Recent studies have shown that the uplift of the moroccan Atlas Mountains resulted from a combination of crustal shortening and mantle thermal processes. Within this framework, to gain insight of the dynamics of these processes in recent times, we have investigated the nature and rates of Quaternary deformation in a case field area, which contains the best dated record of fan and terrace deposits, and a moderate seismicity. The area selected is the northern Ouarzazate basin, at the southern orogenic front ofthe Atlas, where folds and thrusts involve a sequence of stepped terraces where recently obtained Terrestrial Cosmogenic Nuclide surface exposure ages provide a basis to calculate shortening rates for the last —250 ky (since the interglacial peak MIS-9c).
Calculated Quaternary shortening rates for individual thrust structures range between 0.13-0.21 mmfy, which are greater that the average for these structures since Miocene times, but not very different from the total shortening rate estimated for the southern Atlas front since then (0.3 mmfy). Seismic reflection profiles show two tectonic styles acting simultaneously within the northern Ouarzazate basin: thick-skinned to the west and thin-skinned to the east. This difference is also reflected on the deformation geometry ofthe Quaternary marker
