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-Provencal, 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.

Detailed tectonic reconstructions of the Western Mediterranean region for the last 35 Ma, insights on driving mechanisms

Exhumation and Surface Evolution of the Western High Atlas and Surrounding Regions as Constrained by Low-Temperature Thermochronology

On the Early Permian shape of Pangea from paleomagnetism at its core

Lithological control on topographic relief evolution in a slow tectonic setting (Anti-Atlas, Morocco)

The High Atlas intracontinental belt is an inverted rift formed along the Northwest African Craton, between the Central Atlantic Ocean and the Africa-Eurasia plates’ boundaries. Due to its particular location at this triple junction, the Moroccan High Atlas is a good example to investigate the tectonic and geodynamic complexity within continental interiors. The present paper aims to give an overview of the actual understanding of the post-Variscan tectonic and structural history of the High Atlas belt and to shed light on some of the most actively debatable questions relating to the geodynamic context of its uplifts. The High Atlas basin Alpine history started with a period of passive rifting during the Middle-Late Triassic-Early Liassic resulting in a complex rift system actuated by the reactivation of Variscan NNE to ENE-trending structures in the framework of a global NW-SE extension. The Late Triassic rift basins were filled by thick salt-bearing red-beds whose post-rift extensive halokinetics has a considerable impact on the structural architecture of the Western and Central High Atlas. Extensional deformation was renewed in the Central High Atlas at the Late Liassic-Early Bajocian associated with the drowning of Liassic carbonate platform coevally with salt mobilization which led to the initiation of NE to ENE-elongated narrow diapiric ridges. By the Middle Jurassic, a major part of the High Atlas basin was submitted to a widespread post-rift epeiorogenic upward motion that lasted up until the Lower Cretaceous, and to which is associated the occurrence of transitional to moderately alkaline magmatism that was emplaced within the established ridges across basement faults. The driving geodynamic mechanisms and the tectonic setting of this uplift are poorly known but the large extent of the exhumed lands in both margins of the Central Atlantic and the synchronicity between the upward movements and the drastic increase of the Central Atlantic Ocean spreading rate suggests a possible causal link between the Central Atlantic dynamics and the Middle Jurassic-Lower Cretaceous post-rift exhumation. The Late Cretaceous signals the onset of the convergence between Africa and Eurasia and the consequent Alpine orogeny. The effective inversion of the Atlas paleo-rift begun during the Eocene and accentuated during the Neogene in an intra-continental environment. The western segment of range witness a basement-involved thick-skinned faulting and folding style, whereas thin-skinned deformation detached mostly on Upper Triassic-Early Liassic evaporitic layers is focused in external forelands. In the Central High Atlas, the salt-involved Cenozoic deformation triggered the evaporites squeezing and extrusion and the inversion of the pre-structured magmatic cored ridges into compressional anticlines. During the Alpine orogeny, the High Atlas orogen underwent weak crustal shortening with the development of a moderate crustal root that resides over a highly elevated Lithosphere-Asthenosphere Boundary. The most prevailing view predicts the occurrence of a hot mantle anomaly, superimposed to the collisional deformation, beneath the Atlas range that maintains the high topography featuring the High Atlas orography. Although advanced studies have been performed, several questions regarding the kinematic history, the origin of the vertical movements, the role played by the week salt layers during both extensional and compressional deformation stages, and the factors controlling the selective inversion of the paleo-rift normal faults and the deep geometry of the range’s major faults, are still not well resolved and deserve to be deeply re-investigated.

The intracontinental High Atlas belt: geological overview and pending questions

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2019TC005563

Tectonic Evolution of the Western High Atlas of Morocco: Oblique Convergence, Reactivation, and Transpression

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Tectonic Evolution of the Western High Atlas of Morocco: Oblique Convergence, Reactivation, and Transpression