An overview of the plutons magnetic fabric studies in the hoggar shield: Evolution of the major shear zones during the Pan-African

Abstract

The magnetic fabric obtained in the Hoggar shield on several plutons is related to various origins: simple flow, syn-deformation flow, stress field during late-magmatic stage and solid-state deformation. These results also evidenced the important role of hosting frame, acting as a more or less efficient “protection” against the effects on the magnetic fabric of the regional stress field. Combined studies, on neighboring sites of the main intrusion and of late-magmatic dykes crosscutting it, yield key-arguments about the acquisition age of this fabric. P′(Km) diagrams clearly highlight the strain gradient in plutons very close to shear zones. The fact that K1 axis is mainly a mineral lineation, at least in three plutons, is evidenced by the determination of the magnetic zone axis. The plutons AMS is associated with different Pan-African stages in the Hoggar: gneissification of Eburnean plutons, syn-thrust pluton emplacement, pluton emplacement under regional shearing context. Accordingly, the main movements along the major shear zones, related to the oblique collision of the Hoggar shield with the West African Craton, are contemporaneous of the first stages. Shearing context during the following period points out that this collision had still active effects, probably associated with a progressive change in orientation of the continental convergence.