The mechanism for plate tectonics is generally accepted to be a combination of convection currents in the mantle coupled with ridge push and slab pull. The poorly understood part includes 1) to what depth are the convection cells active, 2) are there several layers of convection cells or only one, 3) is the lithosphere the upper part of the convection cell or a passive participant, 4) to what degree to slab-pull and ridge-push move the plates, among others. Below are two images showing how the convection cells in the upper mantle may be configured.
|Figure 3: Plate Tectonic mechanism showing that the oceanic plate shown in the diagram is a passive participant in the convection cell. It is moved through convection traction as well as slab pull and ridge push (Earle, Steven, BC Open Textbook)|
Figure 4: Plate Tectonic mechanism showing that the oceanic plate shown in the diagram is an active participant in the convection cell. The lithosphere forms the top of the convection cell. Ridge push and slab pull are also playing an important role. (Earle, Seven, BC Open Textbook)