slab pull

{{Short description|Part of the motion of a tectonic plate caused by its subduction}}

Slab pull is a geophysical mechanism whereby the cooling and subsequent densifying of a subducting tectonic plate produces a downward force along the rest of the plate. In 1975 Forsyth and Uyeda used the inverse theory method to show that, of the many forces likely to be driving plate motion, slab pull was the strongest.{{Cite journal|last1=Forsyth|first1=Donald|last2=Uyeda|first2=Seiya|date=1975-10-01|title=On the Relative Importance of the Driving Forces of Plate Motion|journal=Geophysical Journal International|language=en|volume=43|issue=1|pages=163–200|doi=10.1111/j.1365-246X.1975.tb00631.x|bibcode=1975GeoJ...43..163F|issn=0956-540X|doi-access=free}} Plate motion is partly driven by the weight of cold, dense plates sinking into the mantle at oceanic trenches.{{Cite journal|last1=Conrad|first1=Clinton P.|last2=Lithgow-Bertelloni|first2=Carolina|author-link2=Carolina Lithgow-Bertelloni|date=2002-10-04|title=How Mantle Slabs Drive Plate Tectonics|journal=Science|language=en|volume=298|issue=5591|pages=207–209|doi=10.1126/science.1074161|pmid=12364804|bibcode=2002Sci...298..207C|s2cid=36766442|issn=0036-8075}}{{Cite web|url=http://powerpoints.geology-guy.com/pipkin/pipkin_chapter3.pdf |title=Plate tectonics, based on 'Geology and the Environment', 5 ed; 'Earth', 9 ed |url-status=dead |archive-url=https://web.archive.org/web/20110711084813/http://powerpoints.geology-guy.com/pipkin/pipkin_chapter3.pdf |archive-date=July 11, 2011 }} 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%.Conrad CP, Lithgow-Bertelloni C (2004)

Carlson et al. (1983){{Cite journal|last1=Carlson|first1=R. L.|last2=Hilde|first2=T. W. C.|last3=Uyeda|first3=S.|date=1983|title=The driving mechanism of plate tectonics: Relation to age of the lithosphere at trenches|journal=Geophysical Research Letters|language=en|volume=10|issue=4|pages=297–300|doi=10.1029/GL010i004p00297|bibcode=1983GeoRL..10..297C}} in Lallemand et al. (2005){{Cite journal|last1=Lallemand|first1=Serge|last2=Arnauld|last3=Boutelier|first3=David|date=2005|title=On the relationships between slab dip, back-arc stress, upper plate absolute motion, and crustal nature in subduction zones: SUBDUCTION ZONE DYNAMICS|journal=Geochemistry, Geophysics, Geosystems|language=en|volume=6|issue=9|pages=n/a|doi=10.1029/2005GC000917|bibcode=2005GGG.....6.9006L |url=https://hal.archives-ouvertes.fr/hal-01261567/file/lallemandG32005.pdf|doi-access=free}} defined the slab pull force as:

:$F\_\{sp\}\; =\; K\; \backslash times\; \backslash Delta\backslash rho\; \backslash times\; L\; \backslash times\; \backslash sqrt\{A\}$

Where:

: K is {{math|4.2g}} (gravitational acceleration = 9.81 m/s²) according to McNutt (1984);{{Cite journal|last=McNutt|first=Marcia K.|date=1984-12-10|title=Lithospheric flexure and thermal anomalies|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=89|issue=B13|pages=11180–11194|doi=10.1029/JB089iB13p11180|bibcode=1984JGR....8911180M}}

: 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:

• 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.{{cn|date=May 2024}} 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.