Slow craton thickening can increase the frequency of kimberlite eruptions

Although cratons are stabilized by their thick and highly viscous lithosphere, their long-term thermal evolution remains poorly understood. Here, kimberlite-hosted mantle xenoliths can provide constraints on past craton thickness, as they erupt almost exclusively beneath thick cratons that protrude into a ‘kimberlite window’ of 160–250 km. Global compilations indicate that kimberlite eruptions become more frequent and continuous after 1500 Ma. Therefore, we link two fundamental questions: how craton thickness evolved through time, and whether this evolution influenced kimberlite magmatism. We present 27 two-dimensional numerical models of craton evolution within a convecting mantle, and explore the effects of initial craton thickness, compositional buoyancy, radiogenic heating, and mantle cooling. Although cratons originated as hot and thick layers in the Archean, gravitational flattening likely thinned them above kimberlite-generating depths. With progressive cooling, craton viscosity and density increased, allowing cratons to undergo gradual thickening after ~ 2000 Ma. We conclude that thickening processes, such as tectonic compression and cooling, operate faster than thinning processes, such as sub-lithospheric dripping, to slowly thicken cratons into the ‘kimberlite window’. Such thickening is a possible explanation for the increasing frequency of kimberlite eruptions after ~ 1500 Ma.