Dynamic interaction between tectonic plates, subducting slabs, and the mantle

Abstract

Mantle convection models have been formulated to investigate the relation between plate kinematics and mantle dynamics. The cylindrical geometry models incorporate mobile, faulted plate margins, a phase change at 670 km depth, non-Newtonian rheology, and tectonic plates. Models with a variety of parameters indicate that a relatively stationary trench is more likely to be associated with a subducted slab that penetrates into the lower mantle with a steep dip angle. However, a subducted slab that is deflected above the 670-km phase change with a shallow dip is more likely to be associated with a margin that has undergone rapid retrograde trench migration. This relation between slab morphology and plate kinematics is consistent with seismic tomography and plate reconstruction of western Pacific subduction zones. The efficiency of slab penetration through the 670-km phase change is controlled by both the buoyancy of the subducting plate and the mobility of the overriding plate. While older subducting plates have a greater propensity for slab penetration, trench mobility reduces the propensity for slab penetration. Smaller overriding plates have a greater mobility. When subducted slabs approach the bottom thermal boundary layer, hot fluid is pushed aside, and plumes form on the periphery of slab accumulations. There are sharp temperature contrasts between the subducted slab and the thermal boundary layer at the core mantle boundary (CMB). Old subducted slabs and a thermal boundary layer lead to large-scale lateral structure near the CMB.