Abstract

A hypothetical model for the plate tectonic evolution of the western Arctic Ocean relates rifting in the Amerasian Basin to sea-floor spreading of the Pacific and Atlantic Ocean basins. The key elements of the model are: (1) the Kaltag shear zone of eastern Alaska and its northeastern projection along the continental margin of Arctic Canada and Greenland, and (2) an older Mesozoic shear system that extended from the American landfall of an ancestral East Pacific rise via the Cordillera and the northern continental margin of Alaska and Siheria to the Laptev Sea at the Asian end of the Lomonosov Ridge. This shear zone was offset by the Kaltag by 560 kilometers during the Late Cretaceous and Paleocene, separating it into a Cordilleran sector that extends from southern California to the northern Yukon and an Arctic sector that follows the Arctic continental shelf edge of Alaska and Siberia. The older system appears to have linked Cretaceous rifting in the Arctic, centered about the Alpha Ridge, with contemporaneous sea-floor spreading in the Pacific through dextral transform fault slip of about 1,200 kilometers.

Paleogeographic reconstruction of the borderlands of the Amerasian Basin suggests that it consisted solely of the Canada Basin during the Late Paleozoic and Early Mesozoic. During those eras, northern Alaska and the contiguous Kolyma area of Siberia lay along the western edge of the North American craton, receiving sediment from it, while Mesozoic terranes of southern Alaska originated still further south in a near-tropical environment. It is suggested that the Mesozoic boundary between the Asian and the combined Kolyma and North American lithospheric plates lay in the Verkhoyansk Geosyncline, which connected the Canada Basin to the Pacific Ocean.

The Brooks Range is interpreted as an allochthonous element of the Canadian Cordillera, with which it has many structural, stratigraphic, and paleontologic affinities, transported to its present position by the Cordilleran and Kaltag shear systems. It is recommended that the use of Canadian Arctic tectonostratigraphic nomenclature in the Brooks Range should be abandoned. The terms Franklinian and Ellesmerian could be replaced by Cordilleran, with Brookian being retained for the youngest sequence.