The longevity of cratons is generally attributed to persistence of neutrally-to-positively buoyant and mechanically strong lithosphere that shields the cratonic crust from underlying mantle dynamics. Here we show that large portions of the cratonic lithosphere in South America and Africa, however, experienced significant modification during and since the Mesozoic era, as demonstrated by widespread Cretaceous uplift and volcanism, present-day high topography, thin crust, and the presence of seismically fast but neutrally buoyant upper-mantle anomalies. We suggest that these observations reflect a permanent increase in lithospheric buoyancy due to plume-triggered delamination of deep lithospheric roots during the Late Cretaceous and early Cenozoic periods. Lithosphere in these regions has been thermally reestablished since then, as confirmed by its present-day low heat flow, high seismic velocities and realigned seismic anisotropy. We conclude that the original lowermost cratonic lithosphere is compositionally denser than the asthenospheric mantle and can be removed when perturbed by underlying mantle upwelling. Therefore, it is the buoyancy of the upper lithosphere that perpetuates stabilization of cratons.

克拉通的寿命一般归因于中性至正浮力和机械强度强的岩石圈的持续存在，这些岩石圈使克拉通地壳免受潜在的地幔动力学影响。在这里，我们表明，南美洲和非洲的克拉通岩石圈的大部分区域在中生代以来和中生代以来经历了重大的变化，如白垩纪隆升和火山作用，当今的高地势，薄的地壳以及地震快速但中性浮力的上地幔异常。我们建议，这些观测结果反映了白垩纪晚期和新生代早期深层岩石圈根系的羽流触发分层，从而使岩石圈的浮力永久性增加。从那时起，这些地区的岩石圈已经热重建，由目前的低热流，高地震速度和重新排列的地震各向异性所证实。我们得出的结论是，原始的最低克拉通岩石圈在成分上比软流圈地幔要密，当受到下伏地幔上升流的干扰时可以被去除。因此，正是上岩石圈的浮力使克拉通保持稳定。