| Plate tectonic forces: | C/ |  |
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| Mantle flow: The case of weak coupling | ||||||
| When the flow in the asthenosphere is at an angle to the subducting slab it can force the steepening or shallowing of the slab.
C/ The asthenospheric "wind" under the subducting slab forces the slab to bend downward, enhancing the slab-pull. This effect is here enhanced by the downward asthenospheric flow above the slab forcing the steepening of the slab. D/ Here the asthenospheric "wind"" supports the subducting slab, opposing the slab-pull. In this sketch the top surface of the slab is also pulled upward by the upward asthenospheric flow, forcing the shallowing of the slab. Overall, the forces (FRP, FSP, FG) acting on the plates, the sub-lithospheric flow and the flow of the mantle in the vicinity of the slab all influence plate motion, and the tectonic regime at continental plate margins. |
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