1. Deformation of Diopside Single Crystals at Mantle P and T E. AMIGUET 1, P. RATERRON 1, P. CORDIER 1,H. COUVY 2, AND J. CHEN 2 1Laboratoire Structure et Propriétés de l’Etat Solide, UMR 8008, UST Lille, France 2Mineral physics Institute and Deparment of Geosciences, Stony Brook University, NY, USA Acknowledgement : L. Wang, MPI / Stony Brook University, USA

2. Upper-mantle seismic anisotropy allows characterizing convective flow directions in this region. Seismic anisotropy results from lattice preferred orientations (LPOs) in elastically anisotropic crystals deformed by dislocation creep, which in peridotite are essentially olivine and pyroxenes crystals. Experiments at high-temperature (T>1000°C) and room pressure, have shown that the easiest dislocation slip systems in diopside are {110}1/2 sytems. They are followed in term of activitiy by {110}[c], then by (100)[001], and finally by the hardest (100)[010] and (010) [100] systems.

3. We present here the first high-pressure (P~7GPa) high-temperature (1100°C<T<1400°C) deformation experiments carried out on oriented diopside crystals, in order to investigate the effect of P on the activity of diopside slip systems and predict clinopyroxenes LPOs at mantle conditions. The ultimate goal is to better constrain pyroxenes’ influence on mantle seismic anisotropy.

10. Preliminary results indicate that P has little or no effect on the hard (100)[010] and (010)[100] systems, while it tends to strongly inhibit the easy {100}1/2 systems, which become ~ 2 orders of magnitude less efficient (in terms of ε ) at 200 km depth. This may significantly affect mantle clinopyroxenes LPOs as predicted from 1-atm deformation experiments. Investigation of the effect of P on [001] glide (crystal orientation [4]) is under way.

11. Raterron and Jaoul (1991),High-temperature deformation of diopside single crystal, J.Geophys. Res, 96, 14, 277-14, 286. Raterron et al. (1994), High temperature deformation of diopside IV : predominance of {110} glide above 1000°C, Phys. Earth Planet Int., 82, 209- 222. Mainprice et al., (2000) The anisotropy of the Earth's mantle : From single crystal to polycrystal. AGU Geophysical Monograph 117. ""Mineral Physics and Seismic Tomography: From Atomic to Global"" (editors S. Karato, A.M. Forte, R.C. Liebermann, G. Masters and L.Stixrude),237- 264."