Allochthonous terranes in Alaska: Implications for the structure and evolution of the Bering Sea shelf

Abstract

Abundant evidence has been gathered in support of the concept that much of the Pacific margin of North America consists of allochthonous terranes that were accreted during Mesozoic and early Tertiary time. In particular, southern Alaska is almost completely composed of separate terranes whose stratigraphy and paleomagnetism indicate distant origins. The Bering Sea continental shelf is among the largest shelves in the world, almost half as large as Alaska itself. Some of the allochthonous terranes in Alaska probably continue beneath the continental shelf, but their distribution beyond the shoreline has not been determined. We believe that much of the continental shelf is probably composed of allochthonous terranes, in much the same way as southern Alaska. Geophysical data from the Bering continental shelf have been used to test this hypothesis. Although inconclusive without extensive drilling, multichannel seismic profiles and magnetic data indicate the composite character of the shelf basement. The magnetic anomalies can be separated into specific domains of limited extent. These magnetic variations suggest a corresponding variation of rock terranes beneath the shelf. In addition, multichannel seismic profiles show possible thrust faults within the shelf basement that could be sutures between separate terranes.