Late Eburnean deformation in the Kolia-Boboti sedimentary basin, Kédougou-Kéniéba Inlier, Sénégal
Résumé
New structural data obtained within the Birimian formations of the Kolia-Boboti sedimentary basin evidenced a third D3 Eburnean phase (2075-1980 Ma) of deformation in the Daléma supergroup of the Kédougou-Kéniéba Inlier (KKI). The D3 phase is well exposed in the sedimentary rocks (quartzites, sandstones, greywackes, . . .). It is expressed by a NW and EW fracture and shear foliation with oblique dips towards the south, southeast and southwest. This foliation is associated with asymmetric ''Z-shaped'' folds and with NW-SE or SW-NE dextral shear bands. The NW-SE and SW-NE dextral shear bands, which could be R and P respectively, are associated with sinistral N80 -90 trended shear bands which represent R0 . The general architecture of the different structures related to the D3 phase is characteristic of a dextral transcurrent deformation, affecting a large NS Sénégalo-Malian tectonic corridor. Locally, the D3 phase produced a moderate dextral reactivation of NS-N20 sinistral shear bands related to the D2 Eburnean phase. The D3 deformation phase is less significant than the D2 phase and D3 structures deform and intersect structures developed during the D2 phase. The main stress responsible for the D3 deformation, deduced from field observations, would be oriented EW to NE-SW.