Briefly describe the three main driving mechanisms of plate tectonics, and comment on which is thought to be the dominant process

Three main mechanisms that drive the latetechtonis are Ridge Push, Conventions in the mental, Slab pull.  

Explanation:

Heat and gravity to be a fundamental process, of these the most dominating factor/process are the convection currents coming from the mantel. It is a slowly creeping motion of the earth's mantle, that transfers the heat from the planet's interior. As the subducted matter sinks inside the earth's interior, the lower mantle starts to burn. The subducted plates trigger volcanic eruptions. Additionally due to varying temperature and pressure difference in the inner mantle this zone gives rise to convective current from the bottom. The convection can be in the form of mental plumes rising from the D layer to the lower mantle to the upper mantle. These have known to be formed the mid oceanic ridges.