Geodynamic Evolution During the Mesozoic and Cenozoic in the Central High Atlas of Morocco from Anisotropy of Magnetic Susceptibility

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.