Pressure Dependence of Creep in Forsterite Olivine: Comparison of Measurements From the D‐DIA and Griggs Apparatus

We present measurements of the creep strength of forsterite olivine at 1200°C from 1 to 7.5 GPa made using a Griggs apparatus at low pressures and a D‐DIA apparatus at high pressures. The same starting material is used for all experiments allowing us to compare measurements made with the two instruments. We find that results from the two apparatus are comparable if the stress measurements made from the alumina piston in the D‐DIA experiments are used as a proxy for the load that the olivine sample supports. The reproducibility of the D‐DIA experiments are improved if microstructural observations of the post experimental integrity of the sample and piston are used to judge experimental validity. Interpretation of the joint dataset indicate that the pressure dependence of creep (ΔV*) for our sample material cannot be described by a constant value over this pressure range, but changes from ~15 cm3/mol at low pressure to closer to ~4 cm3/mol at high pressure. These results are consistent with changes in the mix of deformation mechanisms operating in forsterite as pressure increases. Key Points Activation energy measurements of forsterite olivine between 1 and 7.5 GPa Comparison of stress measurements between the Griggs and D‐DIA apparatus Reproducibility of stress measurements in the D‐DIA apparatus