Inhomogeneous shearing related to rock composition: evidence from a major late-Panafrican shear zone in the Tuareg shield (Algeria)

This study describes the deformation in zones affected by regional shearing, and its relation with local factors, in particular rock compositions. The Tihaliouine and Teg Orak plutons were emplaced close to a major shear zone of the Tuareg shield. Their magmatic to sub-magmatic fabrics were determined by using measurements of anisotropy of magnetic susceptibility; they are similar to those of some other late Panafrican plutons of the Tuareg shield. The eastern part of the Teg Orak pluton displays a coherent fabric with a subhorizontal lineation oblique to the 4°50 major shear zone located just to the east. This fabric is clearly related to shearing by a dextral strain-slip movement along the shear zone during magma crystallization. The fabric in the western part of the Teg Orak pluton and in the Tihaliouine massif presents much more scattered principal axes. It was much less affected by shearing along the shear zone. This difference strongly depends on the nature of the host-rocks: Granitic host-rocks around the Tihaliouine and the western part of the Teg Orak acted as a rigid block, protecting the intrusions from regional deformation, while basic plutonic and metamorphic host-rocks around the eastern part of the Teg Orak pluton had a more plastic behavior and transmitted the regional strain to the intrusion.