Evidence for slab rollback in westernmost Mediterranean from improved upper mantle imaging

The prevailing idea for the geologic evolution of the western Mediterranean in the Cenozoic is based on north dipping subduction near the gulf of Lyon undergoing vigorous rollback since ∼30 Ma as a consequence of slow Africa–Eurasia convergence across the ∼130 My old Alpine Tethys oceanic lithosphere (Lonergan and White, 1997; Malinverno and Ryan, 1986; Royden, 1993). As rollback propagated south, the subduction zone broke into three segments that continued to retreat independently to the east, south and west (Faccenna et al., 2004; Lonergan and White, 1997; Spakman and Wortel, 2004). The model for the evolution of the eastern slab is well established and generally accepted. That slab is now found under the Calabrian and Apenninic arcs and its roll-back led to the rotation of the Corsica–Sardinia block and the stretching of the crust in a back-arc setting producing the Liguria– Provençal and Thyrrhenian basins (Fig. 1) (Faccenna et al., 2004; Rosenbaum and Lister, 2004; Spakman and Wortel, 2004). The southern and western subduction segments are thought to have retreated to the south towards Africa and west towards Gibraltar, leading to the opening the Algerian basin, and extension in the Alborán terrane (Fig. 1) (Faccenna et al., 2004; Lonergan and White, 1997; Spakman and Wortel, 2004). The latter part of this accounting is controversial, especially with regard to the geologic history of the Alborán domain and the associated Betic and Rif mountain range uplift (Fig. 1). From 27 to 5 Ma the Alborán continental crust underwent an episode of hightemperature metamorphism, was then uplifted, and transported a few hundred km into the westernmost Mediterranean where it was thrust onto the continental margins of Africa and Iberia as it