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Subduction is a geological process in which the
oceanic lithosphere A lithosphere ( grc, λίθος [] for "rocky", and [] for "sphere") is the rigid, outermost shell of a terrestrial planet, terrestrial-type planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion of ...
is
recycled Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the p ...
into the
Earth's mantle Earth's mantle is a layer of silicate rock between the crust and the outer core Earth's outer core is a fluid layer about thick and composed of mostly iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt ...
at convergent boundaries. Where the oceanic lithosphere of a
tectonic plate This is a list of tectonic plates on Earth's surface Earth is the third planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibriu ...
converges with the less dense lithosphere of a second plate, the heavier plate dives beneath the second plate and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with the average rate of convergence being approximately two to eight centimeters per year along most plate boundaries. Subduction is possible because the cold
oceanic lithosphere A lithosphere ( grc, λίθος [] for "rocky", and [] for "sphere") is the rigid, outermost shell of a terrestrial planet, terrestrial-type planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion of ...
is slightly denser than the underlying
asthenosphere The asthenosphere ( grc, ἀσθενός 'asthenos''meaning "without strength", and thus "weak", and 'sphaira''meaning "sphere") is the highly viscous The viscosity of a fluid In physics, a fluid is a substance that continually Defor ...
, the hot, ductile layer in the
upper mantle The upper mantle of Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth's surface is land consisting of continent A continent is one of several large landmasses. ...
underlying the cold, rigid lithosphere. Once initiated, stable subduction is driven mostly by the negative buoyancy of the dense subducting lithosphere. The
slab Slab or SLAB may refer to: Physical materials * Concrete slab, a flat concrete plate used in construction * Stone slab, a flat stone used in construction * Slab (casting), a length of metal * Slab (geology), that portion of a tectonic plate that is ...
sinks into the mantle largely under its weight.
Earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth Earth is the third planet from the Sun and the only astronomical object known t ...

Earthquake
s are common along the subduction zone, and fluids released by the subducting plate trigger
volcanism Volcanism (or volcanicity) is the phenomenon of eruption of molten rock (magma) onto the Earth#Surface, surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics and volcanic gases erupt through a break in the surface called ...
in the overriding plate. If the subducting plate sinks at a shallow angle, the overriding plate develops a
belt Belt may refer to: Apparel * Belt (clothing), a leather or fabric band worn around the waist * Championship belt, a type of trophy used primarily in combat sports * Colored belts, such as a black belt, worn by martial arts practitioners to signify ...
of
deformation Deformation can refer to: * Deformation (engineering), changes in an object's shape or form due to the application of a force or forces. ** Deformation (mechanics), such changes considered and analyzed as displacements of continuum bodies. * Defo ...
characterized by crustal thickening,
mountain building A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. A mountain differs from a plateau in having a limited summit area, and is larger than a hill, typically rising at lea ...
, and metamorphism. Subduction at a steeper angle is characterized by the formation of
back-arc basin Back-arc basins are geologic Structural basin, basins, submarine features associated with island arcs and subduction zones. They are found at some convergent boundary, convergent plate boundaries, presently concentrated in the western Pacific Ocean ...
s.


Subduction and plate tectonics

According to the theory of
plate tectonics upright=1.35, Diagram of the internal layering of Earth showing the lithosphere above the asthenosphere (not to scale) Plate tectonics (from the la, label=Late Latin Late Latin ( la, Latinitas serior) is the scholarly name for the written L ...
, the Earth's
lithosphere A lithosphere ( grc, λίθος [] for "rocky", and [] for "sphere") is the rigid, outermost shell of a terrestrial planet, terrestrial-type planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion o ...
, its rigid outer shell, is broken into sixteen larger
tectonic plates This is a list of tectonic plates on Earth's surface. Tectonic plates are pieces of Earth's crust 350px, Plates in the crust of Earth Earth's crust is a thin shell on the outside of Earth, accounting for less than 1% of Earth's volume. It is ...

tectonic plates
and several smaller plates. These are in slow motion, due to
convection Convection is single or multiphase fluid flow In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including ''aerodynami ...

convection
in the underlying ductile mantle. This process of convection allows heat generated by
radioactive decay Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

radioactive decay
to escape from the Earth's interior. The lithosphere consists of the outermost light crust plus the uppermost rigid portion of the mantle. Oceanic lithosphere ranges in thickness from just a few km for young lithosphere created at
mid-ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics File:Earth cutaway schematic-en.svg, upright=1.35, Diagram of the internal layering of Earth showing the lithosphere above the asthenosphere (not to scale) Plate ...
s to around for the oldest oceanic lithosphere. Continental lithosphere is up to thick. The lithosphere is relatively cold and rigid compared with the underlying
asthenosphere The asthenosphere ( grc, ἀσθενός 'asthenos''meaning "without strength", and thus "weak", and 'sphaira''meaning "sphere") is the highly viscous The viscosity of a fluid In physics, a fluid is a substance that continually Defor ...
, and so tectonic plates move as solid bodies atop the asthenosphere. Individual plates often include both regions of the oceanic lithosphere and continental lithosphere. Subduction zones are where the cold oceanic lithosphere sinks back into the mantle and is recycled. They are found at convergent plate boundaries, where the oceanic lithosphere of one plate converges with the less dense lithosphere of another plate. The heavier oceanic lithosphere is overridden by the leading edge of the other plate. The overridden plate (the ''
slab Slab or SLAB may refer to: Physical materials * Concrete slab, a flat concrete plate used in construction * Stone slab, a flat stone used in construction * Slab (casting), a length of metal * Slab (geology), that portion of a tectonic plate that is ...
'') sinks at an angle of approximately twenty-five to seventy-five degrees to Earth's surface. This sinking is driven by the temperature difference between the slab and the surrounding asthenosphere, as the colder oceanic lithosphere has, on average, a greater density.
Sediments Sediment is a naturally occurring material that is broken down by processes of weathering Weathering is the deterioration of rocks A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categ ...
and some trapped water are carried downwards by the slab and recycled into the deep mantle. Earth is so far the only planet where subduction is known to occur, and subduction zones are its most important tectonic feature. Subduction is the driving force behind
plate tectonics upright=1.35, Diagram of the internal layering of Earth showing the lithosphere above the asthenosphere (not to scale) Plate tectonics (from the la, label=Late Latin Late Latin ( la, Latinitas serior) is the scholarly name for the written L ...
, and without it, plate tectonics could not occur. Oceanic subduction zones are located along of convergent plate margins, almost equal to the cumulative of mid-ocean ridges.


Structure of subduction zones


Arc-trench complex

The surface expression of subduction zones are arc-trench complexes. On the ocean side of the complex, where the subducting plate first approaches the subduction zone, there is often an ''
outer trench high The outer trench swell, outer trench high, or outer rise is a subtle ridge on the seafloor near an oceanic trench, where a descending plate begins to flex and fault in preparation for its descent into the Earth's mantle, mantle at a subduction zon ...
'' or ''outer trench swell''. Here the plate shallows slightly before plunging downwards, as a consequence of the rigidity of the plate. The point where the slab begins to plunge downwards is marked by an ''
oceanic trench , while the lithosphere is subducted back into the asthenosphere at trenches Oceanic trenches are prominent long, narrow topography, topographic depressions of the ocean floor. They are typically wide and below the level of the surrounding ocean ...
''. Oceanic trenches are the deepest parts of the ocean floor. Beyond the trench is the ''
forearc 275px A forearc is the region between an oceanic trench , while the lithosphere is subducted back into the asthenosphere at trenches Oceanic trenches are topography, topographic depressions of the seafloor, relatively narrow in width, but very l ...

forearc
'' portion of the overriding plate. Depending on sedimentation rates, the forearc may include an
accretionary wedge An accretionary wedge or accretionary prism forms from sediment Sediment is a naturally occurring material that is broken down by processes of weathering Weathering is the deterioration of rocks A rock is any naturally occurring ...

accretionary wedge
of sediments scraped off the subducting slab and accreted to the overriding plate. However, not all arc-trench complexes have an accretionary wedge. Accretionary arcs have a well-developed forearc basin behind the accretionary wedge, while the forearc basin is poorly developed in non-accretionary arcs. Beyond the forearc basin, volcanoes are found in long chains called ''
volcanic arc A volcanic arc is a chain of es formed above a subducting plate, positioned in an arc shape as seen from above. Offshore volcanoes form islands, resulting in a volcanic . Generally, volcanic arcs result from the of an oceanic tectonic plate und ...
s''. The subducting basalt and sediment are normally rich in
hydrous In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understoo ...
minerals and clays. Additionally, large quantities of water are introduced into cracks and fractures created as the subducting slab bends downward. During the transition from basalt to eclogite, these hydrous materials break down, producing copious quantities of water, which at such great pressure and temperature exists as a supercritical fluid. The supercritical water, which is hot and more buoyant than the surrounding rock, rises into the overlying mantle, where it lowers the melting temperature of the mantle rock, generating
magma Magma () is the molten or semi-molten natural material from which all igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others ...

magma
via
flux melting In igneous petrology and volcanology, flux melting occurs when water and other volatile components are introduced to hot solid rock, depressing the Solidus (chemistry), solidus enough. In engineering and metallurgy, Flux (metallurgy), flux is a subs ...
. The magmas, in turn, rise as
diapir A diapir (; , ) is a type of geologic intrusion in which a more mobile and ductily deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh–T ...
s because they are less dense than the rocks of the mantle. The mantle-derived magmas (which are initially basaltic in composition) can ultimately reach the Earth's surface, resulting in volcanic eruptions. The chemical composition of the erupting lava depends upon the degree to which the mantle-derived basalt interacts with (melts) Earth's crust or undergoes fractional crystallization. Arc volcanoes tend to produce dangerous eruptions because they are rich in water (from the slab and sediments) and tend to be extremely explosive.
Krakatoa Krakatoa (), also transcribed Krakatau (; id, Krakatau), is a caldera A caldera is a large cauldron A cauldron (or caldron) is a large cast iron Cast iron is a group of iron-carbon alloys with a carbon content more than 2%. Its ...

Krakatoa
,
Nevado del Ruiz The Nevado del Ruiz (), also known as La Mesa de Herveo ( en, Mesa A mesa is an isolated, flat-topped elevation, ridge A ridge or a mountain ridge is a geographical feature consisting of a chain of mountains or hills that form a c ...

Nevado del Ruiz
, and
Mount Vesuvius Mount Vesuvius ( ; it, Vesuvio ; nap, 'O Vesuvio , also or ; la, Vesuvius , also , or ) is a somma A somma volcano (also known as a sommian) is a volcano, volcanic caldera that has been partially filled by a new central volcanic cone, ...
are all examples of arc volcanoes. Arcs are also associated with most
ore ore – psilomelane Psilomelane is a group name for hard black manganese oxides including hollandite and romanechite. Psilomelane consists of hydrous manganese Manganese is a chemical element Image:Simple Periodic Table Chart- ...

ore
deposits. Beyond the volcanic arc is a
back-arc region The back-arc region is the area behind a volcanic arc. In island arc, island volcanic arcs it consists of back-arc basins of oceanic crust with abyssal depths, which may be separated by remnant arcs, similar to island arcs. In continental arcs the b ...
whose character depends strongly on the angle of subduction of the subducting slab. Where this angle is shallow, the subducting slab drags the overlying continental crust, producing a zone of
compression Compression may refer to: Physical science *Compression (physics), size reduction due to forces *Compression member, a structural element such as a column *Compressibility, susceptibility to compression *Gas compression *Compression ratio, of a co ...
in which there may be extensive folding and
thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault Reverse or reversing may refer to: Arts ...

thrust fault
ing. If the angle of subduction is deep, the crust will be put in
tension Tension may refer to: Science * Psychological stress * Tension (physics), a force related to the stretching of an object (the opposite of compression) * Tension (geology), a stress which stretches rocks in two opposite directions * Voltage or elect ...
instead, often producing a
back-arc basin Back-arc basins are geologic Structural basin, basins, submarine features associated with island arcs and subduction zones. They are found at some convergent boundary, convergent plate boundaries, presently concentrated in the western Pacific Ocean ...
.


Deep structure

The arc-trench complex is the surface expression of a much deeper structure. Though not directly accessible, the deeper portions can be studied using
geophysics Geophysics () is a subject of natural science Natural science is a branch A branch ( or , ) or tree branch (sometimes referred to in botany Botany, also called , plant biology or phytology, is the science of plant life and a b ...

geophysics
and
geochemistry Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the e ...
. Subduction zones are defined by an inclined zone of
earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth Earth is the third planet from the Sun and the only astronomical object known ...

earthquake
s, the
Wadati–Benioff zone Image:Kuril Benioff zone.JPG, 240px, Seismicity cross-section, Kuril Islands subduction zone, 2006 Kuril Islands earthquake, 15 November 2006, 8.3 Mw event marked as star A Wadati–Benioff zone (also Benioff–Wadati zone or Benioff zone or Beniof ...
, that dips away from the trench and extends down to the 660-kilometer discontinuity. Subduction zone earthquakes occur at greater depths (up to ) than elsewhere on Earth (typically less than depth); such deep earthquakes may be driven by deep
phase transformation In chemistry, thermodynamics, and many other related fields, phase transitions (or phase changes) are the Physical process, physical processes of transition between the basic State of matter, states of matter: solid, liquid, and gas, as well as p ...
s,
thermal runaway Thermal runaway describes a process that is accelerated by increased temperature, in turn releasing energy that further increases temperature. Thermal runaway occurs in situations where an increase in temperature changes the conditions in a way th ...
, or dehydration
embrittlementEmbrittlement is a significant decrease of ductility Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can ...
.
Seismic tomography Seismic tomography is a technique for imaging the subsurface of the Earth with seismic waves produced by earthquakes or explosions. P-, S-, and surface waves can be used for tomographic models of different resolutions based on seismic wavelength, ...
shows that some slabs can penetrate the lower mantle and sink clear to the
core–mantle boundary The core–mantle boundary (CMB) of Earth lies between the planet's silicate In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and io ...
. Here the residue of the slabs may eventually heat enough to rise back to the surface as
mantle plume A mantle plume is a proposed mechanism of convection Convection is single or multiphase fluid flow that occurs Spontaneous process, spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, ...

mantle plume
s.


Subduction angle

Subduction typically occurs at a moderately steep angle right at the point of the convergent plate boundary. However, anomalous shallower angles of subduction are known to exist as well as some that are extremely steep. *
Flat-slab subductionFlat slab subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle Earth's mantle is a layer of silicate rock between the crust and the outer core. It has a mass of 4.01 × 1024 kg ...
(subducting angle less than 30°) occurs when the slab subducts nearly horizontally. The relatively flat slab can extend for hundreds of kilometers. That is abnormal, as the dense slab typically sinks at a much steeper angle. Because subduction of slabs to depth is necessary to drive subduction zone volcanism, flat-slab subduction can be invoked to explain volcanic gaps. Flat-slab subduction is ongoing beneath part of the
Andes The Andes, Andes Mountains or Andean Mountains ( es, Cordillera de los Andes) are the List of mountain ranges#Mountain ranges by length, longest continental mountain range in the world, forming a continuous highland along the western edge of Sou ...

Andes
, causing segmentation of the
Andean Volcanic Belt Image:MAGMAARC1.jpg, 300px, The andes mountains are one of the tallest.Map of the volcanic arcs in the Andes, and subduction, subducted structures affecting volcanism The Andean Volcanic Belt is a major volcanic belt along the Andes, Andean cordil ...
into four zones. The flat-slab subduction in northern Peru and the Norte Chico region of Chile is believed to be the result of the subduction of two buoyant aseismic ridges, the
Nazca Ridge The Nazca Ridge is a submarine ridge, located on the Nazca Plate off the west coast of South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion ...
and the Juan Fernández Ridge, respectively. Around
Taitao Peninsula The Taitao Peninsula ( Spanish: ''Península de Taitao'') is a westward projection of the mainland of Chile Chile (, ; ), officially the Republic of Chile (), is a country in western South America. It occupies a long, narrow strip of land bet ...
flat-slab subduction is attributed to the subduction of the
Chile Rise Image:Chile Rise.jpg, 300px The Chile Rise or Chile Ridge is an oceanic ridge, a Divergent boundary, divergent plate boundary between the Nazca Plate, Nazca and Antarctic Plate, Antarctic plates. Its eastern end is the Chile Triple Junction where ...

Chile Rise
, a
spreading ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics File:Earth cutaway schematic-en.svg, upright=1.35, Diagram of the internal layering of Earth showing the lithosphere above the asthenosphere (not to scale) Plate ...
. The
Laramide Orogeny The Laramide orogeny was a time period of mountain building in western North America North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can also be described as the nort ...
in the
Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range A mountain range is a series of mountains ranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with simila ...

Rocky Mountains
of the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

United States
is attributed to flat-slab subduction. During this orogeny, a broad volcanic gap appeared at the southwestern margin of North America, and deformation occurred much farther inland; it was during this time that the
basement A basement or cellar is one or more Storey, floors of a building that are completely or partly below the storey, ground floor. It generally is used as a utility space for a building, where such items as the boiler, water heating, water heate ...
-cored mountain ranges of Colorado, Utah, Wyoming, South Dakota, and New Mexico came into being. The most massive subduction zone earthquakes, so-called "megaquakes", have been found to occur in flat-slab subduction zones. * Steep-angle subduction (subducting angle greater than 70°) occurs in subduction zones where Earth's
oceanic crust The oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates This is a list of tectonic plates on Earth's surface. Tectonic plates are pieces of Earth's crust 350px, Plates in the crust of Earth Earth's crust i ...
and lithosphere are old and thick and have, therefore, lost buoyancy. The steepest dipping subduction zone lies in the
Mariana Trench The Mariana Trench or Marianas Trench is located in the western Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, de ...
, which is also where the oceanic crust, of
Jurassic The Jurassic ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other earth ...
age, is the oldest on Earth exempting
ophiolite An ophiolite is a section of Earth's oceanic crust The oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates This is a list of tectonic plates on Earth's surface. Tectonic plates are pieces of Earth's crust ...

ophiolite
s. Steep-angle subduction is, in contrast to flat-slab subduction, associated with
back-arc Back-arc basins are geologic Structural basin, basins, submarine features associated with island arcs and subduction zones. They are found at some convergent boundary, convergent plate boundaries, presently concentrated in the western Pacific Ocea ...
extension of crust, creating volcanic arcs and pulling fragments of continental crust away from continents to leave behind a
marginal sea This is a list of seas of the World Ocean The ocean (also the sea or the world ocean) is the body of Saline water, salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Water distribution on Earth, Earth's w ...
.


Life cycle of subduction zones


Initiation of subduction

Although stable subduction is fairly well understood, the process by which subduction is initiated remains a matter of discussion and continuing study. Subduction can begin spontaneously if the denser oceanic lithosphere can founder and sink beneath the adjacent oceanic or continental lithosphere through vertical forcing only; alternatively, existing plate motions can induce new subduction zones by horizontally forcing the oceanic lithosphere to rupture and sink into the asthenosphere. Both models can eventually yield self-sustaining subduction zones, as the oceanic crust is metamorphosed at great depth and becomes denser than the surrounding mantle rocks. The compilation of subduction zone initiation events back to 100 Ma suggests horizontally-forced subduction zone initiation for most modern subduction zones, which is supported by results from numerical models and geologic studies. Some analogue modeling shows, however, the possibility of spontaneous subduction from inherent density differences between two plates at specific locations like passive margins. There is evidence this has taken place in the Izu-Bonin-Mariana subduction system. Earlier in Earth's history, subduction is likely to have initiated without horizontal forcing due to the lack of relative plate motion, though an unorthodox proposal by A. Yin suggests that meteorite impacts may have contributed to subduction initiation on early Earth.


End of subduction

Subduction can continue as long as the oceanic lithosphere moves into the subduction zone. However, the arrival of buoyant crust at a subduction zone can result in its failure, by disrupting downwelling. The arrival of continental crust results in a ''collision'' or ''terrane accretion'' that disrupts subduction. Continental crust can subduct to depths of or more but then resurfaces. Sections of crustal or intraoceanic arc crust greater than in thickness or oceanic plateau greater than in thickness can disrupt subduction. However, island arcs subducted end-on may cause only local disruption, while an arc arriving parallel to the zone can shut it down. This has happened with the Ontong Java Plateau and the Vitiaz Trench.


Effects


Metamorphism

Subduction zones host a unique variety of rock types created by the high-pressure, low-temperature conditions a subducting slab encounters during its descent. The metamorphic conditions the slab passes through in this process creates and destroys water bearing (hydrous) mineral phases, releasing water into the mantle. This water lowers the melting point of mantle rock, initiating melting. Understanding the timing and conditions in which these dehydration reactions occur, is key to interpreting mantle melting, volcanic arc magmatism, and the formation of continental crust. A
metamorphic facies A metamorphic facies is a set of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs natu ...

metamorphic facies
is characterized by a stable mineral assemblage specific to a pressure-temperature range and specific starting material. Subduction zone
metamorphism Metamorphism is the change of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs nat ...
is characterized by a low temperature, high-ultrahigh pressure metamorphic path through the
zeolite Zeolites are microporous, aluminosilicate Aluminosilicate mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Ear ...

zeolite
, prehnite-pumpellyite,
blueschist of a thin section vein in mica Mica is a group of sheet silicate minerals, not to be confused with Micah. Mica or MICA may also refer to: Companies * Mica DIY, a UK Retailer Co-operative, Symbol group Acronyms * Mahone Islands Conser ...
, and
eclogite Eclogite () is a metamorphic rock containing garnet (Garnet#Almandine, almandine-Garnet#Pyrope, pyrope) hosted in a Matrix (geology), matrix of sodium-rich pyroxene (omphacite). Accessory minerals include kyanite, rutile, quartz, lawsonite, coesi ...

eclogite
facies stability zones of subducted oceanic crust.Zheng, Y.-F., Chen, R.-X., 2017. Regional metamorphism at extreme conditions: Implications for orogeny at convergent plate margins. Journal of Asian Earth Sciences 145, 46-73.
Zeolite Zeolites are microporous, aluminosilicate Aluminosilicate mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Ear ...

Zeolite
and prehnite-pumpellyite facies assemblages may or may not be present, thus the onset of metamorphism may only be marked by blueschist facies conditions. Subducting slabs are composed of basaltic crust topped with
pelagic sediments Pelagic sediment or pelagite is a fine-grained sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently sediment transport, transported by the action of wind, water, or ic ...
; however, the pelagic sediments may be accreted onto the forearc-hanging wall and not subducted. Most metamorphic phase transitions that occur within the subducting slab are prompted by the dehydration of hydrous mineral phases. The breakdown of hydrous mineral phases typically occurs at depths greater than 10 km. Each of these metamorphic facies is marked by the presence of a specific stable mineral assemblage, recording the metamorphic conditions undergone but the subducting slab. Transitions between facies causes hydrous minerals to dehydrate at certain pressure-temperature conditions and can therefore be tracked to melting events in the mantle beneath a volcanic arc.


Volcanic activity

Volcano A volcano is a rupture in the crust of a planetary-mass object A planet is an astronomical body orbit In physics, an orbit is the gravitationally curved trajectory of an physical body, object, such as the trajectory of a planet a ...

Volcano
es that occur above subduction zones, such as
Mount St. Helens Mount St. Helens (known as Lawetlat'la to the Indigenous Cowlitz people The term Cowlitz people covers two culturally and linguistically distinct indigenous peoples of the Pacific Northwest; the Lower Cowlitz or Cowlitz proper, and th ...

Mount St. Helens
,
Mount Etna Mount Etna, or simply Etna ( it, Etna or ; scn, Muncibbeḍḍu or ; la, Aetna; grc, Αἴτνα and ), is an active stratovolcano A stratovolcano, also known as a composite volcano, is a conical A cone is a three-dimensional sp ...

Mount Etna
, and
Mount Fuji , located on the island of Honshū , historically called , is the largest and most populous main island of Japan , image_flag = Flag of Japan.svg , alt_flag = Centered deep red circle on a white r ...

Mount Fuji
, lie approximately one hundred kilometers from the trench in arcuate chains called
volcanic arc A volcanic arc is a chain of es formed above a subducting plate, positioned in an arc shape as seen from above. Offshore volcanoes form islands, resulting in a volcanic . Generally, volcanic arcs result from the of an oceanic tectonic plate und ...
s. Two kinds of arcs are generally observed on Earth:
island arcs Island arcs are long chains of active volcano A volcano is a rupture in the of a , such as , that allows hot , , and to escape from a below the surface. On Earth, volcanoes are most often found where are or , and most are found underw ...
that form on the oceanic lithosphere (for example, the Mariana and the
Tonga Tonga (, ), officially named the Kingdom of Tonga ( to, Puleʻanga Fakatuʻi ʻo Tonga), is a Polynesia Polynesia (, ; from grc, πολύς "many" and grc, νῆσος "island") ( to, Faka-Polinisia; mi, Porinihia; haw, Polenekia; ...

Tonga
island arcs), and
continental arc Continental may refer to: Places * Continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven regions are commonly regarded as continents. Or ...
s such as the
Cascade Volcanic Arc :''This article is for the volcanic arc. For the namesake mountain range see Cascade Range.'' The Cascade Volcanoes (also known as the Cascade Volcanic Arc or the Cascade Arc) are a number of volcanoes in a volcanic arc in western North America ...

Cascade Volcanic Arc
, that form along the coast of continents. Island arcs (intraoceanic or primitive arcs) are produced by the subduction of oceanic lithosphere beneath another oceanic lithosphere (ocean-ocean subduction) while continental arcs (Andean arcs) form during the subduction of oceanic lithosphere beneath a continental lithosphere (ocean-continent subduction). An example of a volcanic arc having both island and continental arc sections is found behind the
Aleutian Trench Image:Aleutian Trench.jpg, 300px, Map of the Aleutian Trench The Aleutian Trench (or Aleutian Trough) is an oceanic trench along a convergent plate boundary which runs along the southern coastline of Alaska and the Aleutian islands. The trench ext ...

Aleutian Trench
subduction zone in Alaska. The arc magmatism occurs one hundred to two hundred kilometers from the trench and approximately one hundred kilometers above the subducting slab. This depth of arc
magma Magma () is the molten or semi-molten natural material from which all igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others ...

magma
generation is the consequence of the interaction between hydrous fluids, released from the subducting slab, and the arc mantle wedge that is hot enough to melt with the addition of water. It has also been suggested that the mixing of fluids from a subducted tectonic plate and melted sediment is already occurring at the top of the slab before any mixing with the mantle takes place. Arcs produce about 10% of the total volume of magma produced each year on Earth (approximately 0.75 cubic kilometers), much less than the volume produced at mid-ocean ridges, but they have formed most
continental crust Continental crust is the layer of igneous Igneous rock (derived from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the ...
. Arc volcanism has the greatest impact on humans because many arc volcanoes lie above sea level and erupt violently.
Aerosols An aerosol (abbreviation of "aero-solution") is a suspension Suspension or suspended may refer to: Science and engineering * Suspension (topology), in mathematics * Suspension (dynamical systems), in mathematics * Suspension of a ring, in mathe ...
injected into the stratosphere during violent eruptions can cause rapid cooling of Earth's
climate Climate is the long-term pattern of weather Weather is the state of the atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a la ...

climate
and affect air travel.


Earthquakes and tsunamis

The strains caused by plate convergence in subduction zones cause at least three types of earthquakes. These are deep earthquakes, megathrust earthquakes, and outer rise earthquakes. Anomalously deep events are a characteristic of subduction zones, which produce the deepest quakes on the planet. Earthquakes are generally restricted to the shallow, brittle parts of the crust, generally at depths of less than twenty kilometers. However, in subduction zones, quakes occur at depths as great as . These quakes define inclined zones of seismicity known as
Wadati–Benioff zone Image:Kuril Benioff zone.JPG, 240px, Seismicity cross-section, Kuril Islands subduction zone, 2006 Kuril Islands earthquake, 15 November 2006, 8.3 Mw event marked as star A Wadati–Benioff zone (also Benioff–Wadati zone or Benioff zone or Beniof ...
s which trace the descending slab. Nine of the ten largest earthquakes of the last 100 years were subduction zone megathrust earthquakes, which included the , which, at M 9.5, was the largest earthquake ever recorded; the
2004 Indian Ocean earthquake and tsunami The 2004 Indian Ocean earthquake and tsunami (also known as the Boxing Day Tsunami and, by the scientific community, the Sumatra–Andaman earthquake) occurred at 07:58:53 in local time (UTC+7 UTC+07:00 is an identifier for a UTC offset, ti ...
; and the
2011 Tōhoku earthquake and tsunami The occurred at 14:46 JST (05:46 UTC) on 11 March. The magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object ...
. The subduction of cold oceanic crust into the mantle depresses the local
geothermal gradient ). Geothermal gradient is the rate of temperature change with respect to increasing depth in Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth's surface is land consi ...
and causes a larger portion of Earth to deform in a more brittle fashion than it would in a normal geothermal gradient setting. Because earthquakes can occur only when a rock is deforming in a brittle fashion, subduction zones can cause large earthquakes. If such a quake causes rapid deformation of the sea floor, there is potential for
tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquake An earthquake (also known as a quake, t ...

tsunami
s, such as the earthquake caused by subduction of the Indo-Australian Plate under the Euro-Asian Plate on December 26, 2004, that devastated the areas around the Indian Ocean. Small tremors which cause small, nondamaging tsunamis, also occur frequently. A study published in 2016 suggested a new parameter to determine a subduction zone's ability to generate mega-earthquakes. By examining subduction zone geometry and comparing the degree of curvature of the subducting plates in great historical earthquakes such as the 2004 Sumatra-Andaman and the 2011 Tōhoku earthquake, it was determined that the magnitude of earthquakes in subduction zones is inversely proportional to the degree of the fault's curvature, meaning that "the flatter the contact between the two plates, the more likely it is that mega-earthquakes will occur." Outer rise earthquakes occur when normal faults oceanward of the subduction zone are activated by flexure of the plate as it bends into the subduction zone. The 2009 Samoa earthquake is an example of this type of event. Displacement of the sea floor caused by this event generated a six-meter tsunami in nearby Samoa.
Seismic tomography Seismic tomography is a technique for imaging the subsurface of the Earth with seismic waves produced by earthquakes or explosions. P-, S-, and surface waves can be used for tomographic models of different resolutions based on seismic wavelength, ...
has helped detect subducted lithosphere, slabs, deep in the mantle where there are no earthquakes. About one hundred slabs have been described in terms of depth and their timing and location of subduction. The great seismic discontinuities in the mantle, at depth and , are disrupted by the descent of cold slabs in deep subduction zones. Some subducted slabs seem to have difficulty penetrating the major discontinuity that marks the boundary between the upper mantle and lower mantle at a depth of about 670 kilometers. Other subducted oceanic plates have sunk to the
core–mantle boundary The core–mantle boundary (CMB) of Earth lies between the planet's silicate In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and io ...
at 2890 km depth. Generally, slabs decelerate during their descent into the mantle, from typically several cm/yr (up to ~10 cm/yr in some cases) at the subduction zone and in the uppermost mantle, to ~1 cm/yr in the lower mantle. This leads to either folding or stacking of slabs at those depths, visible as thickened slabs in
Seismic tomography Seismic tomography is a technique for imaging the subsurface of the Earth with seismic waves produced by earthquakes or explosions. P-, S-, and surface waves can be used for tomographic models of different resolutions based on seismic wavelength, ...
. Below ~1700 km, there might be a limited acceleration of slabs due to lower viscosity as a result of inferred mineral phase changes until they approach and finally stall at the
core–mantle boundary The core–mantle boundary (CMB) of Earth lies between the planet's silicate In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and io ...
. Here the slabs are heated up by the ambient heat and are not detected anymore ~300 Myr after subduction.


Orogeny

Orogeny is the process of mountain building. Subducting plates can lead to orogeny by bringing oceanic islands, oceanic plateaus, and sediments to convergent margins. The material often does not subduct with the rest of the plate but instead is accreted (scraped off) to the continent, resulting in exotic terranes. The collision of this oceanic material causes crustal thickening and mountain-building. The accreted material is often referred to as an
accretionary wedge An accretionary wedge or accretionary prism forms from sediment Sediment is a naturally occurring material that is broken down by processes of weathering Weathering is the deterioration of rocks A rock is any naturally occurring ...

accretionary wedge
or prism. These accretionary wedges can be identified by
ophiolites , Newfoundland An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crust 350px, The thickness of Crust (geology)#Earth's cr ...
(uplifted ocean crust consisting of sediments, pillow basalts, sheeted dykes, gabbro, and peridotite). Subduction may also cause orogeny without bringing in oceanic material that collides with the overriding continent. When the subducting plate subducts at a shallow angle underneath a continent (something called "flat-slab subduction"), the subducting plate may have enough traction on the bottom of the continental plate to cause the upper plate to contract to lead to folding, faulting, crustal thickening, and mountain building. Flat-slab subduction causes mountain building and volcanism moving into the continent, away from the trench, and has been described in North America (i.e. Laramide orogeny), South America, and East Asia. The processes described above allow subduction to continue while mountain building happens progressively, which is in contrast to continent-continent collision orogeny, which often leads to the termination of subduction.


Beginnings of subduction on Earth

Modern-style subduction is characterized by low
geothermal gradient ). Geothermal gradient is the rate of temperature change with respect to increasing depth in Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth's surface is land consi ...
s and the associated formation of high-pressure low-temperature rocks such as
eclogite Eclogite () is a metamorphic rock containing garnet (Garnet#Almandine, almandine-Garnet#Pyrope, pyrope) hosted in a Matrix (geology), matrix of sodium-rich pyroxene (omphacite). Accessory minerals include kyanite, rutile, quartz, lawsonite, coesi ...

eclogite
and
blueschist of a thin section vein in mica Mica is a group of sheet silicate minerals, not to be confused with Micah. Mica or MICA may also refer to: Companies * Mica DIY, a UK Retailer Co-operative, Symbol group Acronyms * Mahone Islands Conser ...
. Likewise, rock assemblages called
ophiolites , Newfoundland An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crust 350px, The thickness of Crust (geology)#Earth's cr ...
, associated with modern-style subduction, also indicate such conditions.
Eclogite Eclogite () is a metamorphic rock containing garnet (Garnet#Almandine, almandine-Garnet#Pyrope, pyrope) hosted in a Matrix (geology), matrix of sodium-rich pyroxene (omphacite). Accessory minerals include kyanite, rutile, quartz, lawsonite, coesi ...

Eclogite
xenolithImage:XenolithSierra.JPG, Gabbroic xenolith in granite in Rock Creek Canyon, eastern Sierra Nevada (U.S.), Sierra Nevada, California A xenolith ("foreign rock") is a rock (geology), rock fragment (country rock) that becomes enveloped in a larger ro ...
s found in the
North China Craton The North China Craton is a continental crustal block with one of Earth's most complete and complex records of igneous Igneous rock (derived from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic ...

North China Craton
provide evidence that modern-style subduction occurred at least as early as 1.8  Ga ago in the Paleoproterozoic Era. Nevertheless, the eclogite itself was produced by oceanic subduction during the assembly of supercontinents at about 1.9–2.0 Ga.
Blueschist of a thin section vein in mica Mica is a group of sheet silicate minerals, not to be confused with Micah. Mica or MICA may also refer to: Companies * Mica DIY, a UK Retailer Co-operative, Symbol group Acronyms * Mahone Islands Conser ...
is a rock typical for present-day subduction settings. The absence of blueschist older than
Neoproterozoic The Neoproterozoic Era is the unit of geologic time The geologic time scale (GTS) is a system of chronological datingChronological dating, or simply dating, is the process of attributing to an object or event a date in the past, allowing such ob ...
reflects more magnesium-rich compositions of Earth's
oceanic crust The oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates This is a list of tectonic plates on Earth's surface. Tectonic plates are pieces of Earth's crust 350px, Plates in the crust of Earth Earth's crust i ...
during that period. These more magnesium-rich rocks metamorphose into
greenschist Greenschists are metamorphic rocks that formed under the lowest temperatures and pressures usually produced by regional metamorphism, typically and 2–10 kilobars (). Greenschists commonly have an abundance of green minerals such as chlorite, ...
at conditions when modern oceanic crust rocks metamorphose into blueschist. The ancient magnesium-rich rocks mean that
Earth's mantle Earth's mantle is a layer of silicate mineral, silicate rock between the Earth's crust, crust and the Earth's outer core, outer core. It has a mass of 4.01 × 1024 kg and thus makes up 67% of the mass of Earth. It has a thickness of making up a ...
was once hotter, but not that subduction conditions were hotter. Previously, the lack of pre-Neoproterozoic blueschist was thought to indicate a different type of subduction. Both lines of evidence refute previous conceptions of modern-style subduction having been initiated in the Neoproterozoic Era 1.0 Ga ago.


History of investigation

Harry Hammond Hess Harry Hammond Hess (May 24, 1906 – August 25, 1969) was an American geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes the Earth and other terrestrial planets, as well as the processes that ...
, who during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a global war A world war is "a war War is an intense armed conflict between states State may refer to: Arts, entertainment, and media Literatur ...
served in the
United States Navy Reserve The United States Navy Reserve (USNR), known as the United States Naval Reserve from 1915 to 2005, is the Reserve Component The reserve components of the United States Armed Forces are military organizations whose Reservist, members generally p ...
and became fascinated in the ocean floor, studied the
Mid-Atlantic Ridge The Mid-Atlantic Ridge is a mid-ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics File:Earth cutaway schematic-en.svg, upright=1.35, Diagram of the internal layering of Earth showing the lithosphere ...
and proposed that hot molten rock was added to the crust at the ridge and expanded the seafloor outward. This theory was to become known as
seafloor spreading Seafloor spreading or Seafloor spread is a process that occurs at mid-ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics File:Earth cutaway schematic-en.svg, upright=1.35, Diagram of the internal l ...
. Since the
Earth's circumference Earth's circumference is the distance Distance is a numerical measurement of how far apart objects or points are. In physics or everyday usage, distance may refer to a physical length or an estimation based on other criteria (e.g. "two coun ...
has not changed over geologic time, Hess concluded that older seafloor has to be consumed somewhere else, and suggested that this process takes place at oceanic trenches, where the crust would be melted and recycled in the
Earth's mantle Earth's mantle is a layer of silicate rock between the crust and the outer core Earth's outer core is a fluid layer about thick and composed of mostly iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt ...
. In 1964, George Plafker researched the
Good Friday earthquake The 1964 Alaskan earthquake, also known as the Great Alaskan earthquake and Good Friday earthquake, occurred at 5:36 PM AKST on Good Friday Good Friday is a Christian holiday commemorating the crucifixion of Jesus and his death at Calvary. It ...
in
Alaska Alaska (; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Central Alaskan Yup'ik language, Yup'ik: ''Alaskaq''; tli, Anáaski) is a U.S. state in the Western United States, on the northwest extremity of the country's West Coast of the United State ...

Alaska
. He concluded that the cause of the earthquake was a megathrust reaction in the
Aleutian Trench Image:Aleutian Trench.jpg, 300px, Map of the Aleutian Trench The Aleutian Trench (or Aleutian Trough) is an oceanic trench along a convergent plate boundary which runs along the southern coastline of Alaska and the Aleutian islands. The trench ext ...

Aleutian Trench
, a result of the Alaskan continental crust overlapping the Pacific oceanic crust. This meant that the Pacific crust was being forced downward, or ''subducted'', beneath the Alaskan crust. The concept of subduction would play a role in the development of the
plate tectonics upright=1.35, Diagram of the internal layering of Earth showing the lithosphere above the asthenosphere (not to scale) Plate tectonics (from the la, label=Late Latin Late Latin ( la, Latinitas serior) is the scholarly name for the written L ...
theory. First geologic attestations of the "subduct" words date to 1970, In ordinary English ''to subduct'', or ''to subduce'' (from Latin ''subducere'', “to lead away”) are
transitive verb A transitive verb is a verb A verb () is a word (part of speech) that in syntax conveys an action (''bring'', ''read'', ''walk'', ''run'', ''learn''), an occurrence (''happen'', ''become''), or a state of being (''be'', ''exist'', ''stand''). ...
s requiring a subject to perform an action on an object not itself, here the lower plate, which has then been ''subducted'' (“removed”). The geological term is "consumed," which happens the geological moment the lower plate slips under, even though it may persist for some time until its remelting and dissipation. In this conceptual model, plate is continually being used up. The identity of the subject, the consumer, or agent of consumption, is left unstated. Some sources accept this subject-object construct. Geology makes ''to subduct'' into an
intransitive verb In grammar In linguistics, the grammar (from Ancient Greek ''grammatikḗ'') of a natural language is its set of structure, structural constraints on speakers' or writers' composition of clause (linguistics), clauses, phrases, and words. Th ...
and a
reflexive verb In grammar In linguistics Linguistics is the scientific study of language, meaning that it is a comprehensive, systematic, objective, and precise study of language. Linguistics encompasses the analysis of every aspect of language, as we ...
. The lower plate itself is the subject. It subducts, in the sense of retreat, or removes itself, and while doing so, is the "subducting plate." Moreover, the word
slab Slab or SLAB may refer to: Physical materials * Concrete slab, a flat concrete plate used in construction * Stone slab, a flat stone used in construction * Slab (casting), a length of metal * Slab (geology), that portion of a tectonic plate that is ...
is specifically attached to the "subducting plate," even though in English the upper plate is just as much of a slab. The upper plate is left hanging, so to speak. To express it geology must switch to a different verb, typically ''to override''. The upper plate, the subject, performs the action of overriding the object, the lower plate, which is overridden.


Importance

Subduction zones are important for several reasons: * Subduction zone physics: Sinking of the oceanic
lithosphere A lithosphere ( grc, λίθος [] for "rocky", and [] for "sphere") is the rigid, outermost shell of a terrestrial planet, terrestrial-type planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion o ...
(sediments, crust, mantle), by the contrast of
density The density (more precisely, the volumetric mass density; also known as specific mass), of a substance is its per unit . The symbol most often used for density is ''ρ'' (the lower case Greek letter ), although the Latin letter ''D'' can also ...

density
between the cold and old lithosphere and the hot asthenospheric mantle wedge, is the strongest force (but not the only one) needed to drive plate motion and is the dominant mode of
mantle convection Mantle convection is the very slow creeping motion of Earth's solid silicate mantle caused by convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heteroge ...
. * Subduction zone chemistry: The subducted sediments and crust dehydrate and release water-rich (
aqueous An aqueous solution is a solution Solution may refer to: * Solution (chemistry) Image:SaltInWaterSolutionLiquid.jpg, upMaking a saline water solution by dissolving Salt, table salt (sodium chloride, NaCl) in water. The salt is the solute an ...
)
fluids In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force ...

fluids
into the overlying mantle, causing mantle melting and
fractionation Fractionation is a separation process A separation process is a method that converts a mixture or solution of chemical substances into two or more distinct product mixtures. At least one of results of the separation is enriched in one or more of ...
of elements between the surface and deep mantle reservoirs, producing island arcs and
continental crust Continental crust is the layer of igneous Igneous rock (derived from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the ...
. Hot fluids in subduction zones also alter the mineral compositions of the subducting sediments and potentially the habitability of the sediments for microorganisms. * Subduction zones drag down subducted oceanic sediments, oceanic crust, and mantle lithosphere that interact with the hot asthenospheric
mantle Mantle may refer to: *Mantle (geology) A mantle is a layer inside a planetary body A planet is an astronomical body Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a n ...
from the over-riding plate to produce
calc-alkaline The calc-alkaline magma series is one of two main subdivisions of the Subalkaline volcanic rock, subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the ...
series melts, ore deposits, and continental crust. * Subduction zones pose significant threats to lives, property, economic vitality, cultural and natural resources, and quality of life. The tremendous magnitudes of earthquakes or volcanic eruptions can also have knock-on effects with global impact. Subduction zones have also been considered as possible disposal sites for nuclear waste in which the action of subduction itself would carry the material into the planetary
mantle Mantle may refer to: *Mantle (geology) A mantle is a layer inside a planetary body A planet is an astronomical body Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a n ...
, safely away from any possible influence on humanity or the surface environment. However, that method of disposal is currently banned by international agreement. Furthermore, plate subduction zones are associated with very large
megathrust earthquake Megathrust earthquakes occur at convergent plate boundaries, where one tectonic plate This is a list of tectonic plates on Earth's surface Earth is the third planet A planet is an astronomical body orbiting a star or Stellar evolut ...
s, making the effects of using any specific site for disposal unpredictable and possibly adverse to the safety of long-term disposal.


See also

* Compaction simulation * * * * * * * *


References


Additional reading

* *


External links


The Subduction Zone Initiation Database
The latest knowledge about the formation of subduction zones


From the Seafloor to the Volcano's Top
Video about the work of the Collaborative Research Center (SFB) 574 Volatiles and Fluids in Subduction Zones in Chile by GEOMAR I Helmholtz Centre for Ocean Research Kiel.
Plate Tectonics Basics 1 - Creation and Destruction of Oceanic Lithosphere
University of Texas at Dallas (~ 9 minutes long).
Atlas of the Underworld
– mapping of subducted plates in the Earth’s mantle and their geological interpretation {{Authority control Plate tectonics Geological processes Lithosphere