Age, character, and significance of Aleutian arc volcanism
The Aleutian volcanic arc stretches nearly 3,000 km, from the Commander Islands off Kamchatka (U.S.S.R.), along the southern Bering Sea margin, and across the continental margin onto the Alaskan landmass. Intimately associated with the arc is the subduction of the Pacific Plate beneath the North American Plate. To the east, subduction is nearly orthogonal but becomes increasingly oblique westward. Near Buldir Island, motion between the two plates becomes strike-slip and volcanism ceases. The Aleutian volcanic front, which has in many places remained nearly fixed for at least several tens of millions of years, contains about 80 major volcanic vents, half of which have been historically active. These vents have yielded a spectrum of rock types, from basalt through andesite to dacite and rhyolite. This diversity of rock types is present throughout the history of nearly all the volcanic centers, almost regardless of volcano size and age.
Several features of the Aleutian volcanic arc—a long history of fixed volcanism extending from continental to oceanic crust, the focusing of large amounts of thermal energy on small areas of crust for long periods of time, the pattern of changing convergence, as well as the diversity of rock types—present an excellent opportunity to study the connection between global tectonics, magmatism, and continent evolution. The study of Aleutian volcanism can shed light both on deep-seated magmatic processes and on the interplay of the chemistry and physics of magma evolution, and particularly on the near-surface behavior of magma in various local tectonic
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