New structural implications for the central Sahara (Algeria), from the revisited Upper Carboniferous “Hassi Bachir” Formation: Paleomagnetic constraints

Paleomagnetic investigations of the folded Upper Namurian-Lower Moscovian “Hassi Bachir” Formation cropping out in the “Ahnet” basin (Central Sahara, Algeria) yield two magnetic components. A pre-folding primary magnetization (D = 136.1°, I = 22.0°, k = 217, α95 = 2.6°) enables us to define a paleomagnetic pole (32.8°S, 55.7°E, K = 328 and A95 = 2.0°) which better constrains a paleopole that was determined by Daly and Irving [Daly, L., Irving, E., 1983. Paléomagnétisme des roches carbonifères du Sahara central; analyse des aimantations juxtaposées; configurations de la Pangée. Ann. Geophys. 1, 207-216] for the same formation. A secondary component consists in a synfolding remagnetization and shows that post-Permian tectonics account for at least about half of the total folding in the studied area. This indicates that Mesozoic folding noted 150 km to the West in the Reggane basin [Smith, B., Derder, M.E.M., Henry, B., Bayou, B., Amenna, M., Djellit, H., Yelles, A.K., Garces, M., Beamud, E., Callot, J.P., Eschard, R., Chambers, A., Aifa, T., Ait Ouali, R., Gandriche, H., 2006. Relative importance of the Hercynian and post-Jurassic tectonic phases in the Saharan platform: a palaeomagnetic study of Jurassic sills in the Reggane basin (Algeria). Geophys. J. Int. 167, 380-396] is not local and affected at least the entire north-western part of the Hoggar area. This reconfirms that the folding of the Paleozoic cover in the Sahara platform should not be restricted to the Hercynian orogeny.