Deformation history of the Yaounde Group in the Awae - Ayos area (Southern- Cameroon): Evidence for Pan-African thrust tectonics

Abstract

Geological mapping and petro-structural analysis of the rocks of the Yaounde Group in the Awae - Ayos area reveal that they experienced at least four successive deformation phases (D1, D2, D3 and D4). Thrusting of these rocks above the Congo craton happened during the D2 and D3 phases. Structural features related these phases (flat lying foliations and shear bands, S-C fabrics, abundant asymmetric folds, asymmetric boudinage and porphyroblasts) suggest that: (1) strain results from large-scale horizontal shearing deformation in a non coaxial regime; (2) the regional stretching/mineral lineation represents the direction of transport; (3) the thrusting probably took place west to south-westwards. The D3 phase was later followed by the development of dextral strike slip shear zones and large scale N-S to NE-SW directed folding related to the D4 phase. This structural evolution show clear similarities with the one observed in the metasediments of the Mintom area, and therefore allow considering all these formations as a single allochthonous structural unit thrust onto the Congo Craton.

Key words: Awae - Ayos; Yaounde Group; thrust tectonics; non coaxial regime; allochthonous structural unit.