No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
The Alboran Sea (Western Mediterranean) revisited with a view from the Moroccan Margin
Abstract
This paper presents a new depth to acoustic basement map based on a grid of seismic profiles. In the Western Alboran Basin the basement is more than 10 km deep. An examination of a seismic profile of this region suggests that Late Oligocene–Early Miocene 5 km thick synrift formation has been accumulated in this basin. This West Alboran basin has been formed in an extensional setting, but in a fore-arc position, south of the Balearic Islands then westwards transported behind a subduction zone.
... The Western Alboran Basin was the first basin to be open, during the extensional phase, that began about 20 Ma ago Watts et al. 1993;Soto et al. 1996Soto et al. , 2010Chalouan et al. 1997;Mauffret et al. 2007;Iribarren et al. 2009). According to some authors , this would be an allochthonous basin that would have moved about 500 to 600 km to the SW to reach its current position (Rosenbaum et al. 2002;Mauffret et al. 2004Mauffret et al. , 2007Spakman and Wortel 2004). ...
... The Western Alboran Basin was the first basin to be open, during the extensional phase, that began about 20 Ma ago Watts et al. 1993;Soto et al. 1996Soto et al. , 2010Chalouan et al. 1997;Mauffret et al. 2007;Iribarren et al. 2009). According to some authors , this would be an allochthonous basin that would have moved about 500 to 600 km to the SW to reach its current position (Rosenbaum et al. 2002;Mauffret et al. 2004Mauffret et al. , 2007Spakman and Wortel 2004). The Southern Alboran Basin would open later; at Tortonian (Ammar et al. 2003) together with the Neogene basins of Boudinar and Melilla-Nador (Guillemin and Houzay 1982) in a geological context characterized by tectonic inversion Chalouan et al. 1997;Mauffret et al. 2007) itself guided mainly by the retreat of the subduction zone of the Western Mediterranean (Do Couto et al. 2016). ...
... According to some authors , this would be an allochthonous basin that would have moved about 500 to 600 km to the SW to reach its current position (Rosenbaum et al. 2002;Mauffret et al. 2004Mauffret et al. , 2007Spakman and Wortel 2004). The Southern Alboran Basin would open later; at Tortonian (Ammar et al. 2003) together with the Neogene basins of Boudinar and Melilla-Nador (Guillemin and Houzay 1982) in a geological context characterized by tectonic inversion Chalouan et al. 1997;Mauffret et al. 2007) itself guided mainly by the retreat of the subduction zone of the Western Mediterranean (Do Couto et al. 2016). Its opening is accompanied by important volcanic manifestations (Hoernle et al. 1999;Ammar et al. 2007;Duggen et al. 2004Duggen et al. , 2008, particularly abundant ( Fig. 1) in the central and eastern parts of the Alboran Sea (Galdeano et al. 1974;Willet 1997). ...
Major changes have affected the Alboran Sea and its periphery since the Tortonian. They are essentially related to the structural evolution marked by tectonic inversion due to shortening. The revisiting of seismic data available on the Moroccan margin and on the adjacent Western Alboran Basin, added to good stratigraphic calibration (in particular, the limit between the Miocene and the Plio-Quaternary) from the oil drilling, allowed us to review the age of the oldest deposits in the Neogene basins of western Rif, thanks to their extension at sea, and to propose a new hypothesis for the opening age of the basin and that of the Strait of Gibraltar. We will also show that the upheaval caused by the progressive uplift of the Alboran Ridge and Xauen and Tofiño banks and the instability of the sediments that it has caused predate the canyon that connects the Strait of Gibraltar to the Algero–Balearic Basin. The continuous supply of Atlantic water into the Alboran Sea explains the thickness of the saline series in the deeper parts of the Mediterranean Sea. We give the arguments to demonstrate that the tectonic inversion guided the evolution of the Alboran Sea since the Tortonian.
... Driussi et al., 2015). The first one is a south-eastern slab retreat that would have led to the displacement and initial extension of the Alboran Domain, as well as to the opening of the Algerian basin as a back-arc process (Gueguen et al., 1997;Mauffret et al., 2007;Romagny et al., 2020;Schettino and Turco, 2011;Spakman et al., 2018;Fig. 1a). ...
... The geological evolution of the Alboran Domain is the consequence of the motion and rifting of the AlKaPeCa Domain (Bouillin et al., 1986) between the Eurasian and African plates, started in the Late Oligocene-Miocene (Chertova et al., 2014;Comas et al., 1999;Mauffret et al., 2007;Romagny et al., 2020;Rosenbaum et al., 2002). The AlKaPeCa Domain is described as a landmass that, before the Miocene, was part of the forearc and accretionary prism that originally formed on the Eurasian side of the African-Eurasian collision (Bouillin et al., 1986). ...
... The emplacement of the NE-SW and NW-SE dipole lineations must have occurred during the initial NNW-SSE extensional stages, based on their trend and disconnection from surface structures (Jolivet et al., 2021 and references therein). In fact, the NE-SW dipole lineation (Fig. 2) has a direction similar to the rift axis proposed in paleogeographic reconstructions of the AlKaPeCa Domain (Do Couto et al., 2016;Faccena et al., 2014;Mauffret et al., 2007;Schettino and Turco, 2011;Spakman et al., 2018). These bodies may have been the relict of the westwards rifting axis of the AlKAPeCa Domain that remained into the crust of the Alboran Domain (Fig. 9a, Bouillin et al., 1986;Mauffret et al., 2007;Romagny et al., 2020;Rosenbaum et al., 2002). ...
In the Alboran Sea there are a few well exposed Neogene and Quaternary volcanic zones, often geographic highs, that are generally associated with magnetic anomalies. In this paper, we present a characterization of these magnetic anomalies based on a recent and accurate magnetic data compilation for the Abloran Sea area. The anomalies reveal the distribution of magmatism and shed light into the discussion about the origin and evolution of the westernmost Mediterranean. One of the most relevant magnetic anomalies is the Nador dipole, which extends from the Gourougou volcano to the Chafarinas Islands, and is related to an E-W crustal scale intrusion. However, the main NE-SW elongated continuous dipoles of the central Alboran Sea are not related to any surface structure, but they are parallel to the Alboran Ridge, which is the main volcanic high in the Alboran Sea, and are located to the north of it. These anomalies extend discontinuously eastward along the NW-SE dipoles located along the Yusuf fault zone. The results of our 2D magnetic forward modeling suggest that the causative bodies of these main magnetic dipoles are deep igneous bodies. According to the tectonic evolution of the region, and the high magnetic susceptibility values obtained, these igneous bodies probably are made of a basic igneous rocks. Their emplacement may represent the westward tip of the rift axis of the AlKaPeCa Domain, which is related to the Oligocene-Miocene NW-SE extension, and associated with the southern slab retreat stage and oceanic spreading of the Algerian basin. Afterwards, these bodies were displaced toward the west, together with the Alboran Domain, and affected by the STEP fault located at its southern limit. Since the Late Miocene, the north Alboran Ridge elongated intrusions acted as a backstop that conditioned the folding and uplift of the Alboran Ridge in a tectonic indentation setting. In this setting, the STEP fault is deformed and the eastern part of the bodies were segmented along the Yusuf transtensional fault system. Simultaneously, the E-W crustal body related to the Nador magnetic dipole was emplaced, possibly evidencing a slab tearing process. The deep seated basic igneous bodies constitute main crustal heterogeneities that reveal and drive the Alboran Sea tectonic inversion.
... The obliquity between the preexisting tectonic fabric and the direction of reactivation, which is the consequence of a transpressive behavior (Tikoff & Teyssier, 1994;Teyssier et al., 1995;Dewey, 2002), leads to a highly distributed deformation in the crust and in the sedimentary cover over time (Fossen & Tikoff, 1998), associated with block rotations (Wilcox et al., 1973). The Alboran domain ( Figure 1) is considered as a thinned continental microplate within the compressive context of the Africa-Europe convergence (Comas et al., 1999;Gutscher et al., 2002;Jolivet et al., 2009;Mauffret et al., 2007;Mauffret et al., 1992). Since the Late Oligocene, the Alboran domain has been shaped by the progressively westward retreat of the Tethyan slab linked to an upper-plate extension (Calvert et al., 2000;Platt et al., 2003;Spakman & Wortel, 2004;Jolivet et al., 2008). ...
... The basement of the Alboran Basin is composed of metamorphic rocks similar to those observed onshore in the internal zone of the Betic Cordillera Soto et al., 1999). This continental block was formed by the extension of the upper plate due to retreat of the westward slab in the context of the Africa-Europe convergence since the end of the Oligocene (Gutscher et al., 2002;Mauffret et al., 2007;Jolivet et al., 2009). The continental collision of the Alboran domain with the former Iberian and African passive margin during the Oligocene-Miocene led to the stacking of three metamorphic complexes in the internal zone: the Nevado-Filabride, the Alpujarride/Sebtide, and the Malaguide/Ghomaride complexes from bottom to top (e.g., Crespo-Blanc & Frizon de Lamotte, 2006). ...
... Offshore, the Alboran Ridge, which is part of the Trans-Alboran Shear Zone, is a 60 km long transpressive NE-SW elongated tectonic discontinuous structure (Muñoz et al., 2008;Ballesteros et al., 2008), made of Miocene and Pliocene sedimentary and volcanic rocks. It is locally intruded by a volcanic body in its eastern part Mauffret et al., 2007;Chalouan et al., 2008;Maad et al., 2010), while its southern termination, called the South Alboran Ridge (SAR), corresponds to a series of Mio-Pliocene sigmoid antiforms and synforms accommodating left lateral motion and uplift (Bourgois et al., 1992;Comas et al., 1992;Chalouan et al., 1997;Mauffret et al., 2007;Galindo-Zaldivar et al., 2018). ...
Since the Miocene, the thinned continental crust below the Alboran Sea and its overlying sedimentary cover have been undergoing deformation caused by both convergence of Eurasia and Africa and by deep processes related to the Tethyan slab retreat. Part of this deformation is recorded at the Xauen and Tofiño banks in the southern Alboran Sea. Using swath bathymetry and multichannel seismic reflection data, we identified different stages and styles of deformation. The South Alboran Basin is made up of Early Miocene to Pliocene sedimentary layers that correlate with the West Alboran Basin depocenter and are dominated by E‐W trending folds and thrusts. The Xauen and Tofiño Banks first recorded the phase of extension and strike‐slip movement during the slab retreat, followed by the phase of compressional inversion since the Tortonian and are now structured by tight folds, thrusts, and mud bodies. This study proposes that the Banks were located on the southern‐inherited Subduction Tear Edge Propagator (STEP) fault related to the westward migration of the Alboran domain during the Miocene. The STEP fault zone, acting as a boundary between the African block and the Alboran block, was located along the onshore Jebha‐Nekor fault and the offshore Alboran Ridge and the Yusuf fault zone. Thick‐skinned and thin‐skinned shortening occurred when slab retreat stopped, and inversion began. The present‐day style of the deformation seems to be linked to a decollement level made of undercompacted shale on top of the Ghomaride complex.
... In the Mediterranean, several extensional basins formed during the Miocene due to the collapse of Alpine orogens at~25-30 Ma and were later partially inverted and deformed under a transpressional regime within a convergent tectonic setting between the African and Eurasian plates (e.g., Cloetingh et al., 2008;Faccenna et al., 2004;Gallais et al., 2011;Giaconia et al., 2015;Horvath & Berckhemer, 1982;Rosenbaum, Lister, & Duboz, 2002;Strzerzynski et al., 2010). The westernmost of these basins is the Alboran Sea, which experienced folding, reverse and strike-slip faulting, and uplift of basin margins during the Plio-Quaternary (e.g., Alvarez-Marrón et al., 1999;Bourgois et al., 1992; Comas, García-Dueñas, Chalouan et al., 1997;Docherty & Banda, 1995;Mauffret et al., 2007; (Figure 1). ...
... Tectonics 10.1002/2017TC004489 García-Dueñas, Balanyá, & Martínez-Martínez, 1992;Maldonado et al., 1992;Platt et al., 1998;Platt & Vissers, 1989;Watts, Platt, & Buhl, 1993). However, little is known about the rifting geometry in the central and southeastern parts of the basin where a significant number of Plio-Quaternary structures are found (e.g., Mauffret et al., 2007;Medaouri et al., 2014). Additionally, the role of preexisting Miocene faults during the shortening phase is still unclear. ...
... The WAB contains the major depocentre, which is thicker than 8.5 km (Soto, Comas, & de la Linde, 1996;Weinzapfel et al., 2003) (Figures 1 and 2). Towards the east, the sedimentary cover thins to 2-2.5 km in the EAB and 3 km in the SAB Mauffret et al., 2007). ...
D seismic reflection data tied to biostratigraphical and log information from wells in the central and south-eastern 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 sub-basins. 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.
... Le bassin d'Alboran, entouré par les chaines bético-rifaines, est considéré comme un bassin d'arrière-arc développé depuis l'Oligocène en liaison avec la migration de l'arc de Gibraltar vers l'Ouest (Platt et Vissers, 1989 ;Maldonado et al., 1992 ;Garcia-Dueñas et al., 1992 ;Watts et al., 1993 ;Comas et al., 1999Comas et al., , 1992Martínez-García et al., 2011). Il regroupe trois bassins principaux ( Fig. I-12) : le bassin Ouest-Alboran (WAB) qui présente la plus importante épaisseur de dépôts (entre 7 et 12 km de sédiments accumulés de 20 Ma ; Comas et al., 1992Comas et al., , 1999Soto et al., 1996 ;Iribarren et al., 2009 ;Soto et al., 2010), le bassin Est-Alboran (EAB) qui renferme près de 2 à 3 Km de dépôts et le bassin Sud-Alboran (SAB) contenant près de 3 km de sédiments (Comas et al., 1997 ;Booth-Rea et al., 2007 ;Mauffret et al., 2007). Le bassin d'Alboran présente une évolution tectonique marquée par deux périodes majeures de déformation ( Fig. I-13 ; Comas et al., 1992 ;Watts et al., 1993 ;Chalouan et al., 1997 ;Comas et al., 1999 ;Mauffret et al., 2007) : ...
... Il regroupe trois bassins principaux ( Fig. I-12) : le bassin Ouest-Alboran (WAB) qui présente la plus importante épaisseur de dépôts (entre 7 et 12 km de sédiments accumulés de 20 Ma ; Comas et al., 1992Comas et al., , 1999Soto et al., 1996 ;Iribarren et al., 2009 ;Soto et al., 2010), le bassin Est-Alboran (EAB) qui renferme près de 2 à 3 Km de dépôts et le bassin Sud-Alboran (SAB) contenant près de 3 km de sédiments (Comas et al., 1997 ;Booth-Rea et al., 2007 ;Mauffret et al., 2007). Le bassin d'Alboran présente une évolution tectonique marquée par deux périodes majeures de déformation ( Fig. I-13 ; Comas et al., 1992 ;Watts et al., 1993 ;Chalouan et al., 1997 ;Comas et al., 1999 ;Mauffret et al., 2007) : ...
... En mer, le site ODP (979) . Une déformation plio-quaternaire extensive à transtensive s'est produite dans tout le bassin en mer Mauffret et al., 2007 ;Martinez-García et al., 2012), comme à terre (Morel, 1988). Par conséquent, la « MES » en offshore du « SAB » est actuellement plus profonde par rapport à sa situation à la fin de la « MSC ». ...
The Neogene geodynamics evolution of the south-Alboran realm in western Mediterranean has been clarified, based on sedimentological and chronostratigraphical studies. This work focuses on three main themes of research, the first is to establish the moments for the opening and closing of the North Rifian Corridor by studying two Neogene basins of the southern edge of the Alboran sea. The second, aims to understand the behavior of these two basins face a major event in the history of the Mediterranean: The Messinian Salinity Crisis. Finally, the third theme aims to understand the modalities Post-MSC reflooding in the southern part of the Alboran realm.
The late Miocene evolution of the North Rifian Corridor is clarified on the basis of chronostratigraphic studies of the Neogene Boudinar and Arbaa Taourirt basins (northeastern Morocco). The marine sediments deposited in the Boudinar basin between the early Tortonian and the late early Messinian (10 Ma to 6.1 Ma) and in the late Tortonian-earliest Messinian interval in the Arbaa Taourirt basin. Palaeoenvironmental data record a major drowning in association with extensive tectonics in the Boudinar basin during the early Messinian at ~7.2 Ma. At the same time, prograding conglomerates and sandstones developed over the late Tortonian marls in the Arbaa Taourirt basin. During the late-early Messinian, a shallowing trend occurred in the Boudinar basin. Thus, the North Rifian Corridor opened at ~7.2 Ma ensuring Atlantic-Mediterranean connections, then was progressively restricted during the late-early Messinian and totally closed at ~6.1 Ma.
New sedimentological and paleontological studies of the late Messinian-early Pliocene deposits in the Boudinar basin provide new information on the Messinian Salinity Crisis (« MSC ») and the Zanclean reflooding in the Alboran sea. The Messinian erosional surface « MES » is of late Messinian age and was emplaced in subaerial settings. It is polygenic, its original geometry is locally preserved and was re-shaped by the Pliocene transgressive surface.
Above the « MES », the Boudinar basin infill is characterized by a wide variety of facies from continental settings to lower offshore conditions. Two major sets are recognized: a latest Messinian-Zanclean set that constitutes a transgressive-regressive megasequence interrupted at the top by a tectonic unconformity, and an Plio-Quaternary regressive set. During the late Messinian Zanclean interval, four successive depositional models were documented. They record major changes in palaeoflow and paleogeography related to base-level fluctuations. No Gilbert-type delta has ben identified at Boudinar. the beginning of base-level rise is marked by normal regressions and by the formation of several lacs and fan-delta complexes on the margins of the basin in the late Messinian and befor the marine reefloding in the early Zanclean. The marine reflooding of the basin appears later, with a transgressive surface of ravinment and a thick package of transgressive deposits. These transgressive deposits onlap over all previous deposits. The major part of the basin infill did not issue from an inner landward position (south of the basin) but from the northwestern side of the basin, i.e. near the Mediterranean. Sediments were subsequently reworked by storms and transported by longshore-drift towards the south. a maximum flooding surface is found several tens of metres above the « MES ». This fiding is consistent with a progressive and not a catastrophic early Zanclean flooding of the westernMediterranean after the Mediterranean base-level fall.
... Extension and subsidence of the Alborán Basin occurred in the Early to Middle Miocene and was accompanied by orogenesis in the surrounding arcuate Betic-Gibraltar-Rif mountain belt (Comas et al. 1999;Jolivet and Faccenna 2000;Lonergan and White 1997). Recent seismic reflection studies suggest that crustal thickness increases from the central Alborán Basin towards the Betic-Gibraltar-Rif mountain belt (e.g. from *6 to *15 km along an eastwest profile) and that three different crustal domains exist in the Alborán Basin: (1) magmatic arc-crust of Miocene age in the centre, (2) connected to oceanic crust in the east that was formed by Miocene back-arc spreading and (3) thinned continental crust between the central Alborán Basin magmatic arc-crust and the arcuate Betic-Gibraltar-Rif mountain belt Mauffret et al. 2007Mauffret et al. , 2004. A fourth crustal domain may exist in the western Alborán Basin, interpreted to have been formed in a fore-arc basin context Mauffret et al. 2007). ...
... Recent seismic reflection studies suggest that crustal thickness increases from the central Alborán Basin towards the Betic-Gibraltar-Rif mountain belt (e.g. from *6 to *15 km along an eastwest profile) and that three different crustal domains exist in the Alborán Basin: (1) magmatic arc-crust of Miocene age in the centre, (2) connected to oceanic crust in the east that was formed by Miocene back-arc spreading and (3) thinned continental crust between the central Alborán Basin magmatic arc-crust and the arcuate Betic-Gibraltar-Rif mountain belt Mauffret et al. 2007Mauffret et al. , 2004. A fourth crustal domain may exist in the western Alborán Basin, interpreted to have been formed in a fore-arc basin context Mauffret et al. 2007). Results from a marine seismic survey argue for an active accretionary wedge in the Gulf of Cadiz (due west of Gibraltar) and for the existence of an eastward dipping slab-like seismic high-velocity anomaly under Gibraltar and the western to central Alborán sea (Gutscher et al. 2002). ...
... Gill et al. (2004) argue that the formation of Alborán Sea basalts is unlikely to result from partial melting of metasomatised upper mantle that stored earlier subduction zone melts as mafic veins. Notably, partial melting of metasomatised lithospheric mantle, containing veins formed during earlier subduction zone processes (involving sediment recycling into the mantle), is proposed for the formation of lamproites in southeastern Spain and shoshonites in northern Morocco (Duggen et al. 2005;El Bakkali et al. 1998;Foley 1992), thus producing highly potassic lavas with strong Coulon et al. 2002;Duggen et al. 2004;Gill et al. 2004;Hoernle et al. 1999), shoshonitic lavas and basanites/alkali basalts on the continental margins of southern Iberia and nortwestern Africa (Coulon et al. 2002;Duggen et al. 2005), vertical-axis rotations in the Betics and Rif (Lonergan and White 1997), fore-arc position of the western Alborán Basin Mauffret et al. 2007), back-arc spreading direction in the Lower to Middle Miocene oceanic crust of the western Algerian Basin (Mauffret et al. 2004) incompatible element enrichments rather than tholeiites with extreme HFSE-depleted arc trace element signatures or calc-alkaline lavas. The Spanish lamproites and Moroccan shoshonites are also clearly distinguished from the Alborán Basin LREE-depleted and LREE-enriched lavas by their Sr-Nd-Pb-isotopic composition (Duggen et al. 2005El Bakkali et al. 1998;Gill et al. 2004). ...
We present new major and trace element and O-Sr-Nd-isotope data for igneous rocks from the western Mediterranean Alborán Sea, collected during the METEOR 51/1 cruise, and for high-grade schists and gneisses from the continental Alborán basement, drilled during the Ocean Drilling Programme (ODP Leg 161, Site 976). The geochemical data allow a detailed examination of crustal and mantle processes involved in the petrogenesis of the lavas and for the first time reveal a zonation of the Miocene Alborán Sea volcanism: (1) a keel-shaped area of LREE-depleted (mainly tholeiitic series) lavas in the central Alborán Sea, generated by high degrees of partial melting of a depleted mantle source and involving hydrous fluids from subducted marine sediments, that is surrounded by (2) a horseshoe-shaped zone with LREE-enriched (mainly calc-alkaline series) lavas subparallel to the arcuate Betic-Gibraltar-Rif mountain belt. We propose that the geochemical zonation of the Miocene Alborán Basin volcanism results from eastward subduction of Tethys oceanic lithosphere coupled with increasing lithospheric thickness between the central Alborán Sea and the continental margins of Iberia and Africa.
... The ancestor of the Betic-Rif orogenic belt is the allochthonous AlKaPeCa micro-continent, a group of east-west trending continental domains originally located in a north-easternmost location in the current western Mediterranean (Fig. 2) (Booth-Rea et al., 2007;Faccenna et al., 2004;Mauffret et al., 2007;Platt et al., 2013;Royden, 1993;van Hinsbergen et al., 2014). From the Late Jurassic to the Cretaceous, a deep oceanic basin -floored by oceanic crust or thinned continental crustseparated the southern AlKaPeCa continental margin from the Maghrebian passive paleomargin (Algarra, 1987;Durand-Delga et al., 2000;Guerrera et al., 2005;Luján et al., 2006). ...
... During the Late Cretaceous-Eocene a subduction zone was initiated in this basin. The lateral extent, location and single or double vergence of the subduction is a current matter of debate (Booth-Rea et al., 2007;Faccenna et al., 2004;Mauffret et al., 2007;Platt et al., 2013;van Hinsbergen et al., 2014;Vergés and Fernàndez, 2012). The most widely accepted hypothesis is that the basement of the Flysch Trough and its sedimentary cover subducted northward beneath the AlKaPeCa continental domain (Fig. 2). ...
... The provenance of the Alborán domain complexes is key to understand the formation of the Betic-Rif belt (Platt et al., 2013;van Hinsbergen et al., 2014, and references therein). Relative to the Early Cretaceous paleogeography of the westernmost Alpine Tethys, the Alborán domain complexes have been regarded either as part of the African or the Southern Iberian margins, or as pieces of the AlKaPeCa continental domain that was placed along the northern passive margin of the Alpine Tethys (Booth-Rea et al., 2007;Bosch et al., 2011;Faccenna et al., 2004;Mauffret et al., 2007;Platt et al., 2013;van Hinsbergen et al., 2014;Vergés and Fernàndez, 2012). These peri-Alpine Tethyan candidates for the derivation of the Alborán domain are built upon Variscan basements with metasediments that testify their Neoproterozoic peri-Gondwanan origin (Stampfli and Hochard, 2009;Stampfli et al., 2013). ...
We present new Sr-Nd-Pb isotope data of the western Alpujárride metamorphic basement and the pre-Miocene Flysch sediments of the Betic Cordillera (southern Spain). Nd model ages are consistent with an increasing detrital input from the Alborán domain to the Flysch Trough in the western Mediterranean during the late Oligocene. The Alpujárride metamorphic crustal rocks derived from Archean-Paleoproterozoic terranes located along the northern margin of Gondwana in the Neoproterozoic. The heterogeneous isotopic signatures of the Alpujárride units indicate that they have different sedimentary protoliths and underwent contrasted Variscan and pre-Variscan tectono-magmatic evolutions. Melts/fluids derived from the western Alpujárride gneisses contaminated the mantle source of the Ronda high-Mg pyroxenite dykes, implying that the Alpujárride lower crust underthrusted the subcontinental lithospheric mantle of the Alborán domain generating subduction-like magmatism in the late Oligocene. The western Alpujárride upper crust is involved in the Neogene volcanism of the Alborán Sea basin, but only contaminated some LREE-enriched calc-alkaline lavas erupted along the continental margins. On the other hand, tholeiitic lavas in the center of the basin show no isotopic evidence of crustal assimilation. This indicates that most of the crust in the central Alborán Sea accreted by Miocene tholeiitic magmatism and that Alpujárride lower crust is absent and likely foundered close to the continental margins of the basin.
... The most important sedimentary depocenter is located on the Western Alboran Basin (WAB) and its axis mimics the arcuate geometry of the orogenic arc (Soto et al., 1996;Iribarren et al., 2009). The sedimentary thickness of the WAB is estimated at between 10 to 12 km (Soto et al., 1996;Mauffret et al., 2007;Iribarren et al., 2009;Weinzapfel et al., 2003) and is mainly affected by shale tectonics (Soto et al., 2010) and associated mud volcanism (Pérez-Belzuz et al., 1997;Sautkin et al., 2003;Blinova et al., 2011;Somoza et al., 2012;Gennari et al., 2013). Three wells, called Alboran-A1, Andalucia-G1 and A C C E P T E D M A N U S C R I P T ...
... Interpretation -This seismic unit has never been drilled in the Alboran Sea. Chalouan et al. (1997) interpreted this tilted unit as belonging to the Middle Miocene, whereas Mauffret et al. (2007) interpreted it as belonging to the deepest Lower Miocene unit VI drilled offshore Malaga (e.g. Comas et al., 1999). ...
... The deepest depression reaches 8 s TWTT offshore Morocco and no more than 7 s offshore Spain. This is in agreement with previous estimates (Soto et al., 1996;Mauffret et al., 2007;Iribarren et al., 2009;Soto et al., 2010). All tectonic structures identified on seismic profiles show the effect of the inversion on the Alboran Sea basement. ...
The Western Alboran Basin (WAB) formation has always been the subject of debate and considered either as a back-arc or a forearc basin. Stratigraphic analyses of high-resolution 2D seismic profiles mostly located offshore Morocco, enabled us to clarify the tectonic and stratigraphic history of the WAB. The thick pre-rift sequence located beneath the Miocene basin is interpreted as the topmost Malaguide/Ghomaride complex composing the Alboran domain. The structural position of this unit compared with the HP–LT exhumed Alpujarride/Sebtide metamorphic basement, leads us to link the Early Miocene subsidence of the basin with an extensional detachment. Above the Early Miocene, a thick Serravallian sequence marked by siliciclastic deposits is nearly devoid of extensional structures. Its overall landward to basinward onlap geometry indicates that the WAB has behaved as a sag basin during most of its evolution from the Serravallian to the late Tortonian. Tectonic reconstructions in map view and in cross section further suggest that the basin has always represented a strongly subsiding topographic low without internal deformation that migrated westward together with the retreating slab. We propose that the subsidence of the WAB was controlled by the pull of the dipping subducting lithosphere hence explaining the considerable thickness (10 km) of the mostly undeformed sedimentary infill.
... Certains auteurs (e.g. Mauffret et al., 2004Mauffret et al., , 2007 imaginent une ouverture très dissymétrique avec une dorsale située dans la partie est du bassin (Fig. V.6a), alors que d'autres (Medaouri et al., 2014) interprètent les anomalies magnétiques observées dans le domaine océanique comme un axe d'accrétion fossile très segmenté par des failles transformantes d'orientation NE-SW à ENE-WSW sub-parallèles à la dérive du bloc Alborán (Fig. V.6c). (Ride d'Hannibal, en rouge, Mauffret et al., 2004, avec un sens de décrochement sénestre en pied de marge de Mostaganem, (b) l'axe d'accrétion se situe à l'ouest de Ténès avec un sens de décrochement dextre en pied de marge de Mostaganem (c) accrétion diffuse, et/ou répartie sur un ou plusieurs axes segmentés (d'après Medaouri et al., 2014, modifié) : le sens de cisaillement le long de la marge de Mostaganem dépend de la géométrie du ou des axes d'accrétion (sénestre sur l'exemple illustré). ...
... A remarquer sur le panneau iso-X situé à X=70 km l'apparition d'un événement courbé (indiqué par la flèche rouge) et correspondant à l'énergie (cercle blanc) entre 9 et 9.5 km de profondeur, la courbure de l'événement est associée à des erreurs de positionnement en profondeur de ce réflecteur. Pour ces profondeurs le modèle de vitesse en utilisant le champ de vitesses MCS ne semble pas adapté……………………………………………………………………………………………………………..108 (2) Mauffret et al., 2004Mauffret et al., , 2007, avec un sens de décrochement senestre au pied de marge de Mostaganem (b) l'axe d'accrétion se situe à l'ouest de Ténès avec une extension continentale du domaine d'Alboran plus à l'ouest avec un sens de décrochement dextre au pied de marge de Mostaganem (c) accrétion diffuse, avec plusieurs axes (d'après Medaouiri et al., 2014) Strzerzynski et al., 2010). Les flèches indiquent le type de contrainte et sa direction moyenne, les numéros indiquent les vitesses de rapprochement dérivées des mesures GPS . ...
... The maximum thicknesses locate in the WAB, where the sedimentary pile is up to 8 km thick and displays a curved depocentre that mimics the orogenic front of the Gibraltar Arc System Soto et al., 1996Soto et al., , 2012Chalouan et al., 1997). Towards the East, the thickness of the sedimentary filling decreases to 2-3 km in the EAB, at the transition towards the Algerian basin, whereas in the SAB, maximum sediment accumulation reaches 4 km (Comas et al., 1995;Booth-Rea et al., 2007;Mauffret et al., 2007, Medaouri et al., 2012Martinez-Garcia et al., 2013). ...
La marge algérienne borde le bassin algérien, formé en position de bassin arrière-arc de la subduction Téthysienne. L'importance de l'étude du segment de marge qui s'étend de Ténès à Mostaganem sur environ 250 km, réside dans sa position charnière entre le domaine continental d'Alborán à l'Ouest et le bassin océanique algérien à l'Est. Dans ce travail nous avons déterminé pour la première fois, la structure et la nature de la croûte de ce segment, à partir de l'inversion tomographique des données de sismique grand-angle d'un profil N-S perpendiculaire à la marge. Grâce aux traitements des données de sismique réflexion multitrace acquises pendant la campagne SPIRAL et aux données industrielles, nous avons pu proposer un schéma tectonique régional et une cartographie de l'extension possible du socle Kabyle en mer. Les résultats révèlent une marge caractérisée par la juxtaposition d'une croûte océanique peu épaisse au nord et d'une croûte continentale amincie au sud de part et d'autre d'un accident vertical. L'ouverture du bassin océanique résulterait de la réponse à la déchirure du panneau lithosphérique en subduction sous Gibraltar, accompagné par la migration du bloc Alborán vers l'Ouest. La propagation de cette déchirure (STEP) a généré une zone de cisaillement qui se focalise dans zone de transition océan-continent. L'inversion tectonique qui affecte plus à l'Est la marge semble s'arrêter à la latitude de Ténès. Cette absence de déformation en mer coïncide avec une lacune de sismicité liée à la résistance mécanique de la marge. Par comparaison à d'autres régions du monde, seules les zones situées sur la croûte continentale pourraient présenter un potentiel pétrolier.
... Fault slip decreases southwards, the fault trace extending onshore over 15 km and ending before the Nekor fault. Offshore, the Boudinar fault is connected northwards with the Al Idrisi fault zone (Martínez-García et al., 2011;Mauffret et al., 2007;Pedrera et al., 2011). Its recent activity is supported by a prominent fault scarp, brittle structures in recent deposits, and coastline deformation. ...
... The seismogenic NNE-SSW sinistral onshore basement fault is probably the most active one in the whole regionthough it does not crop outand acts as a transfer fault for the recent N-S shortening orthogonal to the coastline shown by GPS data (Palano et al., 2013). This sinistral NNE-SSW fault zone (Fig. 2) would extend into the Alboran sea (d' Acremont et al., 2014;Mauffret et al., 2007;Pedrera et al., 2011), affecting shallow crustal levels and bounding the western part of the Alboran ridge (Martínez-García et al., 2011). ...
... In the northeastern Rif, N-S normal and normal-oblique faults develop mainly along the coastal strip of northward continental crustal thinning, to accommodate E-W extension in a setting of vertical to N-S compression. Fault activity extends towards the thin continental crust of the Alboran Sea (d' Acremont et al., 2014;Mauffret et al., 2007) and connects with the so-called Al Idrisi faults and Alboran ridge active structure (Martínez-García et al., 2011). Southwards, however, slip along main fault surfaces decreases progressively up to the fault tips, probably due to increased crustal thickness (Fullea et al., 2007), which, in turn, gives rise to a more resistant area that produces a change in the deformation features. ...
... The fault activity of the northern flank of the Alboran and Xauen Seamounts is clear, as is that of the minor Adra margin fault anticline. A vertical secondary transpressive component has been identified in the central segment of Al Idrissi fault, while a transtensive component characterizes the Yusuf-Habibas fault, with an associated pull-apart basin (Mauffret et al. 2007). Faults of this WNW-ESE family include the Averroes fault zone (Estrada et al. 2018a). ...
... The Yusuf-Habbibas fault zone, which corresponds to the eastern boundary of the Alboran Ridge indenter(Estrada et al. 2018a), features a 175 km-long right-lateral strike-slip fault with a transtensional component, divided into two segments. Its morphology is marked by the main rectilinear escarpment with a relief ranging from 800 to 2000 m, plus a pull-apart basin in the relay zone of the two segments(Mauffret et al. , 2007 Gómez de la Peña et al. 2018). ...
... The fault activity of the northern flank of the Alboran and Xauen Seamounts is clear, as is that of the minor Adra margin fault anticline. A vertical secondary transpressive component has been identified in the central segment of Al Idrissi fault, while a transtensive component characterizes the Yusuf-Habibas fault, with an associated pull-apart basin (Mauffret et al. 2007). Faults of this WNW-ESE family include the Averroes fault zone (Estrada et al. 2018a). ...
... The Yusuf-Habbibas fault zone, which corresponds to the eastern boundary of the Alboran Ridge indenter(Estrada et al. 2018a), features a 175 km-long right-lateral strike-slip fault with a transtensional component, divided into two segments. Its morphology is marked by the main rectilinear escarpment with a relief ranging from 800 to 2000 m, plus a pull-apart basin in the relay zone of the two segments(Mauffret et al. , 2007 Gómez de la Peña et al. 2018). ...
The Gulf of Cadiz and the Alboran Sea are characterized by tectonic activity due to oblique convergence at the boundary between the Eurasian and Nubian plates. This activity has favored a variety of tsunamigenic sources: basically, seismogenic faults and submarine landslides. The main tsunamigenic faults in the Gulf of Cadiz would comprise the thrust systems of Gorringe Ridge, Marquês de Pombal, São Vicente Canyon, and Horseshoe faults with a high susceptibility; meanwhile in the Alboran Sea would be the thrust system of the northern Alboran Ridge with high susceptibility, and the thrust systems of north Xauen and Adra margin, the transpressive segment of Al Idrissi fault, and the Yusuf-Habibas and Averroes faults, with moderate to high susceptibility. The areas with the greatest potential to generate tsunamigenic submarine landslides are in the Gulf of Cadiz, the São Vicente Canyon, Hirondelle Seamount, and Gorringe Ridge; and in the Alboran Sea are the southern and northern flanks of Alboran Ridge. Both sources are likely to generate destructive tsunamis in the Gulf of Cadiz, given its history of bigger earthquakes (>7 Mw) and larger landslides. To fully assess tsunamigenic sources, further work needs to be performed. In the case of seismogenic faults, research focus on geometry, offsets, timing, paleoearthquakes, and recurrence, and in landslides on early post-failure evolution, age, events, and recurrence. In situ measurements, paleotsunami records, and long-term monitoring, in addition to major modeling developments, will be also necessary.
... Cependant, il a été aussi proposé qu'une partie du bassin d'Alboran (la partie Ouest (WAB)) se soit formée en avant-arc (e.g. Mauffret et al., 2007 Chalouan et al. (2008) ...
... Cette importante compression a été enregistrée dans les Bétiques orientales (par exemple, Weijermars et al., 1985 ;Galindo-Zaldívar et al., 1993 ;Augier et al., 2013 ;Do Couto, 2014), et dans les Bétiques occidentale (par exemple Crespo-Blanc et al., 2016). Cet événement de compression est également reconnu en mer dans le bassin d'Alboran où il résulte d'un plissement WSW-ENE (Chalouan et al., 1997(Chalouan et al., , 2006Mauffret et al., 2007 ;Crespo-Blanc et al., 2016 ;Do Couto et al., 2016 ;Estrada et al., 2016). ...
https://theses.fr/2021COAZ4034 All rights are reserved.
Located at the extreme tip of the western Mediterranean, the Betic-Rif orogenic system is built through a complex alpine orogenic history involving processes of subduction related to the convergence between Africa and Eurasia since the Cretaceous. A remarkable discovery during the last four decades of geological investigations, has been the remains of a variscan event in the internal zones of the belt. These results underline the presence of two superimposed orogenic systems, the internal zones of the belt thus remain a privileged area to study the importance of the structural and the metamorphic heritage in the partial or the total reactivation by the most recent events. This work is located in the Beni Bousera sector, where crustal and mantle rocks that form the innermost units of the chain are exposed. Based on structural and petrological analyses, U-Th-Pb dating on monazite and 40Ar-39Ar dating on micas and amphiboles. The history of the Betic-Rif belt can be summarized as it follows: 1) a HP-HT event affects the base of the internal domain at around 281 ± 3 Ma. These new petrological and geochronological data obtained in the internal Rif, are correlated with the Betics, the Kabyle, the Edough massif of Algeria, the Mauritanian, and the Appalachian belts, attesting a convergent domain during the late Carboniferous – early Permian. All these orogenic segments are part of the North African Variscides built at the north-western margin of Gondwana in response to convergence between the later and Laurentia. 2) at around 29-26 Ma, a Barrovian to Abukuma metamorphic event affects the Sebtides (the innermost units of the chain) and interpreted as the evolution of the upper plate of a subduction zone. This alpine event is typically characterized by a prograde metamorphic path marked by heating affecting the base of the Sebtides between 26 to 22 Ma, such conditions reflect thinning and heating of the crust related to the asthenosphere upwelling due to slab roll-back. This event marks the beginning of a major extensive event. 3) In the Miocene around 22-20 Ma, the internal zones are affected by an E-W extension contemporary to the opening of the Alboran Basin in a back-arc context, and the intrusion of granitic dykes into the peridotites and the crustal metamorphic units, the exhumation of the Sebtides was complete at this time. 4) From early to middle Miocene, the Betic-Rif belt acquired its arcuate geometry (the Gibraltar Arc) during the collision between the Internal and the external zones, attested by NE-SW to E-W shortening phases across the arc. 5) more lately prior to Pliocene, the Gibraltar arc was subjected to contractional processes related to a N-S shortening phase, which drastically altered its geometry.
... This fault zone connects southwards with the active onshore faults of the Al Hoceima region and the southwestern Rif deformation (Chalouan et al., 2014;d'Acremont et al., 2014;Galindo-Zaldívar et al., 2015;Lafosse et al., 2018), and northwards with the active faults of the Adra region in southern Iberia Galindo-Zaldívar et al., 2013) and the Eastern Betic Shear Zone by means of La Serrata-Carboneras Fault (Gràcia et al., 2006;Borque et al., 2019). The right-lateral strike-slip family corresponds to the Yusuf Fault (Mauffret et al., 2007;Martínez García et al., 2017), connected to the east with the Algerian compressive region, which accomodates the current deformation between Nubia and Eurasia (Vázquez et al., 2021b). ...
... The Yusuf Fault Zone (YF) is a right-lateral strike-slip fault with a transtensional component (Figure 7). It is 175 km long and 15 km wide and is divided into two main segments separated by a relay zone Mauffret et al., 2007;Gràcia et al., 2014;Gómez de la Peña et al., 2016). The fault zone is characterized by the development of several strike-slip faults with a general transtensive geometry. ...
The aim of this work is to make a synthesis at regional scale focused on the geophysical characterization of submarine faults around the Iberian margin to identify active structures and analyze their development in the framework of the present plate organization. Most of these submarine faults show seabed morphological expressions mapped with high-resolution swath bathymetry data, high-resolution parametric sub-bottom profiles and multichannel seismic profiles. Present active tectonics, deformation, seismicity, and tsunami-affected coastal areas is mainly focused on south Iberia at the Eurasian and Nubia plate boundary. Submarine active faults in these areas are represented by long strike-slip fault systems and arcuate fold-thrust systems. Their development takes place in response to present NW-SE convergence between the Eurasian and Nubia plates. We propose a strain partitioning model of the plate boundary into simple and pure shear zones to explain the distribution and mechanisms of active submarine faults along the Gulf of Cádiz, Gibraltar Arc and Alborán Sea in response to the present-day shear stress orientation. Nevertheless, deformation is also focused in the NW Iberian margin. Thus, along the Galician and Portuguese margin, several submarine faults mapped as thrust fault systems with high-seismic activity along the Iberian ocean-continent transition reflect the re-activation of former structures. We suggest that submarine active faults in the NW and W Iberia are also the response to the eastwards transfer of short-offset transform faults of the Mid Atlantic Ridge into the oceanic Iberian along a weakness as the former plate boundary between the oceanic Iberia and Eurasia domains. The distribution and activity of submarine faults mapped in this work from geophysical and bathymetric data are in good agreement with geodetic data and focal mechanisms.
... (1) la première hypothèse considère une ouverture E-W Mi-Miocène, avec formation d'une croûte océanique à l'ouest du Centre d'accrétion formée par la ride d'Hannibal entre 16 et 8 Ma Mauffret et al., 2007a ;Camerlenghi et al., 2009]. Selon cette hypothèse, l'ouverture du bassin est associée à la migration vers l'ouest de l'Arc de Gibraltar, et est postérieure à la collision des Kabylies avec le Nord de l'Afrique (Fig I.28 (2) la seconde hypothèse se base sur une ouverture N-S à NO-SE, en position arrière-arc à l'arrière de la zone de subduction de la Téthys Alpine qui migre alors vers le S-SE [Frizon de Lamotte et al., Si l'on considère qu'à cet époque le domaine d'AlKaPeCa est rattaché au Promontoire Baléares, cet épisode serait relié à l'initiation ou à l'accélération de la subduction de l'océan téthysien sous la paléomarge nord téthysienne [Frizon de Lamotte et al., 2000 ;Roca et al., 2004]. ...
... Until now, no unequivocal interpretation of magmatic anomalies, rifting mechanisms (symmetric, asymmetric), direction and rate of opening have been proposed for the Algerian basin and surrounding margins [Schettino and Turco, 2006 ;Mauffret et al., 2007a, and can thus induced asymmetry of the OCT between conjugated margin. For margins formed in a backarc position, the transition zone at the passive margin born on the same side of the subduction zone with respect to the extended area, seems thus to be narrower than the transition zones formed on the other side, which can partially explain the sharp OCT found in this study at the Algerian margin. ...
L'inversion des marges passives apparaît comme le premier stade vers l'initiation de nouvelles zones de subduction. Cette étape cruciale dans la tectonique des plaques soulève néanmoins encore de nombreuses questions. L'étude des marges actuellement réactivées en compression apparaît ainsi comme essentielle pour mieux comprendre ce processus. Ces marges sont peu nombreuses, situées dans des contextes géodynamiques variés, et les facteurs déterminant leur évolution mal contraints. Située au nord de l'Afrique, la marge algérienne fait partie de ces rares exemples potentiels à travers le monde. L'évolution de cette marge formée au Miocène en contexte d'arrière-arc s'intègre dans le puzzle complexe de l'histoire de la Méditerranée occidentale. Elle est depuis quelques millions d'années réactivée en compression dans le cadre de la convergence lente entre les plaques européenne et africaine, générant un potentiel sismogène fort au nord de l'Algérie. La relative jeunesse du bassin algérien, la charge sédimentaire, les forces aux limites compressives, constituent des conditions favorables à la formation d'une future subduction. A la suite des travaux menés depuis une dizaine d'années, les principales lacunes de connaissances identifiées portent sur (1) la structuration profonde du bassin algérien et de sa marge sud (type de marge, nature du socle,dimension et nature de la transition océan-continent, style et distribution de la déformation compressive), et (2) l'histoire de l'évolution cinématique et géodynamique du bassin, ce qui limite à l'heure actuelle une analyse approfondie des modalités d'inversion de cette marge. L'étude menée se focalise sur la marge centre-algérienne, dans le secteur de Tipaza (à l'ouest d'Alger), un endroit clé pour la compréhension des mécanismes d'ouverture du bassin algérien. Le traitement et l'analyse de nouvelles données de sismique profonde grand-angle et multitraces acquises dans le cadre du projet franco-algérien SPIRAL (Sismique Profonde et Investigations Régionales en Algérie, 2009) ont notamment permis de déterminer la structure crustale du bassin algérien et de sa marge sud, ainsi que la structuration pseudo-3D d'une structure spécifique au secteur d'étude constituée par le haut topographique sous-marin de Khayr-al-Din. L'analyse de la structure profonde de la marge indique un certain nombre de structures héritées de son évolution complexe : (1) une croûte de nature continentale de plus de 15 km d'épaisseur sur le haut de marge (banc de Khayr-al-Din), (2)une croûte fine de nature océanique de 5-6 km d'épaisseur dans le bassin incluant des vitesses légèrement élevées à sa base (7,2 km/s - 7,3 km/s), (3) des similitudes avec des marges formées dans des contextes de déformation transformante, (4) un approfondissement progressif de l'ensemble de la pile sédimentaire et l'épaississement des sédiments Plio-Quaternaire, depuis le bassin profond distal vers le pied de marge,coïncidant avec (5) une flexuration à grande longueur d'onde du socle. Les résultats obtenus apportent de nouvelles contraintes sur (1) la géométrie et la nature de la marge et du bassin, (2) l'évolution de la marge,suggérant une histoire multiphasée comprenant un stade de rifting et/ou d'accrétion océanique, suivi d'un épisode de déformation coulissante tardive liée à la migration du bloc Alboran vers l'ouest, et d'une reprise en compression distribuée du bassin profond au haut de la marge au Plio-Quaternaire; (3) les modalités de réactivation qui se traduisent par des chevauchements aveugles néoformés à pendages sud, notamment au pied du banc de Khayr-al-Din, suggérant un soulèvement du banc de 0,2 mm/an à 0,75 mm/an au Plio-Quaternaire et un début d'écaillage crustal.
... This subsidence is coeval with the uplift of the surrounding areas including the Alboran ridge at the northern edge of the basin (Comas et al., 1999). Pliocene to Quaternary extensional to transtensional deformation occurred throughout the offshore basin (Comas et al., 1999;Mauffret et al., 2007;Martinez-García et al., 2012) similar to the onshore part of the basin (Morel, 1988). Consequently, the MES in the offshore SAB is lying deeper at the present-time than it was at the end of the MSC. ...
... Above basement heights, it corresponds to an important, irregular erosion surface. Above Miocene basins, it is a low angle-dipping (b6°) erosion surface with features similar to the ones observed onshore: it is a tilted, flat, smooth surface with very localized and rare incisions, concordant with underlying seismic units (Mauffret et al., 2007;Martinez-García et al., 2012). There, continental deposits are believed to have been deposited before the marine Zanclean flooding (Martinez-García et al., 2012). ...
... In the Alboran Sea and the Gulf of Cadiz, a variety of tsunamigenic sources have appeared as a result of the oblique convergence of the Eurasian and Nubian plates (Vázquez et al., 2022), despite the modest annual deformation rate of about 4.7 mm (McClusky et al., 2003;Serpelloni et al., 2007;Stich et al., 2006). According to geophysical and geomorphological data, the presence of fractures and faults testifies to the possibility and capacity to generate large earthquakes (Ballesteros et al., 2008;Gràcia et al., 2006;Maestro-González et al., 2008;Mauffret et al., 2007). These tsunamigenic sources, such as the Al Idrissi fault and the Yusuf-Habibas and Averroes faults, have a moderate to high probability to generate tsunamis (Vázquez et al., 2022). ...
The Mediterranean coast of Morocco is potentially exposed to tsunamis, such as the one triggered by the Algerian Djijelli earthquake in 1856, also known as the most destructive event in the region. This type of coastal hazard could have disastrous effects on several cities along the Mediterranean coast, such as Martil, which is located near the main sources of tsunamis in the Alboran Sea and receives large numbers of national and international tourists each year. This work intends to simulate the potential tsunami of Averroes faults, corresponding to a magnitude Mw = 7.0 earthquake and to estimate the property and life losses. We used the Nonlinear Shallow Water with Nested Grids (NSWING) code integrated into Mirone software to simulate the tsunami phenomenon, combining a series of bathymetric and topographic grid layers with an initial water elevation generated using Mansinha formulations and assuming instantaneous seabed motion. For this investigation, we considered a scenario associated with a potential seismic source for the Averroes fault located in the Alboran Sea. The simulation results obtained reveal that the maximum water height at the regional scale of the Alboran Sea exceeds 1 m. On the other hand, on a local scale in the study area of the Martil city, the flow depth varies between 0.5 and 7 m, with a flooded surface area of 70 km². In addition, the arrival time of the first tsunami waves exceeds 40 min. Material losses could reach 3.72 M$, while the loss of life could be as high as 31,000 victims. The results should be useful to policymakers in developing tsunami protection and raising coastal community awareness of tsunami risks in Morocco.
... From Burdigalian on compressive tectonics should shift to the MFB and the External Riz Zone (ERZ) (Maaté et al., 2017;Martín-Martín et al., 2022). In the IRZ a strike-slip faults phase as main responsible of the new sedimentari basins during middle-late Miocene was proposed (Mauffret et al., 2007). This phase would be partially contemporaneous of late Miocene wedge-top basins In the ERZ (Abbassi et al., 2021). ...
... The complexity of the evolution of the Alboran domain results in several debates focusing on the Tertiary kinematics of the Alboran block (timing and amount of Westward displacement if indeed existing) [e.g. Gueguen et al., 1998;Mauffret et al., , 2007Duggen et al., 2004;Platt et al., 2006] and the amount, timing, and nature of the magmatic and volcanic activity that has considerably (and extensively) modified and altered the crustal structures [e.g. Duggen et al., 2004;Booth-Rea et al., 2007], and thus may mask the importance of tectonic features and the nature of the basement [Medaouri et al., 2014]. ...
... 5.4 and 5.10). It is the thickest sedimentary depocenter in the Alboran Basin, estimated to lie at a depth between 10 and 12 km (Soto et al. 1996(Soto et al. , 2010Mauffret et al. 2007;Iribarren et al. 2009;Do Couto et al. 2016). Its geometry in plain view is arched, its axis mimicking the arcuate geometry of the orogenic arc, forming a curvilinear "bean" shape that continues toward the north to a secondary E-W basin. ...
... In the Eastern Alboran Sea, we have identified a boundary segment (B8 in Fig. 8) that follows the transcurrent Yusuf fault system (Mauffret et al., 2007). This segment, which is mostly inferred from seismological data reported in Table 1 and is characterized by a right-lateral transpressive kinematics, mostly coincides with the previous boundary proposed by DeMets et al. (2010) (Fig. 8). ...
In the western Mediterranean, following the intervening continent-continent collision, the subduction of the Tethyan ocean has progressively come to an end or almost in large sectors. Compressional deformation connected with the ongoing Africa–Eurasia convergence has therefore progressively resumed mostly along the southern passive margins of the Mediterranean back-arc basins. The aim of this paper is to trace this nascent boundary and constrain its kinematics through geodetic and seismological data recorded between the Ionian Sea and Gulf of Cadiz, and through pre-existing tectonic data. Based on these data, the nascent plate boundary is drawn, kinematically defined, and compared with the previously identified boundaries in the same region. The nascent boundary is weaving and formed by variably oriented inherited structures. It is characterized by a discrepancy between the general motion of Africa with respect to Eurasia and the local contractional/compressive axes deduced from geodetic and seismic data. The oblique convergence along the nascent boundary matches that recorded in other instances of subduction initiation elsewhere; however, the average convergence rate (∼5mm/yr) in the Mediterranean seems currently too small for such a subduction initiation. Based on the assumption of a future northward tectonic vergence (i.e., Eurasian foreland), the Tyrrhenian, Algerian, and Betic salients, the Oran and Fès recesses, and the Ionian, Trans-Alboran, and Gibraltar transfer zones are identified along the nascent boundary. The latter zones connect salients and recesses through strike-slip displacements. The Algerian offshore hosts a long segment of the boundary characterized by locally increased seismic rate and actual northward vergence that would suggest this area being the first nucleus of subduction initiation in the western Mediterranean, as was previously proposed.
... The geometry and nature of the crust and lithosphere of this region are not well defined due to the scarcity of geophysical data and the difficulty to unambiguously interpret them, particularly onshore. Offshore studies show that the crust of the Algerian Basin is mainly oceanic with an approximate thickness of about 6 km overlaid by 3-km-thick Neogene sedimentary cover (e.g., Vidal et al., 1998;Mauffret et al., 2004;Mauffret et al., 2007;Leprêtre et al., 2013;Medaouri et al., 2014;Aïdi et al., 2018). ...
The geodynamic evolution of the Western Mediterranean related to the closure of the Ligurian-Tethys ocean is not yet fully resolved. We present a new 3D numerical model of double subduction with opposite polarities fostered by the inherited segmentation of the Ligurian-Tethys margins and rifting system between Iberia and NW Africa. The model is constrained by plate kinematic reconstructions and assumes that both Alboran-Tethys and Algerian-Tethys plate segments are separated by a NW-SE transform zone enabling that subduction polarity changes from SE-dipping in the Alboran-Tethys segment to NW-dipping in the Algerian-Tethys segment. The model starts about late Eocene times at 36.5 Ma and the temporal evolution of the simulation is tied to the geological evolution by comparing the rates of convergence and trench retreat, and the onset and end of opening in the Alboran Basin. Curvature of the Alboran-Tethys slab is imposed by the pinning of its western edge when reaching the end of the transform zone in the adjacent west-Africa continental block. The progressive curvature of the trench explains the observed regional stress reorientation changing from N-S to NW-SE and to E-W in the central and western regions of the Alboran Basin. The increase of the retreat rates from the Alboran-Tethys to the Algerian-Tethys slabs is compatible with the west-to-east transition from continental-to-magmatic-to-oceanic crustal nature and with the massive and partially synchronous calc-alkaline and alkaline magmatism.
... The Alboran Sea was formed due to westward Tethyan slab retreat (Calvert et al., 2000;Jolivet et al., 2008;Platt et al., 2003;Spakman and Wortel, 2004;Do Couto et al., 2016;d'Acremont et al., 2020) within a compressive context of the African-European convergence since the end of the Oligocene (Comas et al., 1999;Gutscher et al., 2002;Jolivet et al., 2009;Mauffret et al., 2007;Mauffret et al., 1992). Above the metamorphic and volcanic basement, a thick Miocene depocenter is located in the western basin where mud volcanoes and other shale tectonic processes affect the seafloor ( Fig. 1) (Pérez-Belzuz et al., 1997;Comas et al., 1999). ...
Earthquakes are the most commonly cited cause of offshore slope failure, followed by high sedimentation rates and ensuing pore pressure build-up. In the South Alboran Sea, the moderate seismicity (Mw = 6.4) of the strike-slip Al Idrissi Fault Zone does not appear to control directly the landslides distribution. To provide a preliminary geohazard assessment, we characterized the spatial distribution, the volume and the ages of the submarine landslides from multibeam and seismic reflection data in the southern part of the Alboran Sea. Since the Quaternary numerous submarine landslide processes have affected the marine sedimentary cover with volumes of the mass transport deposits (MTD) estimated between 0.01 and 15 km³. West of the Al Idrissi Fault Zone, along the South Alboran Ridge's northern flank, the distribution of the MTD follows the SW-NE bank and ridge trend that correlates with blind thrusts and folds covered by a plastered contourite drift. A pockmark field, related to fluid escape, is visible near landslide scars where the contourite drift is relatively thicker. In this area, landslide scars occur on variable slopes (2–24°) and their associated MTDs show variable decompacted volumes (0.01-10 km³). East of the Al Idrissi Fault Zone, between the Alboran Ridge and the Pytheas Bank, the mapped MTDs have uneven volume. The smaller ones (<1 km³) have their slide scars on steep slopes (>10°), whereas those of the largest ones (3–15 km³) occur on gentler slopes (<5°).
These observations and a slope stability analysis suggest that the combination of seismic shaking, blind thrusts activity, relatively high sedimentation rate of contourite deposits with potential weak layers, and fluid escape dynamics are likely the main controlling mechanisms. These causal factors would explain the concentration of landslide head scarps at the edge of the thickest parts of the contourite drifts (i.e. crest). Slides may have been controlled locally by fluid overpressures in line with blind thrusts. Additionally, low to moderate seismicity potentially triggered by nearby faults might regionally have played a role in destabilising the landslides since 1.12 Ma (Q2 unit), which coincides with the propagation of the Al Idrissi Fault Zone in the southern Alboran Sea.
... Mesozoic and Tertiary sedimentary rocks of the Maghrebian (Rif and Tell) continental paleomargins (Mauffret et al., 2007 ;Chalouan et al., 2008 ;Frets et al., 2014 and reference therein). According to geochronological studies of peridotites and pyroxenites, as well as their metamorphic country rocks, the Beni Bousera peridotite massif was exhumed and emplaced into the continental crust formations between 19 and 23 Ma owing to rapid extension that produced an extremely attenuated continental lithosphere in the westernmost Mediterranee (e.g., Afiri et al., 2011 ;Van Hinsberger et al., 2014 ;Frets et al., 2014). ...
This paper explores the unusual sulphide–graphite association of a selection of Beni Bousera garnet clinopyroxenites that initially equilibrated within the diamond stability field. Compared with common graphite-free garnet pyroxenites analysed so far, these rocks display tenfold S enrichment with concentrations up to 5550 μg g–1. Fe–Ni–Cu sulphides (up to 1·5 wt%) consist of large (up to 3 mm across), low-Ni pyrrrhotite (<0·1 wt% Ni) of troilite composition, along with volumetrically minor chalcopyrite and pentlandite. Such assemblages are interpreted as low-temperature (<100 °C) subsolidus exsolution products from homogeneous monosulphide solid solution. Troilite compositions of the pyrrhotite indicate strongly reducing conditions that are estimated to be slightly above the iron–wüstite (IW) buffer. Bulk-sulphide compositions are closer to the FeS end-member (i.e. Cu- and Ni-depleted) than other sulphide occurrences in mantle-derived pyroxenites described so far. Moreover, troilite contains trace metal microphases (Pb and Ag tellurides, molybdenite) that have never been reported before from mantle-derived garnet pyroxenites but occur in diamond-hosted eclogitic sulphide inclusions. Beni Bousera sulphides also show strong similarities to diamond-hosted sulphide inclusions of eclogitic affinity for a wide range of chalcophile–siderophile trace element contents. In view of the widespread molybdenite exsolution, coupled with Mo and S/Se/Te systematics of sulphide compositions (7872 < S/Se < 19 776; 15 < Se/Te < 31), black-shale pyrite is a potential sedimentary component to contribute to the petrogenesis of Beni Bousera garnet clinopyroxenites. Black shales would have recycled along with cumulates from the oceanic crust in the mantle source of Beni Bousera pyroxenites. Pyrite underwent desulfidation and replacement by troilite during subduction and prograde metamorphism, releasing its fluid-mobile elements (As, Sb, Pb) while suffering minimum S loss because of the strongly reduced conditions. Taken as a whole, our body of data supports a common origin for carbon (−27 ‰ < δ13C < −17 ‰) and sulphur and concomitant formation of diamond and sulphides. Both elements were delivered by an extraneous sedimentary component mixed with the altered oceanic crust rocks that was involved in the genesis of Beni Bousera garnet pyroxenites, prior to a Proterozoic partial melting event.
... 5.4 and 5.10). It is the thickest sedimentary depocenter in the Alboran Basin, estimated to lie at a depth between 10 and 12 km (Soto et al. 1996(Soto et al. , 2010Mauffret et al. 2007;Iribarren et al. 2009;Do Couto et al. 2016). Its geometry in plain view is arched, its axis mimicking the arcuate geometry of the orogenic arc, forming a curvilinear "bean" shape that continues toward the north to a secondary E-W basin. ...
The Alboran Basin is a Neogene-Quaternary extensional basin located within the Betic-Rif alpine cordillera. The region where the current basin is located holds great oceanographic relevance, as it lies in the area of connection between the western (Atlantic Ocean basin) and eastern seas (ocean basins of the Ligurian Tethys and then Western Mediterranean Sea) of Iberia. The extensional collapse of the Eocene Alpine orogen led to the crustal thinning and formation of the Western Mediterranean basin and the splitting of lithospheric fragments, the Alboran Domain among them, along its margins. The N-S convergence of the African and Eurasian plates, together with the westward escape of the Alboran Domain and its extensional tectonics in the back-arc region linked to the retreat of a subduction zone northwestward has determined the basin’s formation and evolution since the upper Oligocene to Tortonian times. The stretching of the continental crust produced its configuration, creating several sub-basins and tectonic highs, and was accompanied by an important magmatic phase that peaked in the middle-late Miocene. The direction of African-Eurasian convergence evolved to NW-SE in the late Tortonian and is presently WNW-ESE, producing an inversion of the basin in its interior, with the uplift of main reliefs (e.g., the Alboran Ridge), and a progressive elevation of adjacent mountain ranges in southern Iberia (Betic) and northern Africa (Rif), substantially reducing the basin’s width. During this phase, convergence is resolved with an indentation tectonic model in the central Alboran Sea; and to accommodate this deformation, two conjugated sets of dextral WNW-ESE and sinistral NE-SW to NNE-SSW faults are generated. The sedimentary infill of the Alboran Basin consists of unconformable Miocene to Quaternary deposits controlled by the tectonic deformation and paleoceanography. Two important events marked the sedimentary evolution: Messinian desiccation and the opening of the Strait of Gibraltar.
... This widespread compression has been recorded in the Eastern Betics (e.g., Weijermars et al., 1985;Galindo-Zaldívar et al., 1993;Augier et al., 2013;Do Couto, 2014), in the Western Betics (e.g., Crespo-Blanc et al., 2016), in the Alboran Domain (e.g., Do Couto et al., 2016). This compression event is also recognized offshore in the Alboran Basin where it results in WSW-ENE folding (Chalouan et al., 1997Mauffret et al., 2007;Crespo-Blanc et al., 2016;Do Couto et al., 2016;Estrada et al., 2017). ...
Located in the Internal domain of the Rif belt, the Beni Bousera massif is characterized by a stack of peridotites and crustal metamorphic units. The massif is intruded by granitic dykes and affected by several normal ductile shear zones. Structural, petrological and ⁴⁰ Ar– ³⁹ Ar dating analyses performed on these two elements highlight that (1) the granitic dykes are emplaced within major N70° to N140° trending normal faults and shear zones, resulted from an NNE-SSW extension (2) the Aaraben fault in its NE part is characterized by N70° to N150° trending ductile normal shear zones, resulted from a nearly N-S extension and (3) the age of this extensional event is comprised between 22 and 20 Ma. Available paleomagnetic data allow a restoration of the initial orientation of extension, which was nearly E-W contemporary with the Alboran Basin opening in back-arc context, during the Early Miocene. At the onset of the extension, the peridotites were somehow lying upon a partially melted continental crust, and exhumed during this event by the Aaraben Normal Shear Zone. Afterward, the Alboran Domain suffered several compressional events.
... The evolution of the Western Mediterranean basin ( Fig. 1) has been started since the late Cretaceous by the slow oblique NW convergence between Africa and Eurasia plates (Le Pichon et al., 1988;Dewey et al., 1989;McClusky et al., 2003;Serpelloni et al., 2007;Billi et al., 2011;Faccenna et al., 2001;Frizon de Lamotte et al., 2009;Gueguen et al., 1998;Mauffret et al., 2007;Meghraoui and Pondrelli, 2012;Morgan et al., 1998;Rosenbaum et al., 2002). In North Africa, the result of this convergence is a large fold-thrust belt bordered to the South by the stable Saharan Platform. ...
... 1A and 4A). The branch is funnelled within the Al-Hoceima Valley ( Ercilla et al., 2016), which represents a passage created between the Moroccan continental margin and the aligned seamounts (e.g., Ammar et al., 2007) (Figs. 1B and 4A). ...
This is an interdisciplinary study that combines morphoseismics, sedimentology and numerical modelling to elucidate at different scales of resolution the influence of alongslope processes on the turbidite systems (TSs) and canyons in the Alboran Sea (southwestern Mediterranean). Nine TSs are mapped in the Spanish margin (La Linea, Guadiaro, Baños, Torrenueva, Fuengirola, Salobreña, Sacratif, Calahonda and Almeria) and two in the Alboran Ridge (Piedra Escuela and Al-Borani). In the Moroccan margin, there are only two canyons (Ceuta and Nekor). Distinctive morphoseismic and sedimentological signatures from TSs and canyons have enabled three regional models of alongslope influence to be distinguished: a) Alongslope processes are dominant. This scenario characterizes the canyons of the Moroccan margin. The diagnostic signature is the lack of leveed channels and lobes at the Ceuta and Nekor Canyon mouths. b) Different degrees of interplay exist between alongslope and downslope processes. This scenario occurs in the TSs of the western Spanish margin. Here, the alongslope influence on TSs (La Linea, Guadiaro, Baños, Torrenueva and Fuengirola) is evidenced by the lack of overbank deposits in the La Linea and Guadiaro Canyons and an alongslope trend in the morpho-architecture of the channelized lobes and in the textural distribution of canyon/channel deposits (mass-flow deposits and turbidites). Both signatures indicate sandier TSs as well as Bouma turbidite sequences lacking the finest levels towards the Strait of Gibraltar. Local intercalations of contourites are also present in the Guadiaro lobe deposits. c) Downslope processes are dominant. This scenario characterizes the TSs of the eastern and central Spanish margin and Alboran Ridge. There, TSs seem to be controlled solely by the characteristics of the downslope gravity flows that transport sediment. The hydrodynamic and sediment dispersion models confirm that the main oceanographic factors governing the variable alongslope influence in TSs and canyons are the following: a vigorous WMDW flow along the Moroccan margin and the energetic Atlantic Jet, western Atlantic anticyclonic gyre and general acceleration of the Mediterranean waters towards the Strait of Gibraltar, along the western Spanish margin. This study demonstrates the pivotal role that alongslope processes can play in the onset and formation of TSs and canyons at continental margins.
... This plate boundary extends from the western Azores triple junction through the Gloria Fault, located westwards of the Gorringe Bank, and continues eastwards into the Gulf of Cadiz along the SWIM fault zone as suggested by recent models (Zitellini et al., 2009). This fault zone connects with the Rift-Tell System on the southern boundary of the Mediterranean Orogenic Belt (Mauffret et al., 2007;Zitellini et al., 2009;Cunha et al., 2012;Rosas et al., 2012) (Fig. 1). Recently it has been proposed that in the south-western Iberia margin a new subduction zone of the Atlantic oceanic crust beneath Iberia may be forming, resolved with northwestern verging thrusts of the Gorringe Bank and the Horseshoe Abyssal Plain and connected by the SWIM fault zone to the Betic-Rif orogen (Duarte et al., 2013). ...
... The western Mediterranean underwent a complex Alpine tectonic evolution that mainly consisted of oceanic subduction initiation, slab fragmentation, and slab rollback during convergence between Africa and Europe (Royden, 1993;Chalouan & Michard, 2004;Faccenna et al., 2004;Mauffret et al., 2007;Platt et al., 2013;van Hinsbergen et al., 2014). In the westernmost Mediterranean, the Alpine orogeny shaped the Gibraltar arc, which is bounded by the Betic, Rif and Tell belts that surround the Albor an and Algerian-Provenc¸al basins (Fig. 1a). ...
Correlations between major and minor transition elements in tectonically emplaced orogenic peridotites
have been ascribed to variable degrees of melt extraction and melt–rock reaction processes,
leading to depletion or refertilization. To elucidate how such processes are recorded in the subcontinental
lithospheric mantle, we processed a large geochemical dataset for peridotites from the
four tectono-metamorphic domains of the Beni Bousera orogenic massif (Rif Belt, northern
Morocco). Our study reveals that variations in bulk-rock major and minor elements, Mg-number
and modal mineralogy of lherzolites, as well as their clinopyroxene trace element compositions,
are inconsistent with simple partial melting and mainly resulted from different reactions between
melts and depleted peridotites. Up to 30% melting at <3 GPa and cryptic metasomatism can
account for the geochemical variations of most harzburgites. In Grt–Sp mylonites, melting and
melt–rock reactions are masked by tectonic mixing with garnet pyroxenites and subsolidus
re-equilibration. In the rest of the massif, lherzolites were mostly produced by refertilization of a
refractory protolith (Mg-number = 91, Ol = 70%, Cpx/Opx = 0.4) via two distinct near-solidus, melt–
rock reactions: (1) clinopyroxene and orthopyroxene precipitation and olivine consumption at
melt/rock ratios <0.75 and variable mass ratio between crystallized minerals and infiltrated melt
(R), which are recorded fairly homogeneously throughout the massif; (2) dissolution of orthopyroxene
and precipitation of clinopyroxene and olivine at melt/rock ratios <1 and R = 0.2–0.3, which affected
mainly the Arie` gite–Seiland and Seiland domains. The distribution of secondary lherzolites
in the massif suggests that the first refertilization reaction occurred prior to the differentiation of
the Beni Bousera mantle section into petro-structural zones, whereas the second reaction was
associated with the development of the tectono-metamorphic domains. Our data support a secondary,
refertilization-related origin for most lherzolites in orogenic peridotite massifs.
... Bathymetry from Smith and Sandwell (1997). Solid thin black lines: SWIM Lineaments; tasz:Trans-Alboran Shear Zone that include the Jebba-N'Kor and Carboneras faults; cafz: Corredor de las Alpujarras Fault Zone (modified after Mauffret et al., 2007). 6b: simplified tectonic sketch of the area; red line: main active faults, black line: inactive faults, arrows: relative motion of Africa with respect to Eurasia. ...
The missing link in the plate boundary between Eurasia and Africa in the central Atlantic is presented and discussed. A set of almost linear and sub parallel dextral strike–slip faults, the SWIM1 Faults, that form a narrow band of deformation over a length of 600 km coincident with a small circle centred on the pole of rotation of Africa with respect to Eurasia, was mapped using a new swath bathymetry compilation available in the area offshore SW Portugal. These faults connect the Gloria Fault to the Rif–Tell Fault Zone, two segments of the plate boundary between Africa and Eurasia. The SWIM faults cut across the Gulf of Cadiz, in the Atlantic Ocean, where the 1755 Great Lisbon earthquake, M ~ 8.5–8.7, and tsunami were generated, providing a new insight on its source location.
... High has been found in the scientific literature. This seamount is part of the Tofiño Bank located in between the Xauen Bank and the Alborán Ridge that corresponds to a fold and thrust belt deforming the sedimentary cover (Bourgois et al., 1992;Mauffret et al., 2007;Ammar et al., 2007;). ...
... According to Schettino & Turco (2010), the Algerian Basin opened during the last phase of rotation of Sardinia and Corsica (19 Ma). An alternative hypothesis is an E-W opening, from 16 to 8 Ma, associated with the westward migration of the Alborán domain (Comas et al. 1992;Platt et al. 1998;Comas et al. 1999;Rosenbaum et al. 2002;Mauffret et al. 2004Mauffret et al. , 2007Booth-Rea et al. 2007;Medaouri et al. 2014; Fig. 1). This second hypothesis is preferred by many authors even if the distance of the westward migration of the Alborán domain is debated and ranges from ∼200 to ∼700 km (Michard et al. 2002;Platt & Houseman 2003;Duggen et al. 2004;Mauffret et al. 2004;Platt et al. 2006;Medaouri et al. 2014). ...
... This decrease in slip rate is supported by the relatively constant sedimentation rates averaged across the Plio-Quaternary time (calculated sedimentation rates from ODP Site 978 are 154 m/Ma for the Upper Miocene, 120 m/Ma for the Lower Pliocene, 111 m/Ma for the Upper Pliocene and 127 m/Ma for the Pleistocene) (Braga and Comas, 1999). These ages are coherent with the ages and rifting phases described for the opening of the western Mediterranean and its later compressive reorganization, which is proposed to have started at around 8 Ma (late Tortonian) (e.g., Mauffret et al., 2007;Billi et al., 2011;Medauri et al., 2012Medauri et al., , 2014Giaconia et al., 2015). ...
... On the Alboran Ridge, the folding of the Messinian Unconformity , and the deformation of younger stratigraphic surfaces , coincident to higher sediment depositional rates in the South Alboran Basin, show tectonic pulses due to regional shortening at 5.33 The Nekor sedimentary basin is located at the southern tip of the TASZ, south of the Al-Idrissi fault (Fig. 1c). Its northern boundary, the Bokkoya fault, has been hypothesized either as a normal left-lateral strike– slip fault (Calvert et al., 1997; El Alami et al., 1998; van der Woerd et al., 2014), or as a normal fault (Mauffret et al., 2007). To the west, the left-lateral Bousekkour– Aghbal fault crosses the shoreline with a N020° direction and offsets the seafloor (d'Acremont et al., 2014). ...
... High has been found in the scientific literature. This seamount is part of the Tofiño Bank located in between the Xauen Bank and the Alborán Ridge that corresponds to a fold and thrust belt deforming the sedimentary cover (Bourgois et al., 1992;Mauffret et al., 2007;Ammar et al., 2007;). ...
General book DOI: http://dx.doi.org/10.2305/IUCN.CH.2015.07.en
... On the Alboran Ridge, the folding of the Messinian Unconformity , and the deformation of younger stratigraphic surfaces , coincident to higher sediment depositional rates in the South Alboran Basin, show tectonic pulses due to regional shortening at 5.33 The Nekor sedimentary basin is located at the southern tip of the TASZ, south of the Al-Idrissi fault (Fig. 1c). Its northern boundary, the Bokkoya fault, has been hypothesized either as a normal left-lateral strike– slip fault (Calvert et al., 1997; El Alami et al., 1998; van der Woerd et al., 2014), or as a normal fault (Mauffret et al., 2007). To the west, the left-lateral Bousekkour– Aghbal fault crosses the shoreline with a N020° direction and offsets the seafloor (d'Acremont et al., 2014). ...
The 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 dataset 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 style of faulting at the southern Alboran Ridge deduced from seismic reflection data reflects complex stress pattern, including southwest-northeast oriented trusting as indicated by folding [e.g., Bourgois et al., 1992;Mauffret et al., 2004Mauffret et al., , 2007Martínez-García et al., 2013]. ...
Seismicity and tectonic structure of the Alboran Sea were derived from a large amphibious seismological network deployed in the offshore basins and onshore in Spain and Morocco, an area where the convergence between the African and Eurasian plates causes distributed deformation. Crustal structure derived from local earthquake data suggests that the Alboran Sea is underlain by thinned continental crust with a mean thickness of about 20km. During the 5months of offshore network operation, a total of 229 local earthquakes were located within the Alboran Sea and neighboring areas. Earthquakes were generally crustal events, and in the offshore domain, most of them occurred at crustal levels of 2 to 15km depth. Earthquakes in the Alboran Sea are poorly related to large-scale tectonic features and form a 20 to 40km wide NNE-SSW trending belt of seismicity between Adra (Spain) and Al Hoceima (Morocco), supporting the case for a major left-lateral shear zone across the Alboran Sea. Such a shear zone is in accord with high-resolution bathymetric data and seismic reflection imaging, indicating a number of small active fault zones, some of which offset the seafloor, rather than supporting a well-defined discrete plate boundary fault. Moreover, a number of large faults known to be active as evidenced from bathymetry, seismic reflection, and paleoseismic data such as the Yusuf and Carboneras faults were seismically inactive. Earthquakes below the Western Alboran Basin occurred at 70 to 110km depth and hence reflected intermediate depth seismicity related to subducted lithosphere.
The Cenozoic sedimentary cover from the Ghomaride Complex (Internal Rif Belt) has been studied in the Tetuan area (N Morocco) where a suite of sedimentary successions from shallow-marine to deep-marine environments crops out. For that purpose stratigraphic relations and petrological and geochemical signatures have been analyzed. Sandstone suites of the overall succession are heterogeneous and testify a multi-source area, in response of accretionary processes of the Ghomaride-Maláguide units and the exhumation of the lower units of the Internal Rif Zone (e.g. Sebtide-Alpujárride Complex). Pre-orogenic and Syn-orogenic (according to the eoalpine phase) deposits have been identified consisting in two depositional sequences: lower Paleocene and Cuisian-Bartonian, and upper Oligocene-upper Aquitanian and lower Burdigalian, respectively. Pre-orogenic deposits are mainly intra-arenite and hybrid arenites made of a minor amount of siliciclastic detritus but with abundance of intrabasinal carbonate grains. The syn-orogenic sandstone suites are quartzolithic, having abundance of low-grade metamorphic and sedimentary lithic fragments. Sedimentary lithic fragments are derived from the Mesozoic successions of the Ghomaride-Maláguide Complex while metamorphic detritus is related to an unknow Internal Rif Zone basement that was exhumed starting from the late Oligocene and mainly early Miocene. Modal analyses of sandstone suites for the extrabasinal grains mainly indicate lower rank metamorphic and sedimentary source terranes of a recycled orogen. Major and trace elements coupled to the mineralogical composition of the mudrock samples indicate a provenance from felsic source area(s) with a minor but not negligible contribution from mafic rocks mainly in the syn-orogenic suites. Geochemical analyses (Al–Ti–Zr ternary plot) indicate minor reworking and recycling processes before the final deposition through prolonged processes of sedimentary transportation. The trends evident in both CIA and CIA’ diagrams indicate source areas characterized by moderate weathering in non-steady-state conditions with a weak change of weathering condition from the pre-orogenic to the syn-orogenic cycle. Deposition during the Paleocene and Eocene, took place in the southern continental margin of the Ghomaride-Malaguide domain as a carbonate ramp. Contrarily, sedimentation in the late Oligocene-late Aquitanian took place in wedge-top basins within the Ghomaride-Malaguide domain. These changes occurred during the Burdigalian, when back arc basins were developed in the Internal Betic-Rif Zone. The Cenozoic reconstructed record was contemporaneous of the structuring of the Circum-Mediterranean chains and the Ghomaride-Maláguide Complex played a key role in the geodynamic evolution of the Rif Cordillera, representing a key tectonic element of the western Mesomediterranean domains.
The Al-Hoceima region is threatened by tsunami hazard because of its location in the coastal area of the Mediterranean Sea, besides the shallow seismically active region south of the Alboran Sea. Therefore, the current study presents a novel model to map coastal flooding potential zones due to tsunami wave run-up in Nekor bay using three natural parameters (distance from coastline, altitude and slope) in a geographic information system (GIS) environment. Furthermore, the coastal flooding simulation using 4 scénarios (1m, 2m, 3m, 4m) based on the run-up elevation according to tsunami wave elevation (TWE) literature of the study area is used to confirm the DAS model result, and to estimate the potential impacts. The result of the DAS model revealed that 1 km from the coast to the Nekor plain is the most exposed to the impact of tsunamis generated south of the Alboran Sea. The coastal flooding simulation confirmed the DAS result, and the damage estimation of the urban area and the agriculture was respectively 2 and 98% for run-up 1 m, 3% and 97% for run-up 2m, 4% and 96% for run-up 3m, and for the worst case scenario of 4 m was 3% and 97%. Therefore, the results obtained show that the major potential impact of coastal flooding in Nekor plain is the salinization of agricultural land. Finally, we propose a sustainable solution utilizing a controlled forest along the coast to reduce future tsunami impacts on Nekor bay.
This thesis consists of six chapters that deal with active tectonics in the Tell Atlas. It describes Pleistocene and Holocene deformation along fault-propagation-folds. The aim is to highlight the relationship between deformation at surface and geometry-behavior of structures at depth. The results are integrated in the evaluation of the seismic risk of Northern Algeria. Chapter I presents the geological, geodynamic and seismotectonic context of the study area. Chapter II details the data used and the methods applied. Chapter III is devoted to a description and analysis of the coastal uplift of the Zemmouri area, affected by 21/05/2003 earthquake Mw 6.8. Chapter IV deals with the TAEH structure and the earthquake that its central segment generated on 22/08/1922 Mw 6.2. Chapter V is a comparison between the Sahel and El Asnam fault-folds where the rupture of 10/10/ 1980 Mw 7.1 occurred, based on kinematic and elastic modelling. We conclude with a discussion and a general conclusion of our main results as well as the perspectives for this work.
Key words: Tell Atlas, active tectonics, tectonic geomorphology, Quaternary geology, Fault-propagation-fold, Pleiades images.
La quantité et la qualité des données sismiques maintenant disponibles, sur la marge méditerranéenne marocaine et le bassin Ouest-Alboran, permettent d'établir une cartographie détaillée des épaisseurs sédimentaires et de mieux comprendre leur répartition et les principaux facteurs qui en sont responsables. Les épaisseurs sédimentaires atteignent leur maximum au pied de la marge marocaine. Elles se répartissent selon un axe orienté NNW-SSE entre le banc de Xauen et le Détroit de Gibraltar recoupé par un deuxième axe (plus important) reliant Oued Martil au chenal d'Alboran. Ce constat permet de penser que l'essentiel de l'alimentation en sédiments provenait du Rif et de la marge qui a, à plusieurs reprises, été exposée à l'érosion consécutivement aux baisses du niveau marin. Le diapirisme alimenté par les argiles burdigaliènnes, constituant les sédiments les plus anciens de la Mer d'Alboran, jouent eux aussi un rôle important dans la répartition des épaisseurs sédimentaires et l'architecture des dépôts qui les surmontent : la montée des diapirs entraine un fluage latéral des argiles vers le centre du bassin et donc une diminution des épaisseurs sur les bordures. La réponse au vide engendré par la mobilité des argiles se fait par des failles normales dans la couverture plus récente. Abstract. The quantity and quality of seismic data now available, on the Moroccan Mediterranean margin and the West-Alboran basin, make it possible to establish a detailed cartography of the sedimentary thicknesses and to better understand their distribution and the main factors responsible for them. The sedimentary thicknesses reach their maximum at the foot of the Moroccan margin. They are distributed along an axis-oriented NNW-SSE between the Xauen bank and the Strait of Gibraltar intersected by a second axis (more important) connecting Oued Martil to the Alboran channel. This finding suggests that most of the sediment supply came from the Rif and the margin which has on several occasions been exposed to erosion following drops in sea level. The diapirism fed by Burdigalien clays, constituting the oldest sediments of the Alboran Sea, also play an important role in the distribution of sedimentary thicknesses and the architecture of the deposits which surmount them : the rise of the diapirs causes a creep of the clays towards the center of the basin and therefore a reduction in thicknesses on the edges. The response to the vacuum generated by the mobility of the clays is through normal faults in the more recent cover.
Slab retreat, slab tearing and interactions of slabs are first-order drivers of the deformation of the overriding lithosphere. An independent description of the tectonic evolution of the back-arc and peripheral regions is a pre-requisite to test the proposed conceptual, analogue and numerical models of these complex dynamics in 3-D. We propose here a new series of detailed kinematics and tectonic reconstructions from 35 Ma to the Present shedding light on the driving mechanisms of back-arc rifting in the Mediterranean where several back-arc basins all started to form in the Oligocene. The step-by-step backward reconstructions lead to an initial situation 35 Ma ago with two subduction zones with opposite direction, below the AlKaPeCa block ( i.e. belonging to the Alboran, Kabylies, Peloritani, Calabrian internal zones). Extension directions are quite variable and extension rates in these basins are high compared to the Africa-Eurasia convergence velocity. The highest rates are found in the Western Mediterranean, the Liguro-Provençal, Alboran and Tyrrhenian basins. These reconstructions are based on shortening rates in the peripheral mountain belts, extension rates in the basins, paleomagnetic rotations, pressure-temperature-time paths of metamorphic complexes within the internal zones of orogens, and kinematics of the large bounding plates. Results allow visualizing the interactions between the Alps, Apennines, Pyrenean-Cantabrian belt, Betic Cordillera and Rif, as well as back-arc basins. These back-arc basins formed at the emplacement of mountain belts with superimposed volcanic arcs, thus with thick, hot and weak crusts explaining the formation of metamorphic core complexes and the exhumation of large portions of lower crustal domains during rifting. They emphasize the role of transfer faults zones accommodating differential rates of retreat above slab tears and their relations with magmatism. Several transfer zones are identified, separating four different kinematic domains, the largest one being the Catalan-Balearic-Sicily Transfer Zone. Their integration in the wider Mediterranean realm and a comparison of motion paths calculated in several kinematic frameworks with mantle fabric shows that fast slab retreat was the main driver of back-arc extension in this region and that large-scale convection was a subsidiary driver for the pre-8 Ma period, though it became dominant afterward. Slab retreat and back-arc extension was mostly NW-SE until ∼ 20 Ma and the docking of the AlKaPeCa continental blocks along the northern margin of Africa induced a slab detachment that propagated eastward and westward, thus inducing a change in the direction of extension from NW-SE to E-W. Fast slab retreat between 32 and 8 Ma and induced asthenospheric flow have prevented the transmission of the horizontal compression due to Africa-Eurasia convergence from Africa to Eurasia and favored instead upper-plate extension driven by slab retreat. Once slab retreat had slowed down in the Late Miocene, this N-S compression was felt and recorded again from the High Atlas to the Paris Basin.
La chaîne Bético-Rifaine, située dans la partie occidentale de la Méditerranée, est le résultat de la convergence des plaques européenne et africaine et des processus de subduction qui en résultent. Il s’agit donc d’un lieu d’exception pour étudier les processus liés à la dynamique de la subduction. Cette thèse se focalise sur l’étude du domaine interne de la chaine du Rif. Deux zones d’étude ont été sélectionnées (Ceuta et Cabo Negro) où affleurent des roches crustales de haute pression-basse température (HP-BT) (seulement à Ceuta) mais aussi des roches de basse pression-haute température (BP-HT) ainsi que des roches ultrabasiques dont la signification tectonique, le mode et les âges de mise en place restent encore très débattus. Une approche multi-pluridisciplinaire a été effectuée pour réaliser ce travail, avec une étude structurale et pétrographique détaillée, ainsi que des datations U/Th/Pb sur zircon, monazite et xénotime et 40Ar/39Ar sur mica blanc. Les résultats obtenus démontrent que : (i) à environ 29 Ma un métamorphisme de moyenne pression-haute température (MP-HT) affecte les unités des Sebtides inférieures et Ghomarides. Cette phase est contemporaine d’un épaississement de la croûte et de la mise en place de sills de diorite ayant une signature géochimique d’arc magmatique calco-alcalin fortement potassique. Cette phase est d'autre part contemporaine du métamorphisme de HP-BT observé dans les unités crustales des Sebtides supérieures, (ii) à environ 21 Ma une phase d’extension contribue à l’exhumation finale de ces roches. Cet évènement est associé à un épisode métamorphique qui se développe à la limite des conditions des facies amphibolites et schistes verts, sous des conditions de 400-550°C et 1-3 kbar. La combinaison quasi-contemporaine d’unités métamorphiques de gradients thermiques radicalement différents est caractéristique des « ceintures métamorphiques appariées ». Dans ce cas nous proposons le modèle suivant : à 29 Ma, pendant la subduction Alpine, les unités des Ghomarides et Sebtides inférieures se situent au niveau de la plaque supérieure du système de subduction où se développe le métamorphisme de MP-HT. En parallèle le métamorphisme de HP-BT se manifeste dans le panneau plongeant constitué par les Sebtides supérieures. La déshydratation de la plaque plongeante induit un magmatisme calco-alcalin dans la plaque supérieure. A 21 Ma, le recul de la plaque plongeante produit une phase d’extension créant l’ouverture du bassin d’Alboran et l’exhumation des unités de HP-BT.
The Miocene is an essential period in the configuration of
the present-day relief of the Betic Cordillera and the
South Iberian continental margin, which determined the
structure and evolution of the Neogene sedimentary
basins (Fig. 3.1). The crustal thinning processes that
occurred during the early and middle Miocene, after the
main metamorphic events, generated major low-angle
normal faults that separate the main metamorphic complexes.
Although a wide variety of tectonic models have
been proposed for this setting, most of them are related to
delamination or to subduction with associated roll-back.
During the late Miocene, the relatively flat and low relief
of the continental crust facilitated the accumulation of
sedimentary deposits, which are interlayered with volcanic
rocks in the eastern Betic Cordillera and Alborán
Sea. The continuous Eurasian-African convergence
finally produced regional uplift since the late Miocene
and the development of large late regional E-W to
NE-SW folds, which determine the main reliefs.
Cette thèse a été conduite dans le cadre du programme de coopération de recherche Algéro-française SPIRAL (Sismique Profonde et Investigations Régionales du Nord de l’Algérie). Ce projet vise à étudier la structure profonde de la marge algérienne par une approche combinée des techniques sismiques ; grand-angle et multi-canal. Le domaine couvert par la présente étude se concentre dans la région de Jijel dans la marge algérienne orientale. L’objectif principal de notre thèse est d'améliorer en profondeur l'imagerie de la marge algérienne en utilisant une combinaison de données sismiques grand-angle (OBS, sismomètres de fond de l'océan) et multi-canal (MCS). Le but de cette thèse est d'apporter de nouvelles connaissances pour répondre à quelques questions sur la nature de la croûte terrestre, la zone de transition continentale-océanique, la présence du sel messénien, sa distribution et sa relation entre les formations sédimentaires superficielles et les structures crustales. Dans cette étude, notre approche est une inversion jointe des enregistrements grand-angle et des données sismiques multi-canal. Nous avons conduit une série de tomographie des premières arrivées, une inversion jointe des arrivées réfractées et réfléchies ainsi qu’une modélisation gravimétrique. Etant donné que la solution du problème inverse n’est pas unique, deux programmes de tomographie ont été utilisés sur les mêmes données pour la même région d’étude à savoir : FAST (First Arrival Seismic Tomography) et Tomo2D. La tomographie a été suivie par une inversion jointe des arrivées réfractées et réfléchies suivant une approche basée sur la combinaison de la migration en profondeur « Kirchhoff » avant sommation (PSDM) des données de sismique réflexion multi-canal (MCS) et la modélisation directe des enregistrements grand-angle sur le fonds marin (OBS). Afin de vérifier la consistance du modèle de la vitesse avec les données gravimétriques, l’anomalie à l'air libre a été modélisée. Les résultats de l’imagerie conduite dans ce travail montrent la structure de la marge, la croûte continentale, la zone de transition continent-océan et la croûte océanique de la Méditerranée. La structure du modèle confirme les études antérieures basées sur des données bathymétriques, gravimétriques et magnétiques. Cette structure montre essentiellement : - un plateau continental étroit et pente continentale une très raide.- l’Expulsion du sel vers le nord impliquant la formation de diapirs au-dessus du flanc nord du bassin (plaine abyssale).- L’approfondissement et l’épaississement des séquences sédimentaires (bassin sédimentaire) près de la marge algérienne. Le modèle de vitesses obtenu et l’épaisseur des différentes unités structurales formant ce modèle apportent des arguments quantitatifs pour enrichir la connaissance de cette partie de la Méditerranée occidentale. Les couches sédimentaires dans le bassin montrent des vitesses sismiques allant de 1,9 km / s à 3,8 km / s. Les formations messéniennes ont été modélisées en utilisant une vitesse située entre 3,7 km / s à 3,8 km / s. La croûte continentale s’amincit sur une bande étroite de la marge dont la distance est d'environ 15 km. La vitesse de la croûte océanique dans cette région présente deux couches distinctes : l’une caractérisée par des vitesses variant de 4,7 km / s à 6.1 et l’autre de 6.2 à 7.1 km / s. La vitesse du manteau supérieur quant à elle a été modélisée par 7,9 km / s.
Oligocene-Miocene turbiditic flows which formed thick sedimentary successions cropping out in the internal sectors of the Betic-Maghrebian Chain, Tell and Calabria-Peloritani Arc, are commonly related to the dismantling of pre-Alpine crystalline basements. These are now included in different tectonic edifices along the central-western peri-Mediterranean Alpine Chain but originally they Could have belonged to the same crustal block, known as the AlKaPeCa Block (Al = Alboran, southern Spain and northern Morocco, Ka = Kabylian, Algeria, and PeCa = Calabria-Peloritani Arc). Detrital modes from Oligocene-Miocene late-orogenic sandstone suites, oil con form ably overlying the uppermost structural units of the Betic-Rifian Chain and the Rifian "Dorsale Calcaire" Units, show a provenance closely related to Source areas mainly formed by Mesozoic carbonate sedimentary covers and, partially, by very slightly metamorphic rocks. In contrast, sandstones of equivalent late-orogenic successions from the Calabria-Peloritani Are appear to be mainly derived by the erosion of high rank metamorphic and plutonic sources, which call be identified with the Hercynian basement rocks, now forming the highest structural units of the Arc. This bimodality of provenance (carbonate covers with, partially, epimetamorphic sources against a mainly plutonic and/or gneissic supply in the Gibraltar and Calabria-Peloritani Arcs, respectively) Occurring between coeval late-orogenic sandstone suites, equivalent for age, geological significance and structural position, can be justified by admitting that the Internal Domains, which played a role as sediment Sources, did not belong to the same crustal block or they were already separated as the consequence of an incipient break-out and fragmentation of the AlKaPeCa Block before the Late Oligocene (age of the base of the studied late-orogenic deposits).
Oligocene-Miocene turbiditic flows which formed thick sedimentary successions cropping out in the internal sectors of the Betic-Maghrebian Chain, Tell and Calabria-Peloritani Arc, are commonly related to the dismantling of pre-Alpine crystalline basements. These are now included in different tectonic edifices along the central-western peri-Mediterranean Alpine Chain but originally they could have belonged to the same crustal block, known as the AlKaPeCa Block (Al = Alboran, southern Spain and northern Morocco, Ka = Kabylian, Algeria, and PeCa = Calabria-Peloritani Arc). Detrital modes from Oligocene-Miocene late-orogenic sandstone suites, unconformably overlying the uppermost structural units of the Betic-Rifian Chain and the Rifian "Dorsale Calcaire" Units, show a provenance closely related to source areas mainly formed by Mesozoic carbonate sedimentary covers and, partially, by very slightly metamorphic rocks. In contrast, sandstones of equivalent late-orogenic successions from the Calabria-Peloritani Arc appear to be mainly derived by the erosion of high rank metamorphic and plutonic sources, which can be identified with the Hercynian basement rocks, now forming the highest structural units of the Arc. This bimodality of provenance (carbonate covers with, partially, epimetamorphic sources against a mainly plutonic and/or gneissic supply in the Gibraltar and Calabria-Peloritani Arcs, respectively) occurring between coeval late-orogenic sandstone suites, equivalent for age, geological significance and structural position, can be justified by admitting that the Internal Domains, which played a role as sediment sources, did not belong to the same crustal block or they were already separated as the consequence of an incipient break-out and fragmentation of the AlKaPeCa Block before the Late Oligocene (age of the base of the studied late-orogenic deposits).
We describe a recent pull-apart basin which lies on the North-African margin. Seismic reflection profiles and other seismological data show that this basin is linked to a large right lateral strike-slip fault. The orientation of this fault (NW-SE to E-W) and the right lateral offset fit well with a N-S convergent motion between the European and Africa Plates. This large strike-slip fault must be taken into account in the geodynamic framework of the South Western Mediterranean.
Data produced by the Moroccan national seismological network and marine seismic reflection profiles are used to investigate the most seismically active region in Morocco, located on the Mediterranean coast at the intersection of the Rif mountain belt and the submarine Alboran Ridge. This region, in the vicinity of the city of Al-Hoceima, marks an east-west transition in the marine and land deformation styles of the distributed plate boundary between Africa and Iberia, and was the site of an Mw = 6.0 earthquake on 26 May 1994.
The epicenter of the Al-Hoceima earthquake is relocated onshore, refining the initial submarine location close to the Alboran Ridge. The spatial distribution of foreshocks and aftershocks shows a NE-SW trend that continues partly offshore and is subparallel to the earlier, yet still prominent, Miocene geologic structural trend. The predominantly strike-slip focal mechanism for the Al-Hoceima event is characteristic of earthquakes in the region. Marine seismic reflection profiles that intersect the offshore region of seismicity image active high-angle faults with possible strike-slip components. The seismicity trend is not directly related to the submarine Alboran Ridge or the geomorphologically prominent Nekor fault. Deformation appears to be occurring on a number of subsidiary strike-slip faults that together compose a NE-SW zone of distributed shear.
The distributed strike-slip and documented normal faulting taking place in the eastern Rif mountains, although characteristic of the Rif region, are in contrast to the thrusting style of deformation that occurs farther to the east in the Algerian Tell Atlas. This may be related to the reported lateral variations and evolution of the convergent plate boundary in these regions during the Neogene and Quaternary times.
A lower Burdigalian clayey-turbiditic formation lying on the Beni Hozmar Ghomaride nappe has been found at Boujarrah (NNE of Tetouan). It shows very different facies, deeper than those of the older Fnideq formation. The new data corroborate, in the Rif, the existence of two sedimentary cycles within the 'Oligo-Miocene' successions of the Betic-Rifian internal zones. The boundary between both cycles coincides with the end of the emplacement of the internal nappes towards the Aquitanian-Burdigalian transition.
The western Mediterranean subduction zone (WMSZ) extends from the
northern Apennine to southern Spain and turns around forming the narrow
and tight Calabrian and Gibraltar Arcs. The evolution of the WMSZ is
characterized by a first phase of orogenic wedging followed, from 30 Ma
on, by trench retreat and back-arc extension. Combining new and previous
geological data, new tomographic images of the western Mediterranean
mantle, and plate kinematics, we describe the evolution of the WMSZ
during the last 35 Myr. Our reconstruction shows that the two arcs form
by fragmentation of the 1500 km long WMSZ in small, narrow slabs. Once
formed, these two narrow slabs retreat outward, producing back-arc
extension and large scale rotation of the flanks, shaping the arcs. The
Gibraltar Arc first formed during the middle Miocene, while the
Calabrian Arc formed later, during the late Miocene-Pliocene. Despite
the different paleogeographic settings, the mechanism of rupture and
backward migration of the narrow slabs presents similarities on both
sides of the western Mediterranean, suggesting that the slab deformation
is also driven by lateral mantle flow that is particularly efficient in
a restricted (upper mantle) style of mantle convection.
This is not an abstract but a short comment.
This paper is important because it proposes, for the first time, that in the Betic-Rif Orogen the Miocene tectonic transport is mainly westward and not northward (Betics) and Southward (Rif) as previously assumed. In addition, the paper emphasizes, also for the first time, the role of subduction and slab retreat in the development of the Betic-Rif Arc.
The southwestern part of the western Mediterranean Alboran Basin, including part of the Alboran ridge (Xaouen Bank), was investigated through the analysis of 28 intersecting multichannel seismic lines. The seismic stratigraphy is tied to the Amoco well El-Jebha 1. Five seismic units or subunits are described from the Quaternary to the middle (and lower?) Miocene. The acoustic basement is interpreted to be mainly Paleozoic and Triassic metamorphic rocks of the Alboran Domain nappes, and, in places, middle Miocene-Messinian calc-alkalic volcanics. In the depocenters, the thickness of the sedimentary infill (mostly clays and turbidites) exceeds 9 km. Normal faults of middle Miocene-Tortonian age are broadly parallel to the coast, and dip either seaward or landward. They were mostly inverted during pre- and post-Messinian episodes of compression, which formed a set of en echelon, north-verging faulted folds in the Alboran ridge area, in relation with sinistral movement along the offshore projection of the Jebha fault. After Pliocene subsidence, a final episode of compression reactivated the earlier folds and pushed the Alboran ridge onto the Moroccan slope. The complex structural history suggests many structural and stratigraphic potential hydrocarbon traps. A high-resolution seismic survey could lead to the definition of new exploration plays.
A number of different geodynamic models have been proposed to explain the extension that occurred during the Miocene in the Alboran Sea region of the western Mediterranean despite the continued convergence and shortening of northern Africa and southern Iberia. In an effort to provide additional geophysical constraints on these models, we performed a local, regional, and teleseismic tomographic travel time inversion for the lithospheric and upper mantle velocity structure and earthquake locations beneath the Alboran region in an area of 800×800km2. We picked P and S arrival times from digital and analog seismograms recorded by 96 seismic stations in Morocco and Spain between 1989 and 1996 and combined them with arrivals carefully selected from local and global catalogs (1964-1998) to generate a starting data set containing over 100,000 arrival times. Our results indicate that a N-S line of intermediate-depth earthquakes extending from crustal depths significantly inland from the southern Iberian coast to depths of over 100 km beneath the center of the Alboran Sea coincides with a W to E transition from high to low velocities imaged in the uppermost mantle. A high-velocity body, striking approximately NE-SW, is imaged to dip southeastwards from lithospheric depths beneath the low-velocity region to depths of ~350 km. Between 350 and 500 km the imaged velocity anomalies become more diffuse. However, pronounced high-velocity anomalies are again imaged at 600 km near an isolated cluster of deep earthquakes. In addition to standard tomographic methods of error assessment, the effects of systematic and random errors were assessed using block shifting and bootstrap resampling techniques, respectively. We interpret the upper mantle high-velocity anomalies as regions of colder mantle that originate from lithospheric depths. These observations, when combined with results from other studies, suggest that delamination of a continental lithosphere played an important role in the Neogene and Quaternary evolution of the region.
The Betics and Rif cordillera constitute the northern and southern segments of the Gibraltar arc. Two different fold-and-thrust
belts, deriving from the South Iberian and Maghrebian paleomargins respectively, developed in front of this orogenic system.
By contrast, the Flysch Trough units and the overlying Alboran crustal domain (internal zones), which are situated in the
uppermost part of the orogenic wedge, are common to both branches of the arc. The Flyschs Trough units constitute an inactive
accretionary prism, derived from a deep elongated trough. From three large-scale profiles and some lithostratigraphic features
of the involved sedimentary sequences, the Betic and Rif external domains are compared, mainly from a structural point of
view. Although they are generally considered to show major similarities, the Betic and Rif external domains are in fact strikingly
different, mainly concerning the structural style, deformation timing and metamorphism: a) the thick-skinned structure in
the External Rif domain vs thin-skinned in the Subbetic domain; b) the pre-Oligocene and Miocene stacking in the External Rif domain vs the exclusively Miocene one in the Subbetic domain, and c) the metamorphism present only in part of the External Rif domain
(low-grade greenschists facies). By contrast, it was not possible to establish any difference in structural style and deformation
timing between the Flysch units outcropping in both branches of the Gibraltar arc.
The Gibraltar arc, which closes the westernmost part of the
Mediterranean basin, is a Miocene A-type subduction arc formed by the
continental collision of various pre-Miocene terranes in the major zone
of collision between the Iberian and African cratons. The hanging-wall
block, known as the Alborán domain, has undergone more than 300
km migration from a more easterly position, where it was the
continuation of the Alpine Cretaceous-Paleogene orogen. Contemporaneous
with thin-skinned thrusting in the footwall, the Alborán domain
underwent two episodes of nearly orthogonal extension in which
extensional systems developed with directions of extension varying from
a NNW-SSE system, orthogonal to the belt axis, in the late
Burdigalian-Langhian to a WSW directed orogen-parallel one in the
Serravallian. The superposition of these two systems resulted in a
chocolate tablet megastructure. This extensional pattern is not
satisfactorily explained in previously proposed models for the evolution
of the arc. Orthogonal extension is plausible in a process of the
gravitational collapse of an overthickened crust; nevertheless,
orogen-parallel extension is more difficult to explain in this context.
We advocate that the WSW directed low-angle normal faults formed during
large-scale extension in connection with important westward arc
migration. The driving force of extension in a general context of
convergence is controversial and varies between a convective removal
model and a delamination model. Constraints on both the timing and the
kinematics of extension, as presented in this paper, seem to support the
contribution of both mechanisms. Convective removal may have started the
process, but continued N-S convergence could have resulted in westward
tectonic escape and asymmetric lateral inflow of asthenospheric material
accompanying lithospheric delamination.
A three-dimensional gravity modeling combined with integrated heat flow and elevation modeling is conducted to map out the crustal and lithospheric mantle thickness in the Alboran Basin, in the westernmost Mediterranean. A ``sediment''-corrected Bouguer anomaly has been derived using a depth-to-the-basement map and densities determined from well logs and seismic data. The gravity effect of the base of the lithosphere has been removed from the sediment-corrected Bouguer anomaly to obtain a ``crustal'' Bouguer anomaly, which has been inverted for crustal thickness. The resulting lithospheric structure is further constrained by elevation data under the assumption of local isostasy. The low residual elevation anomalies obtained (+/-100 m in average) suggest that the area is in local isostasy, particularly the medium- and long-wavelength topography features. Variations in crustal thickness range from 36 km underneath the Betic and Rif Chains to
I I SUMMARY: The kinematic understanding of the relationship between relative plate motion and the structure of orogenic belts depends upon a knowledge of relative plate motion across the plate boundary system, the relative motion of small blocks and flakes within the system, an evaluation of orogenic body forces, and an understanding of the thermomechanical evolution of the upper part of the orogenic lithosphere in determining strength and detachment levels. We have built a preliminary model for the Cenozoic kinematic evolution of the western Mediterranean oceanic basins and their peripheral orogens that integrates (1) the motion of Africa relative to Europe based upon a new study of Atlantic fracture zones using SEASAT data and the Lamont-Doherty magnetic anomaly database, (2) a new interpretation of the rotation of Corsica/Sardinia and the opening of the Balearic and Tyrrhenian oceanic basins, (3) sedimentary facies sequences in the Apennines, Calabria, and Sicily, and (4) Apenninelcalabrian structure and structural sequence.
Since the early Pliocene, the active tectonic setting of the Eastern Alboran Sea has been characterized by active strike-slip
tectonism, causing the main bathymetric depressions to form in the eastern part of the Alboran Sea, the Eastern Alboran Basin,
the Yusuf Basin, the Alboran Channel, and the South Alboran Basin. The Eastern Alboran Basin is a 2000-m-deep, mostly flatbottomed,
triangular-shaped graben developed between the Iberian and African continental margins. Ocean Drilling Program
(ODP) Leg 161 data provide the time frame for the late Miocene to Holocene history of the basin. At Site 977, 600 m of
Miocene(?)-Pliocene to Holocene marine sediments were drilled, and 700 m of upper Miocene to Pleistocene marine sediments
at Site 978. Within the sedimentary package, several unconformities reveal the active strike-slip tectonism that occurred during
this time.
At the southern border of the Eastern Alboran Basin the active, right lateral strike-slip Yusuf Fault is developing. Reflection
seismic profiling shows that, at a right stepover of the Yusuf Fault, a developing negative flower structure is causing the Yusuf
Basin to form, in which active tectonic subsidence has been ongoing since at least the late Miocene. Above the interpreted
Messinian reflections, the sedimentary fill forms a northeastward-thickening wedge of syntectonic sediments of Pliocene to
Holocene age.
In the South Alboran Basin, drilling at Site 979 penetrated Pliocene to Holocene syntectonic sediments, which form growth
strata geometries related to a south-dipping monocline that evolved above a north-dipping thrust fault in the basement. North of
the Alboran Ridge, a narrow strike-slip basin is forming in the Alboran Channel next to the strike-slip fault at the northern flank
of the ridge.
In recent years, the origin of the Betic-Rif orocline has been the subject of considerable debate. Much of this debate has focused on mechanisms required to generate rapid late-orogenic extension with coeval shortening. Here we summarize the principal geological and geophysical observations and propose a model for the Miocene evolution of the Betic-Rif mountain belts, which is compatible with the evolution of the rest of the western Mediterranean. We regard palaeomagnetic data, which indicate that there have been large rotations about vertical axes, and earthquake data, which show that deep seismicity occurs beneath the Alboran Sea, to be the most significant data sets. Neither data set is satisfactorily accounted for by models which invoke convective removal or delamination of lithospheric mantle. Existing geological and geophysical observations are, however, entirely consistent with the existence of a subduction zone which rolled or peeled back until it collided with North Africa. We suggest that this ancient subducting slab consequently split into two fragments, one of which has continued to roll back, generating the Tyrrhenian Sea and forming the present-day Calabrian Arc. The other slab fragment rolled back to the west, generating the Alboran Sea and the Betic-Rif orocline during the early to middle Miocene.
The evolution of the oceanic Maghrebian Flysch Basin and its continuation in the Southern Apennines was studied by reconstructing mainly representative stratigraphic successions. In all sectors a common evolution has been identified. Rifting and drifting phases are indicated by remnants of oceanic crust, Jurassic limestones, Cretaceous–Palaeogene turbiditic and pelagic deposits. The pre-orogenic sedimentation was mainly controlled by extensional tectonics and sea-level changes. The occurrence of a generalized foredeep stage since the Early Miocene is testified by thick siliciclastic and volcaniclastic syn-orogenic flysch successions. The deformation of the oceanic areas began in the Burdigalian and the resulting nappes were stacked in the growing chains. During the Middle Miocene, piggy-back basins developed and the building of the chains was accomplished in the Late Tortonian. Areal distribution and ages of flysch deposits represent an important tool for the study of the diachronous growth of the accretionary wedges.
The Ocean Drilling Program (ODP) Leg 161 drilled in the Western Mediterranean Sea (May–June, 1995) to investigate out-standing processes in the origin and structural evolution of the Alboran Basin. Studies at the Site 976 basement high, in the West Alboran Basin, demonstrate that the basin is floored with metamorphic rocks of continental origin (high-grade schist, migmatitic gneiss, marble, and calc-silicate rock, cross-cut by granite dikes) from the Alpujárride Complex of the Alboran Crustal Domain. Sediments encountered at the tops of the basement high are middle Miocene in age (about 11–12 Ma, late Ser-ravallian). The pressure-temperature (P-T) evolution of the high-grade schist shows heating during decompression, from pres-sures of up to 10.5 kbar at about 500°C (corresponding to a burial depth of around 40 km) to final temperature conditions of 650º–700°C at a pressure of 3–4 kbar. The decompression was followed by cooling to T < 500º–600°C and P < 2–3 kbar. Ar/Ar dating on coexisting muscovite and biotite shows that this cooling occurred from 426°C at 20.0 ± 0.2 Ma to 330°C at 19.2 ± 0.7 Ma. Apatite fission-track shows that final cooling of the basement below 60°C took place at 18.3 ± 1.0 Ma (Burdigalian). Site 976 reveals two periods of subsidence, in the middle Miocene (synrift subsidence, at 11–10.7 Ma; rate of 3 km/m.y.) and since the latest Pliocene (postrift transtensive? subsidence, at 2.5–0 Ma earliest rate of 0.5 km /m.y.), and uplift at 5–2.5 Ma (early Pliocene). Conspicuous lateral variations in rift-related subsidence phases in the basin suggest migration of the locus of exten-sion, and probably also changes in tectonic-transport direction during the Miocene rifting. Miocene crustal thinning in the Alb-oran Domain is related to low-angle intracrustal detachments and shallow normal faulting. Since the latest Tortonian, relatively uplifted and subsided areas coexist, but a generalized, continuous, and slower subsidence developed within the marine basin. Drilling results in the East and South Alboran basins (Sites 977, 978, and 979) define the timing of the later (post-Messinian) tectonic reorganization of the Alboran Basin into the present-day Alboran Sea basin. Ar/Ar dating of reworked but representa-tive volcanic pebbles from tholeiitic, calc-alkaline, and shoshonitic series (Sites 977 and 978) constrains episodes of middle-to-late Miocene volcanism in the eastern Alboran region at 12.1 ± 0.2 Ma, 9.90 ± 0.4 Ma, 9.29 ± 0.02 Ma, and 6.1 ± 0.3 Ma. Incompatible elements in these rocks include both depleted (MORB-source) component and an ocean-island or plume-type component ("arc signature"). Calc-alkaline magmatic affinities and incompatible-element systematics were considered to sup-port a Miocene oceanic subduction zone (from 6 Ma to at least 12 Ma) beneath the eastern Alboran region. However, these magmatic signatures prove to have also originated from variable crustal-contamination of MORB-type melts, produced by shallow melting during asthenosphere-mantle upwelling. Alternatively, modeled P-T paths in basement rocks suggest removal of mantle lithosphere below about 60 km depth (to explain further heating during decompression at shallow depth) and rapid exhumation during lithosphere stretching (4.5 km/m.y.), followed by final cooling with a minimum exhumation rate of 4 km/ m.y. It took ~9 m.y. for the exhumation of the basement rocks from 40 km depth to reach the surface at about 18 Ma, thus sug-gesting that extension in the Alboran Domain started at about 27 m.y. (late Oligocene), before the marine transgression occurred. We consider that strong evidence from rocks at the Site 976 basement high favors models that use the removal of mantle lithosphere as the driving force for extension generating the Alboran Basin. Further geological and geophysical data from the westernmost Mediterranean region are needed to corroborate our conclusions to define a fully satisfying model for the Neogene evolution of the lithosphere beneath the Alboran Basin.
A Lower Burdigalian clayey-turbiditic formation lying on the Beni Hozmar Ghomaride nappe has been found at Boujarrah (NNE of Tetouan). It shows very different facies, deeper than those of the older Fnideq formation. The new data corroborate, in the Rif, the existence of two sedimentary cycles within the "Oligo-Miocene' successions of the Betic-Rifian internal zones. The boundary between both cycles coincides with the end of the emplacement of the internal nappes towards the Aquitanian-Burdigalian transition. There is an abridged English version. -English summary
In the Betic Chain, south of Sierra Nevada, two Neogene sedimentary sequences were dated on the basis of planktonic foraminiferal associations: marls, which show ages between upper Langhian and upper Serravallian, and the underlying conglomerates, in which intercalated marls include the lower Langhian. These sediments were deposited when the low-angle normal faults of two brittle extensional systems were active. The so-called Contraviesa system, with northward transport direction, is therefore Langhian, and the Filabres system, with southwestward transport, is Serravallian. The faults limit the Alpujarride and Malaguide extensional units and contributed to the rifting of the Alboran Domain. There is an abridged English version. -English summary
The emplacement of the internal nappes of the Rif and their Alpine metamorphism accurred prior to deposition of the "Oligo-Miocene' deposits upon the various ghomaride units. Two formations are defined within the "Oligo-Miocene' deposits: the Fnidek formation (upper Oligocene-Aquitanian p.p.?, NP 25 and NN 1) and the Sidi Abdeslam formation (Aquitanian p.p. and lower Burdigalian NN 1 and NN2) with silexites. The J. Zem Zem and Riffiene allochthonous units were thrust over these "Oligo-Miocene' formations. The possible relations between radiometric dating and the age of the upper Oligocene transgression are then discussed. There is an abridged English version. -English summary
Data from 11 wells, a dense seismic grid, and the ECORS deep seismic profiles provide a precise picture of the geological history of the Gulf of Lions. Four sequences are identified from the late Oligocene-early Miocene synrift to the Pliocene-Quaternary progradational shelf. The middle Miocene is characterized by a highstand system tract established on a paleoself. These seismic-stratigraphical observations can be placed into their tectonic framework. The Gulf of Lions area first underwent a compressional phase related to the Pyrenean orogeny, then a later extensional phase caused by the opening of the Provencal basin. When suitably oriented, the former thrusts are reactivated as detachment due to subsequent extension. -Authors
L’histoire tectono-sédimentaire du Rif (Maroc) et de son Avant-pays, du Tortonien inférieur jusqu’à l’actuel, est contrôlée par des effets de deux phénomènes: la convergence de l’Afrique vers l’Europe et l’expulsion du Rif vers le SW.
Dans le détail, ces deux processus ne sont pas aussi tranchés, il peut y avoir passage d’un système à l’autre dans le temps et dans l’espace.
Les directions moyennes du raccourcissement dépendent de la prépondérance de l’un ou de l’autre.
Depuis le Pliocène, l’expulsion vers le SW est bloquée et de ce fait, seuls les effets de la convergence se font sentir. Ils se traduisent par une direction moyenne NW-SE à NS du raccourcissement.
The Middle Jurassic–Lower Cretaceous Fossil Bluff Group of Alexander Island, Antarctica represents the fill of a fore-arc basin unconformably overlying an accretionary complex. Like most fore-arc basins, this example had been considered to have a passive origin, as a topographic hollow between the arc and the trench-slope break. Recent discoveries of igneous rock coeval with sedimentation have altered this view. Oxfordian–Kimmeridgian basaltic and rhyolitic sills and lava flows are found in a restricted area at the north of the basin, within a single formation. Chemically, most basalts are high-Nb types, which cannot have originated in a supra-subduction zone setting. Since the age of emplacement of these rocks coincides with a gap in the record of plutonism in the Antarctic Peninsula volcanic arc, it is concluded that a late Jurassic pause in subduction led to active rifting to form the fore-arc basin.
Using the peri-Mediterranean blueschist belts as a case study we discuss the mech- anisms of exhumation of high-pressure and ultra-high-pressure rocks focussing on syn-orogenic exhumation. The Mediterranean examples, within an overall convergent zone, show a variety of tectonic contexts due to variations in the rates of convergence, rates of slab retreat, available space, and various stages of maturation of accretionary complexes that can be used as natural experiments. After a compilation of the de- formation history and the kinematic boundary conditions and their evolution through time, we discuss available P-T-t paths. Most of the structures found in the field to- day relate to the exhumation stage and very often to quite superficial events related to syn-orogenic detachments. However the most important part of exhumation occurs along the subduction plane following cold P-T paths from the depth of eclogites (or UHP eclogites) to the depth of the blueschist or greenschist facies. UHP rocks do not seem to occur in retreating subduction contexts because an easy circulation in an open subduction channel favors an early detachment of sediments from their base- ment. Subducted sediments also act as lubricants of the subduction channel so that the basement is not affected by a strong shearing and is not involved in the return flow. This early exhumation is rapid and the thermal regime in the subduction channel is partly controlled by kinematic boundary conditions such as the velocity of con- vergence and the velocity of slab retreat as well as by the chemical composition of the subducted material. Final exhumation occurs within the accretionary complex at a much slower rate below extensional detachments. The removal of the overburden is achieved primarily by extension in the upper part of the accretionary complex. Exten- sional faults and shear zones root in the brittle-ductile transition of the accretionary complex. Some deeper SextensionalT shear zones represent the deformation along the & cedil;roof of the subduction channel. We discuss a model with several levels of circulation of subducted material and compare it with available thermomechanical models.
We study the set of limiting tangent hyperplanes of normal surface germ. We characterize these hyperplanes by the non-minimality of the Milnor number of their section with the surface. Then we generalize the results of [4] by means of weak simultaneous resolution of hyperplane sections family, and hence we precisely determine some exceptional tangents of a normal surface singularity. Applying this, we prove that “Tyurina components” of a reasonable desingularization contract to fixed points of the linear system of polar curves.
Several features of the Alboran Sea suggest that it may have been a high
collisional ridge in Paleogene time that subsequently underwent
extensional-collapse, driving radial thrusting around the Gibraltar arc.
(1) The basin is underlain by thin (13-20 km) continental crust, has an
east-west-trending horst and graben morphology, was the locus of Neogene
volcanism, and has subsided 2-4 km since the middle Miocene. (2)
Extension and subsidence in the basin coincided in time with outwardly
directed thrusting in the surrounding mountain chains. (3) Africa and
Europe were converging slowly during this period, so extension must have
been driven by internally generated forces. (4) Onshore, rocks
metamorphosed at 40 km depth are exposed beneath major low-angle normal
faults that separate them from low-grade rocks above. (5) Emplacement of
solid bodies of Iherzolite at asthenospheric temperature into the base
of the collisional edifice in late Oligocene time suggests detachment of
the lithospheric root beneath the collision zone. This would have
increased the surface elevation and the potential energy of the system
and would have favored extensional collapse of the ridge.
A number of tectonic events occurred contemporaneously in the Mediterranean region and the Middle East 30-25 Myr ago. These events are contemporaneous to or immediately followed a strong reduction of the northward absolute motion of Africa. Geological observations in the Neogene extensional basins of the Mediterranean region reveal that extension started synchronously from west to east 30-25 Myr ago. In the western Mediterranean it started in the Gulf of Lion, Valencia trough, and Alboran Sea as well as between the Maures massif and Corsica between 33 and 27 Ma ago. It then propagated eastward and southward to form to Liguro-Provençal basin and the Tyrrhenian Sea. In the eastern Mediterranean, extension started in the Aegean Sea before the deposition of marine sediments onto the collapsed Hellenides in the Aquitanian and before the cooling of high-temperature metamorphic core complexes between 20 and 25 Ma. Foundering of the inner zones of the Carpathians and extension in the Panonnian basin also started in the late Oligocene-early Miocene. The body of the Afro-Arabian plate first collided with Eurasia in the eastern Mediterranean region progressively from the Eocene to the Oligocene. Extensional tectonics was first recorded in the Gulf of Aden. Afar triple junction, and Red Sea region also in the Oligocene. A general magmatic surge occurred above all African hot spots, especially the Afar one. We explore the possibility that these drastic changes in the stress regime of the Mediterranean region and Middle East and the contemporaneous volcanic event were triggered by the Africa/Arabia-Eurasia collision, which slowed down the motion of Africa. The present-day Mediterranean Sea was then locked between two collision zones, and the velocity of retreat of the African slab increased and became larger than the velocity of convergence leading to backarc extension. East of the Caucasus and northern Zagros collision zone the Afro-Arabian plate was still pulled by the slab pull force in the Zagros subduction zone, which created extensional stresses in the northeast corner of the Afro-Arabian plate. The Arabian plate was formed by propagation of a crack from the Carlsberg ridge westward toward the weak part of the African lithosphere above the Afar plume.
We applied time domain moment tensor inversion of local and regional waveforms to small and moderate (Mw = 3.5-5.7) shallow earthquakes from the Iberian Peninsula, northern Morocco, and northern Algeria. For the 6+ years period from November 1995 to March 2002 and the previous Network of Autonomously Recording Seismograms (NARS) experiment, moment tensor solutions were obtained for 58 events, considerably increasing the total number of available solutions in the study area. For each event we performed a moment tensor inversion and a double-couple grid search. For simple faulting events the grid search is valuable as a quality test for its ability to reveal potential ambiguities of the solutions and to assess confidence limits of fault plane parameters or principal axes orientation. The computed mechanisms show regional consistency: A large part of the Iberian Peninsula is characterized by normal faulting mechanisms with SW-NE oriented T axes. Thrusting and SE-NW compression is dominant in Algeria. In the Alboran Sea, the westernmost part of the Mediterranean, and the transition between both regimes, strike-slip mechanisms dominate with approximately N-S oriented P axes. This pattern suggests a regional anomaly characterized by clockwise rotation of the principal horizontal stress orientations.
We integrate observations based on teleseismic P wave travel times and available geologic data to infer that the lithosphere beneath the intraplate Atlas mountains is thin and/or it is characterized by lower P wave velocities, while beneath the interplate Rif mountains and the adjacent Alboran Sea a previously thickened lithosphere has been delaminated into the upper mantle. Using surface geology and geochronology data, previous studies have proposed that lithospheric delamination took place in this region. In this study we show through analysis of teleseismic P wave residuals the existence of a high-velocity (>3%) upper mantle body, which is interpreted to be the delaminated, rigid lithosphere. This high-velocity layer is overlain by a very low velocity uppermost mantle material (Pn velocities of about 7.6-7.7 km s-1) interpreted to be asthenospheric material replacing the delaminated lithosphere. Teleseismic P waves recorded by a recently installed digital seismic network and an older analog network in Morocco provide the residuals database. A total of 734 P wave residuals from 92 selected teleseismic earthquakes are used to document the spatial pattern of upper mantle velocity structure beneath northern Morocco and the Alboran Sea. Subsequent use of these residuals in a tomographic inversion scheme produced a three-dimensional velocity image of the upper mantle. We infer from the P residuals that strong upper mantle velocity anomalies exist beneath both the Rif and Atlas regions. The Rif stations show negative residuals (~1-1.5 s) for ray paths from the east and northeast and show positive residuals (~1-1.5 s) for ray paths from the northwest and southwest. Tomographic results indicate the existence of a high-velocity body (~3% higher velocities) in the upper mantle beneath the eastern Rif and Alboran Sea, extending approximately from subcrustal depths down to a depth of at least 350 km. In the western Rif, however, 1-2% lower velocity material is imaged in the upper mantle. The residuals of the Atlas stations also show azimuthal variations. In general, most of the P waves that travel beneath the High and Middle Atlas have about 0.5-1.0 s delays. In contrast, the rays that travel beneath the northwestern margin of the Atlas mountains and the adjacent Moroccan Meseta area show negative residuals (~1 s), suggesting that higher velocity material exists beneath the platform area adjacent to the Atlas mountains. Tomographic results indicate that beneath most of the Atlas system the uppermost mantle has about 1% lower velocities. Beneath the Alboran Sea region, however, reported low uppermost mantle Pn velocities contrast strongly with higher velocity upper mantle velocities obtained by our analysis. Low-velocity uppermost mantle beneath the Alboran Sea underlain by a high-velocity upper mantle material is used to support earlier interpretations of lithospheric delamination beneath the Rif and Alboran Sea regions. The enigmatic occurrence of subcrustal earthquakes in these regions is also consistent with this active delamination mechanism.
Granite and gneiss sampled from the submarine fault scarps of the Sardinia Channel were dated using the apatite fission-track method. One sample provides an age of 22.8± 1.3 Ma, which is in the range of the cooling ages of the Calabrian-Peloritan basement, where cooling is due to erosion. Three other samples have ages around 10 Ma, probably due to a tectonic denudation during the Tortonian extension in the Sardinia Channel.
During the BASACALB-TTR9 cruise of the R/V Professor Logachev (1999), two mud volcanoes (called Marrakech and Granada) were discovered in the southern sector of the mud diapir province in the West Alboran Basin (WAB). This paper presents micropaleontological and geophysical data on these mud volcanoes from gravity core samples, sidescan sonar (OKEAN) images and high-resolution seismic lines. Mud breccia recovered from the Granada mud volcano is matrix-supported with well-consolidated clasts of limestone, marlstone, claystone, siltstone, sandstone and mudstone, whereas mud breccia from the Marrakech mud volcano contains unconsolidated clasts. The mud breccia matrix contains abundant Miocene calcareous nannofossils (CN), together with Pliocene–Pleistocene species and reworked late Cretaceous and Paleocene–Eocene species. CN dating indicates that clasts in the mud breccia derive from late Cretaceous, Paleocene, Eocene, and probable Miocene sediments. These data suggest that the mud diapirs and mud volcanoes in the WAB can be derived from the olistostromes of Unit VI, the basal stratigraphic sequence in the Alboran Sea basin. Unit VI consists of lower Miocene sediments that incorporated late Cretaceous and Paleocene–Eocene materials and basement-derived rock fragments. The mud volcanic deposits are covered by a thin drape of pelagic marls, suggesting that these two volcanoes are currently inactive. Structures determined on high-resolution seismic profiles across mud volcanoes and surrounding diapirs correspond to the late-stage, Pliocene-to-Quaternary diapir development. This stage is thought to have developed during a compressional tectonic setting that produced folding and wrench tectonics throughout the basin. Mud ascent at that time resulted in active diapirism and mud volcanoes on the seafloor.
High-resolution seismic reflection profiles (2000 km) were collected across the southern continental margin and major structural trends of the Alboran Sea. Seismic units are dated on the basis of well-known marine Neogene onshore sections and offshore dredged samples. A better assessment of margin structuration and Neogene chronology is made. A conformable succession of Pliocene-Quaternary and older series provides evidence for the non-evaporitic nature of the Upper Miocene, similar to the facies from the onshore Neogene Boudinar and Melilla basins. It also suggests that Alboran Ridge is in part sedimentary rather than only volcanic. This Ridge appears as an "en echelon" anticlinal complex. Conformable Upper Miocene and Lower Pliocene-Quaternary strata are folded and faulted. Primarily important manifestation of the movements is dated as Pliocene, but the main vertical relative movements are of Quaternary to recent age as emphasized by well-developed divergent strata lying above. Submarine volcanism, probably Miocene in age, often controls the morphology and structure of the eastern Moroccan continental margin and adjacent south Alboran Basin. The latter one is characterised by a thick sedimentary accumulation; it is tectonically bounded, except on the southwestern part seaward of the Bokkoyas cliffs. Vertical movements occur during much of Plio-Quaternary time, prevailing during the Quaternary. The structure and related morphology of the study area are mainly the result of neotectonic events.
The Western Mediterranean Sea is explained as a marginal basin, generated by a N-NW subduction of the African—Apulian plates beneath the European plate. Following an Oligocene rifting phase, oceanic accretion occurred between −21 and −18 m.y., along three main spreading axis trending NE-SW in the Liguro—Provençal Basin, NW-SE in the southern Sardo—Balearic Basin and E-W in the North Algerian Basin. Such kinematics and chronology are consistent with: (a) paleomagnetic data supporting the Sardinian rotation; (b) basin and margin structure; (c) subsidence since 21 m.y., especially during Messinian time; and (d) heat-flow measurements.
The hinterland basins of the Rif-Betic Cordillera (Western Alboran Sea) and the Carpathians (Pannonian Basin) are in part composed of a thick (in excess of 3–4 km) thermal sag basin sequence. The underlying crust has been thinned to 25 km in parts of the Pannonian Basin and to 15 km in parts of the Alboran Sea. Modern tectonic models for these areas envision tectonic collision and thickening of the crust followed by crustal thinning, either by gravitational collapse, back-arc extension or a combination of the two contemporaneous with thrusting. Basin and Range-type extension has been envisioned for parts of these extensional collapse systems. Extensional features are common, and they interact in a complex way with strike-slip systems. Flexural cantilever modelling agrees with earlier McKenzie-type pure shear modelling of the extensional systems in suggesting that extension alone cannot generate sufficient thermal decay to explain the great thickness of the sag basins associated with the Alboran Sea and Pannonian Basin. Consequently, it is suggested that uplift of the asthenosphere accompanying subduction roll-back is an important factor in the evolution of these basins. Roll-back of the mantle lithosphere permits hot asthenospheric mantle to upwell and lie close to the base of the crust. Initially, uplift and erosion of the crust overlying the asthenosphere occurs. As the thermal perturbation cools, the crust thermally subsides to produce a large sag basin.
Using the peri-Mediterranean blueschist belts as a case study we discuss the mechanisms of syn-orogenic exhumation of high-pressure (HP) and ultra-high-pressure (UHP) rocks. The Mediterranean examples, within an overall convergent zone, show variations in the rates of convergence, rates of slab retreat, available space, and various stages of maturation of accretionary complexes. After a compilation of the deformation history and the kinematic boundary conditions and their evolution through time, we discuss P-T-t paths. Most of the structures found in the field today relate to the exhumation stage and often to quite superficial events related to syn-orogenic detachments. However a significant vertical motion occurred from the depth of eclogites (or UHP eclogites) to the depth of the blueschist or greenschist facies along cold P-T paths. Two types of mountain belts are described: those where a single thermal gradient was recorded throughout its’ history, like the Franco-Italian Alps, which suggest a steady-state evolution; and those where the thermal gradient has changed through time (and space), such as the Aegean region, which suggest a non-steady-state evolution. Slab retreat within a subduction complex does not lead to the exhumation of UHP rocks because the open subduction channel allows for fast circulation and detachment of sediments from the subducting basement. Subducted sediments lubricate the subduction channel and the basement is thus not involved in the return flow. Early exhumation is fast and the thermal regime in the subduction channel is partly controlled by the velocity of convergence and the velocity of slab retreat as well as by the nature of the subducted material. Final exhumation occurs within the accretionary complex at a much slower rate below extensional detachments. The removal of the overburden is achieved primarily by extension in the upper part of the accretionary complex. Extensional faults and shear zones are rooted in the brittle-ductile transition of the accretionary complex. Deeper “extensional” shear zones result from shearing along the base of the upper plate. We discuss a model with several levels of circulation of subducted material and compare it with available thermo-mechanical models.
The reprocessing of MCS reflection lines and sampling data across the SW Tyrrhenian Basin, from the Sardinia–Tunisia Strait (STS) to the Orosei Canyon Line (OCL), show that the acoustic basement of the area is made by Variscan crystalline-metamorphic rocks covered by a thick sequence of sediments, including the Messinian interval. The pre-Messinian sequence can be subdivided into three seismic intervals or subunits, largely calibrated by sampling data. The oldest pre-Messinian subunit is strongly deformed by compressional and/or transpressional structures and the recovered samples are deep-water arkosic sediments, Aquitanian in age; however, the whole interval may encompass a wider time span, probably from Late Oligocene to Langhian. This subunit was laid down in a fore-arc basin located between a volcanic arc (Sardinia) and an accretionary wedge (Calabrian–Peloritanian–Kabilide or CK units) prior to the collision of the latter elements with the continental margin of Africa in Sicily and Tunisia along the so-called Drepano Thrust Front (DTF). Coeval to collision, the generation of the Main Sardinia Thrust (MST) occurred, carrying the Sardinia basement rocks over the CK units, and deforming the fore-arc basin sediments. The intermediate pre-Messinian sedimentary subunit spans from part of Serravallian to part of Tortonian. It is post-tectonic with respect to the underlying subunit, but it represents a pre-rift succession, if related to the overlying one. It consists of terrigenous deposits prograding from Sardinia to the ENE into a basin some hundreds of meters deep, which was left in the area after collision. The youngest pre-evaporitic subunit (late Tortonian–early Messinian in age) displays wedge-shaped reflectors in the Sardinia Basin, and forms the lower portion of a syn-rift complex including the Messinian and part of the Pliocene sediments. This succession records the onset of extensional tectonics in the area, as also testified by the Tortonian age of exumation of the basement. While in the Tyrrhenian Basin, north of the OCL, intra-Tortonian to intra-Pliocene rifting was strong but discontinuous and migrating with time to the east, in the SW Tyrrhenian Basin, in contrast, rifting was less severe but continuous during the same time interval. This emphasizes the role played by the OCL, a inherited Mesozoic discontinuity reactivated as a transfer zone during the Neogene. These new data allow correlation of the main Miocene deformational events observed in the study area to those of the adjacent emerged areas, namely the Peloritani and Maghrebian units in Sicily, prior to the Pliocene–Quaternary full development of the southern Tyrrhenian Sea.
The distribution and morphology of the mud diapirs in the Western Alboran Basin were studied using multichannel and high resolution seismic profiles (airgun). The diapirism in the Western Alboran Basin forms diapiric ridges and mud volcanoes. Three types of contact relationships between the diapirs and the sedimentary cover have been identified: (1) inverse-piercing contacts; (2) normal-fault contacts; and (3) subvertical contacts. These geometric relationships and the study of the sedimentary cover composed of six seismic units (Lower Miocene to Quaternary) allow us to establish the timing and the geodynamic framework under which the diapirism has evolved. The diapir distribution was controlled through the geodynamic evolution of the Alboran Basin related to extensive, compressive and strike-slip processes. Four phases of diapirism are proposed in order to explain the evolution of diapirism: reactive, active, passive and collapse phases. We establish an evolutionary model of diapirism from the Langhian to the present. Diapirism started in the Langhian-lower Serravallian controlled by extensional processes that allowed a reactive phase to develop. Upper Serravallian-lower Tortonian diapirism was characterized mainly by active diapirism induced by compressional and strike-slip processes. During the upper Tortonian-lower Messinian passive diapirism was predominant until the upper Messinian, when an active diapiric phase developed under a transtensive tectonic setting. Extensional processes continued acting during the Pliocene and Lower Quaternary in the Western Alboran Sea, inducing reactive diapirism though it was punctuated by several active phases. The Upper Quaternary was characterized by a generalised collapse phase linked to extensional processes that developed in many mud ridges, although mud volcanism and active diapirism was also favoured by differential loading produced by a contouritic drift.
A discussion is made on the general significance of an Early Miocene (22–23 Ma, K/Ar dating) basaltic dike swarm that outcrops within large areas of the central and western Betic Zone of the Betic Cordilleras (Southern Spain). This dike swarm is thought to represent the remains of one of the earliest magmatic episodes within the the Neogene volcanic province that is associated with the late orogenic evolution of the Alboran region, and undoubtedly offers the best preserved igneous material related to this early stage that is known at present. The dike rocks (hypabyssal equivalents of andesitic basalts and basaltic andésites) have both major and trace-element abundance patterns that are akin to those of arc-tholeiitic suites. The field relationships and areal distribution of the dike swarm suggest, on the other hand, that a major E-W-trending rifting belt could have been developing within the Alboran Block in oligo-miocene times, previous to its collision with adjacent continental borderlands in the Early-Middle Miocene.
Because of their magmatic character and wide distribution, it is proposed that these dike rocks may be regarded as an indication of the existence of roughly contemporaneous (Oligo-Miocene) Benioff-Wadati zone activity under the Alboran Area, which also points towards the previous existence of subductable lithosphere in its surroundings. The main dilatational vector during dike emplacement was already normal to the present E-W stretching of the Alboran Basin proper, which also adds to the possibility that the latter had already started to individualize tectonically in Oligo-Miocene times, and that some of its present crustal features, especially a prominent E-W-trending pattern of magnetic anomalies, had been generated in relation with the dike event. Continued postcollisional Middle Miocene to Pliocene calc-alkaline to ultrapotassic volcanism in the same area could hence have resulted from decompression partial melting of an already contaminated, and still thermally anomalous, mantle wedge, connected with the occurrence of traverse strike-slip and extensional deep faulting within a crustal segment that stretches from southeastern Spain to Morocco.
Granite and gneiss have been sampled on the submarine fault scarps of the Sardinia Channel and have been dated using the 40Ar/39Ar method. The majority of rocks partially preserve Hercynian ages. Some of them display Lower Cretaceous ages. In addition, Upper Eocene-Oligocene argon resetting is recorded only in rocks from the southeast sector of the Channel. We thus propose that the basement of the Sardinia Channel occupied a shallow position within the stack of the Alpine tectonic units, behind the more deformed front of the internal zones of the Maghrebide Chain.
Reflection profiles characterize the structure and the upper Mesozoic to Cenozoic deposits of the Gulf of Cadiz region. Two long ENE–WSW multichannel seismic lines (ca. 400–500 km long) are analyzed to study the evolution of the area from the continental shelf to the Horseshoe and Seine abyssal plains. The huge allochthonous deposits emplaced in this region (the socalled ‘‘Olistostrome’’ of the Gulf of Cadiz) are described in terms of three different domains on the basis of the seismic architecture, the main tectonic features and the nature of the basement, oceanic or continental. The eastern domain extends along the continental shelf and upper and middle slope and corresponds to the offshore extension of the Betic–Rifean external front. It is characterized by salt and shale nappes later affected by extensional collapses. The central domain develops along the lower slope between the Betic–Rifean front and the abyssal plains and is characterized by a change in dip of the allochthonous basal surface and the basement. The allochthonous masses were emplaced by a combined gravitational and tectonic mechanism. The northern boundary of this domain is marked by the occurrence of an outstanding WNW–ESE-trending thrust fault with a strike-slip component, termed here as the Gorringe–Horseshoe fault. The westernmost domain corresponds to the abyssal plains, where the distal emplacement of the allochthonous body takes place; it is characterized by thrust faults affecting both the sedimentary cover and the oceanic basement. The allochthonous masses show a less chaotic character and the thickness decreases notably. These domains represent different evolutionary steps in the mechanisms of emplacement of the allochthonous units. The eastern domain of the allochthonous units was emplaced as part of the pre-Messinian orogenic wedge related to the collision that gave rise to the Betic–Rifean Belt, whereas the allochthonous wedge of the central and western domains were emplaced later as a consequence of the NE–SW late Miocene compression that continues in present times.
The Valencia Trough is a rift formed during the late Oligocene – early Miocene opening of the western Mediterranean Sea. In this paper, we focus on the crustal structure and on the deep structure of the basin which is hard to delineate because of the widespread volcanism that conceals part of the basement. This work is the result of the study of a dense network of seismic profiling surveys and exploratory wells made in the region. The structure of the deep basement reveals the importance of transfer fracture zones which represent steps in the deepening of the basin. The thinning of the crust follows the basement deepening and we find the same partitioning of structural blocks at the crustal level. Transfer faults also represent limits in the thinning of the crust and each compartment thus delineated has a different thinning and different extensional ratios. Such a discrepancy between the thinning of the upper crust and the thinning of the lower crust may be common in many other rift zones, but is seldom as well imaged as in this study of the Valencia Trough. The transfer zones are related to extensional processes but a simple shear opening is envisaged to explain the discrepancies between thinning and extension and the asymmetry of the margins. The more efficient thinning in the lower crust can be explained by a thermal anomaly in accordance with the recent evolution of the trough. The steady thinning of the margins is discussed in terms of a marginal basin in a compressional context.
We present geophysical and geological evidence of fast (2 cm yr−1 in the east and 5 cm yr−1 in the west) E–W spreading between 16 and 8 Ma in the region behind the Gibraltar Arc in the Algerian Basin.
A simple mechanism of arcuate fold belt and back-arc basin formation is presented based on the opening of mega-continental tension gashes along pre-existing, deep, parallel and steep faults that separate lithospheric units with different properties. If plate convergence is parallel to these faults, the fault-bounded units open at right angles to the convergence vector, adopting an arcuate shape with thrusting in front of the bowed-out units and extensional basin opening between the separated units. This model is applied to the Cenozoic geodynamic evolution of the western Mediterranean. After the Iberian collision 35–30 Ma, several ellipsoidal basins (Valencia, Alboran, North Algerian and Liguro–Provençal) developed by 10 Ma along the eastern margin of the Iberian plate. The formation of these basins is attributed to an increase in NE–SW horizontal tectonic palaeostress during early–middle Miocene times resulting from the post-subduction collision of the Tethyan oceanic lithosphere.
The Alboran Sea is an extensional basin of Neogene age that is surrounded by highly arcuate thrust belts. Multichannel seismic (MCS) reflection profile data suggest the basin has a complex tectonic fabric that includes extensional, compressional and strike-slip structures. The early Miocene history appears to be dominated by graben formation with border faults that are in large part contemporaneous with thrust movements in the external zones of the Betic and Rif mountains. Extension appears to have continued into the late Miocene although the main movements were probably completed by the time of the Messinian ‘salinity crisis’. The Pliocene and younger history of the basin is dominated by infilling of the Messinian topography, gentle subsidence, and extensional, compressional and strike-slip movements. There is evidence from the sea-floor morphology and seismicity patterns that the basin is actively deforming in response to present-day plate motions. Backstripping of well data in the basin margin suggests that the initial extensional event was accompanied by crustal and lithospheric thinning. The depth to Moho inferred from backstripping is greater than the depth expected based on seismic and gravity modelling, suggesting that backstripping underestimates the true amount of thinning. One explanation is that some of the thinning occurred while the crust was above sea level, perhaps as a result of either crustal thickening, or a period of lithospheric heating and thinning, prior to rifting. We found that a model with a ‘normal’ crustal thickness of 31.2 km, a lithospheric thickness of 50 km, and β= 1.4 predicts 0.8 km of initial uplift. These parameters fit the well subsidence data and bring the backstripped Moho into better agreement with the seismic and gravity Moho. The origin of such a thin lithosphere is not constrained by the data, but we believe that it may be a result of the detachment of a cold lithospheric ‘root’ that formed during pre-Neogene collisional orogeny in the region.
The western Mediterranean late Oligocene–Miocene basins (Alboran, Valencia and Provençal basins) are a coherent system of interrelated troughs. In all basins normal faults and thermal subsidence migrated toward the east progressively moving to the Miocene-to-Pleistocene Algerian and Tyrrhenian basins. All those troughs appear elements of the back-arc opening related to the eastward roll-back of the W-directed Apennines–Maghrebides subduction zone, similarly to western Pacific back-arc settings.
These late Oligocene–early Miocene basins nucleated both within the Betic cordillera (e.g. Alboran sea) and in its foreland (Valencia and Provençal troughs). The N40–70° direction of grabens is oblique to the coexisting N60–80°-trending orogen and shows its structural independence from the orogenic roots. Thus, as the extension cross-cuts the orogen and developed also well outside the thrust belt front, the westernmost basins of the Mediterranean had to develop independently from the Alps-Betics orogen. Therefore, the Alboran extension, considered a classic example of a basin generated by the collapse of an orogen, cannot be ascribed to the detachment or annihilation of the lithospheric root. In contrast with the eastward migrating extensional basins, the Betic-Balearic thrust front was migrating westward producing interference or inversion structures.