Characterization of the Damagaram Province Pan - African basement Deformation (South - East, Niger)

This paper focuses on the characterization of the deformation of the Damagaram basement (Southeastern, Niger), which represents the northeastern part of the Benin - Nigerian Shield. The Pan - African terrains belonging to this mobile zone, which is located to the east of the West African Craton, are mainly represented by gneisses, migmatites, metasediments and granitoids. They are intruded by a complex of granites with annular structures commonly called "Younger Granites", which are Carboniferous to Permian in age. The methodological approach implemented combines microtectonic field analysis with petrostructural study of rocks fine section by using a polarizing microscope. The analysis of the schistosity / foliation fabric (symmetric or asymmetric) and of the rheological behavior of rock materials (ductile, semi - ductile or brittle) during the deformation allowed to determine the chronological succession of the deformation phases. The results of microtectonic and petrostuctural analyses highlight a polyphase tectonics history marked, firstly by a D1 extension stage with ~ N20? trending stretching, probably ante - Panafrican, and secondly by three compressive deformation phases (D2, D3 and D4), Panafrican in age. The D2 phase consists of two episodes noted D2a and D2b: (i) the D2a, which is a pure - shear - dominated episode, is ductile to brittle, and related to NW - SE shortening (~ N130?); (ii) whereas the D2b episode, semi - ductile to brittle, is marked by mylonitic deformation, related to an ENE - WSW shortening (~ N80?). The D3 deformation phase, semi - ductile to brittle, was related to a NE - SW shortening. The last deformation phase D4, really brittle, is marked by N - S shortening. Preliminary results of the structural analysis highlight a progressive counter clockwise sinistral rotation of the shortening direction, from azimuth N130? to N00?. This progressive rotation of the shortening direction reflects a continuum of Pan - African deformation, in connection with the convergence between the West African, S?o Francisco, Congo cratons and the Saharan Metacraton.