Peeling Off of Crustal Eclogite From the Downgoing Slab at the Top of the Lower Mantle

Abstract The peeling‐off of oceanic crust from the downgoing slab at the top of the lower mantle is considered a key mechanism contributing to the formation of low‐velocity anomalies in the mantle transition zone and seismic scatterers in the lower mantle. However, its controlling factors and geodynamic feasibility remain debated. In this study, we systematically investigate the influence of key parameters—including the viscosity structure within and surrounding the slab, the Clapeyron slope of the ringwoodite‐bridgmanite phase transition, and the age of the subducting plate—on crust‐mantle separation using two‐dimensional geodynamic modeling. Results show that the weakening of the upper oceanic crust and hydrated slab mantle, as well as the presence of a low‐viscosity “lower mantle wedge” formed by deep subduction, promotes the peeling off of crustal eclogite from the downgoing slab. Large‐scale peeling off and accumulation of oceanic crust at and below 660 km depth occur only when both the lower mantle wedge ( η = 10 19 Pa·s, ∼1,000 times weaker than the ambient mantle) and the hydrated slab mantle ( η = 10 22 Pa·s, ∼100 times weaker than the cold slab mantle) are extremely weakened. By integrating rock physics and geophysical constraints, we demonstrate the physical feasibility of this process. Crust–mantle separation provides an alternative explanation for the observed weakening of the P660P seismic phase, the development of low‐velocity zones atop the lower mantle, and the formation of seismic scatterers. This mechanism also offers new insights into global mid‐ocean ridge basalt recycling and Large Low Shear Velocity Province evolution.