Evidence for an active sinistral shear zone in the western Alboran region

The Alboran Basin and the surrounding Betic-Rif Cordilleras (see Fig. 1) constitute an arc-shaped thrust-belt that exempli®es contemporaneous internal extension and frontal thrusting in an overall compressional setting. The complex tectonic evolution of the region is the result of ongoing convergence between Africa and Eurasia since late Mesozoic. Until the amalgamation of Iberia with Europe, forming the Pyrenees, the relative motion between Africa and Iberia was minor. From late Eocene to the present, the active plate boundary between Eurasia and Africa was located near to or in the study region. Crustal thickening in the Internal Zones, subsequent nearly radial frontal continental thrusting and contemporaneous internal extension (Watts et al., 1993) have been the main processes in the tectonic evolution. The relationship between these processes is a matter of ongoing debate ± see, e.g., Vissers et al. (1995) and Lonergan and White (1997) ± and beyond the scope of this paper. As in other arc-shaped belts, e.g. the Carpathians (Matenco et al., 1997), space problems are accommodated by strikeslip zones enabling large block rotations (Lonergan andWhite, 1997). The importance of strike-slip tectonics in at least the late stage tectonic evolution of the Alboran/Betic region has been put forward by several authors (e.g. Biermann, 1995, and Sanz de Galdeano, 1996). The present paper focuses on recent to present-day deformation of the region, from discussion of datasets to their implications for the location of a previously unrecognized tectonic feature. This compilation and newconstraintsonthe thermo-mechanical structure support a scenario in which late Miocene to present-day tectonic evolution of the region is accommodated by (predominantly) strike-slip reactivation of inherited crustal structures.