Tectonic shortening and topography in the central High Atlas (Morocco)



[1] Three cross sections of the Moroccan High Atlas illustrate the structural geometry and relationship between tectonic shortening and topography in this Cenozoic intracontinental mountain range. The structure is dominated by thick-skinned thrusting and folding, essentially by inversion of Mesozoic extensional faults and by buckling of both pre-Mesozoic basement and its sedimentary cover. Detached, thin-skinned thrusting is limited and apparently related to basement underthrusting, which did not always create structural relief. Despite the high topography, tectonic shortening is moderate, with faults and folds being spaced and separated by broad tabular areas. Section restoration indicates that shortening decreases along strike from east to west in the High Atlas, while topographic elevation generally increases. This inverse correlation suggests that crustal thickening does not fully explain the observed topography and suggests a mantle contribution to uplift. This is supported by geophysical indications of a thin lithosphere and by alkaline volcanism in the vicinity. Mantle-related uplift, which occurs in a broad region, may also explain the scarce foreland basin record adjacent to the High Atlas. The relief of the Atlas Mountains is interpreted as a combination of isostatic and dynamic topography.