Slow Thickening of Cratons Has Increased Kimberlite Frequency Over Time

Kimberlites are exclusively found on cratons, some of which have remained stable for more than 3 billion years. Kimberlite melts are generated at temperatures of at least 1300°C and pressures of 5–7 GPa, corresponding to depths of 160–250 km. Cratons, being thicker than normal lithosphere, are thus natural hosts for kimberlite melts. Analyzing the frequency of kimberlite eruptions over time, we found that their frequency gradually increased after 1.5 Gyr. Notably, before 2 Gyr, only 4-5 records of kimberlite eruptions have been documented. As kimberlites are found on stable cratons, preservation bias due to tectonic or erosional destruction may not fully explain the scarcity of older kimberlites. This paucity motivated us to explore a potential correlation between craton thickness and kimberlite frequency. Analysing previous studies we hypothesize that, initially, cratons were less than 150 km thick — below the kimberlite stability depth –  and they have thickened over time, eventually reaching depths conducive to kimberlite stability. Mechanisms for craton growth remain poorly understood, although gravitational thickening and self-compressive thickening have been proposed. To investigate these mechanisms within the context of supercontinental cycles, we developed 2D box models using the finite element code ASPECT. Starting with a 150 km thick craton, we allowed mantle flow to evolve over 3 Gyr. Due to their high viscosity and thickness, cratons can divert mantle flow, creating a self-compressive environment during supercontinental assembly. During supercontinental breakup, mantle flow generates an extensional environment that thins the craton. We simulated four supercontinental cycles corresponding to Superia, Columbia, Rodinia, and Pangea. Our results show that cratons became progressively thicker during each cycle. After 1.5 Gyr, craton thickness increased to approximately 160 km, entering the kimberlite stability field. By the time of the Rodinia assembly, craton thickness had reached levels suitable for diamondiferous kimberlite formation, potentially explaining the sudden increase in kimberlite eruptions around 1.1 Ga. We tested various parameters, including viscosity, density, initial thickness, and craton width, against different background mantle flow velocities. Our preliminary results suggest that the gradual thickening of cratons after 1.5 Gyr increased the likelihood of kimberlite eruptions on Earth.