Polyphase deformation in the Mbé - Sassa-Bersi area: Implications on the tectono-magmatic history of the area and the tectonic evolution of the Tcholliré-Banyo and Central Cameroon Shear Zones (Central North Cameroon)

Field petrographic and structural data of the Mbe-Sassa-Bersi area exposed two main group of rock (metamorphics and plutonics) which were affected by polyphase deformation. The structural evolution is marked by four deformation phases called D1, D2, D3 and D4. The geometrical arrangement of D1 structures (flat-lying foliation, horizontal lineation, recumbent folds and overlapping) allow to linked this deformation phase to tectonic nappe verging toward SSE. The second deformation stage (D2) corresponds to simple shear dominated transpression and characterized by the evolution of the Tchollire-Banyo shear zone (TBSZ) that showing sinistral movement. The third deformation phase (D3), is marked by strain partitioning induced by transpression and links to the evolution of the Central Cameroon shear zone (CCSZ) that displays dextral motion. D1, D2 and D3 are associated to migmatization, development and emplacement of granitic magmatism. During D2 and D3, the magmatic rocks are emplaced under the control of the two main crustal shear zones (TBSZ and CCSZ). D4 deformation is responsible for the development of faults, fracture and joints and corresponds to brittle tectonic. The main NW-SE direction of faults and fractures suggest that D4 stage shows traces of the Benue trough. On the whole, Nappe tectonic, followed by transpressive tectonic are the main tectonic type developed during the Pan-African Orogeny in Central North Cameroon.