Temporal variations of the segmentation of slow to intermediate spreading mid-ocean ridges. 2. A three-dimensional model in terms of lithosphere accretion and convection within the partially molten mantle beneath the ridge axis

International audienceWe present three-dimensional numerical models of convection within the partially molten mantle beneath the ridge axis. The modeling takes into account the cavity flow driven by plate spreading, the diffuse upwelling due to plate accretion, and the shearing movement generated by large-scale mantle flow. The ridge axis is free to move in the spreading direction to adjust to the maxima of tension at the lithosphere-mantle interface induced by the convective circulation. The melt distribution in the mantle and the crustal production at the ridge axis are estimated using the formalism of McKenzie and Bickle [1988]. During the experiments the record of the ridge axis positions and crustal production is used to compute synthetic maps of the isochrons and oceanic crustal thickness. Close to the ridge, the ascending convective flow consists of 80- to 100-km-long hot sheets oriented either roughly parallel or orthogonal to spreading. Most ridge segments fit with the top of hot upwelling sheets, while transient transform faults coincide with the top of cold downwelling flows. The crustal maps display lineations subparallel or slightily oblique to spreading, a few tens of million years long, and separated b