Effects of lithospheric mantle layering on craton stability

Cratons are long-term stable, ancient tectonic units in the continental lithosphere. They are usually surrounded by relatively young mobile zones. The lateral variation in lithospheric thickness between the two can induce edge-driven mantle convection. In recent years, increasing evidence indicates that the vertical composition and structure layering are widely found in the cratonic lithospheric mantle. How the vertical layering structure of the lithospheric mantle affects craton's stability in the context of edge-driven mantle convection remains unclear. Here, we use two-dimensional thermo-mechanical numerical simulations to systematically explore the vertical density and viscosity variations and distribution pattern of the mid-lithosphere discontinuity (MLD) in the cratonic lithospheric mantle affect craton's stability under the condition of edgedriven convection. Modeling results show that: (1) When no MLD is included in the cratonic lithospheric mantle, the horizontal extent of lithospheric thinning is limited (<100 km), mainly occurring at the craton's edge, even if the craton has a density-layered lithospheric mantle. (2) When the cratonic lithospheric mantle has a continuous MLD layer, the horizontal extent of lithospheric thinning enlarges as the lower portion of the lithospheric mantle becomes dense. As the strength of the lower portion of the lithospheric mantle increases, the lithospheric thinning style transforms from filiform dripping to block detachment. (3) When the cratonic lithospheric mantle has a discontinuous MLD layer, we find that the gaps between two adjacent MLD segments effectively delay the speed of lithospheric thinning. The sparse the MLD gaps, the rapid the lithospheric thinning, and vice versa. In this case, the lithospheric thinning style changes from slow filiform dripping at the early stage to rapid block detachment at the later stage. The North China Craton (NCC) experienced a long-lasting process (>100 Ma) of destruction, and the peak period of destruction mainly occurred at the Early Cretaceous (130 similar to 120 Ma). The present-day position of the lithospheric thinning front of the eastern NCC concurs with the eastern termination of MLD beneath the Trans-North China orogen. Based on modeling results, we suggest that the spatial and temporal scope of the NCC destruction was mainly caused by piecewise mantle detachment induced by the lithospheric layering in density and strength and the discontinuous distribution of MLD.