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.

The Niamey sandstones belong to a group of Neoproterozoic (Infracambrian) deposits of the Nigerian Liptako, sporadically outcropping along the eastern edge of the West African Craton and following the Niger River valley. They rest in major unconformity on the Paleoproterozoic (Birimian) basement of the Niger Liptako. Previous work on these deposits has been fragmentary, particularly as regards their structure, and the investigations carried out aim to make up for these shortcomings. The aim of this study is to determine the deformations that have affected the Niamey sandstones. To achieve these objectives, an integrative approach based essentially on analyses and measurements of deformation structures in the field and their projections in the Win-Tenseur program, in order to calculate stress tensors (σ1, σ2, σ3), was implemented. Structural analysis has identified an extensive pre-Pan-African D1 phase, trending NNW-SSE to NNE-SSW, concomitant with the opening of the Neoproterozoic Ocean, and two Pan-African compressive episodes, NNW-SSE to NW-SE trending D2a and ENE-WSW trending D2b.