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The Messinian Salt Layer Squeezed by Active Plate Convergence in the Western Mediterranean Margins


The structural style developed in continental margins including a salt layer is very well documented and consists in updip marginal extension that promote downslope, gravity gliding or spreading of the suprasalt sequences, and an associated deepwater contractional fold and thrust belt with pinched-off diapirs and eventually extruded salt. In comparison with this scenario, we document by the first time the structural style across the Western Mediterranean margins, where the compressional reactivation of the basement interacts with the deformation of an initially flat, intra-sedimentary Messinian salt layer.

Using deep-penetrating seismic profiles from offshore Algeria to SE Spain, we have reconstructed the crustal structure of the Algerian margin in the South, the eastern domain of the Alboran Sea Basin in the West, and the SE margins of Iberia in the North. During the Cenozoic, and with a variable oblique convergence between the African and Eurasian plates, the western Mediterranean has experienced thinning and extension behind a tight orogenic arc formed by the Betics, Rif and Tell cordilleras. The Messinian salt layer is mostly resting in the deep domains of the South-Balearic Sea, which is floored by a thin oceanic crust of probable Miocene age. Since the Early Miocene, active shortening in the Tell-Atlas domain accommodates most of the plate convergence in the western Mediterranean basin, whereas the eastern margin of the Alboran Sea and the SE Iberian margins experienced eastward and southward extension, respectively. In the southern margin of the basin, incipient thrusting of the Algerian continental crust over the oceanic crust occurred since the Late Miocene and most of the convergence is accommodated by the Messinian salt layer with diapir squeezing and suprasalt folding, whereas the presalt sequence still preserves extensional half-grabens. Salt tectonic processes along the northern and western margins of the western Mediterranean basin show nevertheless a contrasting structural style, formed by narrow extensional and transtensional domains with rafts and gentle diapirs.

A singular salt tectonic style is documented in the margins of the Western Mediterranean, departing from the gravity-driven model, because the horizontal Messinian salt and the suprasalt sequences underwent significant shortening in the southern margin simultaneously to extensional and transtensional salt-detached deformations in the northern and eastern margins.