Evidence of Quartz, Feldspar and Amphibole Crystal Plastic Deformations in the Paleoproterozoic Nyong Complex Shear Zones Under Amphibolite to Granulite Conditions (West Central African Fold Belt, SW Cameroon)

The Paleoproterozoic is characterised by a global-scale period of crust formation, extensive mafic to granitic magmatism, crustal reworking and intracrustal partial melting. Since a dramatic strength drop is associated with the presence of melt in crystallising or melting rocks, Paleoproterozoic continental deformation is thought to have been largely accommodated by shearing of high-grade gneisses and syntectonic granitoids. The Paleoproterozoic Nyong complex, which is made up of volumetrically dominant granitoids, metapelites and granitic gneisses, quartzites and banded iron formations; has been affected by the Eburnean/Transamazonian polyphase ductile and brittle deformation responsible of S1/2 foliation and S2 schistosity, L2 stretching and mineral lineations, F3 meso- and large-scale folds, S2/C3 structures and faults. Its shear zone strain anisotropies represent a natural laboratory to study the effect of crystal plastic deformation of felsic minerals and amphibole as predicted by numerical experiments and tectonic models. This paper describes the geometry of the deformation and focus on microstructural evidence of dynamic recrystallization features that were active under granulite conditions (>800 °C, >8.5 Kbar). These thermal conditions can be extended in similar Proterozoic worldwide shear zones.