Experimental study on the conditions of inclusions capturing during diamond growth in the upper mantle

Abstract

<p>Primary inclusions in natural diamonds provide unique information about deep-seated mantle minerals and fluids. Findings of the VI and VII modifications of H<sub>2</sub>O-ice as inclusions in diamonds show the presence of aqueous fluids at different depths in the diamond-bearing mantle (Kagi et al., 2000; Tschauner et al., 2018). In this work, we apply various experimental techniques for the investigation of mineral associations and H<sub>2</sub>O phases, captured as inclusions in diamonds, in the pressure range from 4 to 8 GPa and at temperatures from 500 °C to 1250 °C. <em>In situ</em> observations using diamond anvil cell (DAC) technique revealed crystallization of ice VII in association with ilmenite and olivine minerals upon cooling from 890 °C at 4 GPa, in agreement with the data, obtained from natural samples by Tschauner et al. (2018). Heating of this assemblage to 1200 °C at 6 GPa results in the formation of another mineral association, which includes ilmenite, pyroxene and clinohumite. Obtained experimental results can be used to reconstruct the pressure and temperature conditions of mineral and fluid inclusions capturing upon diamond growth and transfer in the lithosphere.  </p><p>This work was supported by grant No. 20-77-00079 from the Russian Science Foundation.</p>