Preliminary results from the new deformation multi-anvil press at the photon factory: Insight into the creep strength of calcium silicate perovskite

A D111 deformation multi-anvil press, which is a larger version of the Deformation T-cup, has been installed at beamline NE7A at PF-AR, KEK, Tsukuba, Japan. Using this apparatus, controlled deformation experiments can be performed by independently moving two opposite second-stage anvils in a Kawai-type 6/8 geometry. This allows both pure and simple shear experiments with sample strain rates of 10 ^-6s ^-1 to be conducted at pressure and temperature conditions up to at least 27 GPa and 1,700 K. Here, the capabilities of the D111 press are demonstrated using experiments investigating the creep strength of calcium silicate perovskite at mantle conditions. Experiments performed at 13 GPa and 1150-1373 K with quantitative stress and strain rate measurements have allowed preliminary evaluation of the creep strength of calcium silicate perovskite. Observations indicate that under dry and wet conditions samples possess grain sizes of between 0.5 and 10 μm, and undergo deformation in a diffusion creep regime with an apparent activation energy of 364 kJ mol ^-1 and a stress exponent of 1.28. Qualitative comparison of preliminary results with the properties of mantle silicate minerals including bridgmanite, wadsleyite, and dry olivine indicates that calcium silicate perovskite is very weak, such that it may strongly influence the geodynamics of the deep mantle especially in regions of subduction.