Lithospheric structure under the western African‐European plate boundary: A transect across the Atlas Mountains and the Gulf of Cadiz

Abstract

We present a two‐dimensional lithospheric thermal and density model along a transect running from the southwestern Iberian Peninsula to the northwestern Sahara. The main goal is to investigate the lithosphere structure underneath the Gulf of Cadiz and the Atlas Mountains. The model is based on the assumption of topography in local isostatic equilibrium and is constrained by surface heat flow, gravity anomalies, geoid, and topography data. The crustal structure has been constrained by seismic and geological data where available. Mantle density is supposed to vary linearly with temperature, providing the link between thermal and density‐related data. The lithospheric thickness varies strongly along the profile, going from near 100 km under the Iberian Peninsula to at least 160–190 km under the Gulf of Cadiz and the Gharb foreland basin in Morocco and to 70 km underneath the Atlas Mountains, coinciding with a region of Neogene volcanism. The thickening of the lithosphere is interpreted as a SW trending lithospheric slab extending from the western Betics to the Gulf of Cadiz and the Gharb Basin, whereas the thin lithosphere underneath the Atlas may be interpreted as plume‐like asthenospheric upwelling similar to those observed in the west European Alpine foreland or as a side effect of a slab penetrating the less viscous asthenosphere.

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

“…3 investigate the deep structure of the Gulf of Cadiz (Dañobeitia et al, 1999;Gràcia et al, 2003;Gutscher et al, 2002Gutscher et al, , 2009Zeyen et al, 2005). The results of these studies show that the crust gently thins from 30-32 km under the Iberian mainland to 25 km in the central part of the Gulf of Cadiz and to 15km in its most western parts.…”

“…Some authors postulate that the Gulf is floored by Avalonian continental crust north of the Guadalquivir and Portimão Banks (Gràcia et al, 2003;Tortella et al, 1997;Zeyen et al, 2005). According to these authors, the transition to the Atlantic oceanic domain is located to the west and no oceanic crust is interpreted south of the Banks.…”

“…Nevertheless, the absence of well defined magnetic anomalies in the area has not permitted the dating of this possible oceanic crust or assigning it unambiguously to the Atlantic or Tethyan domains. Gràcia et al (2003) and Zeyen et al (2005) identified the Guadalquivir-Portimão Bank as a feature across which dramatic crustal thinning occurred. This thinning coincides with an ENE-WSW striking gravity anomaly high that extends along the Guadalquivir and Portimão Banks (Fig.…”

“…15) and well log data. For the deeper part of the profiles, from top basement to the base of the crust we have used information from all available wideangle and refraction seismic data, and previous 2D crustal and lithosphere geophysical modeling (Fernàndez et al, 2004;González et al, 1998;Gutscher et al, 2002;Zeyen et al, 2005). Along the Iberia continental margin, Moho depths were taken from the compilation of Diaz et al (2016) for the lower crust and uppermost lithospheric mantle we have used 2900 and 3300 kg/m 3 , respectively.…”

Thick-Skinned and Thin-Skinned Tectonics: A Global Perspective

“…The section passing through Imilchil coincides with the traverse from southern Portugal to the Sahara Craton for which [267] determined the lithosphere structure. According to this study, the lithosphere/asthenosphere boundary is at a depth of 70 km only in the Middle Atlas and 100 km in the Anti-Atlas.…”