Slab pull is a

geophysical Geophysics () is a subject of natural science concerned with the physical processes and properties of Earth and its surrounding space environment, and the use of quantitative methods for their analysis. Geophysicists conduct investigations acros ...

mechanism whereby the cooling and subsequent densifying of a

subducting Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second pla ...

tectonic plate Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...

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. Plate motion is partly driven by the weight of cold, dense plates sinking into the mantle at

oceanic trench Oceanic trenches are prominent, long, narrow topography, topographic depression (geology), depressions of the seabed, ocean floor. They are typically wide and below the level of the surrounding oceanic floor, but can be thousands of kilometers ...

es. This force and slab suction account for almost all of the force driving

plate tectonics Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...

. The ridge push at rifts contributes only 5 to 10%. Carlson et al. (1983) in Lallemand et al. (2005) defined the slab pull force as: :

F_ = K \times \Delta\rho \times L \times \sqrt

Where: : ''K'' is (gravitational acceleration = 9.81 m/s²) according to McNutt (1984); : ''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 The back-arc region is the area behind a volcanic arc. In island arc, island volcanic arcs, it consists of back-arc basins of oceanic crust with abyssal zone, abyssal depths, which may be separated by remnant arcs, similar to island arcs. In conti ...

extension as in the Izu–Bonin–Mariana Arc. * And as the Aleutian and

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

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 Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...

, 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 The Basin and Range Province is a vast United States physiographic region, physiographic region covering much of the inland Western United States and Northern Mexico, northwestern Mexico. It is defined by unique basin and range topography, charac ...

under extension, with slab break off, smaller slab width, more edges and mantle return flow. Some early models of

envisioned the plates riding on top of convection cells like conveyor belts. However, most scientists working today believe that the

asthenosphere The asthenosphere () is the mechanically weak and ductile region of the upper mantle of Earth. It lies below the lithosphere, at a depth between c. below the surface, and extends as deep as . However, the lower boundary of the asthenosphere i ...

does not directly cause motion by the

friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Types of friction include dry, fluid, lubricated, skin, and internal -- an incomplete list. The study of t ...

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 In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear Fault (geology), downfaulted depression, called a graben, or more commonly ...

including the African and

Ethiopian Ethiopians are the native inhabitants of Ethiopia, as well as the global diaspora of Ethiopia. Ethiopians constitute several component ethnic groups, many of which are closely related to ethnic groups in neighboring Eritrea and other parts of ...

rift valleys.

See also

References

Further reading