Geophysical Evidence for a Transform Margin Offshore Western Algeria: A Witness of A Subduction-Transform Edge Propagator?

daniel alexander loen;

For the first time, a deep seismic data set acquired in the frame of the Algerian–French SPIRAL program provides new insights regarding the origin of the westernmost Algerian margin and basin. We performed a tomographic inversion of traveltimes along a 100-km-long wide-angle seismic profile shot over 40 ocean bottom seismometers offshore Mostaganem (Northwestern Algeria). The resulting velocity model and multichannel seismic reflection profiles show a thin (3–4km thick) oceanic crust. The narrow ocean–continent transition (less than 10km wide) is bounded by vertical faults and surmounted by a narrow almost continuous basinfilled with Miocene to Quaternary sediments. This fault system, as well as the faults organized in a negative-flower structure on the continent side, marks a major strike-slip fault system. The extremely sharp variation of the Moho depth (up to 45 ± 3◦) beneath the continental border underscores the absence of continental extension in this area. All these features support the hypothesis that this part of the margin from Oran to Tenes, trending N65–N70◦E, is a fossil subduction-transform edge propagator fault, vestige of the propagation of the edge of the Gibraltar subduction zone during the westward migration of the Albor´an domain.