Print this pageThe Tectonic Evolution of the Atlas Mountains, Morocco
BEAUCHAMP, WELDON, RICHARD W. ALLMENDINGER, MUAWIA BARAZANGI, AHMED DEMNAI, and MOHAMED EL ALJI
The Atlas mountains of North Africa were formed by the reactivation of a major intracontinental rift system. This rift system extended from what is now the Atlantic margin of Morocco, to the Mediterranean coast of Tunisia. The Atlas rift system began in the Triassic and was active through the Jurassic. The post-rift inversion phase of the Atlas rift system began in the Cretaceous and extended into the present. The syn-rift and post-rift sedimentary rocks were uplifted by the reactivation of syn-rift normal faults, with further shortening along newly formed thin-skinned thrust faults. This major uplift phase occurred between 20-30 Ma (Miocene-Oligocene), and corresponds to the Alpine orogenic event.
Seismic reflection data acquired by ONAREP was reprocessed, and combined with field mapping, LANDSAT-TM and gravity and magnetic data to enable the construction of a balanced cross section across the Atlas mountains. This cross section indicates large amounts of shortening (~30 percent) along low angle thrust faults. The original depth to the extensional detachment of the Atlas rift system was approximately twelve kilometers. The convergence of the African and European plates resulted in reactivation of the detachment and related syn-rift normal faults as thrusts. Fault-bend and fault-propagation style folding, originating from syn-rift Triassic evaporites, resulted in additional shortening Further shortening above the reactivated basal rift detachment, may have occurred by a duplex fault zone in the Paleozoic. Superposed phases of folding recognized in the Atlas mountains, may represent reactivation of syn-rift normal faults across an accommodation zone in a single phase of deformation. The styles of faulting interpreted in the High Atlas from field data and geophysical data offer unexplored hydrocarbon potential in footwall subthrust traps.