Evidence of quaternary transtensional tectonics in the Nekor basin (NE Morocco)

Abstract

International audienceThe geodynamic processes in the western Mediterranean are driven by both deep (mantle) processes such as slab-rollback or delamination, oblique plate convergence and inherited structures. The present-day deformation of the Alboran Sea and in particular the Nekor basin area is linked to these coeval effects. The seismically active Nekor basin is an extensional basin formed in a convergent setting at the eastern part of the Rif Chain whose boundaries extend both onshore and offshore Morocco. We propose a new structural model of the Nekor basin based on high-resolution offshore data compiled from recent seismic reflection profiles, swath bathymetry acquisitions and industrial seismic reflection profiles. The new data set shows that the northern limit of the basin is oriented N49° with right-stepping faults from the Bousekkour–Aghbal fault to the sinistral Bokkoya fault zone. This pattern indicates the presence of an inherited left-lateral basement fault parallel to the major inherited Nekor fault. This fault has been interpreted as a Quaternary active left-lateral transfer fault localized on weak structural discontinuities inherited from the orogenic period. Onshore and offshore active faults enclose a rhombohedral tectonic Nekor Basin. Normal faults oriented N155° offset the most recent Quaternary deposits in the Nekor basin, and indicate the transtensional behaviour of this basin. The geometry of these faults suggests a likely rollover structure and the presence at depth of a crustal detachment. Inactive Plio-Quaternary normal faults to the east of the Ras Tarf promontory and geometries of depocentres seem to indicate the migration of deformation from east to west. The local orientations of horizontal stress directions deduced from normal fault orientations are compatible with the extrusion of the Rifian units and coherent with the westward rollback of the Tethyan slab and the localization of the present-day slab detachment or delamination

The Tell-Rif orogenic system (Morocco, Algeria, Tunisia) and the structural heritage of the southern Tethys margin

“…South and west of this limit, the recent and active deformation remains under the control of the westward retreat of the delaminated sub-continental mantle (Pérouse et al, 2010). This westward translation is accommodated in the Central Rif by vertical axis counterclockwise rotation measured in the Upper Miocene wedge-top basins (Cifelli et al, 2008) and by development of N-S extensional faults (Lafosse et al, 2017). The NE-SW left-lateral Nekor Fault, inherited from the Lower Jurassic rifting (Figs.…”

“…Hall et al, 2003 for minimum convergence rate avoiding thermal re-equilibration). Meghraoui et al (1996), Rabaute and Chamot-Rooke (2014), Lafosse et al (2017) and Yelles et al (2009). GALTEL abbreviation is for Gorringe-Alboran-Tell after Morel and Meghraoui (1996).…”

The South-Western Alboran Earthquake Sequence of January-March 2016 and Its Associated Coulomb Stress Changes

“…[12] [13] [14]. The main physiographic lows are: the almost-radial West Alboran basin, the narrow Alboran channel (ENE-WSW), prolonged by the also volcanic Tofiño bank and the sedimentary Xauen bank [6] [12] [15] [16], the Algarrobo-Herradura-Djibouti banks off the Spanish margin [17], the Pytheas-Cabliers-Provençaux banks [12], and the WNW-ESE Yusuf-Habibas lineament consisting of a ridge and a scarp [18].…”

“…Along the Spanish margin, there are conspicuous structures such as the NE-SW Adra and Serrata-Carboneras faults [17] and smaller structures described in detail [19], while along the Moroccan margin, some surface expressions of the Bousekkour-Aghbal and Trougout faults were described by [13] [14] [20].…”

Analysis of the recent Plio-Quaternary deformation and the correlation with the focal mechanisms of the significant earthquakes in the Bokoya, Ras Tarf (Eastern Rif)

“…L'analyse des mécanismes au foyer des séismes majeurs (figure 10), a permis de mettre en évidence deux directions de failles en profondeur, NE-SW et NW-SE [24]. On note que les données issues de la méthode de sismique réflexion haute résolution ont permis de mettre en évidence l'existence des failles dans le large de la mer d'Al Hoceima de directions NE-SW [26]. Cela nous ramène à proposer que l'activité sismique dans la région d'Al Hoceima est guidée par des failles de direction allant de N-S a NE-SW (avec une pré-dominance des failles de direction NE-SW qui restent les plus abondantes dans la région d'Al Hoceima et de la mer d'Alboran).…”