The upward migration of self-convecting magma bodies

Abstract

A magma body existing in an upper mantle containing a small percentage of partial melt should be subject to internal convection. The presence of partial melt means that the matrix follows closely the temperature gradient versus pressure, or depth, of the mantle solidus. This gradient is several times the adiabatic gradient of a mixed magma body, and the difference is available to drive convection. Larger bodies move more rapidly than smaller ones and would tend to sweep them up, as well as concentrating incompatible elements into the melt. The difference between ridge-crest upwelling, where mantle matrix rises to near the surface as well as does the magma, and island "hot spot' volcanism, where the crystals are irreversibly left behind, can account for the differences in basalt composition. -from Author