Deformation of olivine at subduction zone conditions determined from in situ measurements with synchrotron radiation

We report measurements of the deformation stress for San Carlos olivine at pressures of 3–5 GPa, temperatures of 25–1150 °C, and strain rates of 10−7–10−5 s−1. We determine a deformation stress of approximately 2.5 GPa that is relatively temperature and strain rate independent in the temperature range of 400–900 °C. The deformation experiments have been carried out on a deformation DIA (D-DIA) apparatus, Sam85, at X17B2, NSLS. Powder samples are used in these experiments. Enstatite (MgSiO3) (3–5% total quality of sample) is used as the buffer to control the activity of silica. Ni foil is used in some experiments to buffer the oxygen fugacity. Water content is confirmed by IR spectra of the recovered samples. Samples are compressed at room temperature and are then annealed at 1200 °C for at least 2 h before deformation. The total (plastic and elastic) strains (macroscopic) are derived from the direct measurements of the images taken by X-ray radiograph technique. The differential stresses are derived from the diffraction determined elastic strains.In the regime of 25–400 °C, there is a small decrease of stress at steady state as temperature increases; in the regime of 400 °C to the ‘transition temperature’, the differential stress at steady state (∼2.5 GPa) is relatively insensitive to the changes of temperature and strain rate; however, it drastically decreases to about 1 GPa and becomes temperature-dependent above the transition temperature and thereafter. The transition temperature is near 900 °C. Above the transition temperature, the flow agrees with power law creep measurements of previous investigations. The anisotropy of differential stress in individual planes indicates that the deformation of olivine at low temperature is dominated by [0 0 1](1 0 0). Accounting to a slower strain rate in the natural system, the transition temperature for the olivine in the slab is most likely in the range of 570–660 °C.

► We report in situ X-ray measurement of deformation of olivine at high P and low T.
► The differential stress at steady states is approximately 2.5 GPa between 400 and 900 °C.
► It is relatively temperature and strain rate independent.
► The deformation of olivine at low temperature is dominated by slip system [0 0 1](1 0 0).
► Deformation of olivine transforms to power-law creep in the slab above 570–660 °C.