The thermal evolution of cratonic roots from assembly to maturity: Constraints from Archean diamonds and modeling of peridotite melting

• Diamonds erupted in Archean times provide unique thermal records of the lithosphere. • Modelling of the latent heat of fusion during peridotite melting cools new lithosphere. • 1-D thermal models of lithosphere created by plume accretion produce initially hot conditions. • Plume accretion models not consistent with the diamond record. • Thermal models of slab-stacking are consistent with the diamond record. The thermal evolution of early cratonic mantle roots is of intense interest because of the constraints offered on craton formation yet few geological constraints are available. Diamonds erupted in Archean times provide invaluable windows into this issue through the thermobarometry of their inclusions and the time- and temperature-dependent aggregation of their nitrogen impurities. The chemistry and pressure–temperature conditions of inclusions in Archean-erupted diamonds largely reflect those of inclusions found within typical lithospheric diamonds erupted in recent times, and indicate that unusually cool thermal conditions pertained in their early evolution. These cool conditions are strongly supported by modelling of the nitrogen aggregation systematics in the diamonds as well as in global lithospheric diamonds. Using 1-D thermal models with initial cooling due to latent heat of fusion during peridotite melting, we simulate lithosphere thermal evolution following active plume melting. These models cannot reproduce the cool conditions of silicate inclusions in Archean erupted diamonds and also cannot reproduce the cool mantle diamond-formation temperatures recorded by silicate inclusions in global peridotitic lithospheric diamonds. In contrast, simple thermal models of slab-stacking, produce complex, highly transient thermal histories in the first 500 Myr of their evolution, initially characterised by very cool local conditions, matching those seen in Archean erupted diamonds. The thermal evolution of our slab-stacking models involves both cooling and heating intervals depending on depth in the evolving lithospheric root. This complex and varied thermal evolution is much more consistent with the constraints offered by the lithospheric diamond record.