Tectonic model of the Bering shelf in Mesozoic and Cenozoic

To understand the tectonic evolution of the Bering Sea Area (BSA), onland geologic data from Alaska and Russia must be integrated with offshore geological and geophysical data. New data from this region, a result of collaborative work between U.S. and Russian researchers, can be used to create a better working model for the formation of this vast, mostly submerged continental region. The BSA includes the continental Bering shelf, and the adjoining Aleutian deep-water basin to the south. Cretaceous oceanic crust, a trapped piece of the Pacific Kula plate, underlies the Aleutian basin. Oceanic crust of this age is also found as tectonic fragments in accretionary complexes in both the Koryak Highlands and southern Alaska. Subduction processes shaped Koryak and Southern Alaska beginning in the Mesozoic, with the development of the many island arcs and accretionaries complexes. Plate tectonic and paleomagnetic data indicate that all terrains accreted in western Koryak traveled on the Izanagi plate. At the same time, accretion of terrains in Central and East Koryak, and also Alaska traveled with the Farallon plate. Subduction/accretion along these plate boundaries was coeval with significant crustal shortening in the Brooks Range culminating in Berriasan-Valanginian time. Medium to high P/T metamorphism and deformation during shortening is dated at 113 Ma (min. age) in Brooks Range, 125 Ma (min. age) on Seward Peninsula, 124 Ma (min. age) in Chegutin Valley, Chukotka and 132 Ma near Providenya Bay. Deformation was linked to the southward motion of the Arctic-Alaska-Chukotka microplate, which became the northern part of the Bering Shelf. Subduction/accretion and crustal shortening set the stage for the main phase of creation of the Bering Shelf at the - 110-115 Ma. Accretionary processes in the Koryak Highlands led to accretion of the Yanranay oceanic terrain, during development of the Kankaran island arc. This phase was over by the end of Albian and resulted in cessation of Kankaran Island Arc magmatism, which stepped seaward with time, in conjunction with roll-back of the subducted slab. Extension of previously deformed and accreted crust occurred in the Brooks Range, Central Alaska, and offshore Bering Shelf as well during the interval 115-90 Ma. At this time, continued of subduction along the continental margin of Asia resulted in the formation of the Okhotsk-Chukchi volcanic belt, which developed in a weakly extensional tectonic regime. The formation of several island arcs all occurred in Late Cretaceous in Koryak as a broad belt of plutons were emplaced in Alaska. The Eocene was an important time, when plate motions changed again and subsequent formation of the Aleutian Arc. Sinking of the subducted slab at this time resulted in continued extension within the Bering Shelf and the beginning of formation of deep sedimentary basins. The combination of extension with right-lateral strike-slip faulting in Alaska resulted in the formation of a right-slip boundary along the edge of the Bering Shelf, with transpressional pull-apart basins developed along the shelf edge as final consequence of these motions. In conclusion, the geodynamic history of the BSA was dictated by a series of events and complex processes related to subduction of oceanic lithosphere along the Pacific plate boundary. In particular, under the active North American continental margin, two similar events involved the southern migration of subduction zones, together with variable extension of crust