The Cordilleran Ribbon Continent of North America
Abstract
The North American Cordilleran Orogen is the result of a two-stage process: (a) Triassic-Jurassic accretion within Panthalassa forming SAYBIA, a composite ribbon continent, and (b) Late Cretaceous collision of SAYBIA with North America. This model requires that a large portion of the continental foreland of the orogen is exotic. The exotic continental component of SAYBIA, Cassiar Platform, is distinguished from the autochthon on the basis of its (a) Triassic Eurasian fauna; (b) involvement in a major Late Triassic-Early Jurassic orogenic event; and (c) young, in part Grenvillian basement and mantle. A mid-Cretaceous magmatic arc records west-dipping subduction beneath the east-margin of SAYBIA. The related accretionary prism consists of imbricated shale, chert, and deep-water limestones (the Medial Basin) and overlies an isotopically juvenile mantle domain. Carbonatite complexes delineate the cryptic suture separating SAYBIA and the autochthon. Paleomagnetic and paleobotanical data place SAYBIA 2000 km to the south relative to the autochthon at 80 Ma. Late Cretaceous thrust belt development records transpression between the north-moving ribbon continent and the autochthon. Pinning against the Okhotsk-Chukotka arc in Siberia buckled SAYBIA, giving rise to the Alaskan promontory.
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