Numerical modelling of plume-induced craton delamination: the role of the Mid-Lithospheric Discontinuity

The Mid-Lithospheric Discontinuity (MLD) is a region of marked scattering of seismic waves which, according to several studies, is caused by mechanical weakness. It is located at an approximate depth of 100 km and has become a subject of intense research since it was identified through active-source seismology. The nature of the MLD is still a topic of intense debate. However, its contribution in destabilizing the continental lithosphere has often been invoked, and particularly in the destruction of cratons. Such a role is further enhanced when combined with other factors that may weaken the lithospheric mantle. Here we show the results of a 2D thermo-mechanical model, where we investigated the role of the MLD in the scenario of the interaction between long-lived mantle plumes and cratonic lithosphere. In this model, we implemented thermal and/or compositional plumes, with subsequent effects on their relative buoyancy with respect to the surrounding sublithospheric mantle. Our findings suggest that the combined effects of mantle plumes and MLD can effectively cause the destabilization and extensive delamination of cratonic lithosphere. However, mantle plumes must reach the MLD to trigger craton destabilization. For such a scenario, the presence of a weakened lithospheric mantle beneath the MLD is pivotal. This weak zone may be tectonic suture zone(s), or regions of melt and/or fluids percolation due to P-T variations in the plume during its ascent. We have verified that when plumes receive a constant material input from lower regions of the mantle, craton delamination can occur with very thin MLDs (< 10 km), and can be induced by cold and small compositional plumes, which are characterized by relatively low buoyancy.