Seismic evidence for the presence of Jurassic oceanic crust in the central Gulf of Cadiz (SW Iberian margin)

Abstract

International audienceWe investigate the crustal structure of the SW Iberian margin along a 340 km-long refraction and wide-angle reflection seismic profile crossing from the central Gulf of Cadiz to the Variscan continental margin in the Algarve, Southern Portugal. The seismic velocity and crustal geometry model obtained by joint refraction and reflection travel-time inversion reveal three distinct crustal domains: the 28-30 km-thick Variscan crust in the north, a 60 km-wide transition zone offshore, where the crust abruptly thins ~ 20 km, and finally a ~ 7 km-thick and ~ 150 km-wide crustal section that appears to be oceanic in nature. The oceanic crust is overlain by a 1-3 km-thick section of Mesozoic to Eocene sediments, with an additional 3-4 km of low-velocity, unconsolidated sediments on top belonging to the Miocene age, Gulf of Cadiz imbricated wedge. The sharp transition between continental and oceanic crust is best explained by an initial rifting setting as a transform margin during the Early Jurassic that followed the continental break-up in the Central Atlantic. The narrow oceanic basin would have formed during an oblique rifting and seafloor spreading episode between Iberia and Africa that started shortly thereafter (Bajocian) and lasted up to the initiation of oceanic spreading in the North Atlantic at the Tithonian (late Jurassic-earliest Cretaceous). The velocity model displays four wide, prominent, south-dipping low-velocity anomalies, which seem to be related with the presence of crustal-scale faults previously identified in the area, some of which could well be extensional faults generated during this rifting episode. We propose that this oceanic plate segment is the last remnant of an oceanic corridor that once connected the Alpine-Tethys with the Atlantic ocean, so it is, in turn, one of the oldest oceanic crustal fragments currently preserved on Earth. The presence of oceanic crust in the central Gulf of Cadiz is consistent with geodynamic models suggesting the existence of a narrow, westward retreating oceanic slab beneath the Gibraltar arc-Alboran basin system

Continental subduction, intracrustal shortening, and coeval upper-crustal extension: P-T evolution of subducted south Iberian paleomargin metapelites (Betics, SE Spain)

“…1). Collision was coeval to subduction of the Tethys oceanic lithosphere under the Alboran domain at the hinge of the arc Lonergan and White, 1997), producing the Flysch-Trough accretionary wedge (Durand-Delga et al, 2000;Gutscher et al, 2012;Luján et al, 2006;Sallarès et al, 2011). The Alboran domain has traditionally included Alpine metamorphic units of the Nevado-Filabride and Alpujarride complexes (e.g., Azañón et al, 1997Azañón et al, , 1998 and the overlying Malaguide complex that underwent very low-grade metamorphism during the Alpine evolution (Abad et al, 2003;Lonergan and Platt, 1995).…”

Seismic and gravity constraints on the nature of the basement in the Africa‐Eurasia plate boundary: New insights for the geodynamic evolution of the SW Iberian margin

“…The multibeam bathymetry merges the SWIM compilation map [ Zitellini et al ., ] and General Bathymetric Chart of the Oceans (GEBCO) digital atlas ( http://www.gebco.net/). Thick gray lines labeled P1 and P2 correspond to the WAS profiles acquired during the NEAREST‐SEIS survey [ Sallarès et al ., , ]. Yellow circles display OBS along the SE segment of the profile P1 presented in this paper (OBS18 to OBS30).…”

Crustal structure of the SW Iberian passive margin: The westernmost remnant of the Ligurian Tethys?

“…The seismic interpretation is tied to onshore geology (Ramos et al, 2016), to 5 wells in the Portuguese offshore (Roque, 2007) and up to 39 wells in the Spanish Gulf of Cadiz area (Lanaja, 1987) (Fig. 4).…”

“…Interpretation was performed in Petrel (Schlumberger) taking into account the unconformity bounded sequences defined by Roque (2007) and Terrinha (1998), which were useful to correlate the MCS seismic reflectors through the margin. Seismic sections and their interpretation were converted to depth using derived from the check-shot data from wells Algarve-1, Algarve-2, Corvina-1, Imperador-1 and Ruivo-1 (Fig.…”