Alternating crustal architecture in West Iberia: a review of its significance in the context of NE Atlantic rifting

The crustal architecture of the Western Iberian Margin is investigated so that the relationship between synrift intraplate segmentation, magmatic events and subsequent margin convergence can be discussed in the context of the evolution of the Central–North Atlantic Ocean. The evidence in this paper indicates distinct crustal architectures for NW Iberia (lower-plate) and SW Iberia (upper-plate), as shown by (1) the different geometries of the rotated tilt-blocks across thinned continental crust, (2) the distinct dips of deep crustal detachments and (3) the presence of first-order strike-slip zones bounding different crustal segments. We demonstrate that a switch in the dip direction of the crustal detachment is accomplished by accommodating persistent transcurrent deformation along first-order transfer zones and associated uplifted hinges, both of which accommodated synrift displacement and post-rift margin inversion. This alternating architecture explains why recurrent magmatism is conspicuously located on the upper-plate margin, which we consider to have favoured, in discrete pulses, the emplacement of magma. Finally, the crustal detachment underlying the upper-plate is interpreted to have been reactivated since the Eocene as the weak zone accommodating ocean–continent convergence and the putative onset of margin subduction.