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Topic: Subduction


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  NationMaster - Encyclopedia: Subduction zone
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.
www.nationmaster.com /encyclopedia/Subduction-zone   (144 words)

  
 Cyberwest - River sediment buildup may be a factor in certain subduction zone earthquakes
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.
www.cyberwest.com /geology/cascadia-subduction-zone-earthquake.shtml   (798 words)

  
 Subduction   (Site not responding. Last check: 2007-11-02)
Subduction is the process in which one plate is pushed downward beneath another plate into the underlying mantle when plates move towards each other.
The jerky movement, as well as the friction between the plates causes much heat, and together with the heat from the mantle and from radioactive decay, causes the subducted plate to melt.
The boundary of such plate movements is 'destructive' as part of the plate melts during subduction and is destroyed.
library.thinkquest.org /17457/platetectonics/5.php   (214 words)

  
 Subduction
This is clearly not the origin of subduction zone igneous activity because subduction zones are primarily places where one plate is moving down beneath the other.
The water escaping from the descending slab is probably the primary cause of volcanic activity at subduction zones.
In subduction zones that affect continental crust, and in areas where continents have come into collision, huge amounts of intermediate to felsic intrusive rock are formed.
www.stmarys.ca /conted/webcourses/GEO/GEO99/pubigneous/subduction.html   (1285 words)

  
 Shear stresses on megathrusts: Implications for mountain building behind subduction zones
The main constraint is that vertical normal stresses beneath the highlands behind the subduction zone are nearly equal to horizontal normal stresses, in the plane of a trench- or arc-normal section.
The A constants are solved individually for each subduction zone, assuming that the maximum depth of interplate slip earthquakes marks the brittle-ductile transition.
In subduction zones where the subducted slab is older than 50 Ma, a significant proportion of the integrated shear force on the megathrust is taken up where it cuts the mantle and temperatures are ≤300°C. In much younger subduction zones, the stress transmission is confined mainly to the crust.
www.agu.org /pubs/crossref/2006/2005JB003916.shtml   (694 words)

  
 Subduction Zone, Active Continental Margins - John Seach   (Site not responding. Last check: 2007-11-02)
A subduction zone is a region where the oceanic lithosphere descends into the mantle.
Subduction zone volcanoes are often explosive and are the world's most dangerous.
Subduction is the result of the old cold plate sinking below the overriding plate.
www.volcanolive.com /subduction.html   (78 words)

  
 Woods Hole Oceanographic Institution (WHOI) - 2002 Annual Report
As the subducting plate plunges into the mantle, magma is generated that can erupt at the surface of the overriding plate.
Traditional thermal models, left, of subduction zones assumed a rigid plate atop a constant viscosity mantle wedge, leading to cooler temperatures at shallower levels than a model produced by WHOI Senior Scientist Peter Kelemen and colleagues.
This simple modification of subduction zone models has resolved a decades-old paradox and significantly improved our understanding of arc volcanism.
www.whoi.edu /annualreport02/highlights/subduction.html   (375 words)

  
 Plate Tectonics : Subduction Zones
If a trench has flipped because of the arrival of a continent, and the newly subducted plate also carries a continent, a collision of land masses is unavoidable.
When this happens, subduction terminates along the collision zone, the trench disappears, and the continents collide, resulting in the birth of a new mountain range.
When this happens, the ridge slowly moves toward the trench and the whole plate is eventually drawn down into the mantle, causing a global rearrangement of other plates and their borders.
www.platetectonics.com /book/page_12.asp   (337 words)

  
  Sea-Floor Spreading and Subduction Model
This process, called subduction, creates a very deep trough near the line of contact between the oceanic and continental plates.
As an oceanic plate is subducted into the Earth it is subjected to increased pressure and temperature.
From the ages of the sea floor and the scale of the model, which is the same in the vertical and horizontal directions, one can determine that the plate in this model is being subducted at a rate of about 50 km/my.
pubs.usgs.gov /of/1999/ofr-99-0132   (1617 words)

  
  Subduction Summary
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.
www.bookrags.com /Subduction   (1744 words)

  
 subduction zone - HighBeam Encyclopedia
subduction zone large-scaled narrow region in the earth's crust where, according to plate tectonics, masses of the spreading oceanic lithosphere bend downward into the earth along the leading edges of converging lithospheric plates where it slowly melts at about 400 mi (640 km) deep and becomes reabsorbed.
Subduction zones are usually marked by deep ocean trenches that often exceed 6 mi (10 km) compared to the ocean's overall depth of 2 to 4 mi (3 to 5 km).
A pattern of earthquakes of shallow, intermediate, and deep focus occurs along the same angle as the descending plate, which is steeply inclined (30°-60°) toward the continent behind the trench in a zone called the Benioff Zone, discovered by the U.S. seismologist Hugo Benioff.
www.encyclopedia.com /doc/1E1-subducti.html   (634 words)

  
 Introduction to Plate Tectonics   (Site not responding. Last check: 2007-11-02)
The lithosphere arrives at the edge of a continent, where it is subducted or sinks into the asthenosphere.
Thus, oceanic lithosphere is created at mid-ocean ridges and consumed at subduction zones, areas where the lithosphere sinks into the asthenosphere.
Earthquakes are generated in the rigid plate as it is subducted into the mantle.
volcano.und.edu /vwdocs/vwlessons/plate_tectonics/part10.html   (194 words)

  
 Subduction Zone: World of Earth Science
Subduction zones occur at collision boundaries where at least one of the colliding lithospheric plates contains oceanic crust.
In accord with plate tectonic theory, collision boundaries are sites where lithospheric plates move together and the resulting compression causes either subduction (where one or both lithospheric plates are driven down and destroyed in the molten mantle) or crustal uplifting that results in orogeny (mountain building).
The subducting oceanic crust pushes the continental crust upward into mountain chains (e.g., the Andes) and may contribute lighter molten materials to the overriding continental crust to form volcanic arcs (e.g., the "ring of fire"; a ring of volcanoes bordering the Pacific Rim.
science.enotes.com /earth-science/subduction-zone   (591 words)

  
 EPS 102: Subduction Lecture
In subduction zones, the geotherm is depressed due to the cold descending slab.
At ~670 km, the density of a subducting slab (crust + lithosphere) approaches that of the ambient mantle and may not be able to sink any further.
In "warm subduction," (figure b) this occurs high in the mantle wedge where it is not warm enough to melt despite the influx of volatiles.
eps.berkeley.edu /cig/depaolo/eps102/PPT11_Subduction.html   (275 words)

  
 Earth's Interior & Plate Tectonics
Subduction is the main method of cooling the mantle below 100 kilometers (62.5 miles).
Continental rift valleys and vast plateaus of basalt are created at plate break up when magma ascends from the mantle to the ocean floor, forming new crust and separating midocean ridges.
Plates collide and are destroyed as they descend at subduction zones to produce deep ocean trenches, strings of volcanoes, extensive transform faults, broad linear rises, and folded mountain belts.
www.solarviews.com /eng/earthint.htm   (1396 words)

  
 Dynamic Earth - subduction zones   (Site not responding. Last check: 2007-11-02)
Subduction zones are the flip side of mid-ocean ridges in plate tectonics.
Computer models can predict the temperature structure of subduction zones and indicate that the downgoing slab can be many hundreds of degrees cooler than the surrounding mantle.
This relationship suggests that it is not the slab itself that melts (its too cool at these depths) but from fluids being driven by metamorphic reactions in the slab reacting with the over-riding mantle wedge.
earth.leeds.ac.uk /dynamicearth/subduction/index.htm   (492 words)

  
 What is a Subduction Zone?
A subduction zone is a convergent boundary where two tectonic plates collide.
Subduction zones create geologic formations such as mountain ranges, ocean trenches, and island arcs, as well as phenomena like earthquakes and volcanoes.
Subduction zones don't only make certain landscape changes, but they recycle rock by melting it into magma so that crust might form at other tectonic zones.
www.wisegeek.com /what-is-a-subduction-zone.htm   (409 words)

  
 CVO Website - Plate Tectonics and Sea-Floor Spreading
The Cascadia subduction zone off the coast of Washington, Oregon, and northern California is a convergent boundary between the large North America plate and the small Juan de Fuca plate to the west.
In sum, the subduction of the Juan de Fuca plate beneath the North America plate is believed to directly or indirectly cause most of the earthquakes and young geologic features in Washington and Oregon.
A 90-kilometer gap free of young volcanoes between Mount Rainier and Glacier Peak is landward of that part of the subducting plate with the least average dip to a depth of 60 kilometers.
vulcan.wr.usgs.gov /Glossary/PlateTectonics/description_plate_tectonics.html   (8248 words)

  
 Great Earthquakes   (Site not responding. Last check: 2007-11-02)
We find that slab pull at these subduction zones is small, indicating that the slab is weakened by the compressional stresses that are exerted on it by the overriding plate.
These patterns indicate that slabs are detached from subducting plates at seismically coupled subduction zones, while the slab pull force is strong for seismically decoupled subduction zones.
This drives a circulation in the upper mantle that tends to push the overriding plate toward the subduction zones, thus increasing the compressional interaction at the subduction zone.
www.jhu.edu /eps/faculty/conrad/resproj/geq/geq.html   (1214 words)

  
 * Subduction - (GIS): Definition
A depression landward of a volcanic arc in a subduction zone, which is lined with trapped sediment from the volcanic arc and the plate interior.
The first association forms when sediments that accumulated on the ocean floor, the underlying basaltic crust, and rarely pieces of oceanic mantle, are scraped-off the lower plate during subduction and transferred, squeegee-fashion,...
These islands arise from volcanoes where the subduction of one plate under another is occurring.
en.mimi.hu /gis/subduction.html   (326 words)

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