The Boomerang Seamount is an active submarine volcano, located northeast of Amsterdam Island,

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

. It was formed by the Amsterdam-Saint Paul hotspot and has a wide

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...

that is deep. Hydrothermal activity occurs within the caldera. The sampled rocks are

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

and

picrite basalt Picrite basalt or picrobasalt is a variety of high-magnesium olivine basalt that is very rich in the mineral olivine. It is dark with yellow-green olivine phenocrysts (20-50%) and black to dark brown pyroxene, mostly augite. The olivine-rich ...

Geology

The seamount is located on the mainly undersea Amsterdam–Saint Paul Plateau of the Antarctic Plate, which was predominantly formed by the volcanic hotspot. There is a magma chamber located at between depth below the nearby Amsterdam Island. The plateau which extends north west towards the Nieuw Amsterdam Fracture Zone (Amsterdam Fracture Zone) and south to beyond the island of St Paul with its presently known active area being delimited by the St. Paul Fracture Zone, is a feature of the sea floor near the Southeast Indian Ridge, which is an active spreading center between the Antarctic plate that the seamount lies on, and the

Australian Plate The Australian plate is or was a major tectonic plate in the eastern and, largely, southern hemispheres. Originally a part of the ancient continent of Gondwana, Australia remained connected to India and Antarctica until approximately when Indi ...

. Samples recovered were tholeiitic to transitional

Tectonics

This tectonically complex area has had detailed study. Helium isotopic compositional studies are consistent with its formation from the combined effects of accretion at the

mid-ocean ridge A mid-ocean ridge (MOR) is a undersea mountain range, seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading ...

and mantle plume activity of a hot spot. This is either the

Kerguelen hotspot The Kerguelen hotspot is a volcanic hotspot at the Kerguelen Plateau in 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, H ...

or a potentially separate Amsterdam-Saint Paul hotspot but resolution of this issue is complicated, due to it being adjacent to the Southeast Indian Ridge, and the influence of the distant Kerguelen hot spot plume. Recent independent authors have favoured a separate Amsterdam and St. Paul hotspot. There are compositional reasons to suggest that the current Kerguelen hotspot influences the present Southeast Indian Ridge volcanics far to its north but also that the isotopic parameters of basalts of the Amsterdam-Saint Paul hot spot is different from the Kerguelen hot spot. However one sample from Boomberang Seamount, from outside the crater, 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 Boomerang Seamount. Which ever hot spot is responsible is moving south as Île Amsterdam rocks are older than St. Paul rocks. The Amsterdam–St. Paul Plateau while formed in the last 10 million years, started this formation beneath the Australian Plate so the island is built on the components of two tectonic plates.

References

Sources

* * * * * * {{Authority control Seamounts of the Indian Ocean Hotspot volcanoes Active volcanoes Volcanoes of the French Southern and Antarctic Lands

Geology

Tectonics

See also

References

Sources