Fig. 5: Far-field effects of rifting on cratonic mantle keel stability through time.

a, Simplified craton structure showing mechanical and thermal boundary layers. b, Rifting generates a steep lithospheric gradient that gives rise to Rayleigh–Taylor instability (dashed white lines depict schematic isotherms). c, Migration, continued growth and detachment of the instability (Fig. 2). Low-density asthenosphere wells up adiabatically (black arrows) to replace removed keel and may entrain fragments of the displaced keel, causing low-degree (<1%) partial melting of a mixture of wet asthenosphere and metasomatized lithosphere. Mixing of the resultant melts produces kimberlitic magmas that ascend rapidly to erupt at Earth’s surface. In regions where the return flow upwelling generates very low-degree (<<1%) melts, these may infiltrate, freeze within and refertilize the keel, thereby promoting further decoupling and magma generation. d, The process repeats: destabilization and convective removal of cratonic keel propagates inboard of the rift, leading to migration of kimberlite volcanism towards the cratonic interior (Fig. 1c,e). The simulations predict that the intensity of lithospheric assimilation declines over time: late-stage melting is dominated by asthenospheric mantle once the cratonic keel has foundered and/or been exhausted during early melting (Supplementary Video 1). Scale bar, 100 km.