Deformation of the northern circum-Pacific margin: Variations in tectonic style and plate-tectonic implications

Abstract

During mid- to Late Cretaceous time, the northern paleo–Pacific Ocean was characterized by subduction for >6000 km along strike. The associated magmatic and orogenic belt now comprises parts of the U.S. and Canadian Cordillera, Alaska, and the Russian Far East. Crustal shortening in the northwestern Cordillera sector of the belt was contemporaneous with extension in northern and interior Alaska and the Bering Strait region, while extensional to neutral tectonics prevailed in the Sea of Okhotsk region, Russian Far East. The along-strike continuity of magmatism during the ≈120–80 Ma time interval resulted from subduction beneath the northern circum-Pacific margin, even beneath the broadest parts of the belt in the Alaska and Bering Strait region, which we suggest were modified by large-magnitude crustal extension. Variations in deformational style along strike of the orogenic belt may be related to changes in the nature of the mechanical coupling between the subducting oceanic and overriding continental plates, where the central extensional part of the belt developed above a part of the slab characterized by southward retreat or rollback of the subduction zone.