Normal oceanic crust in the North Atlantic is typically formed in strips 50 to 80 km wide separated by fracture zones. Anomalous seismic crustal structure (less than 10 km wide) is found beneath fracture zones regardless of the amount of offset. Although many of these fracture zones exhibit minor and variable offsets in the seafloor-spreading magnetic lineations, they separate crust with distinctively different basement morphology and magnetic signatures even when there is no offset apparent in the magnetic lineations. The pattern of both the basement relief and the magnetic anomalies provides the evidence for the persistence of minor and variable offset fracture zones formed by the decoupling of adjacent spreading centers over a period of at least 15 m.y. of seafloor spreading.

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