Three Possible Driving Forces Of Plate Tectonics

Convection

Causes oceanic lithosphere to move sideways and away from the mid-ocean ridge because of hot rock expanding and rising and cool rock becoming dense and sinking

Ridge Push

Makes oceanic lithosphere slide downhill under the force of gravity

Slab Pull

Oceanic lithosphere is denser than the asthenosphere so the edge of the tectonic plate that contains oceanic lithosphere pulls the rest of the tectonic plate with it.