Evidence of Brittle Tectonic Continuity Between Precambrian Basement of Aïr and Its Sedimentary Cover (Northeast Niger)

Aïr Precambrian basement (NE Niger) is unconformably overlain by deposits of the Tim Mersoi basin at West and of the Tenere basin at Southeast. The present work addresses the structural relationship between the basement and the overlying sedimentary cover. A methodological approach combining geophysic data (magnetic and seismic) interpretation and fieldwork was implemented. The field observation carried out along the major unconformity between the Tim Mersoi basin and Aïr basement revealed a fault and fracture system mostly oriented N135° to N180° (NNW-SSE) affecting similarly the sandstone formations called “Agadez sandstones” and its underlying basement formations. Structural interpretation of magnetic and seismic maps highlighted two regional lineament systems: the NNW-SSE seismic lineament affecting both the Aïr basement and Tenere basin in the East (Termit basin) and the magnetic one corresponds to the regional N-S In-Azaoua-Arlit fault system prolongated in the Tim Mersoi basin in the west. Interpretation of seismic section across the petroleum system of Termit basin showed that the same NNW-SSE fault system revealed by the fieldwork and seismic map affects similarly the sedimentary cover and the underlying basement. The combined analysis of obtained data reveals a continuum of brittle tectonic between Aïr basement and Tim Mersoi basin in the west and Tenere basin in the east. In the Tim Mersoi basin, this brittle tectonic would control the setup of the uranium mineralization in Arlit region, and in Tenere basin it constitutes a NNW-SSE petroleum system of Termit basin. This regional brittle deformation, deriving from the reactivation of sub-meridian Raghane shear zone (8° 30′) which was considered as a late to post Pan-African tectonic lineament.