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Encyclopedia > Oceanic trench
Oceanic crust is formed at an oceanic ridge, while the lithosphere is subducted back into the asthenosphere at trenches.
Oceanic crust is formed at an oceanic ridge, while the lithosphere is subducted back into the asthenosphere at trenches.

The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. They are also the deepest parts of the ocean floor. Image File history File links Oceanic_spreading. ... Image File history File links Oceanic_spreading. ...


Trenches define one of the most important natural boundaries on the Earth’s solid surface, that between two lithospheric plates. There are three types of lithospheric plate boundaries: divergent (where lithosphere and oceanic crust is created at mid-ocean ridges), convergent (where one lithospheric plate sinks beneath another and returns to the mantle), and transform (where two lithospheric plates slide past each other). Trenches are the spectacular and distinctive morphological features of plate boundaries. Plates move together along convergent plate boundaries at convergence rates that vary from a few millimeters to ten or more centimeters per year. A trench marks the position at which the flexed, subducting slab begins to descend beneath another lithospheric slab. Trenches are generally parallel to a volcanic island arc, and trenches about 200 km from a volcanic arc. Oceanic trenches typically extend 3 to 4 km (1.9 to 2.5 mi) below the level of the surrounding oceanic floor. The deepest ocean depth to be sounded is in the Challenger Deep of the Mariana Trench at a depth of 10,911 m (35,798 ft) below sea level. Oceanic lithosphere disappears into trenches at a global rate of about a tenth of a square meter per second. The tectonic plates of the lithosphere on Earth. ... In plate tectonics, a divergent boundary or divergent plate boundary (also known as a constructive boundary or an extensional boundary) is a linear feature that exists between two tectonic plates that are moving away from each other. ... In plate tectonics, a convergent boundary – also known as a convergent plate boundary or a destructive plate boundary – is an actively deforming region where two (or more) tectonic plates or fragments of lithosphere move toward one another. ... In plate tectonics, a transform boundary (also known as transform fault boundary, transform plate boundary, transform plate margin, strike-slip boundary, sliding boundary, transverse boundary, or conservative plate boundary) is said to occur when tectonic plates slide and grind against each other along a transform fault. ... Geometry of a subduction zone - insets to show accretionary prism and partial melting of hydrated asthenosphere. ... Look up Slab in Wiktionary, the free dictionary Slab can refer to: Slab (computer science) - a unit of storage unique to the NCR 315. ... Mariana Islands, an oceanic island arc Cascade Volcanic Arc, a continental volcanic arc A volcanic arc is a chain of volcanic islands or mountains formed by plate tectonics as an oceanic tectonic plate subducts under another tectonic plate and produces magma. ... This article needs additional references or sources for verification. ... This article is about the geographical feature. ...

Contents

Geographic distribution

There are about 50,000 km of convergent plate margins, mostly around the Pacific Ocean – the reason for the reference “Pacific-type” margin - but they are also in the eastern Indian Ocean, with relatively short convergent margin segments in the Atlantic Ocean and in the Mediterranean Sea. Trenches are sometimes buried and lack bathymetric expression, but the fundamental structures that these represent mean that the great name should also be applied here. This applies to Cascadia, Makran, southern Lesser Antilles, and Calabrian trenches. Trenches along with volcanic arcs and zones of earthquakes that dip under the volcanic arc as deeply as 700 km are diagnostic of convergent plate boundaries and their deeper manifestations, subduction zones. Trenches are related to but distinguished from continental collision zones (like that between India and Asia to form the Himalaya), where continental crust enters the subduction zone. When buoyant continental crust enters a trench, subduction eventually stops and the convergent plate margin becomes a collision zone. Features analogous to trenches are associated with collisions zones; these are sediment-filled foredeeps referred to as peripheral foreland basins, such as that which the Ganges River and Tigris-Euphrates rivers flow along. In plate tectonics, a convergent boundary – also known as a convergent plate boundary or a destructive plate boundary – is an actively deforming region where two (or more) tectonic plates or fragments of lithosphere move toward one another. ... Mediterranean redirects here. ... Structure of the Cascadia subduction zone Area of the Cascadia subduction zone The Cascadia subduction zone is a very long sloping fault that stretches from northern Vancouver Island to northern California. ... Makran is the southern region of Balochistan, in Iran and Pakistan along the coast of the Arabian Sea and the Gulf of Oman. ... Location of the Lesser Antilles (green) in relation to the rest of the Caribbean Islands of the Lesser Antilles The Lesser Antilles, also known as the Caribbees,[1] are part of the Antilles, which together with the Bahamas and Greater Antilles form the West Indies. ... For other uses, see Calabria (disambiguation). ... Mariana Islands, an oceanic island arc Cascade Volcanic Arc, a continental volcanic arc A volcanic arc is a chain of volcanic islands or mountains formed by plate tectonics as an oceanic tectonic plate subducts under another tectonic plate and produces magma. ... This article is about the natural seismic phenomenon. ... Categories: Geology stubs | Plate tectonics ... Perspective view of the Himalaya and Mount Everest as seen from space looking south-south-east from over the Tibetan Plateau. ... The thickness of the Earths crust (km). ... This article is about the river. ...


History of the term "Trench"

Trenches are the most spectacular morphologic feature on Earth’s solid surface but they were not clearly defined until the late 1940’s and 1950’s. The bathymetry of the ocean was of no real interest until the late 19th and early 20th centuries, with the initial laying of Transatlantic telegraph cables on the seafloor between the continents. Even then the elongated bathymetric expression of trenches was not recognized until well into the 20th century. The term “trench” does not appear in Murray and Hjort’s (1912) classic oceanography book. Instead they applied the term “deep’ for the deepest parts of the ocean, such as Challenger Deep. Experiences from World War I battlefields emblazoned the concept of the trench warfare as an elongate depression defining an important boundary, so it was no surprise that the term “trench” was used to describe natural features in the early 1920’s. The term was first used in a geologic context by Scofield two years after the war ended to describe a structurally-controlled depression in the Rocky Mountains. Johnstone, in his 1923 textbook An Introduction to Oceanography first used the term in its modern sense for any marked, elongate depression of the sea bottom. Bathymetry is the underwater equivalent to topography. ... The first transatlantic telegraph cable crossed the Atlantic Ocean from Foilhommerum, Valentia Island, in western Ireland to Hearts Content, in eastern Newfoundland. ... Sir John Murray (March 3, 1841 - March 16, 1914), pioneering Scots-Canadian oceanographer and marine biologist. ... Thermohaline circulation Oceanographic frontal systems on the southern hemisphere Oceanography (from the greek words Ωκεανός meaning Ocean and γράφω meaning to write), also called oceanology or marine science, is the branch of Earth Sciences that studies the Earths oceans and seas. ... This article needs additional references or sources for verification. ... “The Great War ” redirects here. ... {{subst:empty template|}} {{Copyviocore |url= |month = {{subst:CURRENTMONTHNAME}} |day = {{subst:CURRENTDAY}} |year = {{subst:CURRENTYEAR}} |time = {{subst:CURRENTTIME}} |timestamp = {{subst:CURRENTTIMESTAMP}}}} Trench warfare is a form of warfare where both combatants have fortified positions and fighting lines are static. ... For individual mountains named Rocky Mountain, see Rocky Mountain (disambiguation). ...


During the 1920’s and 1930’s, Felix Andries Vening Meinesz developed a unique gravimeter that could measure gravity in the stable environment of a submarine and used it to measure gravity over trenches. His measurements revealed that trenches are sites of downwelling in the solid Earth. The concept of downwelling at trenches was characterized by Griggs in 1939 as the tectogene hypothesis, for which he developed an analogue model using a pair of rotating drums. World War II in the Pacific led to great improvements of bathymetry in especially the western and northern Pacific, and the linear nature of these deeps became clear. The rapid growth of deep sea research efforts, especially the widespread use of echosounders in the 1950’s and 1960’s confirmed the morphological utility of the term. The important trenches were identified, sampled, and their greatest depths sonically plumbed. The heroic phase of trench exploration culminated in the 1960 descent of the Bathyscaphe "Trieste", which set an unbeatable world record by diving to the bottom of the Challenger Deep. Following Robert S. Dietz’ and Harry Hess’ articulation of the seafloor spreading hypothesis in the early 1960’s and the plate tectonic revolution in the late 1960’s the term ‘trench’ has been redefined with plate tectonic as well as bathymetric connotations! Felix Andries Vening Meinesz (July 30, 1887 – August 10, 1966) was a Dutch geologist and geodesist. ... An accelerometer or gravimeter is a device for measuring acceleration and the effects of gravity. ... Gravity is a force of attraction that acts between bodies that have mass. ... Downwelling is the process of accumulation and sinking of higher density material beneath lower density material, such as cold or saline water beneath warmer or fresher water or cold air beneath warm air. ... Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000... The bathyscaphe Trieste Trieste was a Swiss-designed deep-diving research bathyscaphe (deep boat) with a crew of two people, which reached a record-breaking depth of about 10,900 m (about 35,760 ft), in the deepest part of any ocean on earth, the Challenger Deep in the Mariana... Robert Sinclair Dietz (September 14, 1914 - May 19, 1995) was Professor of Geology at Arizona State University. ... Harry Hammond Hess (1906-1969) was an American geologist. ... The tectonic plates of the world were mapped in the second half of the 20th century. ...


Modern understanding of trenches

Trenches define one of the most important natural boundaries on the Earth’s solid surface, that between two lithospheric plates. There are three types of lithospheric plate boundaries: divergent (where lithosphere and oceanic crust is created at mid-ocean ridges), convergent (where one lithospheric plate sinks beneath another and returns to the mantle), and transform (where two lithospheric plates slide past each other). Trenches are the spectacular and distinctive morphological features of convergent plate boundaries. Plates move together along convergent plate boundaries at convergence rates that vary from a few millimetres to ten or more centimetres per year. Trenches form where oceanic lithosphere is subducted at a convergent plate margin, presently at a global rate of about a tenth of a square metre per second.


Trench rollback

Although trenches would seem to be positionally stable over time, it is hypothesized that some trenches, particularly those associated with subduction zones where two oceanic plates converge, retrograde, that is, they move backward into the plate which is subducting, akin to a backward-moving wave. This has been termed trench rollback (also hinge rollback). This is one explanation for the existence of back-arc basins. Back-arc basins (or retro-arc basins) are geologic features, submarine basins associated with island arcs and subduction zones. ...


Morphologic expression

     The Peru-Chile Trench
     The Peru-Chile Trench

Trenches are centerpieces of the distinctive physiography of a convergent plate margin. Transects across trenches yield asymmetric profiles, with relatively gentle (~5°) outer (seaward) slope and a steeper (~10-16°) inner (landward) slope. This asymmetry is due to the fact that the outer slope is defined by the top of the downgoing plate, which must bend as it starts its descent. The great thickness of the lithosphere requires that this bending be gentle. As the subducting plate approaches the trench, it is first bent upwards to form the outer trench swell, then descends to form the outer trench slope. The outer trench slope is disrupted by a set of subparallel normal faults which staircase the seafloor down to the trench. The plate boundary is defined by the trench axis itself. Beneath the inner trench wall, the two plates slide past each other along the subduction decollement, the seafloor intersection of which defines the trench location. The overriding plate contains volcanic arc (generally) and a forearc. The volcanic arc is caused by physical and chemical interactions between the subducted plate at depth and asthenospheric mantle associated with the overriding plate. The forearc lies between the trench and the volcanic arc. Forearcs have the lowest heatflow from the interior Earth because there is no asthenosphere (convecting mantle) between the forearc lithosphere and the cold subducting plate. Image File history File links Download high resolution version (573x1500, 212 KB) Summary The Peru-Chile oceanic trench. ... Image File history File links Download high resolution version (573x1500, 212 KB) Summary The Peru-Chile oceanic trench. ... The Peru-Chile Trench, also called Atacama Trench, is a submarine trench in the eastern Pacific Ocean, about 100 miles (160 km) off the coast of Peru and Chile. ... The outer rise is a subtle ridge on the seafloor near an oceanic trench where descending plate begins to flex and fault in preparation for its descent into the mantle. ... Geologic faults, fault lines or simply faults are planar rock fractures, which show evidence of relative movement. ... A décollement horizon is a tectonic surface that acts as a gliding plane between two masses in a thrust fault relationship. ... Mariana Islands, an oceanic island arc Cascade Volcanic Arc, a continental volcanic arc A volcanic arc is a chain of volcanic islands or mountains formed by plate tectonics as an oceanic tectonic plate subducts under another tectonic plate and produces magma. ... Categories: Plate tectonics | Sedimentology | Geology stubs ... This article does not cite any references or sources. ... This article does not cite any references or sources. ...


The inner trench wall marks the edge of the overriding plate and the outermost forearc. The forearc consists of igneous and metamorphic crust, and this crust acts as buttress to a growing accretionary prism (sediments scraped off the downgoing plate onto the inner trench wall, depending on how much sediment is supplied to the trench). If the flux of sediments is high, material will be transferred from the subducting plate to the overriding plate. In this case an accretionary prism grows and the location of the trench migrates progressively away from the volcanic arc over the life of the convergent margin. Convergent margins with growing accretionary prisms are called accretionary convergent margins and make up nearly half of all convergent margins. If the sediment flux is low, material will be transferred from the overriding plate to the subducting plate by a process of tectonic ablation known as subduction erosion and carried down the subduction zone. Forearcs undergoing subduction erosion typically expose igneous rocks. In this case, the location of the trench will migrate towards the magmatic arc over the life of the convergent margin. Convergent margins experiencing subduction erosion are called nonaccretionary convergent margins and comprise more than half of convergent plate boundaries. This is an oversimplification, because different parts of a convergent margin can experience sediment accretion and subduction erosion over its life. Igneous rocks (etymology from Latin ignis, fire) are rocks formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Quartzite, a form of metamorphic rock, from the Museum of Geology at University of Tartu collection. ...


The asymmetric profile across a trench reflects fundamental differences in materials and tectonic evolution. The outer trench wall and outer swell comprise seafloor that takes a few million years to move from where subduction-related deformation begins near the outer trench swell until sinking beneath the trench. In contrast, the inner trench wall is deformed by plate interactions for the entire life of the convergent margin. The forearc is continuously subjected to subduction-related earthquakes. This protracted deformation and shaking ensures that the inner trench slope is controlled by the angle of repose of whatever material it is composed of. Because they are composed of igneous rocks instead of deformed sediments, non-accretionary trenches have steeper inner walls than accretionary trenches. This article is about the natural seismic phenomenon. ...


Filled trenches

The composition of the inner trench slope and a first-order control on trench morphology is determined by sediment supply. Active accretionary prisms are common for trenches near continents where large rivers or glaciers reach the sea and supply great volumes of sediment which naturally flow to the trench. These filled trenches are confusing because in a plate tectonic sense they are indistinguishable from other convergent margins but lack the bathymetric expression of a trench. The Cascadia margin of the northwest USA is a filled trench, the result of sediments delivered by the rivers of the NW USA and SW Canada. The Lesser Antilles convergent margin shows the importance of proximity to sediment sources for trench morphology. In the south, near the mouth of the Orinoco River, there is no morphological trench and the forearc plus accretionary prism is almost 500 km wide. The accretionary prism is so large that it forms the islands of Barbados and Trinidad. Northward the forearc narrows, the accretionary prism disappears, and only north of 17°N the morphology of a trench is seen. In the extreme north, far away from sediment sources, the Puerto Rico Trench is over 8600 m deep and there is no active accretionary prism. A similar relationship between proximity to rivers, forearc width, and trench morphology can be observed from east to west along the Alaskan-Aleutian convergent margin. The convergent plate boundary offshore Alaska changes along its strike from a filled trench with broad forearc in the east (near the coastal rivers of Alaska) to a deep trench with narrow forearc in the west (offshore the Aleutian islands). Another example is the Makran convergent margin offshore Pakistan and Iran, which is a trench filled by sediments from the Tigris-Euphrates and Indus rivers. Thick accumulations of turbidites along a trench can be supplied by down-axis transport of sediments that enter the trench 1000-2000 km away, as is found for the Peru-Chile Trench south of Valparaíso and for the Aleutian Trench. Convergence rate can also be important for controlling trench depth, especially for trenches near continents, because slow convergence causes the capacity of the convergent margin to dispose of sediment to be exceeded. This article or section cites very few or no references or sources. ... Animated, colour-coded map showing the various continents. ... For other uses, see River (disambiguation). ... Perito Moreno Glacier Patagonia Argentina Aletsch Glacier, Switzerland Icebergs breaking off glaciers at Cape York, Greenland This article is about the geological formation. ... The tectonic plates of the world were mapped in the second half of the 20th century. ... Bathymetry is the underwater equivalent to topography. ... Structure of the Cascadia subduction zone Area of the Cascadia subduction zone The Cascadia subduction zone is a very long sloping fault that stretches from northern Vancouver Island to northern California. ... Location of the Lesser Antilles (green) in relation to the rest of the Caribbean Islands of the Lesser Antilles The Lesser Antilles, also known as the Caribbees,[1] are part of the Antilles, which together with the Bahamas and Greater Antilles form the West Indies. ... For other uses, see Orinoco (disambiguation). ... For other uses, see Trinidad (disambiguation). ... Location map Puerto Rico trench - USGS The Puerto Rico Trench is an oceanic trench located on the boundary between the Caribbean Sea and the Atlantic Ocean. ... For other uses, see Alaska (disambiguation). ... Aleutian refers to: Aleutian Islands Aleut people Aleut language This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... Makran is the southern region of Balochistan, in Iran and Pakistan along the coast of the Arabian Sea and the Gulf of Oman. ... The Tigris is the eastern member of the pair of great rivers that define Mesopotamia, along with the Euphrates, which flows from the mountains of Anatolia through Iraq. ... For the song River Euphrates by the Pixies, see Surfer Rosa. ... ‹ The template below (Citations missing) is being considered for deletion. ... USGS image Turbidite geological formations have their origins in turbidity current deposits, deposits from a form of underwater avalanche that are responsible for distributing vast amounts of clastic sediment into the deep ocean. ... The Peru-Chile Trench, also called Atacama Trench, is a submarine trench in the eastern Pacific Ocean, about 100 miles (160 km) off the coast of Peru and Chile. ... For other places with the same name, see Valparaiso (disambiguation). ...


There an evolution in trench morphology can be expected as oceans close and continents converge. While the ocean is wide, the trench may be far away from continental sources of sediment and so may be deep. As the continents approach each other, the trench may become filled with continental sediments and become shallower. A simple way to approximate when the transition from subduction to collision has occurred is when the plate boundary previously marked by a trench is filled enough to rise above sealevel.


Accretionary prisms and sediment transport

Accretionary prisms grow by frontal accretion, whereby sediments are scraped off, bulldozer-fashion, near the trench, or by underplating of subducted sediments and perhaps oceanic crust along the shallow parts of the subduction decollement. Frontal accretion over the life of a convergent margin results in younger sediments defining the outermost part of the accretionary prism and the oldest sediments defining the innermost portion. Older (inner) parts of the accretionary prism are much more lithified and have steeper structures than the younger (outer) parts. Underplating is difficult to detect in modern subduction zones but may be recorded in ancient accretionary prisms such as the Franciscan Group of California in the form of tectonic mélanges and duplex structures. Different modes of accretion are reflected in morphology of the inner slope of the trench, which generally shows three morphological provinces. The lower slope comprises imbricate thrust slices that form ridges. The mid slope may comprise a bench or terraces. The upper slope is smoother but may be cut by submarine canyons. Because accretionary convergent margins have high relief, are continuously deformed, and accommodate a large flux of sediments, they are vigorous systems of sediment dispersal and accumulation. Sediment transport is controlled by submarine landslides, debris flows, turbidity currents, and contourites. Submarine canyons transport sediment from beaches and rivers down the upper slope. These canyons form by channelized turbidites and generally lose definition with depth because continuous faulting disrupts the submarine channels. Sediments move down the inner trench wall via channels and a series of fault-controlled basins. The trench itself serves as an axis of sediment transport. If enough sediment moves to the trench, it may be completely filled so that turbidity currents are able to carry sediments well beyond the trench and may even surmount the outer swell. Sediments from the rivers of SW Canada and NW USA spill over where the Cascadia trench would be and cross the Juan de Fuca plate to reach the spreading ridge several hundred kilometres to the west. For other uses, see Bulldozer (disambiguation). ... Age of oceanic crust Oceanic crust is the part of Earths lithosphere that surfaces in the ocean basins. ... A Submarine canyon is a steep-sided valley on the seafloor of the continental slope. ... This article is about geological phenomenon. ... A turbidity current or density current is a current of of rapidly moving, sediment-laden water moving down a slope through air, water, or another fluid. ... For other uses, see Beach (disambiguation). ... A map of the Juan de Fuca Plate The Juan de Fuca Plate, named after the explorer, is a tectonic plate arising from the Juan de Fuca Ridge, and subducting under the northerly portion of the western side of the North American Plate. ...


The slope of the inner trench slope of an accretionary convergent margin reflects continuous adjustments to the thickness and width of the accretionary prism. The prism maintains a ‘critical taper’, established in conformance with Mohr-Coulomb Theory for the pertinent materials. A package of sediments scraped off the downgoing lithospheric plate will deform until it and the accretionary prism that it has been added to attain a critical taper (constant slope) geometry. Once critical taper is attained, the wedge slides stably along its basal decollement. Strain rate and hydrologic properties strongly influence the strength of the accretionary prism and thus the angle of critical taper. Fluid pore pressures modify rock strength and are important controls of critical taper angle. Low permeability and rapid convergence may result in pore pressures that exceed lithostatic pressure and a relatively weak accretionary prism with a shallowly tapered geometry, whereas high permeability and slow convergence result in lower pore pressure, stronger prisms, and steeper geometry. Mohr-Coulomb Theory is a mathematical model describing the response of rubble piles to the shear forces produced by gravity. ...


The Hellenic trench system is unusual because this convergent margin subducts evaporites. The slope of the surface of the southern flank of the Mediterranean Ridge (its accretionary prism) is low, about 1°, which indicates very low shear stress on the decollement at the base of the wedge. Evaporites influence the critical taper of the accretionary complex, as their mechanical properties differ from those of siliciclastic sediments, and because of their effect upon fluid flow and fluid pressure, which control effective stress. In the 1970s, the linear deeps of the Hellenic trench south of Crete were interpreted to be similar to trenches at other subduction zones, but with the realization that the Mediterranean Ridge is an accretionary complex, it became apparent that the Hellenic trench is actually a starved forearc basin, and that the plate boundary lies south of the Mediterranean Ridge. A sample of evaporite material Evaporites (IPA: ) are water-soluble, mineral sediments that result from the evaporation of bodies of surficial water. ... For other uses, see Crete (disambiguation). ...


Water and biosphere

The volume of water escaping from within and beneath the forearc results in some of Earth’s most dynamic and complex interactions between aqueous fluids and rocks. Most of this water is trapped in pores and fractures in the upper lithosphere and sediments of the subducting plate. The average forearc is underrun by a solid volume of oceanic sediment that is 400 m thick. This sediment enters the trench with 50-60% porosity. These sediments are progressively squeezed as they are subducted, reducing void space and forcing fluids out along the decollement and up into the overlying forearc, which may or may not have an accretionary prism. Sediments accreted to the forearc are another source of fluids. Water is also bound in hydrous minerals, especially clays and opal. Increasing pressure and temperature experienced by subducted materials converts the hydrous minerals to denser phases that contain progressively less structurally-bound water. Water released by dehydration accompanying phase transitions is another source of fluids introduced to the base of the overriding plate. These fluids may travel through the accretionary prism diffusely, via interconnected pore spaces in sediments, or may follow discrete channels along faults. Sites of venting may take the form of mud volcanoes or seeps and are often associated with chemosynthetic communities. Fluids escaping from the shallowest parts of a subduction zone may also escape along the plate boundary but have rarely been observed draining along the trench axis. All of these fluids are dominated by water but also contain dissolved ions and organic molecules, especially methane. Methane is often sequestered in an ice-like form (methane clathrate, also called gas hydrate) in the forearc. These are a potential energy source and can rapidly break down. Destabilization of gas hydrates has contributed to global warming in the past and will likely do so in the future. Categories: Plate tectonics | Sedimentology | Geology stubs ... Porosity is a measure of the void spaces in a material, and is measured as a fraction, between 0–1, or as a percentage between 0–100%. The term porosity is used in multiple fields including manufacturing, earth sciences and construction. ... For other uses, see Clay (disambiguation). ... For other uses, see Opal (disambiguation). ... Methane is a chemical compound with the molecular formula . ... Burning ice. Methane, released by heating, burns; water drips (USGS). ...


Chemosynthetic communities thrive where cold fluids seep out of the forearc. Cold seep communities have been discovered in inner trench slopes down to depths of 6000 m in the western Pacific, especially around Japan, in the Eastern Pacific along North, Central and South America coasts from the Aleutian to the Peru-Chile trenches, on the Barbados prism, in the Mediterranean, and in the Indian Ocean along the Makran and Sunda convergent margins. These communities receive much less attention than the chemosynthetic communities associated with hydrothermal vents. Chemosynthetic communities are located in a variety of geological settings: above over-pressured sediments in accretionary prisms where fluids are expelled through mud volcanoes or ridges (Barbados, Nankai and Cascadia); along active erosive margins with faults; and along escarpments caused by debris slides (Japan trench, Peruvian margin). Surface seeps may be linked to massive hydrate deposits and destabilization (e.g. Cascadia margin). High concentrations of methane and sulfide in the fluids escaping from the seafloor are the principal energy sources for chemosynthesis. Chemosynthesis is the biological conversion of 1 or more carbon molecules (usually carbon dioxide or methane) and nutrients into organic matter using the oxidation of inorganic molecules (e. ... A hydrothermal vent A hydrothermal vent is a fissure in a planets surface from which geothermally heated water issues. ... Formally, sulfide is the dianion, S2−, which exists in strongly alkaline aqueous solutions formed from H2S or alkali metal salts such as Li2S, Na2S, and K2S. Sulfide is exceptionally basic and, with a pKa > 14, it does not exist in appreciable concentrations even in highly alkaline water. ...


Empty trenches and subduction erosion

Trenches distant from an influx of continental sediments lack an accretionary prism, and the inner slope of such trenches is commonly composed of igneous or metamorphic rocks. Non-accretionary convergent margins are characteristic of (but not limited to) primitive arc systems. Primitive arc systems are those built on oceanic lithosphere, such as the Izu-Bonin-Mariana, Tonga-Kermadec, and Scotia (South Sandwich) arc systems. The inner trench slope of these convergent margins exposes the crust of the forearc, including basalt, gabbro, and serpentinized mantle peridotite. These exposures allow easy access to study the lower oceanic crust and upper mantle in place and provide a unique opportunity to study the magmatic products associated with the initiation of subduction zones. Most ophiolites probably originate in a forearc environment during the initiation of subduction, and this setting favors ophiolite emplacement during collision with blocks of thickened crust. Not all non-accretionary convergent margins are associated with primitive arcs. Trenches adjacent to continents where there is little influx of sediments carried by rivers, such as the central part of the Peru-Chile Trench, may also lack an accretionary prism.


Igneous basement of a nonaccretionary forearc may be continuously exposed by subduction erosion. This transfers material from the forearc to the subducting plate and can be accomplished by frontal erosion or basal erosion. Frontal erosion is most active in the wake of seamounts being subducted beneath the forearc. Subduction of large edifices (seamount tunneling) oversteepens the forearc, causing mass failures that carry debris towards and ultimately into the trench. This debris may be deposited in graben of the downgoing plate and subducted with it. In contrast, structures resulting from subduction erosion of the base of the forearc are difficult to recognize from seismic reflection profiles, so the possibility of basal erosion is difficult to confirm. Subduction erosion may also diminish a once-robust accretionary prism if the flux of sediments to the trench diminishes.


Nonaccretionary forearcs may also be the site of serpentine mud volcanoes. These form where fluids released from the downgoing plate percolate upwards and interact with cold mantle lithosphere of the forearc. Mantle peridotite is hydrated into serpentinite, which is much less dense than peridotite and so will rise diapirically when there is an opportunity to do so. Some nonaccretionary forearcs are subjected to strong extensional stresses, for example the Marianas, and this allows buoyant serpentinite to rise to the seafloor where they form serpentinite mud volcanoes. Chemosynthetic communities are also found on non-accretionary margins such as the Marianas, where they thrive on vents associated with serpentinite mud volcanoes. For other uses, see Serpentine (disambiguation). ... A gaseous mud volcano The term mud volcano or mud dome is used to refer to formations created by geologically excreted liquids and gases, although there are several different processes which may cause such activity. ... Peridotite xenolith from San Carlos, southwestern United States. ...


Factors affecting trench depth

There are several factors that control the depth of trenches. The most important control is the supply of sediment, which fills the trench so that there is no bathymetric expression. It is therefore not surprising that the deepest trenches (deeper than 8,000 m) are all nonaccretionary. In contrast, all trenches with growing accretionary prisms are shallower than 8000 m. A second order control on trench depth is the age of the lithosphere at the time of subduction. Because oceanic lithosphere cools and thickens as it ages, it subsides. The older the seafloor, the deeper it lies and this determines a minimum depth from which seafloor begins its descent. This obvious correlation can be removed by looking at the relative depth, the difference between regional seafloor depth and maximum trench depth. Relative depth may be controlled by the age of the lithosphere at the trench, the convergence rate, and the dip of the subducted slab at intermediate depths. Finally, narrow slabs can sink and roll back more rapidly than broad plates, because it is easier for underlying asthenosphere to flow around the edges of the sinking plate. Such slabs may have steep dips at relatively shallow depths and so may be associated with unusually deep trenches, such as the Challenger Deep. Image File history File linksMetadata Download high resolution version (1500x1076, 330 KB)Perspective view of the sea floor of the Atlantic Ocean and the Caribbean Sea. ... Image File history File linksMetadata Download high resolution version (1500x1076, 330 KB)Perspective view of the sea floor of the Atlantic Ocean and the Caribbean Sea. ... Location map Puerto Rico trench - USGS The Puerto Rico Trench is an oceanic trench located on the boundary between the Caribbean Sea and the Atlantic Ocean. ... This article needs additional references or sources for verification. ...


Major oceanic trenches

Trench Ocean Depth
Marianas Trench Pacific Ocean 10,911m
Tonga Trench Pacific Ocean 10,882m
Kuril Trench Pacific Ocean 10,542m
Philippine Trench Pacific Ocean 10,540m
Kermadec Trench Pacific Ocean 10,047m
Izu-Bonin Trench (Izu-Ogasawara Trench) Pacific Ocean 9,780 m
Japan Trench Pacific Ocean 9,000m
Puerto Rico Trench Atlantic Ocean 8,605 m
Peru-Chile Trench or Atacama Trench Pacific Ocean 8,065 m
Trench Location
Aleutian Trench West of Alaska
Bougainville Trench South of New Guinea
Cayman Trench Western Caribbean Sea
Cedros Trench (inactive) Pacific coast of Baja California
Hikurangi Trench East of New Zealand
Japan Trench Northeast Japan
Kuril-Kamchatka Trench Near Kuril islands
Mariana Trench (deepest known part of the oceans) Western Pacific ocean; east of Mariana Islands
Middle America Trench
New Hebrides Trench West of New Caledonia
Puerto Rico Trench (deepest known part of the Atlantic Ocean) Boundary of Caribbean Sea and Atlantic ocean
Peru-Chile Trench Eastern Pacific ocean; off coast of Peru & Chile
Philippine Trench East of Philippine Islands
Ryukyu Trench Eastern edge of Japan's Ryukyu Islands
South Sandwich Trench
Sunda Arc and Java Trench
Tonga Trench North-east of Australia
Yap Trench Western Pacific ocean; between Palau Islands and Mariana Trench

The Mariana Trench is the deepest known submarine trench, and the deepest location in the Earth itself. ... The Tonga Trench is located in the Pacific ocean and is 32,000 ft (9,900 m) deep. ... The Kuril-Kamchatka Trench or Kuril Trench is an oceanic trench with a maximum depth of 10500 m (34000 ft). ... The Philippine Trench is a submarine trench to the east of the Philippine islands. ... The Kermadec trench is one of the deepest parts of the Pacific Ocean. ... The Japan Trench is an oceanic trench, a part of the Pacific Ring of Fire, in the floor of the northern Pacific Ocean off northeast Japan. ... Location map Puerto Rico trench - USGS The Puerto Rico Trench is an oceanic trench located on the boundary between the Caribbean Sea and the Atlantic Ocean. ... The Peru-Chile Trench, also called Atacama Trench, is a submarine trench in the eastern Pacific Ocean, about 100 miles (160 km) off the coast of Peru and Chile. ... The Peru-Chile Trench, also called Atacama Trench, is a submarine trench in the eastern Pacific Ocean, about 100 miles (160 km) off the coast of Peru and Chile. ... The Aleutian Trench is an oceanic trench in the Earths crust. ... For other uses, see Alaska (disambiguation). ... Cayman Trench, also called Bartlett Deep, or Bartlett Trough, is a submarine trench on the floor of the western Caribbean Sea between Jamaica and the Cayman Islands. ... Map of Central America and the Caribbean The Caribbean Sea (pronounced or ) is a tropical sea in the Western Hemisphere, part of the Atlantic Ocean, southeast of the Gulf of Mexico. ... Location within Mexico Municipalities of Baja California Country Capital Municipalities 5 Largest City Tijuana Government  - Governor José Guadalupe Osuna Millán (PAN)  - Federal Deputies PAN: 8  - Federal Senators Alejandro González (PAN) Rafael Díaz (PAN) Fernando Castro (PRI) Area Ranked 12th  - Total 69,921 km² (26,996. ... The Hikurangi Trench lies in the Pacific Ocean off the east coast of New Zealand. ... The Japan Trench is an oceanic trench, a part of the Pacific Ring of Fire, in the floor of the northern Pacific Ocean off northeast Japan. ... The Kuril-Kamchatka Trench or Kuril Trench is an oceanic trench with a maximum depth of 10500 m (34000 ft). ... For the political history of the sovereignty conflict, see Kuril Islands dispute. ... This article is about the geographical feature. ... Animated map exhibiting the worlds oceanic waters. ... Pacific redirects here. ... The Mariana Islands (also the Marianas; up to the early 20th century sometimes called Ladrones Islands, from Spanish Islas de los Ladrones meaning Islands of Thieves) are an archipelago made up by the summits of 15 volcanic mountains in the north-western Pacific Ocean between the 12th and 21st parallels... The trench lies at the convergence of the Pacific, Cocos, Nazca, North American, and Caribbean plates The Middle America Trench is an oceanic trench in the eastern Pacific Ocean, stretching from central Mexico to Costa Rica. ... Location map Puerto Rico trench - USGS The Puerto Rico Trench is an oceanic trench located on the boundary between the Caribbean Sea and the Atlantic Ocean. ... Map of Central America and the Caribbean The Caribbean Sea (pronounced or ) is a tropical sea in the Western Hemisphere, part of the Atlantic Ocean, southeast of the Gulf of Mexico. ... Atlantic and North Atlantic redirect here. ... The Peru-Chile Trench, also called Atacama Trench, is a submarine trench in the eastern Pacific Ocean, about 100 miles (160 km) off the coast of Peru and Chile. ... The Philippine Trench is a submarine trench to the east of the Philippine islands. ... The Philippine islands is a commonly mistaken description for the Philippines. ... The Ryukyu Trench is an 1,398 mile long ocean trench running north along the eastern edge of Japans Ryukyu Islands in the Philippine Sea. ... Location of Ryukyu Islands The Ryukyu Islands, in Japanese called the Nansei Islands ) are a chain of Japanese islands in the western Pacific Ocean at the eastern limit of the East China Sea. ... The South Sandwich Trench is the deepest trench of the Southern Atlantic Ocean, and the second deepest of the Atlantic Ocean, after the Puerto Rico Trench. ... Categories: Geology stubs | Plate tectonics ... The Java Trench, also called Sunda Trench, with a length of 2 600 km and a maximum depth of 7 725 meters at 10°19N, 109°58E, was long thought to be the deepest trench of the Indian Ocean, but is in fact second to the Diamantina Trench... The Tonga Trench is located in the Pacific ocean and is 32,000 ft (9,900 m) deep. ... The Yap Trench is an oceanic trench in the western Pacific Ocean. ... The Republic of Palau (also spelled Belau) is an island nation in the Pacific Ocean, located some 500 km east of the Philippines. ...

Ancient oceanic trenches

Trench Location
Intermontane Trench Western North America; between Intermontane Islands and North America
Insular Trench Western North America; between Insular Islands and Intermontane Islands
Farallon Trench Western North America
Tethyan Trench South of Turkey, Iran, Tibet and Southeast Asia

The Intermontane Trench was an ancient oceanic trench during the Triassic time. ... North American redirects here. ... The Intermontane Islands where a volcanic chain in the Pacific Ocean during the Jurassic period. ... The Insular Islands were a giant chain of active volcanic islands somewhere in the Pacific Ocean during the Cretaceous time that rode on top a microplate called the Insular Plate, beginning around 130 million years ago. ... The Farallon Trench was an ancient trench on the west coast of North America during the late Cretaceous period. ... The Tethyan Trench was an ancient oceanic trench that existed in the northern part of the Tethys Ocean during the Jurassic era. ... This article is about historical/cultural Tibet. ... Location of Southeast Asia Southeast Asia is a subregion of Asia. ...

References

  • R. J. Stern 2002. "Subduction Zones". Reviews of Geophysics. 10.1029/2001RG000108
  • A.B. Watts, 2001. Isostasy and Flexure of the Lithosphere. Cambridge University Press. 458p.
  • D. J. Wright, S. H. Bloomer, C. J. MacLeod, B. Taylor and A. M. Goodlife, 2000. "Bathymetry of the Tonga Trench and Forearc: a map series". Marine Geophysical Researches 21: 489–511, 2000.
  • M. Sibuet, K. Olu, 1998. "Biogeography, biodiversity and fluid dependence of deep-sea cold-seep communities at active and passive margins." Deep-Sea Research II 45, 517-567.
  • W. H. F. Smith, D. T. Sandwell, 1997. "Global sea floor topography from satellite altimetry and ship depth soundings". Science, vol.277, no.5334, pp.1956-1962.
  • "Deep-sea trench". McGraw-Hill Encyclopedia of Science & Technology, 8th edition, 1997.
  • R. von Huene and D. W. Scholl 1993. "The return of sialic material to the mantle indicated by terrigeneous material subducted at convergent margins". Tectonophysics 219, 163-175.
  • J.W. Ladd, T. L. Holcombe, G. K. Westbrook, N. T. Edgar, 1990. "Caribbean Marine Geology: Active margins of the plate boundary", in Dengo, G., and Case, J. (eds.) The Geology of North America, Vol. H, The Caribbean Region, Geological Society of America, p. 261-290.
  • W. B. Hamilton 1988. "Plate tectonics and island arcs". Geological Society of America Bulletin: Vol. 100, No. 10, pp. 1503–1527.
  • R. D. Jarrard, 1986. "Relations among subduction parameters". Reviews of Geophysics, vol.24, no.2, pp.217-284.
  • J. W. Hawkins, S. H. Bloomer, C. A. Evans, J. T. Melchior. 1984. "Evolution of Intra-Oceanic Arc-Trench Systems". Tectonophysics 102, 175-205.
  • R. L. Fisher and H. H. Hess 1963. "Trenches" in M.N. Hill ed. The Sea v. 3 The Earth Beneath the Sea. New York: Wiley-Interscience, p. 411-436.

See also

An oceanic ridge is an underwater mountain range, usually formed by plate tectonics. ... The tectonic plates of the world were mapped in the second half of the 20th century. ... World Oceans Physical oceanography is the study of physical conditions and physical processes within the ocean, especially the motions and physical properties of ocean waters. ... A landform comprises a geomorphological unit. ... The following is a list of the deepest parts of the Earths oceans and seas. ...

  Results from FactBites:
 
Oceanic trench - Wikipedia, the free encyclopedia (3732 words)
Trenches along with volcanic arcs and zones of earthquakes that dip under the volcanic arc as deeply as 700 km are diagnostic of convergent plate boundaries and their deeper manifestations, subduction zones.
Trenches are centerpieces of the distinctive physiography of a convergent plate margin.
Trenches distant from an influx of continental sediments lack an accretionary prism, and the inner slope of such trenches is commonly composed of igneous or metamorphic rocks.
  More results at FactBites »

 
 

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