Thèse de Mourad Medaouri
Ce thème a fait l’objet de la thèse de Mourad Medaouri dont le manuscrit sera bientôt ici, et de deux publications dont le pdf est ici. Les résumés de la publication (1) et les conclusions de la publication (2) synthétisent quelques résultats obtenus sur ce sujet :
(1) Medaouri, M., J. Déverchère, D. Graindorge, R. Bracene, R. Badji, A. Ouabadi, K. Yelles-Chaouche, and F. Bendiab (2014), The transition from Alboran to Algerian basins (Western Mediterranean Sea) : Chronostratigraphy, deep crustal structure and tectonic evolution at the rear of a narrow slab rollback system, Journal of Geodynamics, in : Special Issue on "Geodynamic evolution of the Alboran domain", Corsini, M., Chalouan, A., Galindo-Zaldivar, J., (Eds.), 77, 186-205, doi:10.1016/j.jog.2014.01.003.
SUMMARY
The eastern Alboran basin and its transition to the Algerian basin is a key area in the Mediterraneanrealm where controversial kinematic and geodynamical models are proposed. Models imply strikingdifferences regarding the nature of the crust, the prevalence of brittle faulting and ductile shear, theorigin of magmatism, the style of Miocene deformation and the driving mechanisms of the Alboran platekinematics. Combining a new chronostratigraphic chart of the Alboran and Algerian basins based on theHabibas (HBB-1) core drill, deep seismic sections striking WSW-ENE and SSE-NNW, and potential fielddata, we re-assess the tectonic evolution that controlled the sedimentation and basement deformationof the westernmost limit of the Algerian basin and its transition with the Alboran domain. A WSW-directed extensional tectonic phase has shaped a stretched continental crust with typical tilted blocksalong ∼100 km from Burdigalian to Tortonian times, which is assumed to result from the WSW-directedmigration of the Alboran block driven by a narrow slab rollback. In the Algerian basin, this event wasfollowed by the emplacement of an oceanic-type crust. Potential field signatures of the deep basin aswell as geometrical correlations with onland outcrops of inner zones suggest a minimum WSW-directeddisplacement of the Alboran terrane of ∼200 km. At the southern foot of the Algerian basin, the continent-ocean transition is sharp and may result from the westward propagation of a slab tear at depth, formingtwo segments of STEP (Subduction-Transform Edge Propagator) margins. Our results support models ofintense shear tractions at the base of an overriding plate governed by slab rollback-induced mantle flow.Finally, Messinian salt tectonics affected overlying deposits until today. A late Tortonian to Quaternarydominantly transpressive tectonic episode linked to the Africa-Iberia convergence post-dates previousevents, deforming the whole margin.
Keywords : Alboran sea, Miocene kinematics, Tectonics, Crustal structure, Seismic reflection, Potential field data, Slab rollback, STEP fault margin.
(2) Medaouri, M., R. Bracene, J. Déverchère, D. Graindorge, A. Ouabadi, and A. K. Yelles-Chaouche (2012), Structural styles and Neogene petroleum system around the Yusuf-Habibas Ridge (Alboran Basin, Mediterranean Sea), The Leading Edge, 31(7), 776–785, doi:10.1190/tle31070776.1.
Conclusions
The Yusuf-Habibas Ridge is a continental fragment of the Alboran plate. Given its unique location at the plate boundary between Europe and Africa, the ridge recorded a long history of deformation between these plates. In particular, the north-south relative convergence of Africa and Europe during the Quaternary is marked by a dextral strike-slip along the Yusuf-Habibas Fault forming the Yusuf pull-apart basin.
A careful study of the available seismic sections tied to well HBB-1 clearly shows that the basement of the Yusuf-Habibas Ridge is mostly metamorphic sediments (whose age remains unclear) and Miocene volcanics. Above this substratum, seismic data depict only Pliocene-to-Quaternary deposits and NNWSSE normal faulting which indicate a collapse toward both Habibas and Algerian and South-Balearic basins. The polyphase structural evolution of the Yusuf-Habibas Ridge is summarized below :
- After the development of an Oligocene-Miocene magmatic arc in the Alboran block, the Yusuf-Habibas Ridge was formed during the Tortonian. The uplift of the ridge is linked with the collision of the Alboran plate to the Rif and Betic domains at ca. 10 Ma. The ENE-WSW Tortonian compressive phase, caused by the northeasterly motion of Africa relative to Europe at that time, led to the formation of NW-SE folds and marks the development of the Messinian piggy-back Habibas Basin.
- During the Messinian, evaporites accumulated in Habibas Basin—Unit II in Figure 4, equivalent of Lower Unit (LU) and Upper Unit (UU) in Figures 6 and 7. Well HBB-1 on the shelf (Figure 1) has not penetrated any Messinian salt deposits. The early Pliocene period is marked by the erosion of the existing ridges and seamounts and the overall sedimentation became progressively sandier.
- During the Pliocene and the Quaternary, the WNW-ESE faults bordering the Yusuf-Habibas Ridge were acting as dextral strike-slip structures. This strike-slip movement induced the opening of the Yusuf pull-apart basin and normal faulting on the flanks of the ridge. A detachment fault was associated with the Messinian salt—forming salt domes, diapirs, and rollover structures in the Plio-Quaternary deposits.
- The proper understanding of the polyphase deformational episodes in the broader Habibas Ridge and Basin appears to have an important impact on the exploration potential of this part of offshore Algeria.
(3) Médaouri, M. (2014), Origine de la segmentation de la marge algérienne et implications sur l’évolution géodynamique et des ressources pétrolières, Doctorat d’université en Sciences de la Terre de l’Université de Bretagne Occidentale, co-tutelle USTBH Alger - Sonatrach Boumerdes - UBO Brest, 308 pp.