Slab pull

Slab pull is a <a href="/facts/Geophysics/ywVQ1sAQ">geophysical</a> mechanism whereby the cooling and subsequent densifying of a <a href="/facts/Subduction/rkasNdTo">subducting</a> <a href="/facts/Plate_tectonics/RtRG5lY4">tectonic plate</a> produces a downward force along the rest of the plate. In 1975 Forsyth and Uyeda used the <a href="/facts/Inverse_problem/Fe01pQ9E">inverse theory</a> 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 <a href="/facts/Mantle_(geology)/RpDdtjCr">mantle</a> at <a href="/facts/Oceanic_trench/sbp2PRk4">oceanic trenches</a>. This force and <a href="/facts/Slab_suction_force/d2AWkN22">slab suction</a> account for almost all of the force driving <a href="/facts/Plate_tectonics/RtRG5lY4">plate tectonics</a>. The <a href="/facts/Ridge_push/uF6Y3FwA">ridge push</a> at rifts contributes only 5 to 10%.
Carlson et al. (1983) in Lallemand et al. (2005) defined the <a href="/facts/Slab_(geology)/eStMGnKx">slab</a> pull force as:

F
          
            s
            p
          
        
        =
        K
        ×
        Δ
        ρ
        ×
        L
        ×
        
          
            A
          
        
      
    
    {\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);<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a>
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 <a href="/facts/Annum/51V242hh">Ma</a> at the trench.
The slab pull force manifests itself between two extreme forms:

<ul><li>The aseismic <a href="/facts/Back-arc_basin/px4uAEVE">back-arc</a> <a href="/facts/Extension_(geology)/AfRyYdRm">extension</a> as in the <a href="/facts/Izu%E2%80%93Bonin%E2%80%93Mariana_Arc/WzA0mUtL">Izu–Bonin–Mariana Arc</a>.</li>
<li>And as the <a href="/facts/Aleutian_Arc/IVNJdXxm">Aleutian</a> and <a href="/facts/List_of_earthquakes_in_Chile/93NyGEMy">Chile</a> tectonics with strong earthquakes and back-arc <a href="/facts/Thrust_fault/qxDnYlS8">thrusting</a>.</li></ul>
Between these two examples there is the evolution of the <a href="/facts/Farallon_Plate/oGDIkKqW">Farallon Plate</a>: from the huge slab width with the <a href="/facts/Nevada_orogeny/zmsva0A8">Nevada</a>, the <a href="/facts/Sevier_orogeny/2g14mA1B">Sevier</a> and <a href="/facts/Laramide_orogeny/QfBCzpss">Laramide orogenies</a>; the <a href="/facts/Mid-Tertiary_ignimbrite_flare-up/RYKTKtFE">Mid-Tertiary ignimbrite flare-up</a> and later left as <a href="/facts/Juan_de_Fuca_Plate/R6eGwVQf">Juan de Fuca</a> and <a href="/facts/Cocos_Plate/t8ExyDcA">Cocos</a> plates, the <a href="/facts/Basin_and_Range_Province/r8d1aXV4">Basin and Range Province</a> under extension, with <a href="/facts/Slab_detachment/RBUQHpI9">slab break off</a>, smaller slab width, more edges and <a href="/facts/Mantle_(geology)/RpDdtjCr">mantle</a> return flow.
Some early models of <a href="/facts/Plate_tectonics/RtRG5lY4">plate tectonics</a> envisioned the plates riding on top of convection cells like <a href="/facts/Conveyor_belt/SC1VXcm6">conveyor belts</a>. However, most scientists working today believe that the <a href="/facts/Asthenosphere/lXpE97oP">asthenosphere</a> does not directly cause motion by the <a href="/facts/Friction/d0108Rpu">friction</a> of such basal forces. The <a href="/facts/North_American_Plate/2H28Etp0">North American Plate</a> is nowhere being <a href="/facts/Subduction/rkasNdTo">subducted</a>, yet it is in motion. Likewise the <a href="/facts/African_Plate/U4akPN82">African</a>, <a href="/facts/Eurasian_Plate/WztRQ8pA">Eurasian</a> and <a href="/facts/Antarctic_Plate/ME0j51xo">Antarctic Plates</a>. Ridge push is thought responsible for the motion of these plates. 
The subducting slabs around the <a href="/facts/Pacific_Ring_of_Fire/UpRWnP2P">Pacific Ring of Fire</a> cool down the Earth and its <a href="/facts/Core-mantle_boundary/EWHuuEdT">core-mantle boundary</a>. Around the African Plate upwelling mantle plumes from the core-mantle boundary produce <a href="/facts/Rifting_(geology)/FAWNKCGF">rifting</a> including the <a href="/facts/African_Rift_Valley/o82Q47Uc">African</a> and <a href="/facts/Ethiopian_Rift_Valley/90BjKzX1">Ethiopian</a> rift valleys.

Slab pull open-in-new

Slab pull