THE LARGE-VOLUME MULTI-ANVIL PRESS AS A HIGH P-T DEFORMATION APPARATUS

The rheological properties of mantle materials are being investigated up to pressures of 16 GPa and temperatures of 1600-degrees-C for times up to 24 h, using a new sample assembly for the 6-8 multi-anvil appar atus. Al2O3 pistons, together with a liquid confining medium, are used to generate deviatoric stress in the specimen. Strain rates are estim ated by monitoring the relative displacement of the guide blocks of th e multi-anvil apparatus, scaled to the total axial strain of the sampl e. The applied stress on the sample is estimated using grain size piez ometry. Strain rates and flow stresses of approximately 10(-4) to 10(- 6) s-1 and 50 to 250 MPa respectively, are presently attainable. Preli minary results on San Carlos olivine single crystals, partially dynami cally recrystallized to a grain size of 10 to 300 mum, indicate that t he effective viscosity of polycrystalline olivine is consistent with v alues obtained from olivine single crystal creep laws. Assuming a disl ocation creep mechanism (n almost-equal-to 3.5) with (010)[001] as the dominant slip system, the data are best fit using a creep activation volume of 5 to 10 X 10(-6) M3 Mol-1.