HR: 17:45h
AN: MR34A-08    [Abstracts]
TI: Experimental Deformation of San Carlos Olivine Single Crystal at Mantle P and T: Evidences for a Slip-System Transition with increasing P.
AU: * Raterron, P
EM: Paul.Raterron@univ-lille1.fr
AF: LSPES, CNRS, Bât C6, Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, F-59655, France
AU: Amiguet, E
EM: Elodie.Amiguet@ed.univ-lille1.fr
AF: LSPES, CNRS, Bât C6, Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, F-59655, France
AU: Chen, J
EM: Jiuhua.Chen@sunysb.edu
AF: Mineral Physics Institute and Department of Geosciences, ESS Building, Stony Brook University, Stony Brook, NY 11794-2100, United States
AU: Li, L
EM: Lilli@ic.sunysb.edu
AF: LSPES, CNRS, Bât C6, Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, F-59655, France
AU: Li, L
EM: Lilli@ic.sunysb.edu
AF: Mineral Physics Institute and Department of Geosciences, ESS Building, Stony Brook University, Stony Brook, NY 11794-2100, United States
AU: Weidner, D
EM: Donald.Weidner@sunysb.edu
AF: LSPES, CNRS, Bât C6, Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, F-59655, France
AU: Weidner, D
EM: Donald.Weidner@sunysb.edu
AF: Mineral Physics Institute and Department of Geosciences, ESS Building, Stony Brook University, Stony Brook, NY 11794-2100, United States
AU: Cordier, P
EM: Patrick.Cordier@univ-lille1.fr
AF: LSPES, CNRS, Bât C6, Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, F-59655, France
AB: Seismic velocity anisotropies observed in the shallow upper mantle are interpreted from lattice preferred orientations (LPO) produced experimentally in olivine, which depends on the dominant dislocation slip systems. At low pressure P<3 GPa, mantle temperature (T), and in dry conditions, olivine [100] dislocation slip dominates the less active [001] slip. This tends to align crystal fast velocity [100] axis with the principal shear direction. Yet recent deformation experiments carried out at P>3 GPa (Couvy et al., 2004, EJM, 16, 877; Raterron et al., 2007, Am. Min., 92, 1436), as well as a theoretical study based on first-principle calculations (Durinck et al., 2005, PCM, 32, 646), show that, in forsterite, [001] slip may be dominant in the (P,T) range of the deep upper mantle. This would promote a shear-parallel slow-velocity [001] axis and may explain the seismic-velocity attenuation with depth observed at depth >200 km (Mainprice et al., 2005, Nature, 433, 731). Although such [100]-slip/[001]-slip transition has previously been attributed to the presence of water (e.g., Jung et al., 2006, Tectonophysics, 421, 1), evidences for shear parallel [001] axis are observed in nature at high P>4 GPa in dry subduction context (Xu et al., Tectonophysics, 421, 111). Whether such pressure-induced slip transition is an important process in the deep upper mantle is still debated in the literature (see, Karato, 2007, Tectonophysics, 429, 287, and Ji et al., 2007, Tectonophysics , 429, 291), and this debate has strong implications for our understanding of upper mantle convective flows. In order to determine the P effect on Fe-bearing olivine [100] and [001] slip activities, deformation experiments were carried out on San Carlos olivine oriented crystals at P>3 GPa and 1100° 2O content < 50 ppm). Two orientations were tested in order to activate either [100](010) or [001](010) slip system alone. Specimens with different orientations were loaded in each cell, thus experiencing the same run conditions, which allowed investigating slip relative activities by comparing specimen relative strains. TEM investigation of run products shows that dislocation creep was responsible for sample deformation. In most of the 14 investigated (P, T, σ) conditions, [001] slip activity appears higher than or comparable to [100]-slip activity. This suggests that the P-induced [100]-slip/[001]-slip transition documented in pure forsterite occurs as well in Fe-bearing olivine.
DE: 3621 Mantle processes (1038)
DE: 3902 Creep and deformation
DE: 3904 Defects
DE: 3924 High-pressure behavior
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting