On the Role of Lower Crust and Midlithosphere Discontinuity for Cratonic Lithosphere Delamination and Recycling

Abstract

Delamination is an important mechanism of continental lithosphere removal and recycling. It has been invoked as a likely cause for the observed thinning in the eastern North China (North China Craton) and several other cratons, returning thick depleted cratonic roots to the deep mantle. However, how delamination occurred, its lateral extent, and detachment depth of delamination are still debated. Here we test this process by means of 2-D numerical modeling and find that delamination below lower crustal depths can only initiate near cratonic margins, where thickening-induced eclogitization can significantly destabilize the lower part of the lithosphere, allowing it to detach and leading to intraplate orogeny. When a weak midlithosphere discontinuity is present, widespread delamination can initiate near cratonic margins and easily propagate to cratonic interiors, yet without obvious intraplate deformation. We illustrate how this delamination mechanism can recycle large volumes of depleted Archean subcontinental lithospheric mantle using numerical models. Our models explain the large-scale delamination in the North China Craton, where a midlithosphere discontinuity is inferred by geophysical studies and shows that large portions of subcontinental lithospheric mantle can be recycled in the deep mantle potentially affecting mantle heterogeneity.