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

Abstract

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.

Eburnean and Pan-African granitoids and the Raghane mega-shear zone evolution: Image analysis, U–Pb zircon age and AMS study in the Arokam Ténéré (Tuareg shield, Algeria)

“…All the characteristics indicate that the magnetic fabric here still corresponds to the magma emplacement and was not tectonically disturbed during the late-magmatic period. The Abdou pluton intruded the same country-rocks as the Hanane pluton and it cannot be claimed for a difference of the regional rheology as in the case of the Teg Orak pluton (Henry et al, 2008). The most likely explanation is that Abdou intruded later than Hanane, when the regional stress field was vanishing.…”

“…Such an orientation of K 1 axes, subvertical and linked to magma flow is very different from that of almost all the other studied plutons in the Hoggar where the fabric is related to regional stress field. Only a part of the Tihaliouine pluton in Central Hoggar (late Taourirt pluton; Azzouni-Sekkal et al, 2003) has a similar structure (Henry et al, 2008). The orientation of the magnetic foliation, often with steep plunge, is rather related to that of the pluton border.…”

“…Concerning the magnetic fabric, the Abdou pluton is an exception: it is one of the two known plutons in Hoggar (with Tihaliouine pluton in Central Hoggar - Henry et al, 2008) that was not submitted to a regional stress field during its late-magmatic phase. This is probably due to the combination of the rigidity of the Arokam basement and to a young age of this intrusion.…”

“…The magnetic fabric is therefore related to the structural conditions that occurred during the late-magmatic evolution of the pluton. The relative scattering of the principal axes suggests moderate effect of these conditions, probably because the Arokam-West orthogneiss, in which the granodiorite intruded, acted as a rigid block, partly protecting the granodiorite from the regional deformation (Henry et al, 2008).…”

“…Terranes of Assodé -As, Issalane -Is, Tazat -Tz, AouzegueurAz, Barghot -Ba, Djanet -Dj and Edembo -Ed. Tihaliouine -Tih, Teg Orak -Teg (Henry et al, 2008), Tesnou -Tes (Djouadi and Bouchez, 1992), Alous En Tides -AET (Henry et al, 2004), In Telloukh -Ite (Henry et al, 2007), Tioueine -To (Djouadi et al, 1997), Tifferkit -Tf, In Tounine -Ito (Henry et al, 2006), Tin Ghoras -TGh, Oued Tiririne, -OTr, Honag -Hon, Adjou -Adj, Kerkour -K r, Oued Touffok -Otf, Arigher -Ari and Ohergehem -Ohr . Arokam Ténéré study-TI.…”