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60-545: The SEIR is the spreading centre closest to the Kerguelen and Amsterdam – Saint-Paul hotspots . The SEIR has an intermediate full spreading rate of 65 mm/a (2.6 in/year), and, because Antarctica is virtually stationary, this results in a northward ridge migration of half that rate. Spreading rates along the SEIR varies from 69 mm/a (2.7 in/year) near 88°E to 75 mm/a (3.0 in/year) near 120°E. During

120-521: A zigzag pattern. This results from oblique seafloor spreading where the direction of motion is not perpendicular to the trend of the overall divergent boundary. A smaller number of such faults are found on land, although these are generally better-known, such as the San Andreas Fault and North Anatolian Fault . Transform boundaries are also known as conservative plate boundaries because they involve no addition or loss of lithosphere at

180-409: A junction with another plate boundary, while transcurrent faults may die out without a junction with another fault. Finally, transform faults form a tectonic plate boundary, while transcurrent faults do not. Faults in general are focused areas of deformation or strain , which are the response of built-up stresses in the form of compression , tension, or shear stress in rock at the surface or deep in

240-533: A magma flow from the Kerguelen–ASP hotspots to the AAD 'cold spot' at 120–128°E. Located at 126°E, the AAD would thus mark the 40 km (25 mi)-long transition between Indian Ocean and Pacific MORBs (mid-ocean ridge basalts), a boundary that has been migrating westward during the past tens of million years. Between 102°E and the AAD, where the spreading rate is constant, the left-stepping transform faults suggest

300-601: A spreading ridge. The lack of a conjugate structure on the Antarctic Plate, however, makes it unlikely that the hotspot was located at a spreading ridge during this long period. As the Antarctic Plate then moved over the Kerguelen hotspot the NKP formed over relatively old oceanic crust. Flood basalts in the Kerguelen archipelago formed 30–24 Ma and less voluminous and more recent volcanism occurred until 1 Ma . During

360-747: A thin oceanic crust and a rough topography with deep valleys. The AAD is found between 120° and 128° E and covers about 500 km (310 mi) of the SEIR which at this point is deep mid-ocean ridge at between 4,000–4,500 m (13,100–14,800 ft) in the centre of the Australian–Antarctic depression. Between the AAD and the Amsterdam and St. Paul islands, spreading rate is constant at 69–75 mm/a (2.7–3.0 in/year) while axial depth increases by more than 2,300 m (7,500 ft). This has been interpreted as an eastward decrease in mantle temperature of perhaps 100 °C (212 °F) caused by

420-418: A transform fault links a spreading center and the upper block of a subduction zone or where two upper blocks of subduction zones are linked, the transform fault itself will grow in length. [REDACTED] [REDACTED] Constant length: In other cases, transform faults will remain at a constant length. This steadiness can be attributed to many different causes. In the case of ridge-to-ridge transforms,

480-460: Is a fault along a plate boundary where the motion is predominantly horizontal . It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subduction zone . A transform fault is a special case of a strike-slip fault that also forms a plate boundary. Most such faults are found in oceanic crust , where they accommodate the lateral offset between segments of divergent boundaries , forming

540-507: Is being created to change that length. [REDACTED] [REDACTED] Decreasing length faults: In rare cases, transform faults can shrink in length. These occur when two descending subduction plates are linked by a transform fault. In time as the plates are subducted, the transform fault will decrease in length until the transform fault disappears completely, leaving only two subduction zones facing in opposite directions. [REDACTED] [REDACTED] The most prominent examples of

600-435: Is constantly created through the upwelling of new basaltic magma . With new seafloor being pushed and pulled out, the older seafloor slowly slides away from the mid-oceanic ridges toward the continents. Although separated only by tens of kilometers, this separation between segments of the ridges causes portions of the seafloor to push past each other in opposing directions. This lateral movement of seafloors past each other

660-515: Is likely to have played a role in the breakup of eastern Gondwana about 136 Ma and be relevant to the formation of the SEIR later but this relevance is still not fully understood. The Kerguelen hotspot, located more than 1,000 km (620 mi) from the SEIR currently, also influences the MORB composition of the SEIR near the ASP Plateau. About 43 to 40 Ma ago, Broken Ridge to the north and

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720-476: Is now considered unsupported, with the plateau situated at a considerable distance from the nearest continents. It finally became submerged 20 million years ago and is now 1,000–2,000 m (3,300–6,600 ft) below sea level. During the austral summer there is a high density of migratory whales including sperm , minke , and humpback whales along the southern end of the Kerguelen Plateau and

780-927: Is the San Andreas Fault on the Pacific coast of the United States. The San Andreas Fault links the East Pacific Rise off the West coast of Mexico (Gulf of California) to the Mendocino Triple Junction (Part of the Juan de Fuca plate ) off the coast of the Northwestern United States , making it a ridge-to-transform-style fault. The formation of the San Andreas Fault system occurred fairly recently during

840-435: Is where transform faults are currently active. Transform faults move differently from a strike-slip fault at the mid-oceanic ridge. Instead of the ridges moving away from each other, as they do in other strike-slip faults, transform-fault ridges remain in the same, fixed locations, and the new ocean seafloor created at the ridges is pushed away from the ridge. Evidence of this motion can be found in paleomagnetic striping on

900-551: 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 plateau

960-790: The Ninety East Ridge formed 82–37 Ma north to south; the Bunbury Basalt ( Western Australia ) 137–130.5 Ma ; the Naturaliste Plateau (offshore Western Australia) formed 132–128 Ma ; the Rajmahal Traps in Northeast India 118–117 Ma ; and finally lamprophyres in India and Antarctica 115–114 Ma . The oldest Australian volcanism that can be attributed to the Kerguelen plume are

1020-705: The Oligocene Period between 34 million and 24 million years ago. During this period, the Farallon plate , followed by the Pacific plate, collided into the North American plate . The collision led to the subduction of the Farallon plate underneath the North American plate. Once the spreading center separating the Pacific and the Farallon plates was subducted beneath the North American plate,

1080-706: The Princess Elizabeth Trough between SKP and Antarctica or along India's conjugate eastern continental margin. The relation between the Kerguelen hotspot and these continental breakup and volcanic margins is instead similar to that between the Réunion hotspot and the Deccan Traps and the breakup between western India and the Seychelles . The peak output of the Kerguelen hotspot coincides with one or several microcontinent formations, such as

1140-738: The Rodriguez Triple Junction . It is separated from Antarctica by the Princess Elizabeth Trough and the Cooperation Sea . The eastern margin north of the William Ridge is steep and formed during the breakup between the Kerguelen Plateau and the Broken Ridge. The southern part of the margin is separated from the Australian–Antarctic Basin by the deep Labuan Basin . From the initial opening of

1200-784: The Antarctic Plate side within 40 km (25 mi) of the SEIR. North-east of the ASP Plateau a string of submarine volcanoes, the Chain of the Dead Poets, 1–3 km (0.62–1.86 mi)-high and 40 km (25 mi)-wide, mark the track of the ASP hotspot across the Australian Plate. This track leads to the intersection of the Broken Ridge and Ninety East Ridge west of Australia. The ASP hotspot ceased to produce these volcanoes some 10 to 5 million years ago when

1260-615: The Bunbury Basalt (137–130.5 Ma ) and the Naturaliste Plateau (132–128 Ma ) in southwestern Australia. The Sylhet and Rajmahal Traps in eastern India (118-115 Ma ), the formation of the oldest portion of the Kerguelen LIP and these continental basalts are linked to the opening of the eastern Indian Ocean. The Bunbury Basalt is not of flood basalt dimensions which suggests that the mantle underlying

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1320-472: The Earth's subsurface. Transform faults specifically accommodate lateral strain by transferring displacement between mid-ocean ridges or subduction zones. They also act as the plane of weakness, which may result in splitting in rift zones . Transform faults are commonly found linking segments of divergent boundaries ( mid-oceanic ridges or spreading centres). These mid-oceanic ridges are where new seafloor

1380-461: The Earth's surface. Geophysicist and geologist John Tuzo Wilson recognized that the offsets of oceanic ridges by faults do not follow the classical pattern of an offset fence or geological marker in Reid's rebound theory of faulting , from which the sense of slip is derived. The new class of faults, called transform faults, produce slip in the opposite direction from what one would surmise from

1440-610: The Elan Bank into a microcontinent and dispersed continental fragments in the SKP, and these structures were eventually left behind as India moved northward. The ridge jump that made the Elan Bank a microcontinent occurred after 124 Ma . The development of the Southern Kerguelen Plateau 118–119 Ma contributed to the oceanic anoxic event 1 . Around 83.5 Ma sea floor spreading between India and Antarctica

1500-467: The Elan Bank. Since the Indian Ocean began to open about 130 Ma , the Kerguelen hotspot has moved 3–10° southward and, consequently, the spreading ridge between India and Antarctica has jumped northward one or several times. Parts of the Kerguelen Plateau, the Elan Bank and the SKP, were originally attached to India and are composed of continental lithosphere. One or several ridge jumps transformed

1560-467: The Indian Ocean ridge and due west of Australia is the Broken Ridge underwater volcanic plateau , which at one time was contiguous with the Kerguelen Plateau before rifting by the mid-ocean ridge . To the north of Broken Ridge is the linear Ninety East Ridge which continues almost due north into the Bay of Bengal and is considered to be a hotspot track. One of the largest igneous provinces (LIPs) in

1620-555: The Indian Ocean until present, the Kerguelen hotspot has produced several, now widely dispersed, large-scale structures. These are now known to cover a time range from 145 to 0 million years ago (Ma) with the oldest assigned structure being the Comei large igneous province in south-eastern Tibet . Historic work had believed that the hotspot became active more recently in what is now south-east Australia. Ongoing analysis of specimens can result in timing changes, so some dates in

1680-496: The Kerguelen Archipelago and were the first to identify the Kerguelen Plateau as of continental origin, in contrast to other LIPs. The presence of soil layers in the basalt which included charcoal and conglomerate fragments of gneiss indicate that much of the plateau was above sea level as what is termed a microcontinent for three periods between 100 million years ago and 20 million years ago (the charcoal

1740-653: The Kerguelen hotspot was neither significantly hot, wet, or voluminous. In contrast, the magmatism that produced the Australia–India breakup 136–158 Ma created the Wallaby Plateau , but no known hotspot has been linked to this event. The output from the Kerguelen hotspot peaked 120–95 Ma , 12–70 Ma after the India–Antarctica breakup. No ridges or hotspot tracks such as Walvis – Rio Grande , Chagos–Laccadive , Greenland–Scotland have been found in

1800-615: The Kerguelen hotspot. The ASP hotspot was originally located beneath Australia and a chain of seamounts connecting it to the southern end of the Ninety East Ridge, i.e. the ASP hotspot track, indicate it probably contributed to the formation of the Ninety East Ridge before the SEIR opened. The opening of the Southern Ocean began west of Australia around 100  million years ago from where it propagated eastward at about 2 cm/year (0.79 in/year). This rifting

1860-399: The Kerguelen plateau to its far south were adjacent, having been formed by the Kerguelen hotspot and the propagation of the SEIR rift fracture has separated them. Many recent authors do not try to portray a continuous connection between Broken Ridge which has Kerguele plume basalts formed 37 Ma ago and the Kerguelen plateau basalts formed between 37 Ma and now for several reasons, including that

Southeast Indian Ridge - Misplaced Pages Continue

1920-699: The SEIR evolves rapidly within the framework of the stable transform faults. Australia and Antarctica were neighbours before the break-up of Gondwana in the Cretaceous and several conjugate structures exist on either side of the SEIR. In south-western Australia the Albany-Fraser Orogen formed during the Mesoproterozoic collision between the Australian Yilgarn and Antarctic Mawson cratons. The continental basement of

1980-425: The SEIR reaches its maximum axial depths. The first-order transform faults are off-set 2–17 km (1.2–10.6 mi) by 19 non-transform discontinuities, resulting in 18–180 km (11–112 mi)-long second-order segments. The flanks of the SEIR are dominated by fracture zones perpendicular to the ridge and gravitational lineations oblique to the spreading direction and sometimes zigzag-shaped. This suggests that

2040-442: The SEIR started to interact with it and the hotspot started to build the shallow plateau. There is an active submarine volcano, the 1,100 m (3,600 ft)-high Boomerang Seamount , 18 km (11 mi) north of Amsterdam Island near the SEIR. Analyses of the isotope composition of basalts recovered from its caldera support that the ASP hotspot contributed to the formation of the southern Ninety East Ridge. The Kerguelen plume

2100-695: The San Andreas Continental Transform-Fault system was created. In New Zealand , the South Island 's Alpine Fault is a transform fault for much of its length. This has resulted in the folded land of the Southland Syncline being split into an eastern and western section several hundred kilometres apart. The majority of the syncline is found in Southland and The Catlins in the island's southeast, but

2160-467: The composition at and near Amsterdam and Saint Paul Island is distinct from other Kerguelen hotspot material, this has suggested to many that the Amsterdam–St. Paul hotspot (ASP) is separate from the Kerguelen hotspot . The ASP Plateau covers an area of 30,000 km (12,000 sq mi) and rises 500 m (1,600 ft) above the surrounding seafloor. Both Amsterdam and St. Paul are located on

2220-456: The constancy is caused by the continuous growth by both ridges outward, canceling any change in length. The opposite occurs when a ridge linked to a subducting plate, where all the lithosphere (new seafloor) being created by the ridge is subducted, or swallowed up, by the subduction zone. Finally, when two upper subduction plates are linked there is no change in length. This is due to the plates moving parallel with each other and no new lithosphere

2280-442: The fault changes from a normal fault with extensional stress to a strike-slip fault with lateral stress. In the study done by Bonatti and Crane, peridotite and gabbro rocks were discovered in the edges of the transform ridges. These rocks are created deep inside the Earth's mantle and then rapidly exhumed to the surface. This evidence helps to prove that new seafloor is being created at the mid-oceanic ridges and further supports

2340-570: The last 21 Ma volcanic structures have formed on the CKP, including Heard Island, and both Heard and McDonald Islands have had recent eruptions. 65 Ma , the CKP–Broken Ridge LIP was located near the Kerguelen plume and the plate boundaries of the Indian Ocean. The LIP was the product of 25 Ma of relatively high magmatic activity followed by a 40 Ma period of lower activity. Schlich et al. 1971 described tilted basement blocks near

2400-717: The last 40000 years. Elevated contributions during the Last Glacial Maximum are thought to be caused by the Antarctic Circumpolar Current and Circumpolar Deep Water and their interaction with the Circumpolar Bottom Water . 47°20′47″S 97°23′48″E  /  47.346294°S 97.396675°E  / -47.346294; 97.396675 Kerguelen Plateau The Kerguelen Plateau ( / ˈ k ɜːr ɡ əl ən / , / k ər ˈ ɡ eɪ l ən / ), also known as

2460-682: The mid- Cretaceous as well as the early Cenozoic . Fossil wood fragments recovered from the Kerguelen Islands were identified as Araucarians and Cypresses , demonstrating that Kerguelen's flora may have been similar to that of the Antarctic flora found across the Southern Hemisphere. The plateau had been proposed as forming a land bridge between India and Antarctica during the Late Cretaceous, though this

Southeast Indian Ridge - Misplaced Pages Continue

2520-846: The mid-oceanic ridge transform zones are in the Atlantic Ocean between South America and Africa . Known as the St. Paul, Romanche , Chain, and Ascension fracture zones, these areas have deep, easily identifiable transform faults and ridges. Other locations include: the East Pacific Ridge located in the South Eastern Pacific Ocean , which meets up with San Andreas Fault to the North. Transform faults are not limited to oceanic crust and spreading centers; many of them are on continental margins . The best example

2580-530: The northern part of the adjacent Princess Elizabeth Trough. These whales choose this location for foraging because the Southern Front of the Antarctic Circumpolar Current is steered off by the Plateau—resulting in a poleward extent for the Southern Front only found near the Kerguelen Plateau. This brings shoaled, nutrient-rich Upper Circumpolar Deep Water to the surface which brings macronutrients to

2640-723: The ocean floor south of the ASP Plateau and north of the Kerguele Plateau is poorly studied. Trending east-west between Australia and Antarctica, the SEIR traverses the Australian-Antarctic Discordance (AAD), a morphologically complex region overlying an area of mantle down-welling. Located midway between the ASP-Kerguelen and the Balleny-Tasmantid hotspots, the AAD overlies a region where cooler mantle temperatures have produced

2700-505: The other continent. In his work on transform-fault systems, geologist Tuzo Wilson said that transform faults must be connected to other faults or tectonic-plate boundaries on both ends; because of that requirement, transform faults can grow in length, keep a constant length, or decrease in length. These length changes are dependent on which type of fault or tectonic structure connect with the transform fault. Wilson described six types of transform faults: Growing length: In situations where

2760-444: The past few million years hotspot activity has produced a 150 km × 200 km (93 mi × 124 mi) plateau straddling on the SEIR. This Amsterdam–St. Paul Plateau while formed in the last 10 million years, started this formation beneath the Australian Plate so the plateau is now built on the components of two tectonic plates (see Kumar et al. for diagram of this complex process). For several reasons, including that

2820-628: The presence of oblique extensional forces while the presence of a long, elevated ridge near the 96°E right-stepping transform suggests a compressional force is also active. Together these features indicate the two tectonic plate made a recent counter-clockwise change in relative motion. Between 88°E and 118°E there are nine transform faults offsetting the SEIR 21–135 km (13–84 mi) of an age of 3.6 to 0.5 million years ago , accompanied by eight first-order segments (older than 5  million years ago ) and five east-migrating rifts. These transform faults and migrating rifts are located were

2880-444: The seafloor. A paper written by geophysicist Taras Gerya theorizes that the creation of the transform faults between the ridges of the mid-oceanic ridge is attributed to rotated and stretched sections of the mid-oceanic ridge. This occurs over a long period of time with the spreading center or ridge slowly deforming from a straight line to a curved line. Finally, fracturing along these planes forms transform faults. As this takes place,

2940-777: The sequence that follows may alter. The Southern Kerguelen Plateau (SKP) formed 120–110 Ma ; the Elan Bank 108–107 Ma , named by Dennis E. Hayes of Lamont Doherty Earth Observatory ; the Central Kerguelen Plateau (CKP) 101–100 Ma ; the Broken Ridge (connected to the CKP before the Eocene breakup) 95–94 Ma ; the Skiff Bank (east of the Kerguelen Islands ) 69–68 Ma ; the Northern Kerguelen Plateau (NKP) 35–34 Ma ;

3000-637: The south and the South Australian and Tasman basins to the north. The AAD forms a saddle across the channel while also offering the deepest connection between the Australian and South Indian basins. There is a voluminous contourite drift along the southern flank of SEIR. Volcanic in origin, it is most likely derived from the slopes of the Kerguelen Plateau and Crozet Islands . This redistribution of sediments has occurred during

3060-634: The standard interpretation of an offset geological feature. Slip along transform faults does not increase the distance between the ridges it separates; the distance remains constant in earthquakes because the ridges are spreading centers. This hypothesis was confirmed in a study of the fault plane solutions that showed the slip on transform faults points in the opposite direction than classical interpretation would suggest. Transform faults are closely related to transcurrent faults and are commonly confused. Both types of fault are strike-slip or side-to-side in movement; nevertheless, transform faults always end at

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3120-470: The submarine Naturaliste Plateau is also associated with this orogeny. The Darling Fault on the Australian west coast has a possible continuation beneath the Antarctic Denman Glacier . Archaean and Paleoproterzoic rocks in the Kalinjala Mylonite Zone of the Eyre Peninsula , Australia, match those found in Terre Adelie in Eastern Wilkes Land, Antarctica. Faults in Tasmania – Victoria and Northern Victoria Land have been identified as Cambrian remains of

3180-611: The surface. Ice is additionally advected north along the eastern side of the plateau. [REDACTED] Africa [REDACTED] Antarctica [REDACTED] Asia [REDACTED] Australia [REDACTED] Europe [REDACTED] North America [REDACTED] South America [REDACTED] Afro-Eurasia [REDACTED] Americas [REDACTED] Eurasia [REDACTED] Oceania 55°12′S 76°06′E  /  55.2°S 76.1°E  / -55.2; 76.1 Transform fault A transform fault or transform boundary ,

3240-408: The theory of plate tectonics. Active transform faults are between two tectonic structures or faults. Fracture zones represent the previously active transform-fault lines, which have since passed the active transform zone and are being pushed toward the continents. These elevated ridges on the ocean floor can be traced for hundreds of miles and in some cases even from one continent across an ocean to

3300-420: The west-dipping subduction zone along the eastern margin of Gondwana. Australia and Antarctica broke-up around 110  million years ago but spreading in the SEIR first began during the Eocene ( 40  million years ago ) when the Kerguelen hotspot separated Broken Ridge from the rest of the Kerguelen Plateau. The SEIR has been migrating northeast since and is now located 1,400 km (870 mi) from

3360-460: The world, the Kerguelen Plateau covers an area of 1,226,230 km (473,450 sq mi) and rises 2,000 m (6,600 ft) above the surrounding oceanic basins. Most of the plateau is less than 3,000 m (9,800 ft) below sea level. Located on the Antarctic Plate , the Kerguelen Plateau is separated from Australia by the Southeast Indian Ridge (SEIR) and from Africa by the Southwest Indian Ridge (SWIR). These two ridges meet at

3420-407: Was asymmetric in the Kerguelen Plateau region with two-thirds of the sea floor created being added to the Antarctic Plate. A ridge jump eventually transferred parts of the Kerguelen Plateau from the Indian Plate to the Antarctic Plate. The Kerguelen hotspot produced the 5,000 km (3,100 mi) long Ninety East Ridge 82–38 Ma , and geochemical evidence suggests that this occurred at or near

3480-459: Was made by wildfires started by lightning or lava flows). Large parts of the now-submarine Southern Kerguelen Plateaus (SKP) and Central Kerguelen Plateaus (CKP) were subaerial during the formation of the LIP. The SKP probably formed an island of 500,000 km (190,000 sq mi) with major peaks reaching 1,000–2,000 m (3,300–6,600 ft) above sea level. The Kerguelen Microcontinent may have been covered by dense conifer forest in

3540-421: Was not the direct product of hotspot interaction as it occurred over a cooler than normal mantle. Initially spreading was extremely slow, a half rate of 2–6 mm/a (0.079–0.236 in/year) during the period 96 to 45 million years ago after which it accelerated to 30–35 mm/a (1.2–1.4 in/year). The SEIR divides the channel between Australia and Antarctica into the South Indian Basin to

3600-406: Was produced by the Kerguelen hotspot , starting with or following the breakup of Gondwana about 130 million years ago. A small portion of the plateau breaks sea level , forming the Kerguelen Islands (a French overseas territory ) plus the Heard and McDonald Islands (an Australian external territory ). Intermittent volcanism continues on the Heard and McDonald Islands. Symmetrically across

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