Structural styles and Neogene petroleum system around the Yusuf-Habibas Ridge (Alboran Basin, Mediterranean Sea)

International audienceThe Algerian offshore is part of the southern margin of the western Mediterranean Sea. The western part of this offshore area represents the transitional margin between the South Algero-Balearic Basin and the Alboran Basin. The study area includes the southern and eastern parts of the Alboran Basin and the northwestern part of the Algerian margin and is in the western part of the plate boundary between Eurasia and Africa (Figure 1). The Yusuf-Habibas Ridge is a major EW-striking structure of this complex plate boundary, separating the eastern and southern parts of the Alboran Basin from the South Algero-Balearic Basin (Martinez-Garcia et al., 2011, and references therein). The ridge played an important role during the Neogene Alboran westward block migration between the Africa and Iberia plates, while the Kabylies blocks migrated southward and accreted to Africa. Furthermore, the ongoing NW-SE convergence between Africa and Iberia has induced a new stress field, since 7 Ma ago, replacing an earlier stress field (Fernandez-Ibañez et al., 2007) and leading to reactivation and polyphased deformation on the main structures in the basin, including the Yusuf-Habibas Ridge

The crustal domains of the Alboran Basin (Western Mediterranean)

The Alboran Basin in the westernmost Mediterranean hosts the orogenic boundary between the Iberian and African plates. Although numerous geophysical studies of crustal structure onshore Iberia have been carried out during the last decade, the crustal structure of the Alboran Basin has comparatively been poorly studied. We analyze crustal‐scale images of a grid of new and reprocessed multichannel seismic profiles showing the tectonic structure and variations in the reflective character of the crust of the basin. The nature of the distinct domains has been ground‐truthed using available basement samples from drilling and dredging. Our results reveal four different crustal types ‐domains‐ of the Alboran Basin: a) a thin continental crust underneath the West Alboran and Malaga basins, which transitions to b) a magmatic arc crust in the central part of the Alboran Sea and the East Alboran Basin, c) the North‐African continental crust containing the Pytheas and Habibas sub‐basins, and d) the oceanic crust in the transition towards the Algero‐Balearic Basin. The Alboran Basin crust is configured in a fore‐arc basin (West Alboran and Malaga basins), a magmatic arc (central and East Alboran), and a back‐arc system in the easternmost part of the East Alboran Basin and mainly Algero‐Balearic Basin. The North‐African continental crust is influenced by arc‐related magmatism along its edge, and was probably affected by strike‐slip tectonics during westward migration of the Miocene subduction system. The distribution of active tectonic structures in the current compressional setting generally corresponds to boundaries between domains, possibly representing inherited lithospheric‐scale weak structures

Mobilité du matériel evaporitique du messinien dans l'offshore occidental Algérien

79 p. : ill. ; 30 cmUne importante série évaporitique s'est déposée dans la Méditerranée occidentale (bassin Algéro Provençal) lors de la crise de salinité messinienne. Parmi ces évaporites, le sel (principalement de l'halite), presque omniprésent dans le bassin profond de la partie ouest de l'offshore algérien, est un matériau ductile, déformable, par opposition aux sédiments sus- jacents de la pile stratigraphique du bassin algérien (évaporites supérieures et Plio- quaternaire) qui présentent un comportement fragile. Pour cerner les mécanismes de mobilité ou fluage l'utilisation des données sismiques et bathymétriques s'avère nécessaire. Sur le plan géométrique, ces évaporites forment des diapirs ou des rides. La mobilité est syn- sédimentaire. Différentes structures s'observent : grabens de crête, rides annulaires et mini- bassins polygonaux. Le glissement gravitaire (lié au soulèvement de la marge ?) est l'un des processus qui permet au sel de glisser vers le bassin profond, soit par l'existence des pentes très faible (moins de 2°) ou par des failles listriques. Des grands éventails détritiques messiniens se retrouvant au pied de la pente passent latéralement aux évaporites qui sont actuellement dans le bassin profond. Ces grès quand ils sont couverts peuvent constituer de bon réservoirs pour les hydrocarbures, si leur répartition est bien cernée. Les évaporites du Messinien constitueraient une bonne couverture pour les réservoirs sous jacents dans les pièges produits par la tectonique (plis ou chevauchements ou autres dispositifs structuraux ou sédimentaires

Back‐arc dynamics controlled by slab rollback and tearing: a reappraisal of seafloor spreading and kinematic evolution of the Eastern Algero‐Balearic basin (western Mediterranean) in the Middle‐Late Miocene

In spite of a clear fan-shaped magnetic anomalies in the Eastern Algero-Balearic Basin (EABB), the way how and the time when seafloor spreading occurred are still debated. In this work, a new seismo-stratigraphic interpretation based on deep-penetration reflection seismic data correlated to reduced-to-the-pole magnetic anomalies and on-offshore litho-stratigraphic correlation of Pre-Messinian units bring new constraints on its age and mode of opening. Our results reveal that the seafloor spreading of the EABB occurred at an intermediate half-spreading rate of 3.7±0.5 cm/yr for 2.45±0.18 Myr during the Langhian-Serravallian times, i.e. after the Corsica-Sardinia block rotation and the collision of Lesser Kabylia with Africa. We revise the kinematics of the Algero- Balearic domain into three stages: (1) birth of a highly stretched continental basin accommodating the southern drift of the Kabylies driven by slab rollback between ∼23 and ∼15 Ma, (2) fast opening of a new EABB between 15.2 and 12.7 Ma by clockwise rotation of a Greater Alboran Block (GALB) promoted by slab tearing, (3) late East-West opening of the western basin in response to the westward retreat of the Gibraltar slab and westward slab tearing propagation and the concomitant migration of the GALB. The last stages match both the late formation of a Subduction-Transform Edge Propagator (STEP) faults at the toes of the Algero-Balearic margins and the post-collisional volcanic migration along the Algerian margin interpreted as related to slab tearing propagation. This new scenario favors a significant stretching and splitting of the GALB into several continental fragments resulting from the westward propagation of the arcuate subduction front by lateral tearing of a narrow slab

Seismo-stratigraphic Mapping Guided by Magnetic Anomalies Stripes: Assessing Opening Models for the Eastern Algerian Oceanic Domain

The Eastern Algerian basin (EAB) occupies a key position at the eastern tip of the Western Mediterranean. Although clear triangular-shaped magnetic anomalies (MA) are well identified since long, the way seafloor spreading occurred during the middle Miocene is still debated. In this work, a new seismo-stratigraphic interpretation of deep penetration seismic data correlated to reduced to the pole MA was used in order to specify the distribution of the oldest sedimentary deposits in the oceanic domain, and thus to assess the best opening models matching the MA fan-shaped pattern. According to this pattern, our results reveal that the seafloor spreading of EAB has occurred along an NW–SE-oriented accretion system giving birth giving birth to six magnetic inversions spanning ca. 2 Myr in Langhian Serravallian times. The oldest units overlying the oceanic floor are of Langhian, i.e., younger than the syn-rift deposits identified on the stretched continental crust further south. We discussed the implications of our findings on the current opening models of the Western Mediterranean Sea

Ongoing Inversion of a Passive Margin: Spatial Variability of Strain Markers Along the Algerian Margin and Basin (Mediterranean Sea) and Seismotectonic Implications

Subduction initiation is an important but still poorly documented process on Earth. Here, we document one of a few cases of ongoing transition between passive and active continental margins by identifying the geometrical and structural signatures that witness the tectonic inversion of the Algerian continental margin and the deep oceanic domain, located at the northern edge of the slow-rate, diffuse plate boundary between Africa and Eurasia. We have analyzed and tied 7900 km of deep seismic reflection post-stacked data over an area of ∼1200 km long and ∼120 km wide. The two-way traveltime lines were converted into depth sections in order to reconstruct and map realistic geometries of seismic horizons and faults from the seafloor down to the acoustic basement. Along the whole length of this young transitional domain, we identify a clear margin segmentation and significant changes in the tectonic signature at the margin toe and in the deep basement. While the central margin depicts a typical thick- and thin-skinned tectonic style with frontal propagation of crustal thrust ramps, the central-eastern margin (Jijel segment) reveals a higher strain focusing at the margin toe together with the largest flexural response of the oceanic lithosphere. Conversely, strain at the margin toe is limited in the western margin but displays a clear buckling of the oceanic crust up to the Spanish margin. We interpret these contrasting, segmented behavior as resulting from inherited heterogeneities in (1) the geometry of the Algerian continental margin from West to East (wrench faulting in the west, stretched margin elsewhere) and (2) the Miocene thermal state related to the diachronous opening of the Algerian basin and to the magmatic imprint of the Tethyan slab tearing at deep crustal levels. The narrow oceanic lithosphere of the Western Algerian basin is assumed to favor buckling against flexure. From the dimension and continuity of the main south-dipping blind thrusts identified at the margin toe, we reassess seismic hazards by defining potential lengths for ruptures zones leading to potential magnitudes up to 8.0 off the central and eastern Algerian margins

Back‐Arc Dynamics Controlled by Slab Rollback and Tearing: A Reappraisal of Seafloor Spreading and Kinematic Evolution of the Eastern Algero‐Balearic Basin (Western Mediterranean) in the Middle‐Late Miocene

International audienceIn spite of clear fan-shaped magnetic anomalies in the Eastern Algero-Balearic Basin (EABB), the way how and the time when seafloor spreading occurred are still debated. In this work, a new seismo-stratigraphic interpretation based on deep-penetration reflection seismic data correlated to reduced-to-the-pole magnetic anomalies and on-offshore litho-stratigraphic correlation of Pre-Messinian units brings new constraints on its age and mode of opening. Our results reveal that the seafloor spreading of the EABB occurred at an intermediate half-spreading rate of 3.7 ± 0.5 cm/yr for 2.45 ± 0.18 Myr during the Langhian-Serravallian times, that is, after the Corsica-Sardinia block rotation and the collision of Lesser Kabylia with Africa. We revise the kinematics of the Algero-Balearic domain into three stages: (a) birth of a highly stretched continental basin accommodating the southern drift of the Kabylies driven by slab rollback between ∼23 and ∼15 Ma, (b) fast opening of a new EABB between 15.2 and 12.7 Ma by clockwise rotation of a Greater Alboran Block (GALB) promoted by slab tearing, and (c) late East-West opening of the western basin in response to the westward retreat of the Gibraltar slab and westward slab tearing propagation and the concomitant migration of the GALB. The last stages match both the late formation of Subduction-Transform Edge Propagator faults at the toes of the Algero-Balearic margins and the post-collisional volcanic migration along the Algerian margin interpreted as related to slab tearing propagation. This new scenario favors a significant stretching and splitting of the GALB into several continental fragments resulting from the westward propagation of the arcuate subduction front by lateral tearing of a narrow sla

Mapping the oceanic flexure off Algeria: along-strike changes in space and time

International audienc

Crustal structures and salt tectonics on the margins of the western Algerian Basin (Mediterranean Region)

We present an overview of the crustal architecture of the continental margins of the oceanic Algerian Basin in the westernmost Mediterranean Sea. During the Cenozoic, and with a variable oblique convergence between the African and Eurasian plates during the Cenozoic, the Western Mediterranean Sea has experienced thinning and extension behind a tight orogenic arc formed by the Betics, Rif, and Tell Cordilleras. This study is focused on the structural style affecting the Messinian salt layer, which is mostly restricted to the deep domains of the Algerian Basin, where it is floored by a thin oceanic crust of probable Miocene age. Using deep-penetrating seismic profiles and wells from offshore western Algeria to southeastern Spain, we have analyzed the crustal structures affecting the domains close to the oceanic-continent transition on the three margins of the western Algerian Basin. Since the Early Miocene, active shortening in the Tell-Atlas domain has accommodated most of the plate convergence in the basin, whereas the Alboran margin in the west and the Iberian margin in the north experienced eastward and southward crustal extension and thinning, respectively, accompanied by volcanism. The Algerian margin in the south shows incipient thrusting of African continental crust over oceanic crust. This shortening occurred since at least the Late Miocene, also promoting decoupling and contraction of the deep, sub-horizontal Messinian salt layer. The salt exhibits diapir squeezing and suprasalt folding, whereas the presalt sequence preserves partially-inverted half-grabens. Salt tectonic processes along the northern and western margins of the Western Mediterranean Basin show contrasting structural styles formed by narrow extensional and transtensional domains with gentle salt anticlines. This region shows therefore a somewhat unusual salt-tectonic style, departing from the gravity-driven model typical of continental margins that contain an initial continuous, gently-dipping salt layer. In the Algerian Basin, salt is mostly restricted to deep water domain floored by oceanic crust, so it does not participate in significant gravity-driven deformation. Instead, Messinian salt and the suprasalt sequences underwent significant shortening along the southern margin, simultaneous with thick-skinned extension involving the Messinian evaporites in the northern and eastern margins