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Geophysical and regional geologic data provide evidence that parts of the oceanic crust in the abyssal basins of the Bering Sea have been created or altered by crustal extension and back‐arc spreading. These processes have occurred during and since early Eocene time when the Aleutian Ridge developed and isolated oceanic crust within parts of the Bering Sea. The crust in the Aleutian Basin, previously noted as presumably Early Cretaceous in age (M1–M13 anomalies), is still uncertain. Some crust may be younger. Vitus arch, a buried 100‐ to 200‐km‐wide extensionally deformed zone with linear basement structures and geophysical anomalies, crosses the entire west central Aleutian Basin. We suggest that the arch and the inferred fracture zones in the Aleutian Basin are early Cenozoic structures related to the early entrapment history of the Bering Sea. These structures lie on trend with known early Cenozoic structures near the Bowers‐Shirshov‐Aleutian ridge junction and on the Beringian continental margin (with possible continuation into Alaska); the structures may have coeval and cogenetic(?) histories for early Cenozoic and possibly younger times. Cenozoic deformation within parts of the Bering Sea region is principally extensional, although the total amount of extension is not known. As examples, the Komandorsky basin formed by back‐arc seafloor spreading, the Aleutian Ridge has been extensively sheared, and extensional block faulting is common. Sedimentary basins of the Bering shelf have formed by extension associated with wrench faulting. The Cenozoic deformation throughout the Bering Sea region probably results from the interaction of major lithospheric plates and associated regional strike‐slip faults. We present models for the Bering Sea over the past 55 m.y. that show oceanic plate entrapment, back‐arc faulting and spreading along Vitus arch, breakup of the oceanic crust in the Aleutian Basin at fracture zones, and back‐arc spreading in Bowers Basin.

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A compilation of marine magnetic profiles from the Bering Sea marginal basin has revealed the existence of north‐south trending magnetic lineations over the deep abyssal basins. The anomalies in the Aleutian and Bowers basins have maximum peak to peak amplitudes of 350 γ and wavelengths characteristic of sea floor spreading anomalies (25–100 km). These lineations are as much as 600 km long. In contrast, linear trends within the Komandorsky Basin are less distinct and have anomalies with variable amplitudes. The magnetic anomalies along an 850‐km profile crossing the Aleutian Basin have been correlated with the M1‐M13 (117–132 m.y.) sequence of Larson's (1974) Mesozoic time scale. These anomalies increase in age from east to west and yield a half spreading rate of 5.1 cm/yr. North‐south trending anomalies within Bowers Basin exhibit shapes and spacings similar to those from the Aleutian Basin, suggesting that these trends may have been connected at one time. Detailed model studies of the anomalies in the Aleutian Basin yield results which support the hypothesis that the igneous crust in the eastern Bering Sea is trapped oceanic plate which may have been part of the Mesozoic Pacific Basin. The model studies have indicated that (1) normalized magnetization intensities are comparable to those estimated for the Mesozoic Hawaiian Lineations in the Pacific, (2) the approximate phase angle of the observed anomalies (−10°±20°) would allow the magnetic lineations either to be formed at their present location or else to be formed at a more southerly site and then moved to their present location, and (3) the width of transitions between adjacent polarity intervals is relatively large (W ≥ 16 km) and may be related to a redistribution of the remanent magnetization within a deeply buried layer 2. The corrected depth to layer 2 is within 5% of the depth predicted for Mesozoic crust (120 m.y.) on the Sclater (1972) depth versus age curves. Although the north‐south trending anomalies in the Aleutian and Bowers basins are interpreted as sea floor spreading anomalies, the origin of the anomaly pattern in the Komandorsky Basin is not understood.

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