9317061 Stevenson There are three major components to this effort: continuation of 3D mantle convection simulations using a viscosity that is only depth dependent; development of a variety of techniques to relate mantle convection modeling to seismic tomography; and development of calculations with temperature-dependent viscosity and compositional variation to carry out 3D (initially Cartesian) studies of the fates of slabs, the stability of plumes from the CMB, and the development of regional (non-plume) and island arc volcanism in a mantle convection context.