Variety of plumes and the fate of subducted basaltic crusts

Subducted basaltic crusts induce various types of plumes in a recently developed self-consistent numerical model of mantle convection with tectonic plates and mantle magmatism. Subducted basaltic crusts segregate from the convecting mantle by their compositionally induced high density. The basaltic crusts are formed into a continuous layer along the core–mantle boundary, if there is no influence of subducting slabs; the layer induces classic hot mantle plumes by basal heating. When influenced by subducting slabs, the subducted basaltic crusts are formed into hot accumulations similar to the Earth's superplumes, provided that the internal heating is weaker than a threshold. Chemical discontinuities often develop within and along the boundaries of the basaltic accumulations, and hot plumes ascend from the uppermost parts of the accumulations. Some of the plumes hit plates, cause hot spot magmatism, and induces new spreading centers. The rest of the plumes often stagnate on the 660 km phase boundary to form basaltic pools. Occasionally, secondary plumes grow from the pools to induce hot spot magmatism. The pools are also sucked up by the ridges that happen to be above the pools, and activate the ridge magmatism. Hot plumes ascend from basaltic accumulations more frequently as the internal heating becomes stronger. When the internal heating becomes too strong, however, the accumulations of subducted basaltic crusts become convectively unstable and no longer work as the sources of plumes. The various types of the plumes observed here are compared to the plumes in the Earth's mantle.