Evidence for transform motion along the South Balearic margin and implications for the kinematics of opening of the Algerian basin

Abstract

Two major types of kinematic models have been proposed to explain the opening of the western Mediterranean basins (Liguro-Provencal and Algerian basins, and Valencia trough). In one type of models, all continental blocks bounding the basins drift to the southeast, driven by the rollback of the Tethys subduction slab. In the other type of models, the Alboran domain drifts to the southwest, implying a westward rollback of the broken subducting slab and a NE-SW opening of the Algerian basin. In most models, however, the structure of the Balearic promontory was not taken into account, despite its key location at the boundary of the three major basins. We used the interpretation of a large seismic database coupled to gravity and magnetic anomaly analyses to characterize the nature and structure of the South Balearic margin. The constraints brought by the new analyses allow us to suggest a new scenario for the opening of the Algerian basin. Seismic profiles show that the South Balearic margin is composed of four segments with different morphologies and crustal structures. Two segments, the Mazarron and the Emile Baudot escarpments, are characterized by steep scarps and sharp crustal thinning. Two other segments, the South Ibiza and South Menorca margins, have a smoother bathymetry and crustal thinning. We interpret the former in terms of transform margins, and the latter as divergent margins. The distribution of faults on the passive margin segments suggests that they have recorded at least two phases of deformation. A first phase of opening, probably in a NW-SE direction, affected the south Balearic margin, and possibly created some oceanic floor. The existence of the transform margin segments and the prominent NW-SE orientation of the magnetic lineations in the eastern Algerian basin suggest that most of this basin opened in a NE-SW direction, in different oceanic corridors. The two eastern corridors formed by the southwestward drift of the Kabylies. The western corridor, bounded by the transform segments of the South Balearic margin and the Algerian margin, results from the southwestward drift of the Alboran domain, as suggested by previous studies.