Mechanisms of transformation and deformation in Mg1.8Fe0.2SiO4 olivine and wadsleyite under non-hydrostatic stress

Catherine Dupas-Bruzek, Thomas Sharp, David C. Rubie, William B. Durham

Research output: Contribution to journalArticle

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Abstract

We have studied the effect of non-hydrostatic stress on the mechanisms of the olivine - wadsleyite-ringwoodite (α-β-γ) phase transformations and deformation mechanisms of olivine and wadsleyite at high pressure. Experiments were performed at 900°C in the β-stability field (15 GPa) for 0.5 h and in the β + γ stability field (16 GPa) for 11 h using a multianvil apparatus with San Carlos olivine as the starting material. A sample assembly designed to produce non-hydrostatic stress was used. The deformed samples have been characterised using optical and transmission electron microscopy. Remnant olivine contains high densities of mostly χ dislocations and deformation occurs by dislocation glide involving the slip systems (010)[001] and (100)[001]. In wadsleyite, dislocations are in a climb configuration, which suggests that self diffusion of Si and/or O is much faster in wadsleyite than in olivine at ~900°C. Wadsleyite also contains (010)β stacking faults which are interpreted to be growth defects that anneal out with time. During the olivine-wadsleyite transformation, non-hydrostatic stress results in anisotropic reaction textures. Wadsleyite nucleates preferentially on olivine grain boundaries that are oriented at a high angle to the direction of principal compressive stress and/or the growth of wadsleyite occurs preferentially in this direction. Wadsleyite transforms to ringwoodite by two competing mechanisms: 1) coherent intracrystalline nucleation on α dislocations, probably where they intersect (010)β stacking faults, and 2) partially-coherent nucleation at wadsleyite grain boundaries. Non-hydrostatic stress enhances transformation rates by increasing the density of dislocations which act as nucleation sites for ringwoodite. Although the samples were partially reacted under non-hydrostatic stress, there is no evidence for transformational faulting.

Original languageEnglish (US)
Pages (from-to)33-48
Number of pages16
JournalPhysics of the Earth and Planetary Interiors
Volume108
Issue number1
DOIs
StatePublished - May 29 1998

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wadsleyite
olivine
dislocation
ringwoodite
nucleation
crystal defects
grain boundaries
grain boundary
stacking
phase transformations
slip
deformation mechanism
textures
assembly
defect
transmission electron microscopy
faulting
transform
defects
texture

ASJC Scopus subject areas

  • Geophysics
  • Space and Planetary Science

Cite this

Mechanisms of transformation and deformation in Mg1.8Fe0.2SiO4 olivine and wadsleyite under non-hydrostatic stress. / Dupas-Bruzek, Catherine; Sharp, Thomas; Rubie, David C.; Durham, William B.

In: Physics of the Earth and Planetary Interiors, Vol. 108, No. 1, 29.05.1998, p. 33-48.

Research output: Contribution to journalArticle

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