Large-scale distributed deformation controlled topography along the western Africa-Eurasia limit: Tectonic constrains

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In the interior of the Iberian Peninsula, the main geomorphic features, mountain ranges and basins, seems to be arranged in several directions whose origin can be related to the N-S plate convergence which occurred along the Cantabro-Pyrenean border during the Eocene-Lower Miocene time span. The Iberian Variscan basement accommodated part of this plate convergence in three E-W trending crustal folds as well as in the reactivation of two left-lateral NNE-SSW strike-slip belts. The rest of the convergence was assumed through the inversion of the Iberian Mesozoic Rift to form the Iberian Chain. This inversion gave rise to a process of oblique crustal shortening involving the development of two right lateral NW-SE shear zones. Crustal folds, strike-slip corridors and one inverted rift compose a tectonic mechanism of pure shear in which the shortening is solved vertically by the development of mountain ranges and related sedimentary basins. This model can be expanded to NW Africa, up to the Atlasic System, where N-S plate convergence seems also to be accommodated in several basement uplifts, Anti-Atlas and Meseta, and through the inversion of two Mesozoic rifts, High and Middle Atlas. In this tectonic situation, the microcontinent Iberia used to be firmly attached to Africa during most part of the Tertiary, in such a way that N-S compressive stresses could be transmitted from the collision of the Pyrenean boundary. This tectonic scenario implies that most part of the Tertiary Eurasia-Africa convergence was not accommodated along the Iberia-Africa interface, but in the Pyrenean plateboundary. A broad zone of distributed deformation resulted from the transmission of compressive stresses from the collision at the Pyrenean border. This distributed, intraplate deformation, can be easily related to the topographic pattern of the Africa-Eurasia interface at the longitude of the Iberian Peninsula. Shortening in the Rif-Betics external zones – and their related topographic features – must be conversely related to more “local” driven mechanisms, the westward displacement of the “exotic” Alboran domain, other than N-S convergence. The remaining NNW-SSE to NW-SE, latest Miocene up to Present convergence is also being accommodated in this zone straddling Iberia and Morocco, at the same time as a new ill-defined plate boundary that is being developed between Europe and Africa.
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