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Trans-Alaska Crustal Transect and continental evolution involving subduction underplating and synchronous foreland thrusting

Gary S. Fuis et al., M/S 977, U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, California 94025, USA. Pages 267-270.

There is perhaps no better place on Earth to study the origin of continents than Alaska. Alaska is composed of fragments of crust that were transported northward on a plate-tectonic conveyor belt and scraped off against the North American continent as the conveyor belt (oceanic plates) descended beneath it. These fragments included volcanic islands and plateaus that formed on the oceanic plates, parts of the continental shelf of North America, and even parts of the oceanic plates. During the last several hundred million years of Alaskan history, oceanic plates slid beneath North America in subduction zones, generating volcanoes inland above places where the descending plates dehydrated and generated melts in overlying mantle and crust. At least twice, fragments of the oceanic plates became doubled up, and, in attempting to subduct, uplifted and compressed the Alaskan crust landward of the subduction zone. One instance was 4060 million years ago when doubled oceanic plates uplifted and compressed the Pacific coastal region of Alaska. This compression was felt as far away as northern Alaska and Canada, where the Brooks Range and Canadian Rockies were uplifted. The second instance was more recent, beginning only a few million years ago, when a piece of abandoned oceanic plate, known as the Yakutat terrane was underthrust by the Pacific plate and, together with the Pacific plate, entered the subduction zone. According to Fuis et al.s and other studies, it appears tha
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