Roles of Continental Mid‐Lithosphere Discontinuity in the Craton Instability Under Variable Tectonic Regimes

Abstract

AbstractThe continental mid‐lithosphere discontinuity (MLD) is widely detected within cratons, with the dominant depth range of 70–100 km and a significant reduction of shear‐wave velocity of 2%–12%. However, the formation mechanism and corresponding strength of the MLD are widely debated, which may strongly affect the roles of MLD in craton evolution. The comparisons among variable mechanisms indicate that the strength of the MLD varies from the relatively high viscosity of wet olivine to the rather low viscosity of antigorite. Thus, systematic numerical modeling has been conducted with the MLD of contrasting strengths, that is, the wet olivine‐induced MLD or antigorite‐induced MLD, to investigate the roles of MLD in the craton instability under variable tectonic regimes (stable, extension, compression, mantle flow traction, or mantle plume). The models show that the cratonic lithosphere with wet olivine‐induced MLD maintains its stability under all the tectonic regimes. In contrast, the antigorite‐induced MLD with lowest viscosity could significantly promote the decoupling of lithosphere, and facilitate the lithospheric deformation. However, lithospheric delamination only occurs with the rather weak MLD interacting with the sub‐plate asthenosphere upwelling during craton extension or mantle plume activity. The sufficient amount of melts is essential for this process, which requires a large amount of extension or a mantle plume with rather high temperature anomaly and large size. Therefore, craton destruction is still difficult, and requires additional strict conditions. This may explain the general stability of most cratons with widespread MLDs.