Construction of a map of basement rocks of Alaska has revealed a complexly deformed, arcuate Paleozoic continental margin that is a northwestern extension of the western margin of North America. Three key areas in Alaska (Nation River, Livengood, and Terra Cotta Mountains) have similar sections of Ordovician to Devonian and locally younger Paleozoic siliceous shale and chert, interfingering with limestone and containing various turbidity-current and slope deposits. Microplates moving north from the Pacific basin have collided with this Paleozoic continental margin and deformed and collapsed the original shale-out facies. A similar south-facing collapsed continental margin of middle and late Paleozoic age can be traced across the western Brooks Range of northern Alaska. We believe that this continental margin in the Brooks Range, although it is mainly younger, may be an extension of the same margin in central Alaska. This continental margin has been offset to the Brooks Range along the Porcupine megashear.

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