From Extension to Shortening: Tectonic Inversion Distributed in Time and Space in the Alboran Sea, Western Mediterranean

Abstract

2D seismic reflection data tied to biostratigraphical and log information from wells in the central and southeastern Alboran Sea have allowed us to constrain the spatial and temporal distribution of rifting and inversion. Normal faults, tilted basement blocks, and growth wedges reveal a thinned continental crust that formed in response to NW‐SE extension. To the east, a secondary SW‐NE trend of extension affects the transitional crust adjacent to the oceanic Algerian Basin. The maximum thickness of syn‐rift sediments is ~3.5 km, and the oldest recorded deposits are Serravallian. The WNW‐ESE Yusuf fault formed a buttress separating and accommodating variable extension between two different tectonic domains: the thinned continental crust of Alboran and the oceanic spreading of the Algerian Basin. Late Tortonian to present‐day NW‐SE Africa/Eurasia plate convergence drove shortening and reactivation of some of the earlier extensional structures as reverse and strike‐slip faults, forming complex, compartmentalised subbasins. Tectonic inversion coexisted with the formation of new faults and folds. Inversion was partial along the Habibas Basin and Al‐Idrisi fault, but complete along the Alboran Ridge, where some SW‐NE trending faults were perpendicular to the recent NW‐SE plate convergence and were reactivated as thrusts. The WNW‐ESE Yusuf fault is oblique to the convergence vector, and therefore, reactivation is mainly expressed as transpressional deformation. Volcanic rocks intruded along the Alboran Ridge and Yusuf faults during the latest stages of extension formed rheological anisotropies that localised the later inversion.

Imaging the Growth of Recent Faults: The Case of 2016–2017 Seismic Sequence Sea Bottom Deformation in the Alboran Sea (Western Mediterranean)

“…The southern end of Al Idrisi Fault trace is located at a deformation zone with smaller faults reaching the sea bottom (Figure ). Previous research of earthquake focal mechanisms (Grevemeyer et al, ; Martínez‐García et al, , , ) suggests a sinistral slip on the Al Idrissi Fault NNE‐SSW vertical fault plane, further confirmed by the short displacement, roughly 5 km, of the antiformal axis of Alboran Ridge with respect to the Francesc Pagès seamount (Martínez‐García et al, , , ).…”

“…The main fracture of morphological and seismic expression, deforming the most recent sediments, is the sinistral Al Idrisi Fault zone (Martínez‐García et al, , , ; Figures and ). This fault has a 50‐km‐long northern segment with N35°E trend.…”

“…However, relationships with the main tectonic structures observed in the seafloor have not yet been analyzed in detail. The few available studies (Martínez‐García et al, , , and references herein; Estrada et al, ) suggest that the NNE‐SSW sinistral Al Idrisi Fault is the main structure with recent and present‐day activity in the southern Alboran Sea (Figure ). This fault is connected onshore with the Trougout Fault in the Al Hoceima region (Morocco margin), which bounds the Nekor Basin (d'Acremont et al, ; Lafosse et al, ), and its propagation toward the Rif is discussed by Galindo‐Zaldívar et al (, ) and Poujol et al ().…”

“…The earthquakes of this seismic sequence have been analyzed in detail by the IGN (http://www.ign.es), Buforn et al (), Medina and Cherkaoui (), and Kariche et al (). They consider different velocity models for epicenter locations, suggesting that activity occurred in the area nearby Al Idrisi Fault, yet they do not compare their results with the more accurate position of this fault obtained by marine geophysical research (Estrada et al, ; Lafosse et al, ; Martínez‐García et al, , ). The comparison of seismological and marine geophysical researches clearly shows that the epicenters of the earliest stage of the sequence are located to the west of the Al Idrisi Fault.…”

“…The sedimentary infill consists of unconformable Miocene to Quaternary deposits (Comas et al, ; Juan et al, ). This sedimentary record is mostly deformed by two conjugated sets of dextral WNW‐ESE and sinistral NE‐SW faults and folded by ENE‐WSW oriented folds (Estrada et al, ; Martínez‐García et al, ), the Alboran Ridge and Francesc Pagès seamount, pertaining to the main antiforms (Bourgois et al, ). The growth of faults and folds takes place in the framework of recent NNW‐SSE shortening and regional Eurasian‐African plate convergence (de Mets et al, ).…”