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Magmatism occurred almost continuously over the past 25 m.y. in the Republic of Djibouti. Lavas are mainly basic to intermediate with some rhyolites. Large chemical and isotopic variations among the volcanic series are interpreted in terms of mantle source heterogeneity. Crustal contribution is only evidenced in the oldest rhyolites emplaced during the initial stages of rifting. Excluding these old rhyolites, a clear evolution through time of the mantle sources is observed in relation to rifting. Three sources were involved in the genesis of these lavas: (1) an old subcontinental lithospheric component (87Sr/86Sr ≈ 0.706, 206Pb/204Pb ≈ 17.9), mainly observed in the oldest lavas (25 to 10 Ma), (2) an HIMU (high U/Pb ratio)‐type reservoir, and (3) a depleted mantle. As rifting goes on, there is an increasing contribution of an HIMU‐type mantle source. It is attributed to the influence of a mantle diapir (Afar plume) thermally eroding the subcontinental lithosphere. The geochemical characteristics of 9 to 1 Ma old lavas, erupted after the strong increase of spreading rate in Afar, reflect this evolution of mantle sources. The influence of the mantle plume is most prominent in the northern youngest lavas (<1 Ma), particularly Manda, characterized by the strongest HIMU signature (87Sr/86Sr ≈ 0.7035, 206Pb/204Pb ≈ l9.2). The contribution of the depleted mantle component originating from the asthenosphere is best recognized in the young (<4 Ma) lavas, particularly Tadjoura and Asal lavas (3 to 1 Ma). The evolution of Djibouti lava sources through time may be accounted for by the recent models developed for plume structure.

International audienceIn the framework of a sinus models family, a new three-noded mechanical beam finite element is designed for the analysis of laminated beams. It is based on a sinus distribution with layer refinement. The transverse shear strain is obtained by using a cosine function avoid-ing the use of shear correction factors. This kinematic accounts for the interlaminar continuity conditions on the interfaces between the layers, and the boundary conditions on the upper and lower surfaces of the beam. A conforming FE approach is carried out using Lagrange and Hermite interpolations. It is important to notice that the number of unknowns is independent from the number of layers.Both static and vibration mechanical tests for thin and thick beams are presented in order to evaluate the capability of this new finite element to give accurate results with respect to elasticity or finite element reference solutions. Both convergence velocity and accuracy are discussed and this new finite element yields very satisfactory results at a low computational cost. In particular, the transverse stress com-puted from constitutive relation is well estimated with regards to classical equivalent single layer models. Moreover, this family of sinus model is very efficient owing to the low number of unknowns

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