Non-Wilsonian break-up predisposed by transforms: examples from the North Atlantic and Arctic

The Atlantic Ocean margins formed the basis for the seminal Wilson cycle concept, which suggests that oceans close, form fold belts, and later reopen in a concertina-like fashion. However, we observe that continental break-up of the North Atlantic–Arctic region only weakly reflects Wilson's concept. Rather than utilizing fold belts, transforms have been the dominant weaknesses that guided break-up, primarily because less force is required to break a plate via strike-slip related shearing than via rifting. Some transforms were inherited features, whereas others formed as part of the continental break-up process. Regardless of cause, once a transform has formed, the plate is broken and further rifting is not required before seafloor spreading can start. This is particularly well expressed in the NE Atlantic, where the line of Early Eocene break-up is very sharp, with minor or no preceding Paleocene rifting. Other examples include the De Geer, Ungava and Lomonosov transforms. We propose that the transform break-up mechanism is an important adjunct to the Wilson cycle theory and that it provides an explanation for ‘non-Wilson’ oceans, where old collision zones are not reactivated.