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Encyclopedia > Subduction
Geometry of a subduction zone - insets to show accretionary prism and partial melting of hydrated asthenosphere.
Geometry of a subduction zone - insets to show accretionary prism and partial melting of hydrated asthenosphere.

In geology, a subduction zone is an area on Earth where two tectonic plates meet and move towards one another, with one sliding underneath the other and moving down into the mantle, at rates typically measured in centimeters per year. An oceanic plate ordinarily slides underneath a continental plate; this often creates an orogenic zone with many volcanoes and earthquakes. In a sense, subduction zones are the opposite of divergent boundaries, areas where material rises up from the mantle and plates are moving apart. Image File history File links Size of this preview: 800 × 589 pixelsFull resolution‎ (1,569 × 1,156 pixels, file size: 522 KB, MIME type: image/jpeg) Diagram to explain processes associated with subduction I, the copyright holder of this work, hereby grant the permission to copy, distribute and/or modify... Image File history File links Size of this preview: 800 × 589 pixelsFull resolution‎ (1,569 × 1,156 pixels, file size: 522 KB, MIME type: image/jpeg) Diagram to explain processes associated with subduction I, the copyright holder of this work, hereby grant the permission to copy, distribute and/or modify... An accretionary wedge is a mass of ocean and rock material that is scraped off of the subducting plate at a convergent plate boundary. ... This article does not cite any references or sources. ... This article includes a list of works cited but its sources remain unclear because it lacks in-text citations. ... This article is about Earth as a planet. ... The tectonic plates of the world were mapped in the second half of the 20th century. ... Earth cutaway from core to exosphere. ... Orogeny (Greek for mountain generating) is the process of mountain building, and may be studied as a tectonic structural event, as a geographical event and a chronological event, in that orogenic events cause distinctive structural phenomena and related tectonic activity, affect certain regions of rocks and crust and happen within... Cleveland Volcano in the Aleutian Islands of Alaska photographed from the International Space Station For other uses, see Volcano (disambiguation). ... This article is about the natural seismic phenomenon. ... In plate tectonics, a divergent boundary (divergent fault boundary or divergent plate boundary), (but 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. ...

Contents

General description

Subduction zones mark sites of convective downwelling of the Earth's lithosphere (the crust plus the strong portion of the upper mantle). Subduction zones exist at convergent plate boundaries where one plate of oceanic lithosphere converges with another plate and sinks below it to depth of approximately 100 km. At that depth the peridotite of the oceanic slab is converted to eclogite, the density of the edge of the oceanic lithosphere increases and it sinks into the mantle. It is at subduction zones that the Earth's lithosphere, oceanic crust, sedimentary layers, and trapped water are recycled into the deep mantle. Earth is the only planet where subduction is known to occur; neither Venus nor Mars have subduction zones. Without subduction, plate tectonics could not exist and Earth would be a very different planet: Earth's crust would not have differentiated into continents and oceans and all of the solid Earth would lie beneath a global ocean. 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. ... The tectonic plates of the Lithosphere on Earth. ... Earth cutaway from core to exosphere. ... The tectonic plates of the Lithosphere on Earth. ... Earth cutaway from core to exosphere. ... Age of oceanic crust Oceanic crust is the part of Earths lithosphere that surfaces in the ocean basins. ... Two types of sedimentary rock: limey shale overlaid by limestone. ... (*min temperature refers to cloud tops only) Atmospheric characteristics Atmospheric pressure 9. ... Adjectives: Martian Atmosphere Surface pressure: 0. ... The tectonic plates of the world were mapped in the second half of the 20th century. ...


Subduction results from the difference in density between lithosphere and underlying asthenosphere. Where, very rarely, lithosphere is denser than asthenospheric mantle, it can easily sink back into the mantle at a subduction zone; however, subduction is resisted where lithosphere is less dense than underlying asthenosphere. Whether or not lithosphere is denser than underlying asthenosphere depends on the nature of the associated crust. Crust is always less dense than asthenosphere or lithospheric mantle, but because continental crust is always thicker and less dense than oceanic crust, continental lithosphere is always less dense than oceanic lithosphere. Oceanic lithosphere is generally not denser than asthenosphere but continental lithosphere is lighter. Exceptionally, the presence of the large areas of flood basalt that are called large igneous provinces (LIPs), which result in extreme thickening of the oceanic crust, can cause some sections of older oceanic lithosphere to be too buoyant to subduct. Where lithosphere on the downgoing plate is too buoyant to subduct, a collision occurs, hence the adage "Subduction leads to orogeny". Most subduction zones are arcuate, where the concave side is directed towards the continent. This is especially so where a back-arc basin develops between the subduction zone and the continent. The arcuate configuration probably results from differential friction between the tectonic plates, and the likely agent that would reduct the interplate friction is serpentinite, but a large batch of unconsolidated sediment could cause similar effects as well. This article does not cite any references or sources. ... Moses Coulee showing multiple flood basalt flows of the Columbia River Basalt Group. ... Large Igneous provinces (LIPS) were originally defined by Coffin and Eldholm (1992) as areas of Earths surface that contain very large volumes of magmatic rocks (typically basalt but including rhyolites) erupted over extremely short geological time intervals of a few million years or less. ... // Orogeny (Greek for mountain generating) is the process of mountain building, and may be studied as a tectonic structural event, as a geographical event and a chronological event, in that orogenic events cause distinctive structural phenomena and related tectonic activity, affect certain regions of rocks and crust and happen within...


Subduction zones are associated with the deepest earthquakes on the planet. Earthquakes are generally restricted to the shallow, brittle parts of the crust, generally at depths of less than 20 km. However, in subduction zones, earthquakes occur at depths as great as 700 km. These earthquakes define inclined zones of seismicity known as Wadati-Benioff zones (after the scientists who discovered them), which outline the descending lithosphere. Seismic tomography has helped outline subducted lithosphere in regions where there are no earthquakes. Some subducted slabs seem not to be able to penetrate the major discontinuity in the mantle that lies at a depth of about 670 km, whereas other subducted oceanic plates can penetrate all the way to the core-mantle boundary. The great seismic discontinuities in the mantle - at 410 and 670 km depth - are disrupted by the descent of cold slabs in deep subduction zones. This article is about the natural seismic phenomenon. ... A Benioff zone (also Benioff-Wadati zone or Wadati-Benioff zone) is a deep active seismic area in a subduction zone. ... Seismic tomography uses digital seismographic records to image the interior of the Earth. ... In mathematics, a continuous function is one in which arbitrarily small changes in the input produce arbitrarily small changes in the output. ... The core-mantle boundary lies between the Earths silicate mantle and its iron-nickel core. ...

Oceanic plates are subducted creating oceanic trenches.
Oceanic plates are subducted creating oceanic trenches.

Subduction causes oceanic trenches, such as the Mariana trench. Trenches occur where one plate begins its descent beneath another. Volcanoes that occur above subduction zones, such as Mount St. Helens and Mount Fuji, often occur in arcuate chains, hence the term volcanic arc or island arc. Not all "volcanic arcs" are arced: trenches and arcs are often linear. Image File history File links Oceanic_spreading. ... Image File history File links Oceanic_spreading. ... The tectonic plates of the world were mapped in the second half of the 20th century. ... The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. ... The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. ... This article is about the geographical feature. ... Cleveland Volcano in the Aleutian Islands of Alaska photographed from the International Space Station For other uses, see Volcano (disambiguation). ... For the mountain in California, see Mount Saint Helena. ... Mount Fuji Mount Fuji , IPA: )  , is the highest mountain in Japan at 3,776 m (12,388 ft). ... 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. ... An island arc is a type of archipelago formed by plate tectonics as one oceanic tectonic plate subducts under another and produces magma. ...


The magmatism associated with the volcanic arc occurs 100-300 km away from the trench. However, a relationship has been found, which relates volcanic arc location to depth of the subducted crust as defined by the Wadati-Benioff zone. Studies of many volcanic arcs around the world have revealed that volcanic arcs tend to form at a location where the subducted slab has reached a depth of about 100 km. This has interesting implications for the mechanism that causes the magmatism at these arcs. Arcs produce about 25% of the total volume of magma produced each year on Earth (~30-35 km³), much less than the volume produced at mid-ocean ridges. Nevertheless, arc volcanism has the greatest impact on humans, because many arc volcanoes lie above sealevel and erupt violently. Aerosols injected into the stratosphere during violent eruptions can cause rapid cooling of the Earth's climate. Magma is molten rock located beneath the surface of the Earth (or any other terrestrial planet), and which often collects in a magma chamber. ... Particulates, alternatively referred to as particulate matter (PM), aerosols or fine particles, are tiny particles of solid or liquid suspended in a gas. ...


Subduction zones are also notorious for producing devastating earthquakes because of the intense geological activity. The introduction of cold oceanic crust into the mantle depresses the local geothermal gradient and causes a larger portion of the earth to deform in a more brittle fashion than it would in a normal geothermal gradient setting. Because earthquakes can only occur when a rock is deforming in a brittle fashion, subduction zones have the potential to create very large earthquakes. If this earthquake occurs under the ocean it has the potential to create tsunamis, such as the earthquake caused by subduction of the Indo-Australian Plate under the Eurasian Plate on December 26, 2004, that devastated the areas around the Indian Ocean. Small tremors that create tiny, unnoticeable tsunamis happen all the time because of the dynamics of the earth. Global earthquake epicenters, 1963–1998. ... The tsunami that struck Malé in the Maldives on December 26, 2004. ...  The Indo-Australian plate, shown in dull orange The Indo-Australian Plate is an overarching name for two tectonic plates that include the continent of Australia and surrounding ocean extending northwest to include the Indian subcontinent and adjacent waters. ...  The Eurasian plate, shown in green The Eurasian Plate is a tectonic plate covering Eurasia (a landmass consisting of the traditional continents of Europe and Asia) except that it does not cover the Indian subcontinent, the Arabian subcontinent, and the area east of the Verkhoyansk Range in East Siberia. ... is the 360th day of the year (361st in leap years) in the Gregorian calendar. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... The 2004 Indian Ocean earthquake, known by the scientific community as the Sumatra-Andaman earthquake,[1] was a great undersea earthquake that occurred at 00:58:53 UTC (07:58:53 local time) December 26, 2004 with an epicentre off the west coast of Sumatra, Indonesia. ...


Importance

Cartoon representation of the Subduction Factory, from Y. Tatsumi JAMSTEC.
Cartoon representation of the Subduction Factory, from Y. Tatsumi JAMSTEC.

Subduction zones are important for several reasons: Download high resolution version (445x615, 119 KB)This is a cartoon of the subduction factory, generated by Dr. Yoshii Tatsumiat JAMSTEC. He tells me it is not copyrighted and that I am welcome to use it on Wikipedia. ... Download high resolution version (445x615, 119 KB)This is a cartoon of the subduction factory, generated by Dr. Yoshii Tatsumiat JAMSTEC. He tells me it is not copyrighted and that I am welcome to use it on Wikipedia. ...

  1. Subduction Zone Physics: Sinking of mantle lithosphere is the strongest force (but not the only one) needed to drive plate motion and is the dominant mode of mantle convection.
  2. Subduction Zone Chemistry: The cold material sinking in subduction zones releases water into the overlying mantle, causing mantle melting and fractionating elements (buffering) between surface and deep mantle reservoirs, producing island arcs and continental crust.
  3. Subduction Zone Biology: Because subduction zones are the coldest parts of the Earth's interior and life cannot exist at temperatures >150°C, subduction zones are almost certainly associated with the deepest (highest pressure) biosphere.
  4. Subduction zones mix subducted sediments, oceanic crust, and mantle lithosphere and mix this with mantle from the overriding plate to produce fluids, calc-alkaline series melts, ore deposits, and continental crust.

Subduction zones have also being considered as possible disposal sites for nuclear waste, where the action would carry the material into the planetary mantle, safely away from any possible influence on humanity or the surface environment, but this method of disposal is currently banned by international agreement[1]. Mantle convection is the slow creeping motion of Earths rocky mantle in response to perpetual gravitationally unstable variations in its density. ... Fractional distillation is the separation of a mixture of compounds by their boiling point, by heating to high enough temperatures. ... The thickness of the Earths crust (km). ... For other uses, see Biosphere (disambiguation). ... Calc-alkaline, or calc-alkalic series rocks, are igneous rocks which share a trend of alkali and calcium enrichment. ... Political Punk band from Victorville, Ca WWW.MYSPACE.COM/NUCLEARWASTEX ... Earth cutaway from core to exosphere. ...


See also

The tectonic plates of the world were mapped in the second half of the 20th century. ... See plate tectonics for a more complete discussion Tectonic plate interactions are of three different basic types: Divergent boundaries are areas where plates move away from each other, forming either mid-oceanic ridges or rift valleys. ... Back-arc basins (or retro-arc basins) are geologic features, submarine basins associated with island arcs and subduction zones. ... In plate tectonics, a divergent boundary (divergent fault boundary or divergent plate boundary) is a linear feature that exists between two tectonic plates where the plates are moving away from each other. ... The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. ... Obduction is the overthrusting of continental crust by oceanic crust or mantle rocks. ... // Orogeny (Greek for mountain generating) is the process of mountain building, and may be studied as a tectonic structural event, as a geographical event and a chronological event, in that orogenic events cause distinctive structural phenomena and related tectonic activity, affect certain regions of rocks and crust and happen within...

References

  1. ^ http://www.world-nuclear.org/info/inf04ap2.html
  • Stern, R.J., 2002, Subduction zones: Reviews of Geophysics, v. 40, 1012, doi: 10.1029/2001RG000108.
  • Stern, R.J., 1998. A Subduction Primer for Instructors of Introductory Geology Courses and Authors of Introductory Geology Textbooks: J. Geoscience Education, 46, 221-228.
  • Tatsumi, Y. 2005. The Subduction Factory: How it operates on Earth. GSA Today, v. 15, No. 7, 4-10.

External links

Look up Subduction in
Wiktionary, the free dictionary.
  • NSF-MARGINSprogram, see especially SEIZE and Subduction Factory initiatives
  • Animation of a subduction zone.

  Results from FactBites:
 
NationMaster - Encyclopedia: Subduction zone (144 words)
Subduction zones are associated with the deepest earthquakes on the planet.
Some subducted slabs seem not to be able to penetrate the major discontinuity in the mantle that lies at a depth of about 670 km, whereas other subducted oceanic plates can penetrate all the way to the core-mantle boundary.
Subduction Zone Biology: Because subduction zones are the coldest parts of the Earth's interior and life cannot exist at temperatures >150°C, subduction zones are almost certainly associated with the deepest (highest pressure) biosphere.
Cyberwest - River sediment buildup may be a factor in certain subduction zone earthquakes (798 words)
Subduction zones — areas of offshore ocean floors where two tectonic plates meet, with one sliding beneath the other — are often where powerful earthquakes occur, including quakes in Indonesia in 2004, Alaska in 1964, Chile in 1960 and the Pacific Northwest in 1700.
As the subducting plate slides beneath the upper plate, stress begins to build where the plates meet and the upper plate can deform to create a large structure — "a forearc basin." The basin, a bowl-shaped depression, fills with sediment from nearby rivers that empty into the ocean.
As the top part of the subducting plate meets more resistance and travels at a slower speed than the bottom part of the plate, greater strain is created in the plate.
  More results at FactBites »

 
 

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