www.MantlePlumes.org © MantlePlumes.org The Hoggar swell and volcanism, Tuareg shield, Central Sahara: Intraplate reactivation of Precambrian structures as a result of Alpine convergence Jean-Paul Liégeois Africa Museum, B-3080 Tervuren, Belgium jean-paul.liegeois@africamuseum.be Introduction Hoggar (or Ahaggar) volcanism, in the Central Sahara, is Eocene to Quaternary in age (35 to nearly 0 Ma; Aït-Hamou et al., 2000 and references therein). Hoggar is located within the African plate far from the recent East African rift system. Associated with a swell 1,000 km in diameter (Figure 1), Hoggar Cainozoic volcanism is classically considered to be a mantle plume product (Sleep, 1990) even though no thermal anomaly has been observed (Lesquer et al., 1989). When considering available geological, geophysical and petrological data, such a model is hardly supported. When integrating the data with the structure of the Precambrian basement and the present geodynamic environment, an alternative model comes to mind. This comprises a source at the lithosphere/ asthenosphere interface melted by adiabatic pressure release in response to stress applied by the Africa-Europe collision on pre-existing shear zones and fractures, within a semi-rigid block (metacraton). Figure 1: The Hoggar swell from GLOBE data, NOAA; processing by Ph. Trefois, MRAC.