Late Tortonian to Pleistocene deformations of Alboran domain (Western Mediterranean): new insights from ALBANEO project and analogue modelling

            The Alboran domain, located in western Mediterranean between Spain and Morocco, is the result of a succession of different tectonic phases. During Oligocene and Miocene, the Alboran domain underwent the Tethyan subduction followed by a westward slab retreat leading to a back-arc extension. During Tortonian, the Africa-Eurasia convergence, striking N135°E, formed folds and thrusts that are currently found along the Alboran Island and high offshore reliefs (Xauen, Tofiño, Francesc-Pages banks). This convergence phase led to the indentation of a crustal African block within the Alboran Sea, delimited by two strike-slip fault systems: the Yusuf and the Al Idrissi fault systems. This globally left lateral system shows significant changes of orientation from north to south and cross-cut the small Al Idrissi volcanic edifice. Estimations for the Al Idrissi initiation varies between 1.1 Ma and 1.8 Ma with a total displacement calculated from offsets of the volcanic basement of 3 km. North of this volcanic edifice, the deformation is distributed along several km-long fault segments whose activity is inferred to have migrated from east to west. South of the volcano, the deformation is localized along a unique segment, the Bokkoya Fault, showing a change of direction compared to the Al Idrissi fault system. Interestingly, this Bokkoya Fault shares the same orientation as the thrusts and fold axis inherited from the previous convergence phase.

            In this study, we propose to investigate the interactions between the compressive structures and the left-lateral strike-slip Al Idrissi fault system with analogue modelling experiments. Two successive phases of deformation are considered: a global oblique convergence of the entire sand pack followed by a left-lateral strike-slip fault phase. The experiment table is set up as a N-S directed basal fault separating a fixed western plate from a mobile eastern one. The first results show strong influences of the thrust faults on the strike-slip fault segmentation and the orientation of the segments. In the first stages of strike-slip displacement, the deformation is accommodated along segments separated by the former thrust faults. These segments does not share the same orientation than the expected Riedel faults for this set up (i.e. 16°), they display an angle of 11° relative to the basal fault. Then, two deformation branches develop, the fault segments link into clearly established strike-slip faults and their orientations remain oblique relative to the basal fault (5°). This strike-slip fault splitting into two branches is not usual, this phenomena is clearly relative to the interaction with the thrust faults. Through the last displacement stages, the deformation accommodation evolves from the western branch to the eastern one. The deformation becomes more localized along segment nearly oriented N-S like the initial basal fault. Some intersection between thrust faults and strike-slip segments still play as relay areas with an oblique orientation. These results will be integrated into models of seismic and tsunamigenic hazard of the Alboran domain in order to improve the hazard assessments.