Couzinie S. auteur aut IRD Menot R. P. auteur aut IRD Doumnang J. C. auteur aut IRD Paquette J. L. auteur aut IRD Rochette P. auteur aut IRD Quesnel Y. auteur aut IRD Deschamps Pierre auteur aut IRD Menot G. auteur aut IRD text journalArticle eng text/pdf born digital access The structure and evolution of the continental crust in the southern part of the Saharan Metacraton (central Africa) is poorly known due to extensive laterite and sediment cover as well as geographic isolation. We report on a series of five crystalline inliers newly discovered near Lake Iro (south-eastern Chad) that offered the opportunity to unravel the nature of the local basement in this area. Two spatially determined petrographic types are exposed in the inliers: a medium-grained porphyritic amphibole-biotite granite and a biotite microgranite with typical embayed (rhyolitic) quartz phenocrysts, both containing fine-grained melanocratic igneous enclaves. Some porphyritic granites display evidence for low temperature deformation along N60 shear zones. The Lake Iro igneous rocks are typified by their ferroan mineralogy, define a ferman alkali-calcic metaluminous to weakly peraluminous potassic association, and exhibit elevated HFSE (Zr, Nb, Y) and REE contents. Therefore, they are best classified as A(2)-type granites. They are variably ferromagnetic with total magnetization lower than 1 A/m. The Lake Im granites most likely correspond to a single subvolcanic-plutonic silicic complex because: (i) firstorder geochemical modelling indicates that the microgranites can be generated by 30% fractional crystallization of a two feldspar-amphibole assemblage from a porphyritic granite melt and (ii) both granite types yield zircon U-Pb emplacement ages consistent within a 575.3 +/- 5.6 to 581.3 +/- 3.8 Ma time frame. The Lake Iro granites thus represent the oldest of a series of post-collisional igneous associations exposed in southern Chad and nearby countries which, collectively, show that the amalgamation of the constituent blocks of the southern Saharan Metacraton is older than 580 Ma. specialized A-type granites Post-collisional magmatism Saharan metacraton Pan-african orogeny Southern Chad TCHAD SAHARA 064 066 172 103960 [18 ] 2020 1464-343X https://www.documentation.ird.fr/hor/fdi:010080541 10.1016/j.jafrearsci.2020.103960 1464-343X [F B010080541] https://www.documentation.ird.fr/hor/fdi:010080541 https://www.documentation.ird.fr/intranet/publi/2021/01/010080541.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2021-02-08 2025-02-24 fdi:010080541 fre