The final rifting evolution at deep magma-poor passive margins from Iberia-Newfoundland: a new point of view

In classical rift models, deformation is either uniformly distributed leading to symmetric fault bounded basins overlying stretched ductile lower crust (e.g. pure shear McKenzie model) or asymmetric and controlled by large scale detachment faulting (simple shear Wernicke model). In both cases rifting is considered as a mono-phase process and breakup is instantaneous resulting in the juxtaposition of continental and oceanic crust. The contact between these two types of crusts is often assumed to be sharp and marked by a first magnetic anomaly; and breakup is considered to be recorded as a major, basin wide unconformity, also referred to as breakup unconformity. These classical models, are currently challenged by new data from deep rifted margins that ask for a revision of these concepts. In this paper, we review the pertinent observations made along the Iberia-Newfoundland conjugate margins, which bear the most complete data set available from deep magma-poor margins. We reevaluate and discuss the polyphase nature of continental rifting, discuss the nature and significance of the different margin domains and show how they document extreme crustal thinning, retardation of subsidence and a complex transition into seafloor spreading. Although our study is limited to the Iberia-Newfoundland margins, comparisons with other margins suggest that the described evolution is probably more common and applicable for a large number of rifted margins. These new results have major implications for plate kinematic reconstructions and invite to rethink the terminology, the processes, and the concepts that have been used to describe continental rifting and breakup of the lithosphere.