Plate tectonic forces:
Three plate tectonic forces: bottom-up vs top-down tectonics
• Ever since plate tectonic theory took hold in the late 1960s, geoscientists have argued over what drives plates: mantle upwelling at ridges that pushes plates apart, mantle circulation that drags plates along, or slab pull have independently or in combination been proposed as driving forces for plate motion.
According to Don Anderson, a geophysicist at Caltech Seismological Laboratory, “... slabs drive tectonics. There is no need for other driving mechanisms such as plumes or mantle convection that are independent of plate tectonics.”
• Based on a simple model of lithosphere and mantle interactions, geophysicists have found that two major tectonic forces — slab pull and slab suction — can interact to explain most observed plate movements today. A slab can pull the rest of the oceanic plate behind it (the "slab pull" force). The slab can also be forced to subduct through the viscous drag of the convective mantle. That flow sucks in the oceanic plate in (the "slab suction" force). In particular, slabs detached from subducting plates, can influence mantle flow and can drive tectonic plates by basal shear traction. This is the "slab suction" force.
The dynamics of plates results from the interplay between mantle flow and forces acting at plate level. The main plate tectonics forces are the "ridge push" (FRP), the "slab pull" (FSP), and the continental gravitational forces (FG). The ridge-push is the gravitational force acting between the high-standing mid-oceanic-ridge and the distant, low-standing abyssal plain. The slab-pull is the pull exerted by the subducting slab on the rest of the oceanic lithosphere. The continental gravitational force is the gravitational force acting between the high-standing continental plate and the low-standing adjacent abyssal plain. The interplay between these forces can result in contrasted tectonic regimes:
Fg>Frp, Fsp Fg~Frp~Fsp Fsp<Frp, Fg