Diamond growth and resorption morphologies reveal the record of mantle fluids and melts

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Diamonds grow in the Earth's mantle over > 600 km depth range during > 4 Ga (~90% of the Earth's history) and are brought to the surface by kimberlites, the deepest magma that reach the surface of the Earth and host economic diamond deposits. Diamonds are unique witnesses of the conditions and processes in the deep inaccessible parts of the mantle. Some crustal rocks subjected to ultra-high pressure in tectonically active continental areas contain microdiamond inclusions inside other minerals. Volatiles (H2O and CO2) play the major role in diamond nucleation as well as in chemical and geodynamic processes affecting the mantle and super-deep crustal rocks, melt production in the mantle, and the rapid ascent of kimberlites. While the record of volatiles in the composition of rock-forming silicate minerals is ambiguous, an array of dissolution features developed on diamond during interaction with high-temperature fluids and melts in the Earth's interior provide a robust record of these fluids and melts and their conditions (temperature, pressure, oxidation). Crystal shape of microdiamonds from deep crustal rocks depend on the pressure and temperature achieved by these rocks prior to the exhumation. The proposed research uses dissolution features and diamond morphology to study deep fluids in the Earth's crust and mantle, their role in kimberlite magmatism and diamond preservation in kimberlites. The work will combine study of surface features on natural diamonds from different kimberlite types and localities, laboratory experiments that replicate dissolution features and growth morphologies of diamond at controlled conditions, and modeling of atomic scale processes of carbon incorporation and removal on diamond surface to imitate the features and morphologies observed on natural diamonds and establish the reaction-controlling parameters. Collaboration with diamond mining companies and DeBeers provides an exceptional access to diamond samples with geological control from specific depths and units within composite kimberlite pipe. Better understanding sources and composition of fluids in subcontinental mantle and the deep crust is essential for reconstructing the geodynamic processes that shaped the top layers of the Earth and their link to kimberlite magmatism. Magma emplacement mechanisms causing the diversity of kimberlites and affecting diamond distribution and preservation in kimberlites are a subject of controversies. As magma emplacement greatly depends on H2O and CO2 content, the proposed research will use diamond dissolution features as a new method for classifying different kimberlite types and modelling distribution of kimberlite units within composite pipes at early exploration stages to improve geological models and predict diamond preservation. The proposed research will help to unravel deep mantle processes and improve exploration techniques to benefit diamond mining industry in Canada, the third world largest diamond producer.