TheKerguelen Plateau (/ˈkɜːrɡələn/,/kərˈɡeɪlən/),[1] also known as theKerguelen–Heard Plateau,[2] is anoceanic plateau andlarge igneous province (LIP) located on theAntarctic Plate, in the southernIndian Ocean.[3] It is about 3,000 km (1,900 mi) to the southwest ofAustralia and is roughly the size ofSouth Africa. Theplateau 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 theKerguelen hotspot, starting with or following the breakup ofGondwana about 130 million years ago. A small portion of the plateau breakssea level, forming theKerguelen Islands (aFrench overseas territory) plus theHeard and McDonald Islands (anAustralian external territory). Intermittentvolcanism continues on the Heard and McDonald Islands.
Symmetrically across the Indian Ocean ridge and due west of Australia is theBroken Ridge underwatervolcanic plateau, which at one time was contiguous with the Kerguelen Plateau before rifting by themid-ocean ridge.
To the north of Broken Ridge is the linearNinety East Ridge which continues almost due north into theBay of Bengal and is considered to be ahotspot track.
One of thelargest igneous provinces (LIPs) in the world, the Kerguelen Plateau covers an area of 1,226,230 km2 (473,450 sq mi) and rises 2,000 m (6,600 ft) above the surrounding oceanic basins.[4][5] Most of the plateau is less than 3,000 m (9,800 ft) below sea level.[6]
Located on theAntarctic Plate, the Kerguelen Plateau is separated from Australia by theSoutheast Indian Ridge (SEIR) and from Africa by theSouthwest Indian Ridge (SWIR). These two ridges meet at theRodriguez Triple Junction. It is separated from Antarctica by thePrincess Elizabeth Trough and theCooperation 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 deepLabuan Basin.[7]
From the initial opening of 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 from145 to 0 million years ago (Ma) with the oldest assigned structure being the Comei large igneous province in south-easternTibet.[8] Historic work had believed that the hotspot became active more recently in what is now south-east Australia.[9] Ongoing analysis of specimens can result in timing changes,[8] so some dates in the sequence that follows may alter. The Southern Kerguelen Plateau (SKP) formed 120–110Ma;[8] the Elan Bank 108–107Ma, named by Dennis E. Hayes ofLamont Doherty Earth Observatory; the Central Kerguelen Plateau (CKP) 101–100Ma; theBroken Ridge (connected to the CKP before the Eocene breakup) 95–94Ma; the Skiff Bank (east of theKerguelen Islands) 69–68Ma; the Northern Kerguelen Plateau (NKP) 35–34Ma; theNinety East Ridge formed 82–37Ma north to south;[8] theBunbury Basalt (Western Australia) 137–130.5Ma;[9] theNaturaliste Plateau (offshore Western Australia) formed 132–128Ma;[10] theRajmahal Traps inNortheast India 118–117Ma; and finallylamprophyres in India and Antarctica 115–114Ma.[11]
The oldest Australian volcanism that can be attributed to the Kerguelen plume are the Bunbury Basalt (137–130.5Ma[9]) and the Naturaliste Plateau (132–128Ma[10]) in southwestern Australia. The Sylhet andRajmahal Traps in eastern India (118-115Ma),[8] the formation of the oldest portion of the Kerguelen LIP and these continental basalts are linked to the opening of the eastern Indian Ocean.[12] The Bunbury Basalt is not of flood basalt dimensions which suggests that the mantle underlying the Kerguelen hotspot was neither significantly hot, wet, or voluminous. In contrast, the magmatism that produced the Australia–India breakup 136–158Ma created theWallaby Plateau, but no known hotspot has been linked to this event.[13]
The output from the Kerguelen hotspot peaked 120–95Ma, 12–70Ma after the India–Antarctica breakup. No ridges orhotspot tracks such asWalvis–Rio Grande,Chagos–Laccadive,Greenland–Scotland have been found in thePrincess 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 theRéunion hotspot and theDeccan Traps and the breakup between western India and theSeychelles.[13]
The peak output of the Kerguelen hotspot coincides with one or several microcontinent formations, such as the Elan Bank.[13] Since the Indian Ocean began to open about 130Ma, 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 the Elan Bank into a microcontinent and dispersed continental fragments in the SKP, and these structures were eventually left behind as India moved northward.[13] The ridge jump that made the Elan Bank a microcontinent occurred after 124Ma.[5] The development of the Southern Kerguelen Plateau 118–119Ma contributed to theoceanic anoxic event 1.[14]
Around 83.5Ma sea floor spreading between India and Antarctica was asymmetric in the Kerguelen Plateau region with two-thirds of the sea floor created being added to the Antarctic Plate. Aridge jump eventually transferred parts of the Kerguelen Plateau from the Indian Plate to the Antarctic Plate.[15]
The Kerguelen hotspot produced the 5,000 km (3,100 mi) long Ninety East Ridge 82–38Ma, and geochemical evidence suggests that this occurred at or near 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 30–24Ma and less voluminous and more recent volcanism occurred until 1Ma. During the last 21Ma volcanic structures have formed on the CKP, including Heard Island, and both Heard and McDonald Islands have had recent eruptions.[13]
65Ma, 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 25Ma of relatively high magmatic activity followed by a 40Ma period of lower activity.[16]
Schlich et al. 1971 described tilted basement blocks near the Kerguelen Archipelago and were the first to identify the Kerguelen Plateau as of continental origin, in contrast to other LIPs.[5][17]
The presence of soil layers in the basalt which includedcharcoal andconglomerate fragments ofgneiss indicate that much of the plateau was above sea level as what is termed amicrocontinent for three periods between 100 million years ago and 20 million years ago[18] (the charcoal was made bywildfires started by lightning or lava flows). Large parts of the now-submarine Southern Kerguelen Plateaus (SKP) and Central Kerguelen Plateaus (CKP) weresubaerial during the formation of the LIP. The SKP probably formed an island of 500,000 km2 (190,000 sq mi) with major peaks reaching 1,000–2,000 m (3,300–6,600 ft) above sea level.[19]
The Kerguelen Microcontinent may have been covered by dense conifer forest in the mid-Cretaceous[20] as well as the earlyCenozoic.[21] Fossil wood fragments recovered from the Kerguelen Islands were identified asAraucarians andCypresses, demonstrating that Kerguelen's flora may have been similar to that of theAntarctic flora found across the Southern Hemisphere.
The plateau had been proposed as forming aland bridge between India and Antarctica during the Late Cretaceous, though this is now considered unsupported, with the plateau situated at a considerable distance from the nearest continents.[22]
It finally became submerged 20 million years ago and is now 1,000–2,000 m (3,300–6,600 ft) below sea level.[23]
During the austral summer there is a high density of migratory whales includingsperm,minke, andhumpback whales along the southern end of the Kerguelen Plateau and the northern part of the adjacent Princess Elizabeth Trough. These whales choose this location for foraging because the Southern Front of theAntarctic 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 the surface. Ice is additionally advected north along the eastern side of the plateau.[24]
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