Slab pull

The Slab pull force is a tectonic plate force due to subduction. Plate motion is partly driven by the weight of cold, dense plates sinking into the mantle at trenches. This force and the slab suction force account for most of the overall force acting on plate tectonics, and the ridge push force accounts for 5 to 10% of the overall force.

Carlson et al. (1983) in Lallemandet al. (2005) defines the slab pull force as:

• Fsp = K times Δρ times L times √A

Where the constant K is set to 4.2 times g (gravitational acceleration = 9.81 ms⁻²) according to McNutt (1984), Δρ = 80 kg.m⁻³ is the mean density difference between the slab and the surrounding asthenosphere, L is the slab length calculated only for the part above 670 km (Upper-lower mantle boundary), and A being the slab age in Ma at the trench.

The slab pull force manifests itself between two extreme forms:

• The aseismic back-arc extension as in the Izu-Bonin-Mariana Arc.
• And as the Aleutian and Chile tectonics with strong earthquakes and back-arc thrusting.

Between these two examples there is the evolution of the Farallon plate: from the huge slab width with the Nevada, the Sevier and Laramide orogenies; the Mid-Tertiary ignimbrite flare-up and later left as Juan de Fuca and Cocos plates, the Basin and Range Province under extension, with slab break off, smaller slab width, more edges and mantle return flow.

Some early models of plate tectonics envisioned the plates riding on top of convection cells like conveyor belts. However, most scientists working today believe that the asthenosphere does not directly cause motion by the friction of such basal forces. The North American Plate, is nowhere being subducted, yet it is in motion. Likewise the African, Eurasian and Antarctic Plates. The subducting slabs around the Pacific Ring of Fire cool down the Earth and its Core-mantle boundary, around the African Plate the upwelling mantle plumes from the Core-mantle boundary produce rifting. The overall driving force for plate motion and its energy source remain subjects of ongoing research.

References

• "Breakthrough Achieved in Explaining Why Tectonic Plates Move the Way They Do". ScienceDaily. 17 July 2010. http://www.sciencedaily.com/releases/2010/07/100716125841.htm.