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
subductingtectonic 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.[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:
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);
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.
^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.
Bibcode:
1983GeoRL..10..297C.
doi:
10.1029/GL010i004p00297.