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Deformation of olivine at mantle pressure using the D-DIA

¹ Mineral Physics Institute, Department of Geosciences, State University of New York at Stony Brook, Stony Brook, NY, 11794-2100, USA
² Laboratoire de Structure et Propriétés de l'État Solide (associated to CNRS), Université des Sciences et Technologies de Lille, F-59655 Villeneuve d'Ascq Cedex, France
³ Lawrence Livermore National Laboratory, Livermore, CA 94550, USA

^* Corresponding author, e-mail: lilli{at}ic.sunnysb.edu

Knowledge of the rheological properties of mantle materials is critical in modeling the dynamics of the Earth. The high-temperature flow law of olivine defined at mantle conditions is especially important since the pressure dependence of rheology may affect our estimation of the strength of olivine in the Earth's interior. In this study, steady-state high-temperature (up to 1473 K) deformation experiments of polycrystalline olivine (average grain size 10 µm) at pressure up to 9.6 GPa, were conducted using a Deformation-DIA (D-DIA) high-pressure apparatus and synchrotron X-ray radiation. The oxygen fugacity (f_o2) during the runs was in-between the iron-wustite and the Ni/NiO buffers' f_o2. The water content of the polycrystalline samples was generally about 150 to 200 wt. ppm but was as low as 35 wt ppm. Typically, 30% strain was generated during the uniaxial compression. Sample lengths during the deformation process as well as the differential stresses were monitored in situ by X-ray radiography and diffraction, respectively. The strain rate was derived with an accuracy of 10^–6 s^–1. Differential stress was measured at constant strain rate ( 10^–5 s^–1) using a multi-element solid-state detector combined with a conical slit. Recovered specimens were investigated by optical and transmission electron microscopy (TEM). TEM shows that dislocation glide was the dominant deformation mechanism throughout the experiment. Evidence of dislocation climb and cross-slip as active mechanisms are also reported. Deformation data show little or no dependence of the dislocation creep flow with pressure, yielding to an activation volume V^* of 0 ± 5 cm³/mol. These new data are consistent with the high-temperature rheological laws at lower pressures, as reported previously.

Key-words: olivine, high pressure, high temperature, synchrotron X-ray imaging, stress, strain, TEM, dislocations, flow, activation volume.

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