How can asymmetric detachment faults generate symmetric Ocean Continent Transitions?

Asymmetry or symmetry of magma-poor rifted margins refers commonly to the crustal architecture and the occurrence or absence of large-scale extensional detachment faults. While distal parts of magma-poor rifted margins are often considered to be asymmetric, the observation of downlapping sedimentary sequences over exhumed mantle domains at conjugate margins suggests a symmetric evolution during mantle exhumation. On the basis of seismic observations along the Iberia-Newfoundland and Australia-Antarctica margins, we propose that their most distal parts show evidence for the development of multiple, out-of-sequence asymmetric detachment faults. We present evidence for cyclic delocalization and re-localization ofdeformation, resulting in an apparent symmetry of the exhumed mantle domain. The interaction between out-of-sequence detachment systems and the successive rise of the asthenosphere may explain the observed transition from fault-controlled to magma-controlled strain accommodation and the transition to more symmetric and localized accretion associated with the formation of a stable spreading center.