The final giant impact stage of planetary accretion has invariably resulted in extensive mantle melting and formation of planetary magma ocean. The outcome of solidification of the magma ocean is highly uncertain, and different models championed in the literature have quite distinct ramifications for mantle evolution. The traditional model for the magma ocean crystallisation involves a rapidly cooling magma ocean from bottom upwards, where the mantle undergoes equilibrium crystallisation and does not develop large-scale compositional heterogeneities. In a model involving a slow cooling magma ocean, where a component of fractional crystallisation is possible, the lower mantle will be enriched in bridgmanite. The third plausible scenario is the mid-mantle crystallisation of the magma ocean, where the basal magma ocean crystallises slowly and survives the solid-state convective stirring of the overlying mantle. Each of these scenarios can create distinct isotopic distributions for Mg and Si, the main cationic constituents of bridgmanite. Our research focuses on the Mg and Si isotopes of modern plume-derived melts and the exploration of these isotopic results in the context of geodynamic models of magma ocean crystallisation and mantle stirring to understand the style and preservation of the Earth's magma ocean heritage.

The timing of the global onset of plate tectonics has been a topic of considerable debate in geology. Subduction is an essential feature of plate tectonics and imparts a distinct geochemical fingerprint to the modern arc volcanics that can be traced back in the geological record. Modern arc lavas show a strong enrichment of Pb, relative to U, yielding low U/Pb values unlike a normal mantle melting scenario, where the continental crust has a high U/Pb value. K-Feldspar minerals have high U/Pb and Rb/Sr values and require minimal correction from in-situ radiogenic growth. Our research focuses on constraining the timing of this distinctive consequence of subduction, where there is a reversal in the sense of U/Pb fractionation from mantle to the crust using coupled U/Pb and Rb/Sr analysis in K-Feldspar minerals.