Paleostress evolution in the Moroccan African margin from Triassic to Present

Abstract

Paleostresses were calculated from more than 1000 fault-slip data on sites located in the Rif moutains, the Middle and High Atlas chains, the occidental Moroccan Meseta and northeastern Morocco. We sorted the state of stress according to the main tectonic events in order to present new synthetic maps of paleostresses of Morocco. In the Late Triassic–Early Cretaceous time, NW–SE to NE–SW extensions occurred. They are consistent with the opening of the Atlasic and Atlantic rifts. In the Late Cretaceous–Paleocene, an E–W to WNW–ESE compression took place. Conjugated strike-slip faults developed in northeastern Morocco and in the Atlas chain. This event was followed by a N–S Eocene compression where most of the reverse faults and the folds of the Atlasic area developed together with strike-slip faulting. Compression extended from Oligocene to Middle Miocene with a NE–SW direction in the Rif chain, the Middle and High Atlas and the coastal Atlantic basins. Continuous deformation during the Neogene in the Atlasic area was responsible for shortening of the basement and detachment of the sedimentary cover. Thrust faults at the front of the Atlas were either visible or blind. In the lower Tortonian, NNE–SSW and ENE–WSW to E–W compressions occurred, respectively, east and west of the Nekor fault. This tectonic regime led to the formation of post-nappes basins separated by emerged lands. In the Tortonian–Early Messinian, the direction of compression varies from N–S to NNE–SSW or NE–SW east and west of the Nekor fault respectively. In the Early Messinian, a large transgression occurred throughout the Meseta domain and the Middle Atlas area. In the Late Messinian, a marine regression was synchronous with the Mediterranean salinity crisis. In the Late Miocene, the Atlas chain emerged and was progressively uplifted together with folding and thrusting of its foreland. Nappes involving Paleozoic basement formed along the axis of the chain. In the Plio-Quaternary, the compression varies from N–S to N140°E and contributes to continuous uplift of the Atlas chain.