The fate of delaminated cratonic lithosphere

Abstract

Cratonic lithosphere delamination has been frequently suggested in recent studies. However, the fate of the delaminated Sub-Cratonic Lithospheric Mantle (SCLM) has not been thoroughly investigated. Here, we use 2D numerical models to study the evolution of initially delaminated SCLM whose density is initially larger than that of the ambient mantle. Our simulations reveal that after the dense lithospheric segments sink into the hot mantle, the increasing thermal buoyancy and/or removal of the dense components reverse their trajectory, and most of these segments eventually relaminate to the base of the above lithosphere. The time needed for the relamination process to complete is 100-300 Myr since initial delamination, with the exact value depending on the buoyancy of the SCLM and the mantle viscosity. Both delamination and relamination could generate a rapid hundred-meter to kilometer scale surface uplift. After the relamination, the subsequent cooling of the SCLM causes gradual subsidence by ∼2 km. This model provides a novel explanation for the observed Phanerozoic vertical motion of many cratons. According to our models, the delamination-to-relamination evolution mode could occur repeatedly during the past one billion years, as could reconcile the apparent long-term intactness of cratonic crusts and the temporal variations of cratonic topography. In addition, some delaminated lithosphere segments could relaminate to the base of the oceanic plate, providing a mechanism for the presence of ancient continental compositions within some oceanic basalts.