Kerguelen hotspot

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, Heard Island, the McDonald Islands, and the Ninety East Ridge.

Hotspots
The Kerguelen hotspot is marked 20 on map.

References

  1. ^ Gupta & Desa; Rabin Sen Gupta; Ehrlich Desa (2001). The Indian Ocean: a perspective, Volume 2. Taylor & Francis. p. 743. ISBN 90-5809-224-0.
Aptian extinction

The Aptian extinction was an extinction event of the early Cretaceous Period. It is dated to c. 116 or 117 million years ago, in the middle of the Aptian stage of the geological time scale, and has sometimes been termed the mid-Aptian extinction event as a result.

It is classified as a minor extinction event, rather than a major event like the famous Cretaceous–Paleogene extinction event that brought about the end of the "age of dinosaurs" and the Mesozoic Era. The Aptian event is most readily detected among marine rather than terrestrial fossil deposits. Nonetheless, "From a palaeobotanical perspective, the Aptian Extinction Event is an episode of importance, deserving a higher status among other minor events."The Aptian event may have been causally connected with the Rahjamal Traps volcanism episode in the Bengal region of India, associated with the Kerguelen hotspot of volcanic activity. (At the time in question, c. 116–117 Ma, India was located in the southern Indian Ocean; plate tectonics had not yet moved the Indian landmass into its present position.)

Note that the stegosaur group of dinosaurs went extinct around this time. Wuerhosaurus, probably the last of the stegosaurs, lived during this time.

Broken Ridge

Broken Ridge or Broken Plateau is an oceanic plateau in the south-eastern Indian Ocean. Broken Ridge once formed a large igneous province (LIP) together with the Kerguelen Plateau. When Australia and Antarctica started to separate, Broken Ridge and the Kerguelen Plateau got separated by the Southeast Indian Ridge. Alkalic basalt from Broken Ridge has been dated to 95 Ma.Broken Ridge stretches 1,200 km (750 mi) from the southern end of Ninety East Ridge towards the south-western corner of Australia. It is up to 400 km (250 mi) wide and reaches 1,000 m (3,300 ft) below sea level. It is separated from the Diamantina Fracture Zone on its southern side by a 3,000 m (9,800 ft) escarpment, while on the northern side the ridge slopes gently towards the abyssal Wharton Basin. The sediment cover on the ridge reaches 800 m (2,600 ft) and the Moho is found at about 20 km (12 mi). It is separated from the Naturaliste Plateau by the Dirck Hartog Ridge.

The Kerguelen LIP covered 2.3×10^6 km2 (0.89×10^6 sq mi) making it the second largest LIP on Earth (after the Ontong Java Plateau in the Pacific). Both these enormous LIPs reaches 2–4 km (1.2–2.5 mi) above the surrounding ocean floor and have a crustal thickness of 20–40 km (12–25 mi) (compared to oceanic crust typically around 7 km (4.3 mi) thick.)

The Broken Ridge and Kerguelen Plateau are now separated by 1,800 km (1,100 mi). When they broke-up, the southern flank of Broken Ridge was uplifted some 2,000 m (6,600 ft) and reached above sea level.The Kerguelen LIP has a long and complicated history, however, and is probably the least "typical" of all LIPs.

Rocks from both the Broken Ridge and the Kerguelen Plateau contain a continental component or "fingerprint". In the Early Cretaceous, the Kerguelen hotspot was split into several diapirs of various sizes, composition, and ascent rates. These separate diapirs created the Bunbury Basalt, the Southern Kerguelen Plateau, the Rajmahal Traps/Indian lamprophyres, Antarctic lamprophyres, and the Central Kerguelen Plateau/Broken Ridge. In the late Cretaceous, activity in the mantle slowed and the Kerguelen hotspot was reduced to a single plume which created the Ninety East Ridge.

120-95 Ma when the Southern and Central Kerguelen Plateau formed together with the Broken Ridge, the Kerguelen hotspot produced 1 km3 (0.24 cu mi)/year, but 95-25 Ma the output decreased to 0.1 km3 (0.024 cu mi).

Crozet Islands

The Crozet Islands (French: Îles Crozet; or, officially, Archipel Crozet) are a sub-antarctic archipelago of small islands in the southern Indian Ocean. They form one of the five administrative districts of the French Southern and Antarctic Lands.

Gondwana

Gondwana ( ) or Gondwanaland was a supercontinent that existed from the Neoproterozoic (about 550 million years ago) until the Jurassic (about 180 million years ago).

It was formed by the accretion of several cratons. Eventually, Gondwana became the largest piece of continental crust of the Paleozoic Era, covering an area of about 100,000,000 km2 (39,000,000 sq mi). During the Carboniferous Period, it merged with Euramerica to form a larger supercontinent called Pangaea. Gondwana (and Pangaea) gradually broke up during the Mesozoic Era. The remnants of Gondwana make up about two thirds of today's continental area, including South America, Africa, Antarctica, Australia, Indian Subcontinent and Arabia.

The formation of Gondwana began c. 800 to 650 Ma 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.

Hotspot (geology)

In geology, the places known as hotspots or hot spots are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle. Their position on the Earth's surface is independent of tectonic plate boundaries. There are two hypotheses that attempt to explain their origins. One suggests that hotspots are due to mantle plumes that rise as thermal diapirs from the core–mantle boundary. The other hypothesis is that lithospheric extension permits the passive rising of melt from shallow depths. This hypothesis considers the term "hotspot" to be a misnomer, asserting that the mantle source beneath them is, in fact, not anomalously hot at all. Well-known examples include the Hawaii, Iceland and Yellowstone hotspots.

Indian Ocean

The Indian Ocean is the third-largest of the world's oceanic divisions, covering 70,560,000 km2 (27,240,000 sq mi) (19.8% of the water on the Earth's surface). It is bounded by Asia on the north, on the west by Africa, on the east by Australia, and on the south by the Southern Ocean or, depending on definition, by Antarctica.

Indian Plate

The Indian Plate or India Plate is a major tectonic plate straddling the equator in the eastern hemisphere. Originally a part of the ancient continent of Gondwana, India broke away from the other fragments of Gondwana 100 million years ago and began moving north. Once fused with the adjacent Australia to form a single Indo-Australian Plate, 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 South Asia—i.e. the Indian subcontinent—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.

Kerguelen Islands

The Kerguelen Islands ( or ; in French commonly Îles Kerguelen but officially Archipel des Kerguelen, pronounced [kɛʁɡelɛn]), also known as the Desolation Islands (Îles de la Désolation in French), are a group of islands in the Antarctic constituting one of the two exposed parts of the Kerguelen Plateau, a large igneous province mostly submerged by the southern Indian Ocean. They are among the most isolated places on Earth, located 450 km (280 mi) northwest of the uninhabited Heard Island and McDonald Islands (Australia) and more than 3,300 km (2,100 mi) from Madagascar, the nearest populated location (excluding the Alfred Faure scientific station in Île de la Possession, about 1,340 km, 830 mi from there, and the non-permanent station located in Île Amsterdam, 1,440 km, 890 mi away). The islands, along with Adélie Land, the Crozet Islands, Amsterdam and Saint Paul Islands, and France's Scattered Islands in the Indian Ocean, are part of the French Southern and Antarctic Lands and are administered as a separate district.

The main island, Grande Terre, is 6,675 km2 (2,577 sq mi) in area and is surrounded by a further 300 smaller islands and islets, forming an archipelago of 7,215 km2 (2,786 sq mi). The climate is raw and chilly with frequent high winds throughout the year. The surrounding seas are generally rough and they remain ice-free year-round. There are no indigenous inhabitants, but France maintains a permanent presence of 45 to 100 soldiers, scientists, engineers and researchers. There are no airports on the islands, so all travel and transport from the outside world is conducted by ship.

Kerguelen Plateau

The Kerguelen Plateau ( , ) is an oceanic plateau and a large igneous province (LIP) located on the Antarctic Plate, in the southern Indian Ocean. It is also a microcontinent and submerged continent. It is about 3,000 km (1,900 mi) to the southwest of Australia and is nearly three times the size of Japan. The plateau extends for more than 2,200 km (1,400 mi) in a northwest–southeast direction and lies in deep water.

The plateau 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 territory) plus the Heard and McDonald Islands (an Australian territory). Intermittent volcanism continues on the Heard and McDonald Islands.

Kolluru Sree Krishna

Kolluru Sree Krishna (born 1958) is an Indian marine geophysicist is the chief scientist at the National Institute of Oceanography, India. He is known for his studies on the evolution of the Indian Ocean and is an elected fellow of all the three major Indian science academies viz. Indian National Science Academy, Indian Academy of Sciences, and the National Academy of Sciences, India. The Council of Scientific and Industrial Research, the apex agency of the Government of Indvia for scientific research, awarded him the Shanti Swarup Bhatnagar Prize for Science and Technology, one of the highest Indian science awards for his contributions to Earth, Atmosphere, Ocean and Planetary Sciences in 2001.

Large igneous province

A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive (sills, dikes) and extrusive (lava flows, tephra deposits), 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 the past 500 million years coincide in time with mass extinctions and rapid climatic changes, which has led to numerous hypotheses about the causal relationships. LIPs are fundamentally different from any other currently active volcanoes or volcanic systems.

List of largest volcanic eruptions

In a volcanic eruption, lava, volcanic bombs and ash, and various gases are expelled from a volcanic vent and fissure. While many eruptions only pose dangers to the immediately surrounding area, Earth's largest eruptions can have a major regional or even global impact, with some affecting the climate and contributing to mass extinctions. Volcanic eruptions can generally be characterized as either explosive eruptions, sudden ejections of rock and ash, or effusive eruptions, relatively gentle outpourings of lava. A separate list is given below for each type.

There have probably been many such eruptions during Earth's history beyond those shown in these lists. However erosion and plate tectonics have taken their toll, and many eruptions have not left enough evidence for geologists to establish their size. Even for the eruptions listed here, estimates of the volume erupted can be subject to considerable uncertainty.

Ninety East Ridge

The Ninety East Ridge (also rendered as Ninetyeast Ridge, 90E Ridge or 90°E Ridge) is a linear structure 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 33°S and 17°N and has an average width of 200 km.The ridge divides the Indian Ocean into the West and East Indian Ocean. The northeastern side is named the Wharton Basin and ceases at the western end of the Diamantina Fracture Zone which passes to the east and almost to the Australian continent.The ridge is primarily composed of Ocean Island Tholeiites (OIT), a subset of basalt which increase in age from approximately 43.2 ± 0.5 Ma in the south to 81.8 ± 2.6 Ma in the north though a more recent analysis using modern Ar–Ar techniques is currently pending publication. This age progression has led geologists to theorize that a hotspot in the mantle beneath the Indo-Australian Plate created the ridge as the plate has moved northward in the late Mesozoic and Cenozoic. This theory is supported by a detailed analysis of the chemistry of the Kerguelen Plateau and Rajmahal Traps, which together, geologists believe, represent the flood basalts erupted at the initiation of volcanism at the Kerguelen hotspot which was then sheared in two as the Indian subcontinent moved northward. However, the existence of so-called deep mantle hotspots is currently a topic of debate in the geologic community, with a few geochemists favoring an alternative hypothesis which postulates a much shallower origin for hotspot volcanism.The ridge has been surveyed several times in the past, including several times by the Deep Sea Drilling Program (DSDP). In 2007, the RV Roger Revelle collected bathymetric, magnetic and seismic data together with dredge samples from nine sites along the ridge as part of an Integrated Ocean Drilling Program (IODP) site survey intended to examine the hotspot hypothesis for the ridge.It had been assumed that the India and Australia are on a single tectonic plate for at least the last 32 million years. However, considering the high level of large earthquakes in the Ninety East Ridge area and the evidence of deformation in the central Indian Ocean, it is more appropriate to consider the deformed region in the central Indian Ocean as a broad plate boundary zone separating the Indian Plate and the Australian Plate.

Rajmahal Traps

Rajmahal Traps is a volcanic igneous province in Eastern India, covering the parts of Jharkhand, West Bengal and Meghalaya. The Rajmahal Hills of Jharkhand is the type area of this province. Multiple layers of solidified lava made the 608-metre-thick (1,995 ft) Rajmahal Traps which are dipping 2–5° towards the north-east. Individual layers vary in thickness from less than one metre (3 ft 3 in) to more than 70 metres (230 ft).

Southeast Indian Ridge

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 (25°S 70°E) in the Indian Ocean and the Macquarie Triple Junction (63°S 165°E) in 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 hotspot.

The SEIR has an intermediate full spreading rate of 65 mm/yr, 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/yr near 88°E to 75 mm/yr near 120°E.

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