The origin of early continental lithosphere is enigmatic. Characteristics of eclogitic components in the cratonic lithospheric mantle (CLM) indicate that some CLM was likely constructed by stacking of subducted oceanic lithosphere in the Archean. However, the dynamic process of converting high-density, eclogite-bearing subducted oceanic lithosphere to buoyant CLM remains unclear. We investigate this process through numerical modeling and show that some subducted and stacked eclogites can be segregated into the asthenosphere through an episodic viscous drainage process lasting billions of years. This process increases the chemical buoyancy of the CLM, stabilizes the CLM, and promotes the preservation and redistribution of the eclogites in the CLM, explaining the current status of early subduction relicts in the CLM revealed by geophysical and petrological studies. Our results also demonstrate that the subduction stacking hypothesis does not conflict with the longevity of CLM.