This study focuses on the petro-structural characterization of the Pan-African terrane of Tchilit in the Gofat-Tafadek sector, within the Aïr Massif (Northern Niger). The Aïr Massif consists of metamorphic rocks intruded by granitoids. Previous works related to the petrographic characterization and structural analysis of the Pan-African terrains in this region are superficial and fragmentary. The general objective of this study is to analyze the petro-structural characteristics of the Pan-African formations. Specifically, the study aims to: (i) determine the petrographic characteristics of different facies, (ii) identify the deformation structures that have affected them, and (iii) establish a relative chronological relationship between the main deformation phases. To achieve these objectives, a methodological approach was implemented, incorporating petrographic analysis and structural measurements. The schistosity/foliation planes, fault planes, and fractures were analyzed using the Win-tensor and Stereonet programs. Petrographic analysis shows that in the Gofat-Tafadek sector, the Tchilit terrane consists of phyllites, chlorite schists, biotite quartzites, mica schists, muscovite quartzites, quartz schists, paragneiss, biotite orthogneiss, amphibolites, metarhyolites, meta-arkoses, two-mica granites, heterogeneous granites, and pegmatites. Structural analysis of the Tchilit terrane in the Gofat and Tafadek sectors reveals three deformation phases: D0, D1 and D2. The extensional deformation phase D0, characterized by a NNE-SSW extension direction (N20°), is evidenced by normal microfault mirrors observed in quartzites. The first deformation phase, D1 (Pan-African), is ductile to semi-ductile and comprises two episodes: D1a (ductile) and D1b (semi-ductile to brittle). The first ductile episode (D1a), related to Pan-African shortening, is characterized by an ENE-WSW shortening direction (N70° on average), while the second semi-ductile to brittle episode (D1b) is marked by an average shortening direction of NE-SW (N40°). The second deformation phase, D2, marked by a shortening direction of N10° (NNE-SSW), is late to post-Pan-African. It is characterized by the development of a fracture schistosity. The structural evolution over time of the shortening direction in the Tchilit terrane highlights a sinistral counterclockwise rotation, from the ENE-WSW direction (Phase D1) to the NNE-SSW direction (Phase D2). This indicates a deformation continuum during the Pan-African event, associated with the convergence between the West African Craton, the São Francisco Craton, the Congo Craton, and the Saharan Metacraton.

This study was carried out in the south-western part of Niger. The study area corresponds to the Niamey region, which straddles the south-eastern edge of the West African Craton and the south-western terminus of the Iullemmeden Basin. The general objective of this work is to determine the context in which the Ct3 deposits were emplaced in the Tondibia, «Rhodesia» and Kongou sectors. Specifically, the aim is to provide a petrographic description of the Ct3 deposits and to characterise the deformation that affected these deposits. The methodology used is based on the macroscopic and microscopic petrographic description of the samples taken and on structural measurements. Three sedimentological sections were taken from the three outcrops selected (Tondibia, Rhodesia and Kongou). The petrographic study of the Continental Terminal 3 (Ct3) deposits identified several facies whose sedimentological characteristics and number varied according to the sectors studied. The facies identified include: kaolinitic sandstones; ferruginous oolitic sandstones; sandstone clays; conglomeratic sandstones; clays intercalated with ferruginous oolitic sandstones; and iron oxide nodule conglomerates. Microscopic observations made it possible to identify several forms of oolitic concretions, namely: type α oolites (Oα), type γ oolites (Oγ), proto-oolites (PO), oolites of type γ (Oγ), oolites of type γ (Oγ), oolites of type γ (Oγ) and oolites of type γ (Oγ). proto-oliths (PO) and composite ooliths (OC). Tectonic analysis has revealed a NW-SE and NE-SW compressive phase of Oligo-Miocene age that affected the deposits of Terminal Continental 3 (Ct3).