Kinetics of intracrystalline olivine-ringwoodite transformation

L. Kerschhofer, D. C. Rubie, Thomas Sharp, J. D C McConnell, C. Dupas-Bruzek

Research output: Contribution to journalArticle

63 Citations (Scopus)

Abstract

We studied the microstructural evolution and kinetics of intracrystalline olivine-ringwoodite transformation in order to evaluate the importance of this mechanism in subducting lithosphere. Intracrystalline transformation occurs within single crystals of San Carlos olivine (Fo90) at T ≥ 900°C and P ≥ 18 GPa and involves four stages: (1) Formation of (100)(α) stacking faults in olivine, (2) coherent nucleation of thin ringwoodite platelets on these stacking faults, (3) semi-coherent growth of the platelets and (4) incoherent nucleation of ringwoodite and/or wadsleyite grains at the platelet interfaces. Because rates of incoherent growth are about two orders of magnitude faster than rates of semi-coherent growth, the final stage is most important for bulk transformation. However, the ringwoodite platelets act as essential nucleation sites for intracrystalline incoherent transformation. The growth of ringwoodite platelets proceeds by the nucleation and migration of interface ledges (1.0-1.5 nm high) and is thermally activated with an activation energy of ~ 270 kJ mol-1. This is similar to the activation energy for incoherent growth, suggesting that both processes are controlled by Si-O bond breaking. The nucleation rate of platelets, as determined from the densities of platelets observed in transmission electron microscopy (TEM) sections, is also strongly temperature-dependent and has a similar activation energy. These results suggest that intracrystalline transformation is likely to be important in subducting lithosphere in addition to the grain boundary nucleation mechanism. The intracrystalline mechanism will reduce the depth interval over which the transformation occurs and may enhance rheological weakening by reducing the grain size of the reaction products. (C) 2000 Elsevier Science B.V. All rights reserved.

Original languageEnglish (US)
Pages (from-to)59-76
Number of pages18
JournalPhysics of the Earth and Planetary Interiors
Volume121
Issue number1-2
DOIs
StatePublished - 2000

Fingerprint

ringwoodite
platelets
olivine
nucleation
kinetics
activation energy
stacking
lithosphere
crystal defects
wadsleyite
ledges
grain boundary
transmission electron microscopy
reaction products
grain size
crystal
grain boundaries
intervals
single crystals
rate

Keywords

  • Nucleation
  • Olivine
  • Phase transformation kinetics
  • Subduction
  • Transmission electron microscopy

ASJC Scopus subject areas

  • Geophysics
  • Space and Planetary Science

Cite this

Kinetics of intracrystalline olivine-ringwoodite transformation. / Kerschhofer, L.; Rubie, D. C.; Sharp, Thomas; McConnell, J. D C; Dupas-Bruzek, C.

In: Physics of the Earth and Planetary Interiors, Vol. 121, No. 1-2, 2000, p. 59-76.

Research output: Contribution to journalArticle

Kerschhofer, L. ; Rubie, D. C. ; Sharp, Thomas ; McConnell, J. D C ; Dupas-Bruzek, C. / Kinetics of intracrystalline olivine-ringwoodite transformation. In: Physics of the Earth and Planetary Interiors. 2000 ; Vol. 121, No. 1-2. pp. 59-76.
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AB - We studied the microstructural evolution and kinetics of intracrystalline olivine-ringwoodite transformation in order to evaluate the importance of this mechanism in subducting lithosphere. Intracrystalline transformation occurs within single crystals of San Carlos olivine (Fo90) at T ≥ 900°C and P ≥ 18 GPa and involves four stages: (1) Formation of (100)(α) stacking faults in olivine, (2) coherent nucleation of thin ringwoodite platelets on these stacking faults, (3) semi-coherent growth of the platelets and (4) incoherent nucleation of ringwoodite and/or wadsleyite grains at the platelet interfaces. Because rates of incoherent growth are about two orders of magnitude faster than rates of semi-coherent growth, the final stage is most important for bulk transformation. However, the ringwoodite platelets act as essential nucleation sites for intracrystalline incoherent transformation. The growth of ringwoodite platelets proceeds by the nucleation and migration of interface ledges (1.0-1.5 nm high) and is thermally activated with an activation energy of ~ 270 kJ mol-1. This is similar to the activation energy for incoherent growth, suggesting that both processes are controlled by Si-O bond breaking. The nucleation rate of platelets, as determined from the densities of platelets observed in transmission electron microscopy (TEM) sections, is also strongly temperature-dependent and has a similar activation energy. These results suggest that intracrystalline transformation is likely to be important in subducting lithosphere in addition to the grain boundary nucleation mechanism. The intracrystalline mechanism will reduce the depth interval over which the transformation occurs and may enhance rheological weakening by reducing the grain size of the reaction products. (C) 2000 Elsevier Science B.V. All rights reserved.

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