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

Abstract

The crustal architecture of the Western Iberian Margin is investigated so that the relationship between synrift intra-plate 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. Supplementary material: Summary of the three main magmatic events on the onshore and offshore West Iberia and their associated occurrences, location and magmatism type, in relation with the syn- to post-rift evolution of the margin are available at https://doi.org/10.6084/m9.figshare.c.3591209

Crustal seismic structure beneath Portugal and southern Galicia (Western Iberia) and the role of Variscan inheritance

“…Figs.2b and 8): the Nazaré-Condeixa-Alvaiázere(NCA), the Candeeiros-Porto de Mós fault (CPM)and the Arrife Fault -Aires-Candeeiros-Montejunto fault system (Arr).These three faults seem to border the low Vp anomaly block, although the grid does not allow a clear image. While these faults are connected with the rifting stages associated with the creation of the Mesocenozoic domain of the LB (Miranda et al, 2009;Pereira et al, 2016;Ribeiro et al, 1990), they are also inherited from the previous Variscan orogeny geometry, the opening of the Atlantic occurring along the Thetys-Rheic suture zone (Linnemann et al, 2008;Nance et al, 2010;Wilson, 1966).…”

“…The actual tectono-structural outline of the W edge of Iberian Peninsula (Portugal) is the result of three main orogenic events: Cadomian orogeny (660-540 My) (Linnemann et al, 2008;Ribeiro et al, 2009), Variscan Orogeny (380-280 My) (Arenas et al, 2016a;Simancas et al, 2013) and Alpine orogeny (125-37My) (Jeanniot et al, 2016;Pereira et al, 2016;Pereira and Alves, 2013). The main and most important orogenic event that delineates all the major faults of the territory and tectonic shape is the Variscan event.…”

“…Since then almost all the reactivation of fault zones takes into account the previous scenario of the three main Variscan tectonic and deformation phases and the last tardi-Variscan fracturation. The Alpine orogeny is controlled by previous orogenic heritage (Miranda et al, 2009;Nance et al, 2010;Pais et al, 2012;Pereira et al, 2016;Wilson, 1966).…”

“…The crust in this area is the result of a complex assemblage history of continental collision and extension: in the Lower Paleozoic, the collision of an unconstrained number of continental blocks resulted in the Variscan Orogeny, the main event of formation of the Iberian lithosphere (e.g. Arenas et al, 2016;Matte, 2001Matte, , 1986Ribeiro et al, 2007a); the subsequent Mesozoic rifting and breakup of the Pangea had a profound effect on the continental crust of the western border of Iberia (Pereira et al, 2016;Ribeiro et al, 1990).…”

A reconstruction of Iberia accounting for Western Tethys–North Atlantic kinematics since the late-Permian–Triassic

“…Because a full-fit reconstruction in southwest Iberia leads to significant overlapping between the Flemish Cap and Galicia, we use the Nazaré Fault (Pereira et al, 2017) to segment western Iberia. This allows us to minimize the overlap of northwest Iberia (Galicia) over the Flemish Cap or to have a gap between southwest Iberia and Newfoundland.…”