Conjugate margins — An oversimplification of the complex southern North Atlantic rift and spreading system?

Abstract

The prevalence of conjugate margin terminology and studies in the scientific literature is testimony to the contribution that this concept and approach has made to the study of passive margins, and more broadly extensional tectonics. However, when applied to the complex rift, transform, and spreading system of the southern North Atlantic (i.e., the passive margins of Newfoundland, Labrador, Ireland, Iberia, and southern Greenland), it becomes obvious that at these passive continental margin settings, additional geologic phenomena complicate this convenient description. These aspects include (1) the preservation of relatively undeformed continental fragments, (2) formation of transform systems and oblique rifts, (3) triple junctions (with rift and spreading axes), (4) multiple failed rift axes, (5) postbreakup processes such as magmatism, (6) localized subduction, and (7) ambiguity in identification of oceanic isochrons. Comparison of two different published reconstructions of the region indicates the ambiguity in conducting conjugate margin studies. This demonstrates the need for a more pragmatic approach to the study of continental passive margin settings where a greater emphasis is placed on the inclusion of these possibly complicating features in palinspastic reconstructions, plate tectonics, and evolutionary models.