R-critical constraints on relamination efficiency: The role of mechanical coupling in continental crust recycling

Shizhong Chen , Xingxing Duan

Relamination—the reincorporation of deeply subducted continental crust into the overriding plate—has been proposed as a major mechanism for continental growth and differentiation. While numerical models and high-pressure experiments demonstrate the thermochemical feasibility of this process, a fundamental question remains: under what mechanical conditions is relamination sufficiently efficient to produce geochemically detectable hybrid melts? Here we introduce the R-critical dimensionless parameter, defined as the ratio between buoyancy-driven mixing forces and viscous resistance at the crust–mantle interface. R-critical quantifies the mechanical coupling required for efficient hybridization of crustal fragments within peridotite matrix. Our analysis demonstrates that relamination efficiency is not solely governed by pressure–temperature conditions, but fundamentally constrained by interface viscosity, density contrast, strain rate, and fragment size. When the mechanical coupling parameter R falls below the critical threshold (R-critical), hybrid melting becomes physically inhibited regardless of experimental temperature or pressure, implying that global relamination fluxes may be substantially lower than previously estimated. This framework provides a quantitative discriminator between relamination and delamination, and offers testable predictions for seismic anisotropy, UHP terrane deformation structures, and post-collisional magmatic signatures.