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 Scotia plate is a minor tectonic plate on the edge of the South Atlantic and Southern oceans. Thought to have formed during the early Eocene with the opening of the Drake Passage that separates Antarctica and South America, it is a minor plate whose movement is largely controlled by the two major plates that surround it: the Antarctic plate and the South American plate. The Scotia plate takes its name from the steam yacht Scotia of the Scottish National Antarctic Expedition (1902–04), the expedition that made the first bathymetric study of the region.
A triple junction is the point where the boundaries of three tectonic plates meet. At the triple junction each of the three boundaries will be one of three types – a ridge (R), trench (T) or transform fault (F) – and triple junctions can be described according to the types of plate margin that meet at them. Of the ten possible types of triple junctions only a few are stable through time. The meeting of four or more plates is also theoretically possible, but junctions will only exist instantaneously.
The Kerguelen Plateau, also known as the Kerguelen–Heard Plateau, is an oceanic plateau and large igneous province (LIP) located on the Antarctic Plate, in the southern Indian Ocean. It is about 3,000 km (1,900 mi) to the southwest of Australia and is nearly three times the size of California. The plateau extends for more than 2,200 km (1,400 mi) in a northwest–southeast direction and lies in deep water.
The Somali plate is a minor tectonic plate which straddles the Equator in the Eastern Hemisphere. It is currently in the process of separating from the African plate along the East African Rift Valley. It is approximately centered on the island of Madagascar and includes about half of the east coast of Africa, from the Gulf of Aden in the north through the East African Rift Valley. The southern boundary with the Nubian–African plate is a diffuse plate boundary consisting of the Lwandle plate.
A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about 2,600 meters (8,500 ft) and rises about 2,000 meters (6,600 ft) above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a divergent plate boundary. The rate of seafloor spreading determines the morphology of the crest of the mid-ocean ridge and its width in an ocean basin.
The Phoenix plate was a tectonic plate that existed during the early Paleozoic through late Cenozoic time. It formed a triple junction with the Izanagi and Farallon plates in the Panthalassa Ocean as early as 410 million years ago, during which time the Phoenix plate was subducting under eastern Gondwana.
The Easter plate is a tectonic microplate located to the west of Easter Island off the west coast of South America in the middle of the Pacific Ocean, bordering the Nazca plate to the east and the Pacific plate to the west. It was discovered from looking at earthquake distributions that were offset from the previously perceived Nazca-Pacific Divergent boundary. This young plate is 5.25 million years old and is considered a microplate because it is small with an area of approximately 160,000 square kilometres (62,000 sq mi). Seafloor spreading along the Easter microplate's borders have some of the highest global rates, ranging from 50 to 140 millimetres /yr.
The Azores triple junction (ATJ) is a geologic triple junction where the boundaries of three tectonic plates intersect: the North American plate, the Eurasian plate and the African plate. This triple junction is located along the Mid-Atlantic Ridge (MAR) amidst the Azores islands, nearly due west of the Strait of Gibraltar. It is classified as an R-R-R triple junction of the T type, as it is an intersection of the Mid-Atlantic Ridge running north–south and the Terceira Rift which runs east-southeast.
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 Central Indian Ridge (CIR) is a north–south-trending mid-ocean ridge in the western Indian Ocean.
The Southwest Indian Ridge (SWIR) is a mid-ocean ridge located along the floors of the south-west Indian Ocean and south-east Atlantic Ocean. A divergent tectonic plate boundary separating the Somali plate to the north from the Antarctic plate to the south, the SWIR is characterised by ultra-slow spreading rates (only exceeding those of the Gakkel Ridge in the Arctic) combined with a fast lengthening of its axis between the two flanking triple junctions, Rodrigues (20°30′S70°00′E) in the Indian Ocean and Bouvet (54°17′S1°5′W) in the Atlantic Ocean.
The Southeast Indian Ridge (SEIR) is a mid-ocean ridge in the southern Indian Ocean. A divergent tectonic plate boundary stretching almost 6,000 km (3,700 mi) between the Rodrigues triple junction in the Indian Ocean and the Macquarie triple junction in the Pacific Ocean, the SEIR forms the plate boundary between the Australian and Antarctic plates since the Oligocene (anomaly 13).
The Bouvet triple junction is a geologic triple junction of three tectonic plates located on the seafloor of the South Atlantic Ocean. It is named after Bouvet Island, which lies about 250 km (160 mi) to the east. The three plates which meet here are the South American plate, the African plate, and the Antarctic plate. The Bouvet triple junction although it appears to be a R-R-R type, that is, the three plate boundaries which meet here as mid-ocean ridges: the Mid-Atlantic Ridge (MAR), the Southwest Indian Ridge (SWIR), and the South American-Antarctic Ridge (SAAR) is actually slightly more complex and in transition.
The South American–Antarctic Ridge or simply American-Antarctic Ridge is the tectonic spreading center between the South American plate and the Antarctic plate. It runs along the sea-floor from the Bouvet triple junction in the South Atlantic Ocean south-westward to a major transform fault boundary east of the South Sandwich Islands. Near the Bouvet triple junction the spreading half rate is 9 mm/a (0.35 in/year), which is slow, and the SAAR has the rough topography characteristic of slow-spreading ridges.
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 Galápagos triple junction (GTJ) is a geological area in the eastern Pacific Ocean several hundred miles west of the Galápagos Islands where three tectonic plates – the Cocos plate, the Nazca plate, and the Pacific plate – meet. It is an unusual type of triple junction in which the three plates do not meet at a simple intersection. Instead, the junction includes two small microplates, the Galápagos microplate and the northern Galápagos microplate, caught in the junction, turning synchronously with respect to each other and separated by the Hess Deep rift.
The Queen Charlotte triple junction is a geologic triple junction where three tectonic plates meet: the Pacific plate, the North American plate, and the Explorer plate. The three plate boundaries which intersect here are the Queen Charlotte Fault, the northern Cascadia subduction zone, and the Explorer Ridge. The Queen Charlotte triple junction is currently positioned adjacent to the Queen Charlotte Sound near the Dellwood Knolls off the coast of Vancouver Island. 10 Ma to 1.5 Ma prior to the triple junction's current location, it was located southwest of Vancouver Island The movements of the triple junction have been characterized by two major shifts in the Pacific-North American Tertiary plate tectonic record. First, at approximately 40 Ma the relative plate motions switched from orthogonal convergence to right-lateral strike slip. The variance in location of the triple junction may have also been related to the formation of an independent basin block. This formation could have been produced by fore-arc bending of the Pacific plate, due to oblique underthrusting prior to 1 Ma which produced stresses sufficient to break the Pacific plate and isolate the block. Transpression of 15–30 mm/yr since 5 Ma has been taking place, as well as varying amounts of both transpression and transtension occurring before then. To the northwest of the triple junction the Pacific plate currently has 15 degrees of oblique convergence, passing under the North American plate along the Queen Charlotte transform fault zone. The Explorer plate is a small chunk of the Juan de Fuca plate that broke away from the Juan de Fuca plate about 3.5 Ma and has moved much slower with respect to North America.
The Pacific Ocean evolved in the Mesozoic from the Panthalassic Ocean, which had formed when Rodinia rifted apart around 750 Ma. The first ocean floor which is part of the current Pacific plate began 160 Ma to the west of the central Pacific and subsequently developed into the largest oceanic plate on Earth.
The Lwandle plate is one of three tectonic microplates, along with the Rovuma plate and Victoria plate, that make up the African plate with the Somali plate and the Nubian plate. Its discovery is very recent, so the velocity of the plate is neither well known nor well understood. Many experiments are ongoing to quantify this. The Lwandle plate lies between 30°E and 50°E, sharing a boundary with the Nubian, Somali, and Antarctic plates.
