Using Paleomagnetic and Field Data for the Paleogeometric Reconstruction of the Northern Border of the Central High Atlas

In this work, we present results of the application of paleomagnetism and the analysis of synsedimentary structures in order to clarify the age and origin of transversal anticlinal ridges in the northern border of the Central High Atlas (CHA). The results are interpreted in terms of paleogeometry of the main structures. The High Atlas fold-and-thrust belt is the result of intracontinental basin inversion during the Cenozoic convergence between the African and European plates. The studied ridges separate the three main synclines of the northern border of the CHA, namely Ait Attab, Ouaouizaght and Taguelft. Samples have been collected along the Tansrift ridge separating the Taguelft and Ouaouizaght synclines and to the west, Ouaouizaght syncline from the Ait Attab syncline. Paleomagnetic data reveal the presence of a magnetization component, stable in different lithologies in the ridges. This magnetization is carried by hematite, as evidenced by rock magnetism experiments on representative samples and by the results of thermal demagnetization of the studied samples, showing a maximum unblocking temperature around 680 °C. The paleomagnetic stable component observed in different specimens shows a systematic normal polarity. This component corresponds to the generalized widespread remagnetization known in the CHA, dated at 100 Ma. Directional analysis shows that this remagnetization is syntectonic (inter-folding), indicating that the studied anticlinal ridges were partially uplifted before 100 Ma, predating basin inversion during the Cenozoic convergence. Synsedimentary structures studied at the borders of these three synclines prove synsedimentary uplifting. These results allow to consider these three synclines as confined mini-basins separated by diapiric ridges at least since Bathonian time.