The Fate of the Oceanic Slab During Subducting Beneath the Cratonic Lithosphere: Implications for the Subduction of the Paleo-Pacific Plate Beneath East Asia

Abstract

The subduction of the Western Pacific plate has been proposed to play a crucial role in the reactivation and destruction of the North China Craton (NCC). However, how the Paleo-Pacific plate subduction affects the lithospheric evolution of the NCC remains unclear. Here, we perform 2-D numerical simulations to study the slab dynamics of an oceanic-continental subduction system. We find that the evolution of the subducted slabs is primarily controlled by the intrinsic density and compositional viscosity contrasts between the overriding lithosphere and the normal mantle, as well as the negative Clapeyron slope of the 660-km phase change, which impedes slab subduction. Generally, a higher density contrast or a larger Clapeyron slope facilitates the flattening and stagnation of the subducted slab. With moderate Clapeyron slopes (e.g., −2.0–−1.0 MPa/K), the subducted slabs are temporally stagnant at the transition zone depth for intermediate density contrast (e.g., −50 kg/m³) or move beneath the overriding lithosphere as a flat-subduction mode for large density contrast (e.g., −75 kg/m³). For smaller density contrasts (e.g., −25 kg/m³), the subducted slabs always directly pass through the 660-km depth into the lower mantle regardless of the Clapeyron slope. Moreover, an increased strength of the overriding lithosphere efficiently promotes the penetration of the subducted slabs into the lower mantle. Our numerical results suggest that the subduction of the Paleo-Pacific plate beneath Eastern Asia is more likely to be in a short-lived stagnation or flat-subduction style rather than in a long-lived stagnation style.