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An island arc is a type of archipelago formed as one oceanic tectonic plate subducts under another and produces magma at depth below the over-riding plate. Island arcs that develop along the edges of a continent (for example, large parts of the Andes/ Central American/ Canadian mountain chain) may be known as a volcanic arc, though most people find the distinction of little benefit.

In the subduction zone, loss of volatiles from the subducted slab induces partial melting of the overriding mantle and generates low-density, calc-alkaline magma that buoyantly rises to intrude and be extruded through the lithosphere of the overriding plate. The resulting volcano chain has the shape of an arc parallel to the convergent plate boundary and convex toward the subducting plate. This is a consequence of the geometry of the spherical plate crumpling along a line on a spherical surface.

On the subducting side of the island arc is a deep and narrow oceanic trench, which is the trace at the Earth’s surface of the boundary between the downgoing and overriding plates. This trench is created by the gravitational pull of the relatively dense subducting plate pulling the leading edge of the plate downward. Multiple earthquakes occur along this subduction boundary with the seismic hypocenters located at increasing depth under the island arc: these quakes define the Wadati-Benioff zones.

Oceans basins that are being reduced by subduction are called 'remnant oceans' as they will slowly be shrunken out of existence and crushed in the subsequent orogenic collision. This process has happened over and over in the geologic history of the Earth.

Examples

Island arc Country Trench Basin or marginal sea Plate Subducting plate
Aleutian Islandsmarker United Statesmarker Aleutian Trenchmarker Bering Seamarker North American Plate Pacific Plate
Kuril Islandsmarker Russiamarker Kuril-Kamchatka Trenchmarker Sea of Okhotskmarker North American Plate Pacific Plate
Japanese Archipelagomarker Japanmarker Japan TrenchmarkerNankai Trough Sea of Japanmarker North American Plate, Eurasian Plate Pacific Plate, Philippine Sea Platemarker
Ryukyu Islandsmarker Japan Ryukyu Trenchmarker East China Seamarker (Okinawa Trough) Eurasian Plate Philippine Sea Plate
Philippine Islandsmarker Philippinesmarker Philippine Trench South China Seamarker, Celebes Seamarker Eurasian Plate Philippine Sea Plate
Sunda Islandsmarker Indonesiamarker Java Trenchmarker Java Seamarker, Flores Seamarker Eurasian Plate Australian Plate
Andaman and Nicobar Islandsmarker Indiamarker Northern Java Trench Andaman Seamarker Eurasian Plate Indo-Australian Plate
Izu Islandsmarker and Bonin Islands marker Japan Izu-Ogasawara Trenchmarker Philippine Sea Plate Pacific Plate
Mariana Islandsmarker United States Mariana Trenchmarker Philippine Sea Plate Pacific Plate
Bismarck Archipelagomarker Papua New Guineamarker New Britain Trench Pacific Plate Australian Plate
Solomon Islands Solomon Islandsmarker San Cristobal Trench Pacific Plate Australian Plate
New Hebridesmarker Vanuatumarker New Hebrides Trench Pacific Plate Australian Plate
Tonga islands Tongamarker Tonga Trenchmarker Australian Plate Pacific Plate
Antilles Puerto Rico Trenchmarker Caribbean Seamarker Caribbean Plate North American Plate, South American Plate
South Sandwich Islands United Kingdommarker South Sandwich Trench Scotia Sea Scotia Plate South American Plate


Ancient Island arcs



References


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