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49-649: These volcanic rocks were formed from the eruptions over the Kerguelen hotspot in the early Cretaceous . The similarity between the geochemical data of Rajmahal volcanos and lavas of the Kerguelen Plateau confirms this. According to plate tectonics , the Indian subcontinent was over this hot spot during the Cretaceous Period. The original lava flow covered an area of nearly 4,100 km (1,600 sq mi). Below

98-605: A North-South trending, fault-controlled basement. This basement connects the Purnea basin of the Ganga valley with the Bengal basin. These faulted contacts, along with the Damodar Gondwana graben , form a triple junction at the mouth of the Bengal basin. The traps evolved along the then eastern continental margin of India, following rifting of Gondwanaland . Over the epochs, the upper part of

147-500: 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 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

196-557: 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 ( 25°S 70°E  /  25°S 70°E  / -25; 70 ) in the Indian Ocean and the Macquarie triple junction ( 63°S 165°E  /  63°S 165°E  / -63; 165 ) in

245-594: Is a school of thought that assigns at least two separate hotspots to the activity assigned by some to a single Kerguelen hotspot and this issue is not resolved by the implications of the latest tectonic plate modelling. The potentially separate Amsterdam-Saint Paul hotspot is assigned in such models to explain historic activity at the Amsterdam-Saint Paul Plateau to the south of the Southeast Indian Ridge with this hotspot's previous activity now to

294-482: Is now the Gulden Draak Knoll off Western Australia at 117  million years ago due to the subsequent tectonic plate motions. A best fit tectonic model explains these events by about 115  million years ago a mantle plume head reaching the surface underneath the forming Indian Ocean between India and Antarctica with extensive melting of thin oceanic crust of both plates. The Central Kerguelen Plateau

343-570: Is to the south of present Southeast Indian Ridge, but composition studies are inconsistent. It is possible that these eruptives come from a second hot spot, and most recent authorities agree. The hot spot is now under the southern Central Kerguelen Plateau again, explaining the recent volcanic activity already commented upon. There is a trend in Kerguelen plume magmatism, from tholeiitic/transitional basalts in those more than 25  million years ago to alkalic basalts. Seamounts dredged between

392-459: 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 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

441-879: The Early Cretaceous in the Comei large igneous province of southeastern Tibet from 145  million years ago . There is an over lap in time with the basalts in this area of Tibet whose youngest rocks at 130  million years ago with those found thousands of miles away at Bunbury, Western Australia which are up to 137  million years ago old but some are as young as 123  million years ago . Previous work had suggested maximum ages at Bunbury at 132.2  ± 0.3 million years ago . Both are relatively small volume volcanism compared to later developments. The continental breakup of India and Antarctica occurred around 132 to 130  million years ago . Between Western Australia and Gulden Draak Knoll on

490-473: The Kerguelen Islands alkalic flood basalts were deposited between 30 and 24 million years ago. However younger lavas towards the south east of the archipelago that are mainly found as dykes or plugs in these flood basalts and have ages between 10 and 6 million years. To the south, the stratovolcano of Mont Ross on Grande Terre is between 2 million years and 100,000 years old. The composition of

539-558: The Pacific Ocean , the SEIR forms the plate boundary between the Australian and Antarctic plates since the Oligocene ( anomaly  13). 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

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588-507: The mantle plume hypothesis give a fair fit to observed ages over the last 130 million years but some compositional details are not explained by the classical plume model. It is important to realise in the discussion below that the dates referred to were obtained over a period of about 50 years and those found by earlier work have been updated where appropriate as more samples analysed. This could result in events before about 40 million years ago having corrections of about 10 million years. There

637-470: The 10 million year old Amsterdam–St. Paul Plateau located near the current plate boundary of the Southeast Indian Ridge has similarities to the eruptives of the Kerguelen hotspot so the recently active volcanoes on it have been assigned by some to this hot spot rather than a separate Amsterdam-Saint Paul hotspot . In such a case Île Amsterdam about 1,400 km (870 mi) to the north–east of

686-476: 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 the presence of oblique extensional forces while

735-518: The ASP-Kerguelen and the Balleny-Tasmantid hotspots, the AAD overlies a region where cooler mantle temperatures have produced 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

784-641: 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 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

833-573: 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 a magma flow from the Kerguelen–ASP hotspots to

882-488: The Bengal basin the flows cover 200,000 km (77,000 sq mi). The Rajmahal volcanics are predominantly tholeiitic basalt , quartz tholeiite, olivine tholeiite and alkali basalt . The Intertrappean Beds are composed of sedimentary rock such as siltstone , claystone and shale . The western boundary of the Rajmahal Traps is faulted and down-thrown towards the east. The eastern boundary of this trap has

931-565: The Indian Ocean was formed between 120 to 110 million years ago , and was a much larger volume of basalt, consistent with a large igneous province. In the meantime the Kerguelen mantle plume also erupted south of the Comei province the two traps of north east India, being the Rajmahal Traps and the Sylhet Traps. These erupted during a period between 118.1  ± 0.3 million years ago , and 115  million years ago . Eruptions also occurred during this period at what

980-633: The Indo-Australian Plate may have 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 , and that the Indian Plate and Australian Plate may have been separate since at least 3  million years ago . Much of the area of the Ninety East Ridge as well as being related to

1029-660: The Kerguelen Archipelago has a volcano that must have erupted within perhaps the last century, the Boomerang Seamount erupted in 1995 and Île Saint-Paul nearby erupted in 1793. The Kerguelen hotspot has been used to help interpret the plate tectonic history of the Indo-Australian Plate , even though the hotspot itself is now situated under the Antarctic Plate . Models of major plate dynamics based on

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1078-513: The Kerguelen Islands and Heard Island were formed in the Miocene by mildly alkalic, olivine and picrite basalt . The composition at and near Amsterdam and Saint Paul Island are distinct from other Kerguelen plume material. The Ninety East Ridge has tholeiite basalt typical of Indian Ocean basalts with no systematic isotopic variation observed along the ridge and this is inconsistent with

1127-581: The Kerguelen hotspot has been near Heard Island and McDonald Islands where there are two active volcanoes, but its current location could be quite a wide area of the Central Kerguelen Plateau extending over a distance of about 440 km (270 mi), back into the Kerguelen Archipelago as there is some current geothermal activity there, with active fumaroles. Some plate tectonic models favour such more north-east locations. The bulk of

1176-587: 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

1225-594: The Kerguelen plateau basalts formed between 37 Ma and now for several reasons, including that 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

1274-635: The Ninety East Ridge is predominantly a historic divergent plate boundary with eruptives from a deep mantle source. One sample from Boomerang Seamount , a volcano of the Amsterdam-Saint Paul Plateau, has a composition that is midway between St Paul Island and Kerguelen Plateau samples and this is consistent with Kerguelen-type source mantle existing beneath the Amsterdam-Saint Paul Plateau. 49°36′S 68°59′E  /  49.6°S 68.99°E  / -49.6; 68.99 Southeast Indian Ridge The Southeast Indian Ridge ( SEIR )

1323-497: 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 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

1372-671: 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

1421-425: 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

1470-461: 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 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

1519-663: The Southern Indian Ocean . The Kerguelen hotspot has produced basaltic lava for about 130 million years and has also produced the Kerguelen Islands , Naturaliste Plateau , Heard Island , the McDonald Islands , the Comei large igneous province in south Tibet, and the Rajmahal Traps . One of the associated features, the Ninety East Ridge , is distinguished by its over 5,000 km (3,100 mi) length, being

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1568-416: The area of the present Naturaliste Plateau. India started its collision with Asia about 70  million years ago . Eastern Australia and Antarctica completed their separation between perhaps as recently as 45  million years ago , but with most historic models by 67  million years ago . Recent studies, and evidence from seismic events such as the 2012 Indian Ocean earthquakes , suggest that

1617-517: The floor of the Indian Ocean are the Naturaliste, Wallaby, and Zenith Plateaus that erupted between 130 to 117 million years ago , now well separated from India. The Seaward Dipping Reflectors, now at the southern end of the Kerguelen Plateau near Antarctica also formed in this period more than 126  million years ago . The Southern Kerguelen Plateau in the enlarging basin of

1666-693: The hot spot of the Northern Kerguelen Plateau on the Antarctic plate, and also explains 20  million years ago age of the Chain of the Dead Poets that connects the ends of the Ninety East Ridge and the Broken Ridge to the northern aspect of the Southeast Indian Ridge. This also could explain the more recent formation of the Amsterdam-Saint Paul Plateau, which is aged at 10  million years ago and

1715-463: The hotspot is part of the diffuse boundary between the Indian Plate and Australian Plate as they go their separate ways toward the north. Present day structures such as the Elan Bank may have their placements due to ridge jumps at propagating rifts during the process of sea floor spreading. The oldest volcanic rocks assigned to the Kerguelen hotspot are now understood to have been erupted during

1764-427: The hypothesis of an ageing mantle plume origin for all of the ridge. . However at least three distinct sources must have contributed to the basalts of the ridge. The isotopic composition is intermediate between those of the basalts found at or near the Kerguelen and Amsterdam-Saint Paul plateaus. . This results in the interpretation that the Kerguelen hotspot as described by some, is at least two separate hotspots, and

1813-477: The latest evidence, because it appears the plume may be under the Australian Plate between 95 to 45 million years ago odd, creating the Broken Ridge for example at 95 to 94 million years ago , rather than continuing to be located at the triple junction as in classic tectonic models. Part of the plume had long believed to be erupting under the Indian Plate as it raced north contributing to

1862-402: The lava deformed in a cold, brittle fashion and formed graben structures. The Intertrappean Beds contain an assemblage of Lower Cretaceous plant fossils . The assemblage includes Cladophlebis indica , Dictyozamites indicus , Taeniopteris spatulata , and Brachyphyllum rhombium . Kerguelen hotspot The Kerguelen hotspot is a volcanic hotspot at the Kerguelen Plateau in

1911-485: The linear feature and ages of the basalts of the Ninety East Ridge with the oldest at the north, 82  million years ago and the youngest at its south, 37  million years ago . However there is good evidence in the form of magnetic measurements to each side of the ridge, that decompression melting along the Ninety East Ridge occurred as well, and the most recent model assigns a prominent role to this. The previous hot spot only hypothesis explained all features by

1960-412: The longest linear tectonic feature on Earth. The total volume of magma erupted in 130 million years with associated features has been estimated to be about 25,000,000 km (6,000,000 cu mi). However, as well as large igneous provinces and seamounts the hotspot has interacted with other seafloor spreading features, so this volume figure has some uncertainty. The most recent activity of

2009-1204: The north of the Southeast Indian Ridge being the seamounts of the Chain of the Dead Poets. The current location of this hotspot, if it exists, is hard to determine as there are areas of recent volcanic activity that might be associated with the still spreading Southeast Indian Ridge. Most recent work has two separate hotspots. One hundred and forty million years ago the present north-eastern aspect of India (Bengal), southern Western Australia and Princess Elizabeth Land portions of Antarctica were adjacent before Gondwana breakup. Initially India and Australia rotated from Antarctica with continental crustal extension between Australia and Antarctica by about 132.5  million years ago . India separated first from Antarctica and this occurred around 132 to 130 million years ago , although earlier work had this happening by 124  million years ago . East Gondwana, comprising present Antarctica, India, and Australia continued to break up between 132.6 to 96 million years ago with India moved north-west from Australia-Antarctica and extension between Australia and Antarctica being at its greatest rate. Seafloor spreading occurred in

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2058-445: The plume splitting with two effective hot spots. Multiple workers postulate that buried under about 5 km (3.1 mi) of sediments on the seafloor of the Bay of Bengal , there is a continuation of the Ninety East Ridge with volcanics deposited about 90  million years ago . The opening of the Southeast Indian Ridge at 40  million years ago resulted in the creation by

2107-580: 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

2156-557: 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

2205-827: 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

2254-469: The surrounding seafloor. Both Amsterdam and St. Paul are located on 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

2303-469: 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

2352-427: Was formed between 110 to 100 million years ago by basalt eruption from the hotspot on a fast-moving Antarctic Plate, with the Elan Bank emplacement in the first 5 million years of this period. At about 105  million years ago the triple junction of the Indian, Australian, and Antarctic plates crosses the plume so crust forms on three different plates at the same time. Matters now get complex with

2401-482: 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

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