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[EN] From the application of the magnetic techniques (Anisotropy of Magnetic Susceptibility and paleomagnetism) it can be seen that to determine the age (and origin) of structures in the Moroccan Central High Atlas is not straightforward from geometrical features only and that similar structures can have different origins, or that the two limbs of a particular structure can have developed at different times. A classification of structures is proposed showing all these possibilities. As a general rule, many structures were initiated before compression and, with local exceptions associated with salt structures, paleo-dips were shallow at the remagnetization stage. This has allowed the restoration of structures and the characterization of the overall geometry of the atlasic basin as a narrow, steer’s head strongly subsiding basin whose geometry strongly conditioned its tectonic inversion during the Cenozoic compressional stage. As a synthesis, the Central High Atlas constitutes a good example of intra-plate chain in which different models of basin formation (continental rifting, salt tectonics, transtension) and inversion (thrust tectonics, transpression, buttressing and internal deformation…) can be tested and visualized.

Previous works developed by our research group have shown that the Jurassic rocks of the Central high Atlas (CHA) have recorded a Cretaceous widespread remagnetization. In this chapter, a high resolution paleomagnetic study on 424 new paleomagnetic sites in Mesozoic units of CHA is presented. This work provides new information about the Cretaceous magnetic overprint of the CHA, as well as contributes to the knowledge of the geodynamic evolution of the Atlas. The new results confirm the extent of remagnetization throughout the study area (10,000 km2) in both carbonates (carried by magnetite) and red beds (carried by hematite) showing systematically normal polarity and an inter-folding acquisition. By using small circle techniques, the remagnetization direction (n = 531, Dec = 335.4°, Inc = 42.7° for carbonates and n = 62, Dec = 344.4°, Inc = 41.7° for red beds) and the age of acquisition (100 Ma ± 5 Ma for limestones) have been determined. The remagnetization properties in the carbonates and their paleomagnetic direction are maintained throughout the studied area and the different stratigraphic units. The small but statistically significant difference between the directions of remagnetization in carbonates and red beds suggests a delay in the acquisition in red beds. Remagnetization directions have been restored using small circle techniques, allowing to generate a set of 593 paleo-dips of the beds at 100 Ma. This valuable information has been used in Chap. “ Kinematics of Structures and Basin Evolution in the Central High Atlas. Constraints from AMS and Paleomagnetic Data ” to elaborate palinspastic reconstructions and to study the evolution of the different structures of the CHA. For this purpose, a new diagram (paleo-dip evolution diagram, PED) is here proposed.

[EN] The anisotropy of magnetic susceptibility provides valuable information on the imprint of the different tectonic processes occurred in the Central High Atlas (CHA), complementing the structural analysis and paleomagnetic information. Different types of magnetic ellipsoids, related with extensional, diapiric or intrusive processes occurred during the Mesozoic, or with the Cenozoic compression, can be recognized. The predominance of one or another type of fabric varies spatially, and a transition can be observed from bedding-related fabrics in Western and Eastern sectors, to more abundant, modified magnetic fabrics in the Central sectors and in the Southern border of the CHA. Extensional fabrics are characterized by the orientation of the kmin axes normal to bedding and the kmax axes clustered in a NW–SE direction within the bedding plane. This direction represents the regional (and local) extension, perpendicular to the main faults. Compressional magnetic fabrics show their kmin axes in NW–SE or N-S directions and/or kmax axes sub-horizontal and clustered in the NE-SW direction, consistently with the shortening direction inferred from the trend of compressional structures (folds and thrusts). Compressional tectonic fabrics are unequivocally interpreted in areas showing regional cleavage. Magnetic lineations vertical or close to the bedding dip direction are found near thrust planes or near the core of narrow and tight anticlines and are related to transport direction or re-tightening of structures, in many cases nucleated in relation to salt tectonics features.

[EN] From a 3-D reconstruction based on serial cross-sections, structural observations, and potential field geophysical data we characterize the major structural frame of the Moroccan Central High Atlas. Its overall structure shows two fold-and-thrust systems (each one showing particular features) at the northern and southern borders of the chain, resulting from the inversion of the Mesozoic basin. Five more zones can be distinguished in the inner part of the chain, according to their structural features, ranging from basement-involved structures in the westernmost sector to completely detached structures in the eastern part. Most compressional structures show an ENE-WSW (atlasic) trend, also pinpointed by the orientation of pressure-solution and slaty cleavage associated with the compressional stage. Large-scale faults of crustal or lithospheric reach can be inferred from the aeromagnetic maps, that show that the gabbro intrusions (some of them showing sigmoidal shape) are aligned in an E-W direction, oblique to the main trend. The overall compressional structure is controlled by a main, low-angle, South-verging thrust involving both the Mesozoic cover and the Paleozoic basement thrusting over the southern foreland of the chain. Branching on this surface there is a series of back-thrusts and faults, some of them resulting from re-activation of extensional structures.