New age constraints on the timing of volcanism in central Afar, in the presence of propagating rifts

Pierre Lahitte (1) , Pierre-Yves Gillot (1) , Tesfaye Kidane (1) , Vincent Courtillot (1) , Abebe Bekele

1 IPGP - Institut de Physique du Globe de Paris

We investigate the relationship between rift propagation and volcanism in the Afar Depression in the last 4 Myr. Potassium-argon and thermoluminescence dating allow detailed reconstruction of the temporal evolution of volcanism. Volcanic activity is almost continuous since 3.5 Ma, with intervals characterized by more intense activity, especially around 2 Ma. Spatial distribution of ages reveals that Stratoid Series volcanism migrated northward along a 200-km trend between 3 and 1 Ma, at about 10 cm/yr, linked to northward propagation of the Gulf of Aden Ridge, after it had cut across the Danakil horst at 4 Ma. Our work underlines the role of rhyolitic volcanism in initiation of rifting. Acid volcanoes, initially formed near the axes of extensional zones, have been subsequently dissected and are presently located on both sides of active rift segments. These lavas were the first to be erupted in areas of low extensional strain and were followed by basaltic lavas as extension increased. Differentiated volcanoes acted as zones of local weakness and guided localization of fractures, then leading to fissural magmatism. This regional-scale, composite style of rifting, including volcanic and tectonic components, can be compared to the large-scale continental breakup process itself. Deformation occurs through propagation of faults and fissures under a regional stress field. These become localized because of weakening of the crust (or lithosphere) due to emplacement of magmas, under the influence of a plume in the large-scale case, or of silicic centers linked to magma chambers in the regional-scale case.

Domaines: Planète et Univers [physics]

Pierre Lahitte, Pierre-Yves Gillot, Tesfaye Kidane, Vincent Courtillot, Abebe Bekele. New age constraints on the timing of volcanism in central Afar, in the presence of propagating rifts. Journal of Geophysical Research : Solid Earth, 2003, 108, p. 289-310. ⟨10.1029/2001JB001689⟩. ⟨insu-03598426⟩