| Plate tectonic forces: | A/ |  |
||||
| Mantle flow: The case of strong coupling | ||||||
| The flow of the asthenosphere below the plates most likely exerts an influence on the overriding plate motion. The extent of this influence is strongly debated as it depends on the level of mechanical coupling between the lithosphere and the convecting asthenosphere.
The sketches on the right illustrate two cases where the mantle exerts a strong but opposite influence on the plates. A/ The subducting slab drags the surrounding asthenosphere into the subduction zone. The asthenosphere resists and slow down the subducting slab. In this case, the sub-lithospheric mantle flow is the result of plate tectonic processes. B/ The flow in the asthenosphere drives plate motion by dragging the oceanic lithosphere into a downwelling zone (suction force through shear traction). Here, it is the flow in the sub-lithospheric mantle that powers plate-tectonic. If the strength of the asthenosphere/lithosphere coupling is not that significant, the convective asthenosphere can still interfer with plate motion. In particular, when the flow in the asthenosphere is at an angle to the subducting slab it can forces the steepening or shallowing of the slab. See next slide. |
||||||
| B/ | ||||||
|
|
 |
|
|
|
 |
 |
 |
 |
 |
||