<P> How mantle convection directly and indirectly relates to plate motion is a matter of ongoing study and discussion in geodynamics . Somehow, this energy must be transferred to the lithosphere for tectonic plates to move . There are essentially two main types of forces that are thought to influence plate motion: friction and gravity . </P> <Ul> <Li> Basal drag (friction): Plate motion driven by friction between the convection currents in the asthenosphere and the more rigid overlying lithosphere . </Li> <Li> Slab suction (gravity): Plate motion driven by local convection currents that exert a downward pull on plates in subduction zones at ocean trenches . Slab suction may occur in a geodynamic setting where basal tractions continue to act on the plate as it dives into the mantle (although perhaps to a greater extent acting on both the under and upper side of the slab). </Li> </Ul> <Li> Basal drag (friction): Plate motion driven by friction between the convection currents in the asthenosphere and the more rigid overlying lithosphere . </Li> <Li> Slab suction (gravity): Plate motion driven by local convection currents that exert a downward pull on plates in subduction zones at ocean trenches . Slab suction may occur in a geodynamic setting where basal tractions continue to act on the plate as it dives into the mantle (although perhaps to a greater extent acting on both the under and upper side of the slab). </Li>

Which of the following is not a mechanism for plate movement