Slab pull

Slab pull is that part of the motion of a tectonic plate caused by its subduction. In 1975 Forsyth and Uyeda showed using inverse theory methods that of the many likely driving forces of plates slab pull was the strongest.[1] Plate motion is partly driven by the weight of cold, dense plates sinking into the mantle at oceanic trenches.[2][3] This force and slab suction account for almost all of the force driving plate tectonics. The ridge push at rifts contributes only 5 to 10%.[4]

Carlson et al. (1983)[5] in Lallemandet al. (2005)[6] defined the slab pull force as:

${\displaystyle F_{sp}=K\times \Delta \rho \times L\times {\sqrt {A}}}$

Where:

K is 4.2g (gravitational acceleration = 9.81 m/s2) according to McNutt (1984);[7]
Δρ = 80 kg/m3 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 (the upper/lower mantle boundary);
A is the slab age in Ma at the trench.

The slab pull force manifests itself between two extreme forms:

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. Ridge push is thought responsible for the motion of these plates.

The subducting slabs around the Pacific Ring of Fire cool down the Earth and its Core-mantle boundary. Around the African Plate upwelling mantle plumes from the Core-mantle boundary produce rifting including the African and Ethiopian rift valleys.

References

1. Forsyth, Donald; Uyeda, Seiya (1975-10-01). "On the Relative Importance of the Driving Forces of Plate Motion". Geophysical Journal International. 43 (1): 163–200. doi:10.1111/j.1365-246X.1975.tb00631.x. ISSN 0956-540X.
2. Conrad, Clinton P.; Lithgow-Bertelloni, Carolina (2002-10-04). "How Mantle Slabs Drive Plate Tectonics". Science. 298 (5591): 207–209. doi:10.1126/science.1074161. ISSN 0036-8075.
3. "Plate tectonics, based on 'Geology and the Environment', 5 ed; 'Earth', 9 ed" (PDF). Archived from the original (PDF) on July 11, 2011.
4. Conrad CP, Lithgow-Bertelloni C (2004)
5. Carlson, R. L.; Hilde, T. W. C.; Uyeda, S. (1983). "The driving mechanism of plate tectonics: Relation to age of the lithosphere at trenches". Geophysical Research Letters. 10 (4): 297–300. doi:10.1029/GL010i004p00297.
6. Lallemand, Serge; Heuret, Arnauld; Boutelier, David (2005). "On the relationships between slab dip, back-arc stress, upper plate absolute motion, and crustal nature in subduction zones: SUBDUCTION ZONE DYNAMICS" (PDF). Geochemistry, Geophysics, Geosystems. 6 (9): n/a. doi:10.1029/2005GC000917.
7. McNutt, Marcia K. (1984-12-10). "Lithospheric flexure and thermal anomalies". Journal of Geophysical Research: Solid Earth. 89 (B13): 11180–11194. doi:10.1029/JB089iB13p11180.

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