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

Abstract

We present a new classification of geological domains at the Africa-Eurasia plate boundary off SW Iberia, together with a regional geodynamic reconstruction spanning from the Mesozoic extension to the Neogene-to-present-day convergence. It is based on seismic velocity and density models along a new transect running from the Horseshoe to the Seine abyssal plains, which is combined with previously available geophysical models from the region. The basement velocity structure at the Seine Abyssal Plain indicates the presence of a highly heterogeneous, thin oceanic crust with local high-velocity anomalies possibly representing zones related to the presence of ultramafic rocks. The integration of this model with previous ones reveals the presence of three oceanic domains offshore SW Iberia: (1) the Seine Abyssal Plain domain, generated during the first stages of slow seafloor spreading in the NE Central Atlantic (Early Jurassic); (2) the Gulf of Cadiz domain, made of oceanic crust generated in the Alpine-Tethys spreading system between Iberia and Africa, which was coeval with the formation of the Seine Abyssal Plain domain and lasted up to the North Atlantic continental breakup (Late Jurassic); and (3) the Gorringe Bank domain, made of exhumed mantle rocks, which formed during the first stages of North Atlantic opening. Our models suggest that the Seine Abyssal Plain and Gulf of Cadiz domains are separated by the Lineament South strike-slip fault, whereas the Gulf of Cadiz and Gorringe Bank domains appear to be limited by a deep thrust fault located at the center of the Horseshoe Abyssal Plain.

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

“…This transition is observed to be controlled by westward dipping extensional faults (Figs. 9, 14) that drop the top of basement to depths similar (10-12km) with that of the oceanic crust interpreted in the Horseshoe Abyssal Plain by Martínez-Loriente et al (2014). The faults identified along the western Algarve Basin coincide in location (see triangle on the seabed in Fig.…”

“…13) and by the work of previous authors (e.g., Gutscher et al, 2009;Martínez-Loriente et al, 2014;Sallarès et al, 2011).…”

“…18b), consistent with the regional trend of the margin. It provides a better estimate of the northern limit of oceanic crust in the Gulf of Cadiz than those proposed to date (e.g., Gutscher et al, 2009;Martínez-Loriente et al, 2014).…”

“…1). Gutscher et al (2009) and Martínez-Loriente et al (2014) proposed the prolongation of this oceanic crust to the east under the Gibraltar arc ( Fig. 1) (Spakman and Wortel, 2004;van Hinsbergen et al, 2014;Vergés and Fernàndez, 2012).…”

“…4 remnant of the Ligurian Tethys (Gutscher et al, 2002;Martínez-Loriente et al, 2014;Sallarès et al, 2011). Plate kinematic reconstructions that are based on magnetic lineations in the Atlantic (Roeser et al, 2002;Schettino and Turco, 2011;Stampfli and Borel, 2002) suggest a Middle to Late Jurassic age for the first oceanic crust formed along southern Iberia.…”