Kerguelen hotspot

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The Kerguelen hotspot is marked 20 on map. Hotspots.jpg
The Kerguelen hotspot is marked 20 on map.

The Kerguelen hotspot is a volcanic hotspot at the Kerguelen Plateau in the Southern Indian Ocean. [1] 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, and Rajmahal Traps. One of the associated features, the Ninety East Ridge, is distinguished by its over 5,000 km (3,100 mi) length, being the longest linear tectonic feature on Earth. [2] [3] The total volume of magma erupted in 130 million years with associated features has been estimated to be about 25,000,000 km3 (6,000,000 cu mi). [4] 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. [5]

Contents

Recent Volcanism

The most recent activity of the 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), [6] back into the Kerguelen Archipelago as there is some current geothermal activity there, with active fumaroles. [7] Some plate tectonic models favour such more north-east locations. [8] The bulk of the Kerguelen Islands alkalic flood basalts were deposited between 30 and 24 million years ago. [6] 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. [6] To the south, the stratovolcano of Mont Ross on Grande Terre is between 2 million years and 100,000 years old. [6]

Île Amsterdam about 1,400 km (870 mi) to the northeast of the Kerguelen Archipelago has a volcano that must have erupted within perhaps the last century, [9] and Île Saint-Paul nearby erupted in 1793. [10] [7]

Historic Volcanism

Tectonics

The 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. [6] Models of major plate dynamics based on 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. [11] 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. [11] This could result in events before about 40 million years ago having corrections of about 10 million years. There 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. [7] 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 the north of the Southeast Indian Ridge being the seamounts of the Chain of the Dead Poets. [12] [7] 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.

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. [13] Initially India and Australia rotated from Antarctica with continental crustal extension between Australia and Antarctica by about 132.5  million years ago. [14] India separated first from Antarctica and this occurred around 132 to 130 million years ago, [15] although earlier work had this happening by 124  million years ago. [13] 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. [14] Seafloor spreading occurred in the area of the present Naturaliste Plateau. [14] India started its collision with Asia about 70  million years ago. [13] Eastern Australia and Antarctica completed their separation between perhaps as recently as 45  million years ago, [16] but with most historic models by 67  million years ago. [13] Recent studies, and evidence from seismic events such as the 2012 Indian Ocean earthquakes, suggest that 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, [17] [18] and that the Indian Plate and Australian Plate may have been separate since at least 3  million years ago. [19] Much of the area of the Ninety East Ridge as well as being related to the hotspot is part of the diffuse boundary between the Indian Plate and Australian Plate as they go their separate ways toward the north. [20] 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. [20]

Eruptive History

The oldest volcanic rocks assigned to the hotspot are now understood to have been erupted during the Early Cretaceous in the Comei large igneous province, of southeastern Tibet from 145  million years ago. [15] [25] 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. [15] 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. [15] The continental breakup of India and Antarctica occurred around 132 to 130  million years ago. [15]

Between Western Australia and Gulden Draak Knoll on the floor of the Indian Ocean are the Naturaliste, Wallaby, and Zenith Plateaus that erupted between 130 to 117 million years ago, [26] [24] 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. [13]

The Southern Kerguelen Plateau in the enlarging basin of the Indian Ocean was formed between 120 to 110 million years ago, [27] 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, [28] and 115  million years ago. [29] Eruptions also occurred during this period at what 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. [30]

The Central Kerguelen Plateau was formed between 110 to 100 million years ago by basalt eruption from the hotspot on a fast-moving Antarctic Plate, [30] with the Elan Bank emplacement in the first 5 million years of this period. [31]

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. [31] Matters now get complex with 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, [31] rather than continuing to be located at the triple junction as in classic tectonic models. [13] Part of the plume had long believed to be erupting under the Indian Plate as it raced north contributing to 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. [32] 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, [2] and the most recent model assigns a prominent role to this. [31] The previous hot spot only hypothesis explained all features by the plume splitting with two effective hot spots. [13] Multiple workers postulate that buried under about 5 km (3.1 mi) of sediments on the seafloor of the Bay of Bengal, [32] there is a continuation of the Ninety East Ridge with volcanics deposited about 90  million years ago. [2]

The opening of the Southeast Indian Ridge at 40  million years ago resulted in the creation by 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, [31] which is aged at 10  million years ago and is to the south of present Southeast Indian Ridge, [13] but composition studies are inconsistent. [7] It is possible that these eruptives come from a second hot spot. [7]

The hot spot is now under the southern Central Kerguelen Plateau again, explaining the recent volcanic activity already commented upon.

Composition

There is a trend in Kerguelen plume magmatism, from tholeiitic/transitional basalts in those more than 25  million years ago to alkalic basalts. [33] Seamounts dredged between the Kerguelen Islands and Heard Island were formed in the Miocene by mildly alkalic, olivine and picrite basalt. [34] The composition at and near Amsterdam and Saint Paul Island are distinct from other Kerguelen plume material. [7] .

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 the hypothesis of an ageing mantle plume origin for all of the ridge. [12] . However at least three distinct sources must have contributed to the basalts of the ridge. [12] The isotopic composition is intermediate between those of the basalts found at or near the Kerguelen and Amsterdam-Saint Paul plateaus. [12] . This results in the interpretation that the Kerguelen hotspot as described by some, is at least two separate hotspots, [12] and the Ninety East Ridge is predominantly a historic divergent plate boundary with eruptives from a deep mantle source. [12] [31]

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A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic hotspots, such as Hawaii or Iceland, and large igneous provinces such as the Deccan and Siberian Traps. Some such volcanic regions lie far from tectonic plate boundaries, while others represent unusually large-volume volcanism near plate boundaries.

<span class="mw-page-title-main">Hotspot (geology)</span> Volcanic regions that are hotter than the surrounding mantle

In geology, hotspots are volcanic locales thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle. Examples include the Hawaii, Iceland, and Yellowstone hotspots. A hotspot's position on the Earth's surface is independent of tectonic plate boundaries, and so hotspots may create a chain of volcanoes as the plates move above them.

<span class="mw-page-title-main">Réunion hotspot</span> Volcanic hotspot in the Indian Ocean

The Réunion hotspot is a volcanic hotspot which currently lies under the island of Réunion in the Indian Ocean. The Chagos-Laccadive Ridge and the southern part of the Mascarene Plateau are volcanic traces of the Réunion hotspot.

<span class="mw-page-title-main">Indian Plate</span> Minor plate that separated from Gondwana

The Indian Plate is a minor tectonic plate straddling the equator in the Eastern Hemisphere. Originally a part of the ancient continent of Gondwana, the Indian Plate broke away from the other fragments of Gondwana 100 million years ago, began moving north and carried Insular India with it. It was once fused with the adjacent Australian Plate to form a single Indo-Australian Plate, and recent studies suggest that India and Australia have been separate plates for at least 3 million years and likely longer. The Indian Plate includes most of modern South Asia and a portion of the basin under the Indian Ocean, including parts of South China and western Indonesia, and extending up to but not including Ladakh, Kohistan and Balochistan.

<span class="mw-page-title-main">Large igneous province</span> Huge regional accumulation of igneous rocks

A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive and extrusive, arising when magma travels through the crust towards the surface. The formation of LIPs is variously attributed to mantle plumes or to processes associated with divergent plate tectonics. The formation of some of the LIPs in the past 500 million years coincide in time with mass extinctions and rapid climatic changes, which has led to numerous hypotheses about causal relationships. LIPs are fundamentally different from any other currently active volcanoes or volcanic systems.

<span class="mw-page-title-main">Kerguelen Plateau</span> Oceanic plateau in the southern Indian Ocean

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.

<span class="mw-page-title-main">Iceland hotspot</span> Hotspot partly responsible for volcanic activity forming the Iceland Plateau and island

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<span class="mw-page-title-main">Oceanic plateau</span> Relatively flat submarine region that rises well above the level of the ambient seabed

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<span class="mw-page-title-main">Southwest Indian Ridge</span> A mid-ocean ridge on the bed of the south-west Indian Ocean and south-east Atlantic 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.

<span class="mw-page-title-main">Southeast Indian Ridge</span> Mid-ocean ridge in the southern Indian 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).

<span class="mw-page-title-main">Ninety East Ridge</span> Linear ridge on the Indian Ocean floor near the 90th meridian

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.

<span class="mw-page-title-main">Macquarie Triple Junction</span> Place where the Indo-Australian Plate, Pacific Plate, and Antarctic Plate meet

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<span class="mw-page-title-main">Tristan hotspot</span> Volcanic hotspot in the Atlantic Ocean

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<span class="mw-page-title-main">Gondwana</span> Neoproterozoic to Cretaceous landmass

Gondwana was a large landmass, sometimes referred to as a supercontinent. It was formed by the accretion of several cratons, beginning c. 800 to 650Ma with the East African Orogeny, the collision of India and Madagascar with East Africa, and was completed c.600 to 530 Ma with the overlapping Brasiliano and Kuunga orogenies, the collision of South America with Africa, and the addition of Australia and Antarctica, respectively. Eventually, Gondwana became the largest piece of continental crust of the Palaeozoic Era, covering an area of about 100,000,000 km2 (39,000,000 sq mi), about one-fifth of the Earth's surface. It fused with Euramerica during the Carboniferous to form Pangea. It began to separate from northern Pangea (Laurasia) during the Triassic, and started to fragment during the Early Jurassic. The final stages of break-up, involving the separation of Antarctica from South America and Australia, occurred during the Paleogene (from around 66 to 23 million years ago. Gondwana was not considered a supercontinent by the earliest definition, since the landmasses of Baltica, Laurentia, and Siberia were separated from it. To differentiate it from the Indian region of the same name, it is also commonly called Gondwanaland.

<span class="mw-page-title-main">Samoa hotspot</span> Volcanic hotspot located in the south Pacific Ocean

The Samoa hotspot is a volcanic hotspot located in the south Pacific Ocean. The hotspot model describes a hot upwelling plume of magma through the Earth's crust as an explanation of how volcanic islands are formed. The hotspot idea came from J. Tuzo Wilson in 1963 based on the Hawaiian Islands volcanic chain.

<span class="mw-page-title-main">Broken Ridge</span> Oceanic plateau in the Indian Ocean

The Broken Ridge or Broken Plateau is an oceanic plateau in the south-eastern Indian Ocean. The Broken Ridge once formed a large igneous province (LIP) together with the Kerguelen Plateau. When Australia and Antarctica started to separate, the Broken Ridge and the Kerguelen Plateau got separated by the Southeast Indian Ridge. Alkalic basalt from the Broken Ridge has been dated to 95 Ma.

Intraplate volcanism is volcanism that takes place away from the margins of tectonic plates. Most volcanic activity takes place on plate margins, and there is broad consensus among geologists that this activity is explained well by the theory of plate tectonics. However, the origins of volcanic activity within plates remains controversial.

References

  1. ↑ Gupta & Desa 2001, p. 743.
  2. 1 2 3 Sreejith & Krishna 2015, pp. 1105–6.
  3. ↑ Bredow & Steinberger 2018, pp. 126, 131.
  4. ↑ Coffin et al. 2002, p. 1135.
  5. ↑ Bredow & Steinberger 2018, pp. 126–129, 131.
  6. 1 2 3 4 5 Weis et al. 2002, p. 2.
  7. 1 2 3 4 5 6 7 Bredow & Steinberger 2018, p. 128.
  8. ↑ Weis et al. 2002, p. 3.
  9. ↑ "Global Volcanism Program:Amsterdam Island" . Retrieved 2023-11-15.
  10. ↑ "Global Volcanism Program:St. Paul" . Retrieved 2023-11-15.
  11. 1 2 Bredow & Steinberger 2018, p. 128-9.
  12. 1 2 3 4 5 6 Nobre Silva et al. 2013, p. 1177.
  13. 1 2 3 4 5 6 7 8 Gaina et al. 2003, p. 410.
  14. 1 2 3 Powell, Roots & Veevers 1988, Abstract.
  15. 1 2 3 4 5 Bredow & Steinberger 2018, p. 126.
  16. ↑ "New Look at Gondwana's Breakup". Livescience.com. 2013-07-05. Retrieved 2015-12-25.
  17. ↑ Hillis & Müller 2003.
  18. ↑ Gaina et al. 2003.
  19. ↑ Stein, Sella & Okai 2002, pp. 248–254.
  20. 1 2 Gaina et al. 2003, pp. 411–12.
  21. ↑ Sandwell et al. 2014.
  22. ↑ Bredow & Steinberger 2018, Fig. 1.
  23. ↑ Sreejith & Krishna 2015, Fig. 1.
  24. 1 2 Olierook et al. 2020, Fig. 1.
  25. ↑ These new ages do nothing to settle any debate as to contribution of hotspots to continental breakup
  26. ↑ Bredow & Steinberger 2018, pp. 126–7.
  27. ↑ Bredow & Steinberger 2018, p. 127.
  28. ↑ Coffin et al. 2002, pp. 1125–26.
  29. ↑ Bredow & Steinberger 2018, p. 127-8.
  30. 1 2 Bredow & Steinberger 2018, p. 130.
  31. 1 2 3 4 5 6 Bredow & Steinberger 2018, p. 131.
  32. 1 2 Nobre Silva et al. 2013, p. 1178.
  33. ↑ Weis et al. 2002, p. 21.
  34. ↑ Weis et al. 2002, p. 20.

Sources

49°36′S68°59′E / 49.6°S 68.99°E / -49.6; 68.99

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