Modelling of CHROMium Enrichment in the mantle and the crust

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The main objective of the CHROME project is to develop thermodynamically consistent multiphase flow models that can explain the formation of podiform chromite deposits in ophiolite units. Ophiolites consist of rocks that show evidence of melting/crystallization processes during their formation. Since chromium is a highly compatible element, it is expected to remain in the residuum during melting. However, our preliminary experimental results show that Cr spinel becomes unstable with increasing H2O content and melts together with the other silicate minerals (mainly pyroxenes). This consumption of Cr spinel leads to a dramatic increase in the Cr content of the melt. However, despite this enrichment process, this Cr concentration is not sufficient to form chromite deposits. Thus, we conclude that additional mobilization and Cr enrichment of these melts is necessary. To model the processes of melt transport, the dynamics of reactive multiphase flows in H2O-rich, Cr-saturated magmas from the Earth's mantle must be considered. By modeling the various end-members of Cr enrichment (e.g., convection or reactive transport), we will be able to confirm/reject or even refine some of the available hypotheses for the formation of podiform Cr deposits. We plan to conduct phase equilibrium experiments on the peridotitic rocks containing the Cr ores. These experiments will allow us to draw conclusions needed for further development of reactive transport models. We plan to apply multiphase reactive flow models to gain insight into the processes associated with ore formation. These models will be run in parallel with experiments in which melts are re-equilibrated with mantle rocks. Our combined modeling/experimental approach will provide a thorough review of the proposed modeling approaches. Our goal is to use reactive multiphase flow models to model ore formation processes (from source to deposit). In doing so, our proposed model will consider petrologic and field evidence from natural podiform chromite deposits.