Emplacement and deformation of the Fomopéa pluton: Implication for the Pan-African history of Western Cameroon

The Fomopéa pluton (622-613 Ma) is located in the western part of the Pan-African belt in Cameroon. It comprises of 3 units: biotite-hornblende granitoids (BHG), biotite monzogranites (BmG) and edenite syenogranites (EsG). The BHG unit displays magnetic fabrics characterized by foliations gently dipping towards the ESE and ENE-trending lineations (D1 event). Microstructures are magmatic to submagmatic. In discrete N-S deformation bands (D2), lineations are rotated towards the North and microstructures indicate solid-state deformation at mid- to low-T conditions, with kinematic indicators pointing to a sinistral motion. The second unit, BmG, displays lineation trajectories suggesting emplacement during the D2 event. The EsG unit displays fabrics consistent with a later emplacement, with no superposed deformation. The last event (D3) corresponds to a dextral shear zone, that runs along the southeastern border of the Fomopéa pluton. It was responsible for protomylonitic deformation of the granitic rocks in greenschist facies conditions, whereas the core of the shear zone registered higher temperatures and strain. This shear zone induced a rejuvenation of the Rb/Sr isotopic system in the pluton at ca 572 Ma. It belongs to the Central Cameroon shear zone system, regarded as the prolongation of the dextral Patos shear zone system in Brazil.