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The Betic (Southern Spain) and the Rif (Morocco) mountain chains, connected through the Gibraltar Strait, shapes a W-E elongated and arcuate Alpine orogenic belt. The Alborán Sea, in continuity to the east with the South Balearic Basin, is located in the inner part of this alpine belt. The Iberian and African continental forelands bound the region as a whole to the north and south, respectively, and to the east it is connected to the oceanic Sardine–Balearic Basin. The peculiarities of these westernmost Mediterranean chains result from: (1) its position between two large convergent plates –Africa and Europe– that have had variable directions of relative motion since the late Cretaceous; and (2) the Neogene westward migration of the orogenic hinterland and its simultaneous “back-arc”-like extension, generating the Alborán Sea basin. The complexes and large paleogeographic terrains traditionally recognized in the Betic and Rif chains belong to four pre–Neogene crustal domains: the South–Iberian and Maghrebian passive continental paleomargins (External Zones of the orogen), the Flysch Units, and the Alborán Crustal Domain composed mainly of a pre– Miocene metamorphosed thrust–stack (Nevado-Filabride, Alpujárride, and Malaguide complexes, from bottom to top). The boundaries between the main metamorphic complexes of the Alborán Domain are extensional detachments, which finally developed under brittle conditions and are commonly sealed by middle-to-late Miocene marine-to-continental sediments. They, nonetheless, are not the most recent structures in the Alborán Domain, because upright, E-W open folds warp the extensional detachments, and finally, high-angle normal faults and strike-slip faults, many of which are still active, offset folds and extensional detachments. The tectonic evolution of the BeticAlborán orogenic system shows close similarities with the one depicted in other arcuate-shaped, Alpine mountain ranges in the Mediterranean, such as the Hellenic Arc and the Aegean Sea. Like in the westernmost Mediterranean, a thickened (pre-Miocene) crust is bounding there a thinned, continental (?) basin. Extension is also formed here in a “back-arc” setting, being developed simultaneously with the N-S convergence between the African and European plates. 1 THE GIBRALTAR ARC AND THE ALBORÁN BASIN IN THE WESTERN MEDITERRANEAN The ENE-WSW Betic Cordillera (SE Spain) and NW-SE to W-E Rif (in Morocco) elongated chains, are connected through the Gibraltar Arc and close in the Alborán Sea corresponding thus to the westernmost Alpine mountain belt in the Mediterranean (Fig. 1). The system as a whole is bounded to the north and south by the Iberian and African continental forelands, and to the east and west by the oceanic Balearic Basin and the Atlantic Ocean (Fig. 1). The peculiarities of this westernmost Mediterranean orogenic ensemble come from the its position between two large convergent plates -Eurasia and Africawhich have undergone variable relative movements from the Mesozoic. Plate-kinematic reconstructions suggest that this plate boundary experienced about 250 km of approximately N-S convergence from mid-Oligocene to late Miocene times (9-8 Ma), followed by about 50 km of W-NW-directed oblique convergence (e.g., Dewey et al., 1989). During the Neogene, and in spite of his plate-convergence scenario, the Al-

TECTONIC EVOLUTION OF THE BETIC CORDILLERA: AN OVERVIEW