An active detachment fault ahead the Aden propagating oceanic rift in Afar: consequences on breaking-up processes

The rift to drift stage in continental breakup systems remains enigmatic, especially when stretching and thinning are associated with significant mantle melting. Here we present the first on-site evidence in the Afar Depression of a segmented detachment fault of Quaternary age, the Doubié detachment, ahead of the proto-oceanic Asal segment, itself located at the tip of the propagating Aden oceanic rift system that separates Arabia from the Somali plate. The active Doubié Fault post-dates the last emplacement of flood basalts in the region and largely controls the development of a major hanging-wall crustal flexure, south of the Danakil block. On the fresh scarp, 36Cl datings show that this fault accommodated about 60% of the plate separation during the Holocene. We suggest that a similar detachment-fault, partly invaded by felsic magma at a late stage, was active before the onset of the Ghoubbet-Asal proto-oceanic segment. We highlight the strong implications of those findings on the dynamics of the latest stages of continental extension ahead propagating ultraslow oceanic spreading systems.