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Mesozoic Rifting in the Western Arctic Ocean Basin and Its Relationship to Pacific Seafloor Spreading
A hypothetical model for the plate tectonic evolution of the western Arctic Ocean relates rifting in the Amerasian Basin to seafloor spreading of the Pacific and Atlantic ocean basins. The key elements in the hypothesis are: (1) the Kaltag shear zone of eastern Alaska and its northeastern projection along the continental margin of Arctic Canada and Greenland; (2) the system of major longitudinal faults in the Canadian Cordillera; (3) the Arctic continental mar gin of Alaska and eastern Siberia. All three elements are proved or probable dextral strike-slip fault and shear zones. It is postulated that during the Mesozoic and possibly late Paleozoic, a shear zone extended from the American land fall of an ancestral East Pacific Rise to the Asian end of the Lomonosov Ridge which, at that time, was part of the Barents shelf. During the Cretaceous, this shear zone linked rifting in the Arctic, centred about the Alpha Ridge, with contemporaneous seafloor spreading in the Pacific, through dextral transform fault slippage along the developing North American Cordillera. It was a Mesozoic analog of the de Geer Transform which linked Cenozoic seafloor spreading of the North Atlantic with the opening of the eastern Arctic Ocean basin. The Mesozoic shear zone was cut by the Kaltag shear zone during the Late Cretaceous and Paleocene, offsetting it by more than 500 kilometres and dividing it into the Cordilleran sector and the Alaska-Siberian sector, marked by the Arctic continental shelf edge of Alaska and Siberia. This movement decoupled the Arctic Ocean Basin from the Pacific and connected it with early opening of the North Atlantic.
Reconstruction of late Paleozoic and early Mesozoic paleogeography of the circum-Arctic regions suggests that, prior to spreading about the Alpha Ridge, the Amerasian Basin consisted solely of the Canada Basin. Northern Alaska and the contiguous Kolyma area of Siberia lay along the western edge of the North American Craton, from which they received sediment during the late Paleozoic and early Mesozoic, while allochthonous terranes of southern Alaska were still further south, in the tropics. The early Mesozoic boundary between the Asian and North American lithospheric plates lay in the Verkhoyansk Geosyncline, which may have been a seaway connecting the Canada Basin with the Pacific Ocean.
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