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

Abstract

At present, the SW Iberian margin is located along the convergent Iberia-Nubia plate boundary. In Mesozoic times, the margin was located at the triple junction of the Ligurian Tethys, Central Atlantic and Northern Atlantic. The characterization of its crustal structure has allowed us to propose a configuration for this triple junction and to determine the role that this transform margin played within the plate kinematic system. In this paper we present an integrated study based on the interpretation of a 2D regional multichannel seismic survey consisting of 58 profiles, tied with onshore geology and exploratory wells, and on gravimetric modeling performed over four NW-SE trending profiles.Integrated interpretation of MCS data combined with 2D gravity modeling reveals a complex pattern in the southward crustal thinning of SW Iberia and supports the possible presence of oceanic crust under the Gulf of Cadiz. The tapering of Iberian crust is characterized by steps with rapid changes in the thickness of the crust, and thinning to <10km under the outer portions of the margin. Based on gravimetric modeling results and the structures interpreted on reflection seismic profiles, 3 crustal domains reflecting progressive thinning have been defined for the SW Iberian margin. These domains trend roughly WSW-ENE, parallel to the main extensional fabric of the margin. Gravimetric modeling results are compatible with the presence of exhumed sub-continental mantle in the distal part of the margin. Integrated modeling also supports the fact that Cenozoic contraction is responsible for major uplift along the Guadalquivir Bank. Margin inversion and the pre-existing extensional crustal structure are responsible for the areal distribution and amplitude of the prominent positive gravity anomaly observed in the Gulf of Cadiz.