Neogene and Quaternary deformation of the northern High Aatlas border [Morocco]: role of the basement and structural consequences

According to major discontinuities, continental deposits in the Cenozoic At las basins are subdivided into three groups (pre-, syn- and post-tectonic). Progressive unconformities are the main characteristic of the syntectonic formations, implying that the Atlas tectonic episode is synchronous with Ne ogene and Quaternary sedimentation. This tectonic episode is responsible fo r the inversion of Early Mesozoic extensional structures within the basemen t, which were reactivated into symmetrical thrusts or transpressional fault s. Shortening of the basement induced the detachment of the cover. Deformat ion of the cover is expressed by thrust faults (with southern and northern vergences), folds and flexures linked to blind thrusts. Kinematic data show that the main regional compression was directed N150+/-10 degrees during t he Neogene and north-south during the Quaternary. The involvement of the up per crust, in the Alpine Atlasic Belt, contributed to create areas of high relief. The High Atlas can be interpreted as resulting from large Cenozoic thrusts, and compared with the Pyrenean Axial Zone, although their pre-Ceno zoic histories can differ markedly. (C) 2000 Elsevier Science Limited. All rights reserved.