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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.

©2018 Amer Geophysical Union This study was financed by the research projects CGL2012-38481 and CGL2016-77560 of the MINECO (Spanish Ministry of Economy and Competitiveness) with also FEDER founding (European Union). Sara Torres-Lopez acknowledges the financial support given by the grant of FPI by the Ministerio de Economia y Competitividad of the Spanish government. The data used are listed in the table., New paleomagnetic data (43 sites) from Mesozoic sediments are contributed in this work, verifying the presence of a pervasive syntectonic Early Cretaceous remagnetization in the easternmost area of the Moroccan High Atlas. Using the small circle intersection method, we have calculated the characteristic remagnetization direction (Dec: 337.3, Inc: 38.4) that fits with a 100-Ma age, according to the Apparent Polar Wander Path of Africa. The paleomagnetic vectors of remagnetization are used to obtain the geometry during the remagnetization stage (100Ma) of one of the most renowned geological cross sections of the High Atlas, the Midelt-Errachidia profile. The partial restoration of the cross section at 100Ma allows us to determine the dips of the beds at the remagnetization stage in five structures (ridges or anticlines). Our results indicate that the five ridges that configure the Midelt-Errachidia profile were initiated to different degrees prior to wholesale compressive deformation during the Cenozoic. This configuration can be explained according to two different scenarios that we discuss in this paper: transpression and diapirism. The geological model obtained, both at present and at 100Ma, indicates the existence of a Mesozoic cover substantially decolled from the Paleozoic basement, what strongly contrasts with previously published transects of the same area., Ministerio de Economía y Competitividad (MINECO), FEDER (European Union), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

[EN] Positive tectonic inversion of sedimentary basins has been recognized as one of the primary mechanisms of mountain building and intraplate deformation. Reconstructing the tectonic history of basins is relatively easy for the inversion stage but becomes more difficult for the basinal stage, especially when strong deformation involving cleavage development is associated with the subsequent compressional tectonics. Since tectonic markers for the extensional episodes are not commonly well developed, Anisotropy of Magnetic Susceptibility (AMS) has provided recently a tool for analyzing early stages in the evolution of sedimentary basins, even in the absence of other outcrop-scale mesostructures. Here, we expose and discuss the applicability of magnetic fabrics (by means of AMS) to different types of intra-plate sedimentary basins in the Western Tethys region formed under extensional or transtensional regimes and which underwent different inversion styles (total or partial inversion, with or without cleavage development, forming part of compressional thrust sheets, etc.) owing to specific particular p-T conditions and structural controls. Factors such as lithology, magnetic mineralogy, position within the sedimentary pile and deformation intensity are key to interpret the obtained magnetic fabrics in terms of tectonic evolution. A basin classification is proposed according to inversion styles and magnetic fabrics: Where inversion did not involve cleavage development, magnetic lineation is parallel to the stretching direction corresponding to the extensional stage. The transition between non-cleaved to inversion-related cleaved units is marked by the switch of magnetic lineations from parallel to extension to parallel to the intersection lineation between cleavage and bedding. These relationships are enhanced when extension and compression are roughly coaxial, then favoring the clustering of axes of the magnetic ellipsoid. Even when extreme inversion occurs and the ea