The Effect of a Weak Asthenospheric Layer on Surface Kinematics, Subduction Dynamics and Slab Morphology in the Lower Mantle

On Earth, the velocity at which subducting plates are consumed their trenches (termed “subduction rate” herein) is typically 3 times higher than trench migration velocities. The subduction rate also 5 estimated lower mantle slab sinking rates. Using simple kinematic analyses, we show that if this present-day “kinematic state” operated into past, lithosphere should have accumulated and folded beneath near-stationary trenches. These predictions consistent with seismic tomography, images localized widened lower-mantle piles. They are, however, odds most dynamic-subduction models, predict rapid retreat inclined slabs in transition zone. We test hypothesis a weak asthenospheric layer (WAL), between lithosphere-asthenosphere boundary 220 km depth, compatible geophysical constraints, can remedy discrepancies numerical models observations. WAL lubricates base of lithosphere, increases while reducing retreat. As consequence, simulations featuring accumulation zone, thicker, mantle. A viscosity only 2–5 adjacent sufficient to shift regimes toward mode vertical folding trenches, across wide range model parameters, producing surface velocities close those observed present-day. findings provide support for existence asthenosphere Earth's complementing independent evidence from various data.