DIAMOND STABILITY WITH RESPECT TO OXIDATION IN EXPERIMENTS WITH MINERALS FROM MANTLE XENOLITHS AT HIGH P-T PARAMETERS

Abstract

Experimental results are presented on the etching of diamond crystals in a system including silicate minerals from mantle xenoliths and C-O-H fluid at 5.5-6.0 GPa and 1450-1500°C. Slight etching patterns were established in the experiments with garnet lherzolite, eclogite, and spinel lherzolite samples. No changes in the weight and morphology of diamond crystals were detected in experiments with dunite and garnet pyroxenite samples. Water was the major component of the experimental fluid; CO2 and CH4 occurred in minor amounts. Hydrogen was detected in two runs, and traces of heavy hydrocarbons were noticed. Our study demonstrated that (1) diamond can in principle be etched with fluids under parameters of its thermodynamic stability and (2) the composition of fluid captured in mantle minerals is close to equilibrium with diamond. Therefore, it can be assumed that diamond is stable for an infinite time under high P-T parameters, if the equilibrium conditions are maintained.