Mantle dynamics and intraplate orogeny: The Atlas of Morocco

Most orogenic belts are close to convergent plate margins. However, some orogens are formed far away from plate boundaries, as a result of compressional stress propagating within plates, basal loading, or a combination of thereof. We focus on the Atlas of Morocco, which is such an intraplate orogeny and shows evidence of mantle driven uplift, and plume-related volcanism. How these processes interact each other is still poorly constrained and it provides clues about intraplate stress propagation, strain localization, and lithospheric weakening due to mantle dynamics. We present three sets of observations constructed by integrating previous data with new analyses. Crustal and thermal evolution constraints are combined with new analyses of topographic evolution and petrological and geochemical data from the Anti-Atlas volcanic fields. Our findings reveal that: i) crustal deformation and exhumation started during middle/late Miocene, contemporaneous with the onset of volcanism; ii) volcanism has an anorogenic signature with a deep source; iii) a dynamic deep mantle source supports the high topography. Lastly, we conducted simple numerical tests to investigate the connections between mantle dynamics and crustal deformation. This leads us to propose a model where mantle upwelling and related volcanism weaken the lithosphere and favor the localization of crustal shortening along preexisting structures due to plate convergence.