The Great Alaskan Terrane Wreck: reconciliation of paleomagnetic and geological data in the northern Cordillera

Abstract

Paleomagnetic studies place much of the Cordilleran orogen ≥3000 km south, relative to autochthonous North America at 85 Ma. This conflicts with geological studies which have been interpreted to indicate minor displacement. The inability to reconcile these interpretations has precluded understanding the tectonic development of the Cordillera, and has cast doubt on global paleogeographic reconstructions which rely upon paleomagnetic studies. I demonstrate that Alaska and Yukon are divisible into a series of geological belts, including the northerly east–west-trending Arctic Alaska, the central southwest-trending Ruby, the southerly east-trending Dillinger and the southeast-trending Yukon–Tanana belts. Each belt is characterized by four regularly arranged rock sequences; (1) a Paleozoic continental margin strata, (2) a Devonian–Mississippian arc assemblage, (3) an ophiolite, and (4) an Early to mid-Cretaceous arc. These correlations greatly simplify the terrane nomenclature of the northern Cordillera and provide a basis for a new palinspastic reconstruction of the Cordillera. Continuity of the belts can be demonstrated through connecting oroclines, and facing a structural vergence directions vary in a consistent and predictable fashion indicating that the belts previously formed part of a linear ribbon continent. This ribbon continent, referred to here as SAYBIA, originally extended south from eastern Siberia and was ∼8000 km long. Northward translation in response to coupling with the Kula plate was accommodated by buckling (oroclinal orogeny) of SAYBIA, much like a derailing train, with scissored ‘cars’ forming much of Alaska. Oroclinal orogeny makes consistent interpretations of available geological and paleomagnetic data in the Cordillera, provides a means for the rapid construction of continent, and may have been an important process involved in the construction of ancient continental nuclei.