Oceanic plateau
Encyclopedia
An oceanic plateau is a large, relatively flat submarine region that rises well above the level of the ambient seabed. While many oceanic plateaus are composed of continental crust
, and often form a step interrupting the continental slope, some plateaus are undersea remnants of large igneous province
s. These were formed by the equivalent of continental flood basalt
s such as the Deccan Traps
in India and the Snake River Plain
in the Pacific Northwest
of the United States
.
Geologists believe that igneous oceanic plateaus may well represent a stage in the development of continental crust
as they are generally less dense than oceanic crust
while still being denser than normal continental crust.
Density differences in crustal material largely arise from different ratios of various elements, especially silicon
. Continental crust has the highest amount of silicon (such rock is called felsic
). Oceanic crust has a smaller amount of silicon (mafic
rock). Igneous oceanic plateaus have a ratio intermediate between continental and oceanic crust, although they are more mafic than felsic.
However, when a plate carrying oceanic crust subducts
under a plate carrying an igneous oceanic plateau, the volcanism which erupts on the plateau as the oceanic crust heats up on its descent into the mantle erupts material which is more felsic than the material which makes up the plateau. This represents a step toward creating crust which is increasingly continental in character, being less dense and more buoyant. If an igneous oceanic plateau is subducted underneath another one, or under existing continental crust, the eruptions produced thereby produce material that is yet more felsic, and so on through geologic time.
Continental crust
The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in...
, and often form a step interrupting the continental slope, some plateaus are undersea remnants of large igneous province
Large igneous province
A Large Igneous Province is an extremely large accumulation of igneous rocks—intrusive, extrusive, or both—in the earth's crust...
s. These were formed by the equivalent of continental flood basalt
Flood basalt
A flood basalt or trap basalt is the result of a giant volcanic eruption or series of eruptions that coats large stretches of land or the ocean floor with basalt lava. Flood basalts have occurred on continental scales in prehistory, creating great plateaus and mountain ranges...
s such as the Deccan Traps
Deccan Traps
The Deccan Traps are a large igneous province located on the Deccan Plateau of west-central India and one of the largest volcanic features on Earth. They consist of multiple layers of solidified flood basalt that together are more than thick and cover an area of and a volume of...
in India and the Snake River Plain
Snake River Plain
The Snake River Plain is a geologic feature located primarily within the state of Idaho in the United States of America. It stretches about westward from northwest of the state of Wyoming to the Idaho-Oregon border. The plain is a wide flat bow-shaped depression, and covers about a quarter of Idaho...
in the Pacific Northwest
Pacific Northwest
The Pacific Northwest is a region in northwestern North America, bounded by the Pacific Ocean to the west and, loosely, by the Rocky Mountains on the east. Definitions of the region vary and there is no commonly agreed upon boundary, even among Pacific Northwesterners. A common concept of the...
of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
.
Geologists believe that igneous oceanic plateaus may well represent a stage in the development of continental crust
Continental crust
The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in...
as they are generally less dense than oceanic crust
Oceanic crust
Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium...
while still being denser than normal continental crust.
Density differences in crustal material largely arise from different ratios of various elements, especially silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
. Continental crust has the highest amount of silicon (such rock is called felsic
Felsic
The word "felsic" is a term used in geology to refer to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium....
). Oceanic crust has a smaller amount of silicon (mafic
Mafic
Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term is a portmanteau of the words "magnesium" and "ferric". Most mafic minerals are dark in color and the relative density is greater than 3. Common rock-forming mafic minerals include olivine,...
rock). Igneous oceanic plateaus have a ratio intermediate between continental and oceanic crust, although they are more mafic than felsic.
However, when a plate carrying oceanic crust subducts
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
under a plate carrying an igneous oceanic plateau, the volcanism which erupts on the plateau as the oceanic crust heats up on its descent into the mantle erupts material which is more felsic than the material which makes up the plateau. This represents a step toward creating crust which is increasingly continental in character, being less dense and more buoyant. If an igneous oceanic plateau is subducted underneath another one, or under existing continental crust, the eruptions produced thereby produce material that is yet more felsic, and so on through geologic time.
Continental oceanic plateaus
- Campbell PlateauCampbell PlateauThe Campbell Plateau is a large submarine plateau to the south of New Zealand and the Chatham Rise. It originated in the Gondwanan breakup and is part of Zealandia, a largely submerged continent. The Bounty Islands, Antipodes Islands, Auckland Islands and Campbell Island are on the...
(South Pacific) - Challenger PlateauChallenger PlateauThe Challenger Plateau is a large submarine plateau west of New Zealand and south of the Lord Howe Rise. It has an approximate diameter of . The plateau originated in the Gondwanan breakup and is one of the five major submerged parts of Zealandia, a largely submerged continent....
(South Pacific)
Igneous oceanic plateaus
- Agulhas Plateau (Southwest Indian)
- Caribbean-Colombian Plateau (Caribbean)
- Exmouth Plateau (Indian)
- Hikurangi PlateauHikurangi PlateauHikurangi Plateau is an Early Cretaceous basaltic oceanic plateau in the southwestern Pacific Ocean. The portion of the plateau exposed on the seafloor has an area of 350,000 km2, and including the portions subducted beneath the...
(Southwest Pacific) - Kerguelen PlateauKerguelen PlateauThe Kerguelen Plateau is an underwater volcanic large igneous province , also the microcontinent and submerged continent in the southern Indian Ocean. It lies about 3,000 km to the southwest of Australia and is nearly three times the size of Japan...
(Indian) - Manihiki PlateauManihiki PlateauThe Manihiki Plateau is an oceanic plateau in the southwest Pacific Ocean. The Manihiki Plateau was formed by volcanic activity 125 to 120 million years ago during the mid-Cretaceous period at a triple junction plate boundary called the Tongareva triple junction....
(Southwest Pacific) - Mascarene PlateauMascarene PlateauThe Mascarene Plateau is an submarine plateau in the Indian Ocean, north and east of Madagascar. The plateau extends approximately 2000 km, from the Seychelles in the north to Réunion in the south. The plateau covers an area of over 115,000 km² of shallow water, with depths ranging from...
(Indian) - Naturaliste PlateauNaturaliste PlateauThe Naturaliste Plateau is one of several large submarine plateaus extending from Western Australia into the Indian Ocean. It covers an area of 90,000 square kilometres and has water depths from 1500 to 5000 metres deep....
(Indian) - Ontong Java PlateauOntong Java PlateauThe Ontong Java Plateau is a huge oceanic plateau located in the Pacific Ocean, lying north of the Solomon Islands. The plateau covers an area of approximately , or roughly the size of Alaska, and reaches a thickness of up to . The plateau is of volcanic origin, composed mostly of flood basalts...
(Southwest Pacific) - Shatsky Rise (North Pacific)
- Vøring Plateau (North Atlantic)
- Wrangellia TerraneWrangellia TerraneThe Wrangellia Terrane is a geologic concept encompassing a large arc of terrain extending from the U.S state of southcentral Alaska through southwestern Yukon and along the Coast of British Columbia in Canada...
(Northeast Pacific) - Yermak Plateau (Arctic)
References
See also
- Abyssal plainAbyssal plainAn abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between 3000 and 6000 metres. Lying generally between the foot of a continental rise and a mid-ocean ridge, abyssal plains cover more than 50% of the Earth’s surface. They are among the flattest, smoothest...
- BathymetryBathymetryBathymetry is the study of underwater depth of lake or ocean floors. In other words, bathymetry is the underwater equivalent to hypsometry. The name comes from Greek βαθύς , "deep", and μέτρον , "measure"...
- List of Oceanic Landforms
- Ocean bank (topography)