Island Arcs


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Island Arcs

 

relief structures of contemporary geosynclinal systems occurring in the transitional zones between continents and oceans. Island arcs are linear mountains that divide the basins of the marginal seas from the deep-sea trenches. The foundations of island arcs are underwater mountain ranges from 40–50 to 200–400 km wide and up to 1,000 or more km long, composed primarily of volcanic strata of basalt, a mixture of andesite and basalt, or andesite. The top of the range rises above sea level in the form of islands. Island arcs frequently consist of two parallel ridges, one of which, usually the outer ridge facing the deep-sea trench, is an underwater mountain range. In such cases the ridges are separated from one another by a longitudinal depression up to 3–4.5 km deep filled with a stratum of sediment 2–3 km deep. Transverse depressions are found in fracture zones and usually form the deeper straits.

Most island arcs are located on the northern and western margins of the Pacific Ocean; the only exceptions are the Antilles, the Lesser Antilles, and the Sunda arcs. In their early stages of development island arcs are a thickening of the ocean crust with volcanic structures on the crest, for example, the Mariana and Kermadec island arcs. In later stages island arcs form large islands and peninsulas, for example, the Japanese Islands, the Kamchatka Peninsula, and New Guinea; here the structure of the crust is similar to that of continents. Island arcs have highly differentiated gravitational and magnetic fields, increased heat flows, and active volcanic and seismic activity. Between island arcs and the deep-water trenches lies the region of earthquake concentration, the Benioff zone, which passes under the island arcs.

REFERENCES

Ostrovnye dugi: Sb. st. Moscow, 1952. (Translated from English.)
Gorshkov, G. S. Vulkanizm Kuril’skoi ostrovnoi dugi. Moscow, 1967.
Pushcharovskii, Iu. M. Vvedenie ν tektoniku Tikhookeanskogo segmenta Zemli. Moscow, 1972.
Udintsev, G. B. Geomorfologiia i tektonika dna Tikhogo okeana. Moscow, 1972.
Mitchell, A. H., and H. G. Reading. “Evolution of Island Arcs.” Journal of Geology, 1971, vol. 79, no. 3.

O. K. LEONT’EV

References in periodicals archive ?
The key trigger, they say, is mountain formation in the tropics as continental land masses collide with volcanic island arcs, such as the Aleutian Islands chain in Alaska.
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Miller, one of Jordan's colleagues at USC, reported in Geophysical Research Letters detecting boundaries in the keels that suggest that island arcs smashed into cratons, piling up against them over time.
Mapping and application of geochemical discrimination tools led to recognition of the diversity among ophiolites and the realization that ophiolites could be generated in different geodynamic environments, not only at mid-ocean ridges, but also in island arcs (Miyashiro 1973).
He adds that plate tectonics conveniently explains many seemingly unconnected phenomena that previously were little understood, like volcanism, distribution of earthquake epicenters, "and those geometrically striking volcanic island arcs that seem to hang like glowing necklaces around the margins of the Pacific Ocean." Dewart's philosophical thoughts and comments are interspersed throughout the book, revealing his views of events on earth.
1973 'Distribution and Petrology of Late Cenozoic Volcanoes in Papua New Guinea'The Western Pacific: Island arcs, marginal seas, geochemistry, P.J.
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"Global Relief" is a physical map of the Earth with land surfaces and ocean floors color coded to emphasize major deserts, mountain ranges, island arcs, and ocean trenches.
negative Nb anomalies and positive spikes generally on Ba and Sr, similar to those of island arcs volcanics.
10d, after Condie 1989) where primitive island arcs have lower ratios than continental (Andean) arcs.