Compressional structures on the West Iberia rifted margin: controls on their distribution

Abstract

The West Iberia margin is a magma-poor rifted margin that resulted from Jurassic to Cretaceous polyphase rifting leading to the opening of the North Atlantic Ocean. The Mesozoic rift structures were overprinted by two compressive tectonic events during Eocene and Miocene times resulting from collision between Iberia, Europe and Africa. The effects of these compressive tectonic events are expressed by faults and folds within the post-rift sedimentary sequence. We mapped and studied these Cenozoic deformation structures throughout the Southern Iberia Abyssal Plain (40°–41°N, 11°–13°W) on the basis of an extensive dataset of time migrated seismic profiles acquired by various academic institutions. Acoustic basement has also been analysed on the basis of its seismic aspect, in order to test potential relationships with the distribution of the post-rift sedimentary deformation.Our observations lead to three major conclusions concerning the deformation affecting the post-rift sediments in the Southern Iberia Abyssal Plain: (1) the deformation occurs within the zone of exhumed continental mantle and not at its transition to continental or oceanic crust; (2) it is localized within a zone overlying basement with well-defined seismic characteristics; and (3) it is closely related to the major topographic features observed in the ocean–continent transition. The localization of the deformation within the zone of exhumed continental mantle and not at its boundaries to the adjacent oceanic and continental crust suggests that the limits between the different types of crust are transitional rather than sharp. Our results show that the zone of exhumed continental mantle represents the weakest zone within the margin that is preferentially deformed during initial convergence. At higher convergence rates, this zone may coincide with the location of a future subduction.

The long-term topographic response of a continent adjacent to a hyperextended margin: A case study from Scandinavia

“…Our results point strongly toward a mechanically weak distal margin, and they support the hypothesis that post-rift cooling does not increase the strength of the lithosphere where it has undergone signifi cant mechanical damage (see previous work by Péron-Pinvidic et al, 2008;Mohn et al, 2010;Lundin and Doré, 2011). In turn, this suggests that horizontal farfi eld forces can be readily accommodated by defor ma tion in the distal margin and the outermost proximal margin, and are thus not responsible for onshore proximal margin deformation.…”

“…While evidence from the type-section Iberian on March 25, 2015 gsabulletin.gsapubs.org Downloaded from margin indicates that during the main rift phase faulting propagated sequentially seaward in the distal margin (e.g., Péron-Pinvidic et al, 2008;Ranero and Peréz-Gussinyé, 2010;Sutra and Manatschal, 2012), our data suggest that normal faulting also propagates landward within the proximal margin. Although it has been called such, this is not really "out-of-sequence."…”

“…The reverse earthquakes associated with the mechanically weak (Péron-Pinvidic et al, 2008;Mohn et al, 2010;Lundin and Doré, 2011) Taper Break are spatially associated with the zone of compressive stress identifi ed by Gudmundsson (1999). The location and tensile nature of the escarpment zone earthquake (see Hicks et al, 2000;Bungum et al, 2010) also fi t Gudmundsson's (1999) doming model.…”

Some remarks on the earthquakes of Fennoscandia: A conceptual seismological model drawn from the perspective of hyperextension

“…Consequently, much of the distal domain can potentially comprise a permanently weakened zone (Masson et al, 1994;Faccenna et al, 1999;Péron-Pinvidic et al, 2008Mohn et al, 2010;Lundin & Doré, 2011;Sutra & Manatschal, 2012;Redfield & Osmundsen, 2013; this paper).…”

“…A parallel implication of our observations and interpretations is that far-field forces may perhaps not be able to propagate very deeply into a hyperextended continental margin. The resolution of contrasting oceanward-directed continental and landward-directed oceanic GPE against the TB and the hyperextended distal domain may perhaps ultimately localize as oceanic-continent subduction (e.g., Masson et al, 1994;Faccenna et al, 1999;Péron-Pinvidic et al, 2008;Marques et al, 2013;Redfield & Osmundsen, 2013).…”