Late Eburnean deformation in the Kolia-Boboti sedimentary basin, Kédougou-Kéniéba Inlier, Sénégal

Abstract

New structural data obtained within the Birimian formations of the Kolia-Boboti sedimentary basin evidenced a third D 3 Eburnean phase (2075–1980 Ma) of deformation in the Daléma supergroup of the Kédougou-Kéniéba Inlier (KKI). The D 3 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 R′. The general architecture of the different structures related to the D 3 phase is characteristic of a dextral transcurrent deformation, affecting a large NS Sénégalo-Malian tectonic corridor. Locally, the D 3 phase produced a moderate dextral reactivation of NS–N20° sinistral shear bands related to the D 2 Eburnean phase. The D 3 deformation phase is less significant than the D 2 phase and D 3 structures deform and intersect structures developed during the D 2 phase. The main stress responsible for the D 3 deformation, deduced from field observations, would be oriented EW to NE–SW.