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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. An island arc that develops along the edge 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.



Island arc Country Trench Basin or marginal sea Plate Subducting plate
Aleutian Islands United States Aleutian Trench Bering Sea North American Plate Pacific Plate
Kuril Islands Russia Kuril-Kamchatka Trench Sea of Okhotsk North American Plate Pacific Plate
Japanese Archipelago Japan Japan TrenchNankai Trough Sea of Japan North American Plate, Eurasian Plate Pacific Plate, Philippine Sea Plate
Ryukyu Islands Japan Ryukyu Trench East China Sea (Okinawa Trough) Eurasian Plate Philippine Sea Plate
Philippine Islands Philippines Philippine Trench South China Sea, Celebes Sea Eurasian Plate Philippine Sea Plate
Sunda Islands Indonesia Java Trench Java Sea, Flores Sea Eurasian Plate Australian Plate
Andaman and Nicobar Islands India Northern Java Trench Andaman Sea Eurasian Plate Indo-Australian Plate
Izu Islands and Bonin Islands (Ogasawara Islands) Japan Izu-Ogasawara Trench Philippine Sea Plate Pacific Plate
Mariana Islands United States Mariana Trench Philippine Sea Plate Pacific Plate
Bismarck Archipelago Papua New Guinea New Britain Trench Pacific Plate Australian Plate
Solomon Islands (archipelago) Solomon Islands San Cristobal Trench Pacific Plate Australian Plate
New Hebrides Vanuatu New Hebrides Trench Pacific Plate Australian Plate
Tonga islands Tonga Tonga Trench Australian Plate Pacific Plate
Antilles Puerto Rico Trench Caribbean Sea Caribbean Plate North American Plate, South American Plate
South Sandwich Islands United Kingdom South Sandwich Trench Scotia Sea Scotia Plate South American Plate

Ancient Island arcs

See also




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