanmar in the northwest and ending at Sumba Island in the southeast.
The geology of Myanmar is shaped by dramatic, ongoing tectonic processes controlled by shifting tectonic components as the Indian plate slides northwards and towards Southeast Asia. Myanmar spans across parts of three tectonic plates separated by north-trending faults. To the west, a highly oblique subduction zone separates the offshore Indian plate from the Burma microplate, which underlies most of the country. In the center-east of Myanmar, a right lateral strike slip fault extends from south to north across more than 1,000 km (620 mi). These tectonic zones are responsible for large earthquakes in the region. The India-Eurasia plate collision which initiated in the Eocene provides the last geological pieces of Myanmar, and thus Myanmar preserves a more extensive Cenozoic geological record as compared to records of the Mesozoic and Paleozoic eras. Myanmar is physiographically divided into three regions: the Indo-Burman Range, Myanmar Central Belt and the Shan Plateau; these all display an arcuate shape bulging westwards. The varying regional tectonic settings of Myanmar not only give rise to disparate regional features, but also foster the formation of petroleum basins and a diverse mix of mineral resources.
Oblique subduction is a form of subduction for which the convergence direction differs from 90° to the plate boundary. Most convergent boundaries involve oblique subduction, particularly in the Ring of Fire including the Ryukyu, Aleutian, Central America and Chile subduction zones. In general, the obliquity angle is between 15° and 30°. Subduction zones with high obliquity angles include Sunda trench and Ryukyu arc.
