The structural evolution of the Dialé-Daléma basin, Kédougou-Kéniéba Inlier, eastern Senegal
Résumé
The Dialé-Daléma group is located in the eastern part of the Kédougou-Kenieba Inlier (KKI) and is essentially composed of Paleoproterozoic rock formations. Lithostructural studies in this area, hassuggested, often controversial, deformational regimes and geodynamic evolution models. In this study, we suggest the existence of an initial tangential D1 deformation and transpressional D2 deformational phases. D1 is characterized by an initial metamorphic schistosity denoted as S1 and by F1 folds with the main shortening stress direction generally oriented in NW-SE direction. D2 in the study area is divided into two stages. The first stage designated as D2a is coaxial and compressive in nature. It is characterized by a N-S to NNE-SSW trending metamorphic schistosity termed S2a. The D2a phase evolves gradually to a transcurrent phase connoted as D2b and characterized by a NNE-SSW S2b metamorphic schistosity which is axial planar to the F2b folds with subvertical fold axes. During the D2 phase, the main shortening stress direction rotates gradually in a clockwise motion from an E-W to a NW-SE direction within a continuum of deformation. The third deformation phase D3 in the Dialé-Daléma basin, is also divided into two stages, thus D3a and D3b. D3a is transcurrent and transtensive in nature and is characterized by NE-SW sinistral shear corridors with local extensional jogs. During this deformation stage, the maximum shortening stress (σ1) direction acts in a N-S direction and rotate to a NE-SW direction, thereby creating a N-S transcurrent dextral shear corridors. D3b component of the D3 deformation is compressive in nature with a weak sinistral shear component. The D4 corresponds to a N-S extensional phase which is characterized by E-W directed normal faults. D4 in the study area denotes the final stage of the evolution of the Eburnean orogeny in the KKI.