| Recent work on discerning the formation conditions of diamonds has concentrated on the study of fluid and mineral inclusions within the diamonds; however, few diamonds have a usable inclusion assemblage. The presence of trace elements in diamonds is known to occur and if calibrated may provide a useful thermometer. To address this, crushed natural diamonds were treated in the presence of synthetic and natural silicates, carbon black, and natural and synthetic fluxes. The silicates, diamond overgrowths, and melts were analyzed via electron microprobe to calibrate a trace element thermometer based on equilibrium constants of reactions with Si incorporation in diamonds from the melts or the silicates. The observed Si concentration in diamond overgrowths ranged up to 4,100 ppm by weight. Thermometers based on the distribution coefficients between diamond and silicates were applied to two suites of natural diamonds. It was observed that the equilibrium constants and distribution coefficients are probably unique to the liquid that the diamond grew in.;The proposed thermometry may best apply to diamonds growing in Si-rich liquids (e.g. metamorphic microdiamonds) and diamonds growing at elevated temperatures such as in the transition zone or lower mantle. Future work stemming from this study includes improvement in the detection of Si in diamonds and their overgrowths and the continuation of experiments to determine the equilibrium constants with differing liquids. |
