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Le relief des Atlas Marocains : contribution des processus asthénosphériques et du raccourcissement crustal, aspects chronologiques.

Abstract : This thesis focuses on the study of vertical movements and the characterization of the main processes controlling them in an intraplate mountain belt. The mechanisms at the origin of the relief evolution are numerous and still poorly known. The High Atlas belt of Morocco is situated at more than 600 km of the Africa-Europe plate boundary, and supports the second highest peak of Africa (Jebel Toubkal, 4165 m). The lack of a significant crustal root under the belt, a consequence of limited shortening (~20 km), implies that another process takes place to explain such elevations. Lithospheric cross-sections allow us to show that a lithospheric thinning explain 1000 m of topography in the Anti-Atlas, the Central High Atlas, the Middle Atlas. Some of the foreland basins are also affected, like the Souss, Ouarzazate and Missour basins. The thinned area is an elongated stripe running North East / South West and crossing over the main structural domains of Morocco and probably the Africa-Europe plate boundary.
The second mechanism explaining the High Atlas topography is the crustal shortening. We present a structural analysis on the basis of field data in the Marrakech High Atlas. The constrated mechanical stratigraphy is described, and numerous potential décollement levels are identified. They are mostly developed in the Visean, Cambrian, Triassic and Senonian units. The complex heritage of this area, situated between the Triassico-Liassic Atlantic and Tethyan rifts, controls their activation on the belt borders. They trigger the formation of various structures, such as tectonic wedges, rabbit ears folds, imbricate fans... A basal rigid group is distinguished, including the Precambrian rocks and locally the Paleozoic and Triasic series. A complete cross section of the belt is presented.
The chronology of the deformation and the age of the lithospheric thinning are finally discussed. We propose a scenario of the foreland evolution in the light of the available geological data combined with new results of fission track thermochronology. A first shortening phase occurred during Upper Eocene to Oligocene. The lithosphere is thinned between the Lower and the Middle Miocene, and a main erosionnal event affects the belt and its foreland. Finally, the crustal shortening starts again during Plio-Quaternary.
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https://tel.archives-ouvertes.fr/tel-00125775
Contributor : Yves Missenard <>
Submitted on : Monday, January 22, 2007 - 3:28:41 PM
Last modification on : Monday, October 19, 2020 - 11:07:16 AM
Long-term archiving on: : Tuesday, April 6, 2010 - 10:25:04 PM

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  • HAL Id : tel-00125775, version 1

Citation

Yves Missenard. Le relief des Atlas Marocains : contribution des processus asthénosphériques et du raccourcissement crustal, aspects chronologiques.. Tectonique. Université de Cergy Pontoise, 2006. Français. ⟨tel-00125775⟩

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