| Gascoyne Seamount | |
|---|---|
  Location of the Gascoyne Seamount | |
| Location | |
| Location | 500 km (310 mi) east of Bermagui, New South Wales, Australia |
| Group | Tasmantid Seamount Chain |
| Coordinates | 36°39′32.2″S156°12′20.2″E / 36.658944°S 156.205611°E |
| Geology | |
| Type | Guyot |
Gascoyne Seamount, also called Gascoyne Guyot or Gascoyne Tablemount, is a guyot in the Tasman Sea of the South Pacific Ocean.
Located 500 km (310 mi) east of the Australian coastal town of Bermagui, Gascoyne Seamount is the southernmost and youngest significant seamount of the Tasmantid Seamount Chain. This is an underwater mountain range extending some 1,300 km (810 mi) to the north. [1] The Tasmantid Seamount Chain has resulted from the Indo-Australian Plate moving northward over a stationary hotspot. [2]
The seamount is about 7 million years old. [3] It incorporates a tropical to subtropical, very shallow water calcareous algal/encrusting foraminiferid biota, suggesting deposition in water 15 to 20 m (49 to 66 ft) deep. Age diagnostic forms have not been recovered. [4]
Gascoyne Seamount is named after HMAS Gascoyne, one of two ships in the Royal Australian Navy assigned to Australian programs in the International Indian Ocean Expedition, which took place from 1960 to 1965. [5]
In marine geology, a guyot, also called a tablemount, is an isolated underwater volcanic mountain (seamount) with a flat top more than 200 m (660 ft) below the surface of the sea. The diameters of these flat summits can exceed 10 km (6.2 mi). Guyots are most commonly found in the Pacific Ocean, but they have been identified in all the oceans except the Arctic Ocean. They are analogous to tables on land.
A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface, and thus is not an island, islet, or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly and are usually found rising from the seafloor to 1,000–4,000 m (3,300–13,100 ft) in height. They are defined by oceanographers as independent features that rise to at least 1,000 m (3,281 ft) above the seafloor, characteristically of conical form. The peaks are often found hundreds to thousands of meters below the surface, and are therefore considered to be within the deep sea. During their evolution over geologic time, the largest seamounts may reach the sea surface where wave action erodes the summit to form a flat surface. After they have subsided and sunk below the sea surface such flat-top seamounts are called "guyots" or "tablemounts".
The Hawaiian–Emperor seamount chain is a mostly undersea mountain range in the Pacific Ocean that reaches above sea level in Hawaii. It is composed of the Hawaiian ridge, consisting of the islands of the Hawaiian chain northwest to Kure Atoll, and the Emperor Seamounts: together they form a vast underwater mountain region of islands and intervening seamounts, atolls, shallows, banks and reefs along a line trending southeast to northwest beneath the northern Pacific Ocean. The seamount chain, containing over 80 identified undersea volcanoes, stretches about 6,200 km (3,900 mi) from the Aleutian Trench off the coast of the Kamchatka peninsula in the far northwest Pacific to the Kamaʻehuakanaloa Seamount, the youngest volcano in the chain, which lies about 35 kilometres (22 mi) southeast of the Island of Hawaiʻi.
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.
The Lord Howe Seamount Chain formed during the Miocene. It features many coral-capped guyots and is one of the two parallel seamount chains alongside the east coast of Australia; the Lord Howe and Tasmantid seamount chains both run north-south through parts of the Coral Sea and Tasman Sea. These chains have longitudes of approximately 159°E and 156°E respectively.
The Hawaiʻi hotspot is a volcanic hotspot located near the namesake Hawaiian Islands, in the northern Pacific Ocean. One of the best known and intensively studied hotspots in the world, the Hawaii plume is responsible for the creation of the Hawaiian–Emperor seamount chain, a 6,200-kilometer (3,900 mi) mostly undersea volcanic mountain range. Four of these volcanoes are active, two are dormant; more than 123 are extinct, most now preserved as atolls or seamounts. The chain extends from south of the island of Hawaiʻi to the edge of the Aleutian Trench, near the eastern coast of Russia.
The Louisville Ridge, often now referred to as the Louisville Seamount Chain, is an underwater chain of over 70 seamounts located in the Southwest portion of the Pacific Ocean. As one of the longest seamount chains on Earth it stretches some 4,300 km (2,700 mi) from the Pacific-Antarctic Ridge northwest to the Tonga-Kermadec Trench, where it subducts under the Indo-Australian Plate as part of the Pacific Plate. The chains formation is best explained by movement of the Pacific Plate over the Louisville hotspot although others had suggested by leakage of magma from the shallow mantle up through the Eltanin fracture zone, which it follows closely for some of its course.
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.
Koko Guyot is a 48.1-million-year-old guyot, a type of underwater volcano with a flat top, which lies near the southern end of the Emperor seamounts, about 200 km (124 mi) north of the "bend" in the volcanic Hawaiian-Emperor seamount chain. Pillow lava has been sampled on the north west flank of Koko Seamount, and the oldest dated lava is 40 million years old. Seismic studies indicate that it is built on a 9 km (6 mi) thick portion of the Pacific Plate. The oldest rock from the north side of Koko Seamount is dated at 52.6 and the south side of Koko at 50.4 million years ago. To the southeast of the bend is Kimmei Seamount at 47.9 million years ago and southeast of it, Daikakuji at 46.7.
The Pacific Ocean evolved in the Mesozoic from the Panthalassic Ocean, which had formed when Rodinia rifted apart around 750 Ma. The first ocean floor which is part of the current Pacific Plate began 160 Ma to the west of the central Pacific and subsequently developed into the largest oceanic plate on Earth.
The Tasmantid Seamount Chain is a 2,000 km (1,200 mi) long chain of seamounts in the South Pacific Ocean. The chain consists of over 16 extinct volcanic peaks, many rising more than 4,000 m (13,000 ft) from the seabed. It is one of the two parallel seamount chains alongside the East Coast of Australia; the Lord Howe and Tasmantid seamount chains both run north-south through parts of the Coral Sea and Tasman Sea. These chains have longitudes of approximately 159°E and 156°E respectively.
The Tasmantid hotspot is a volcanic hotspot located in the South Pacific Ocean. Due to plate tectonics the hotspot was under different parts of the seabed in the past. It was initially centred under what is now the southern Coral Sea 60 million years ago where the first Tasmantid volcano was created. As the Indo-Australian Plate continued to drift northwards the hotspot was positioned in the northern Tasman Sea 20 million years ago, eventually reaching its current location east of Tasmania in response to ongoing northward plate motion. The erupted volcanics are saturated tholeiitic to transitional alkali-olivine basalt.
The Mid-Pacific Mountains (MPM) is a large oceanic plateau located in the central North Pacific Ocean or south of the Hawaiian–Emperor seamount chain. Of volcanic origin and Mesozoic in age, it is located on the oldest part of the Pacific Plate and rises up to 2 km (1.2 mi) above the surrounding ocean floor and is covered with several layers of thick sedimentary sequences that differ from those of other plateaux in the North Pacific. About 50 seamounts are distributed over the MPM. Some of the highest points in the range are above sea level which include Wake Island and Marcus Island.
Arago hotspot is a hotspot in the Pacific Ocean, presently located below the Arago seamount close to the island of Rurutu, French Polynesia.
The Louisiade Plateau, also called the Louisiade Rise, is a poorly studied oceanic plateau in the northern Coral Sea of the South Pacific Ocean. To its west is the Louisiade Archipelago that it is named after. It has been described as a continental fragment that rifted away from the northwestern continental margin of Australia but its position at the northern end of the Tasmantid Seamount Chain also suggests that the Louisiade Plateau might be a large igneous province formed by the arrival of the Tasmantid hotspot. A sample of volcanic rock from the southern spur of the Louisiade Plateau was dated at 56.4 ± 0.6 million years ago by Ar-Ar methodology which is not inconsistent with Tasmantid Seamount Chain timings. Recent sampling however along the northernmost part of the plateau found serpentinized peridotites, mid-ocean ridge basalt and volcaniclastic breccia–conglomerates consistent with placement of oceanic crust during a subduction initiation event in the formation of this part of the plateau.
The Rarotonga hotspot is a volcanic hotspot in the southern Pacific Ocean. The hotspot is claimed to be responsible for the formation of Rarotonga and some volcanics of Aitutaki but an alternative explanation for these islands most recent volcanics has not been ruled out. Recently alternatives to hotspot activity have been offered for several other intra-plate volcanoes that may have been associated with the Rarotonga hotspot hypothesis.
The Taupo Bank is an extinct volcanic seamount of the Tasmantid Seamount Chain.
The Derwent Hunter Guyot is an extinct volcanic seamount of the Tasmantid Seamount Chain.
The Britannia Guyots are a line of extinct volcanic seamounts in the Tasmantid Seamount Chain.