Kimberlites from source to surface: Insights from experiments

High-pressure experiments are unconvincing in explaining kimberlites as direct melts of carbonated peridotite because the appropriate minerals do not coexist stably at the kimberlite liquidus. High-pressure melts of peridotite with CO₂ and H₂O have compositions similar to kimberlites only at pressures where conditions are insufficiently oxidizing to stabilize CO₂: they do not replicate the high K₂O/Na₂O of kimberlites. Kimberlite melts may begin their ascent at ≈300 km depth in reduced conditions as melts rich in MgO and SiO₂ and poor in Na₂O. These melts interact with modified, oxidized zones at the base of cratons where they gain CO₂, CaO, H₂O, and K₂O and lose SiO₂. Decreasing CO₂ solubility at low pressures facilitates the incorporation of xenocrystic olivine, resulting in kimberlites’ characteristically high MgO/CaO.