The viscosity of CaMgSi2O6 liquid at pressures up to 13 GPa

The viscosity of CaMgSi2O6 (diopside) liquid has been determined up to 13 GPa and 2200 °C using in situ falling sphere viscometry with X-ray radiography. The experiments were carried out in a 1500 t multianvil apparatus at the SPring-8 synchrotron (Japan). A new, high-pressure sample assembly was developed with LaCrO3 replacing the traditionally used graphite furnace material, allowing experiments within the diamond stability field to be carried out. The viscosity of CaMgSi2O6 liquid increases slightly from 3.5 to 10 GPa and then decreases slightly at higher pressures. However, over the entire ranges of temperature (2030–2473 K) and pressure (3.5–13 GPa) investigated, variation in viscosity does not exceed ±0.5 log units. The viscosity results from this study are consistent with those calculated from the pressure dependence of oxygen self-diffusion in CaMgSi2O6 liquid using the Eyring equation with a translation distance (λ) of 0.45 nm providing the best correlation. Both sets of results indicate a change in pressure dependence at approximately 10 GPa, where viscosity results show a maximum with pressure and silicon and oxygen self-diffusivity results show a minimum.