HR: 1340h
AN: DI53A-1100    [Abstracts]
TI: Kinetics of the olivine-wadsleyite transition from time resolved synchrotron XRD
AU: * PERRILLAT, J
EM: perrilla@esrf.fr
AF: European Synchrotron Radiation Facility, BP220, Grenoble, 38043, France
AU: DANIEL, I
EM: isabelle.daniel@univ-lyon1.fr
AF: Laboratoire de Sciences de la Terre, Université de Lyon ; UCB Lyon 1 - ENS Lyon - CNRS UMR5570, 2 Rue Raphael Dubois, Villeurbanne, 69622, France
AU: BOLFAN-CASANOVA, N
EM: N.Bolfan@opgc.univ-bpclermont.fr
AF: Laboratoire Magmas et Volcans, CNRS UMR6524, 5 Rue Kessler, Clermont-Ferrand, 63032, France
AU: CHOLLET, M
EM: melanie.chollet@ens-lyon.fr
AF: Laboratoire de Sciences de la Terre, Université de Lyon ; UCB Lyon 1 - ENS Lyon - CNRS UMR5570, 2 Rue Raphael Dubois, Villeurbanne, 69622, France
AU: MORARD, G
EM: morard@esrf.fr
AF: European Synchrotron Radiation Facility, BP220, Grenoble, 38043, France
AB: The mechanisms of the olivine transformation to its high-pressure polymorphs have wide implications for mantle dynamics; in particular for the origin of deep-focus earthquakes. In order to study the kinetics of this transition, α-(Mg,Fe)Si₂O₄ samples have been reacted in the stability field of wadsleyite (β phase), at 12.5-15 GPa and temperatures up to 1100 K, in a Paris-Edinburgh press. Product phases and extent of transformation were monitored as a function of time by synchrotron X-ray diffraction at ESRF (beamline ID27). The sequence of XRD spectra reveals the early formation of a spinel-structured phase, as observed in previous quenched experiments. This spinel phase further transforms to β phase with increasing temperature and/or time, so that it always disappeared before completion of the reaction. Transformation-time curves are constructed from the relative proportions of the α, β and spinel phases determined by Rietveld refinement of XRD patterns. The kinetic data are analyzed in terms of the Avrami's theory of nucleation and growth in order to determine reaction rates. The influence of sample microstructure and differential stress on transformation rates are also investigated, as well as the effects of iron and water contents. In the light of these kinetic data, we discuss the persistence of a metastable wedge of olivine in the cold interior of subducting slabs.
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 3630 Experimental mineralogy and petrology
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting