Forces acting on a subducting oceanic plate

Free conductive flows in the asthenosphere, layer C, and subduction zone are considered on the basis of experimental and theoretical simulation. The main forces acting on the oceanic lithospheric plate in the subduction zone are described. The horizontally directed forces arising due to free convection in the asthenosphere and transferring the oceanic lithospheric plate toward subduction zone have been estimated. These are friction force Fa and force of gravitational sliding Frd. Thermogravitational force Ftg, which is created because the subducting lithospheric plate has a lower average temperature than the ambient mantle, is estimated. The force created owing to phase transitions in the subducted plate has been estimated as well. The tangential stress at the contact of the subducting plate with the continental lithosphere and underlying upper mantle has been determined. The horizontal force arising due to different lateral temperature gradients in the upper mantle on the left and on the right of the subducting plate has been estimated. The results of experimental modeling of the effect exerted upon subduction by counter free convective flows developing in the asthenosphere are considered. The experiments show that the position of the descending free convective flow and thus of the subduction zone depends on the ratio of the thermal power of astehnospheric countercurrents. The pressure arising near the 670 km boundary gives rise to spreading of the subducting plate over this boundary.