On the kinetics of olivine-spinel transition

Details On the kinetics of olivine-spinel transition On the kinetics of olivine-spinel transition

Aug 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981pepi...26..179p&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 26, Issue 3, p. 179-187.

Physics

33

Scientific paper

A kinetic model has been derived for a martensitic olivine-spinel transition, brought about by the propagation in the olivine lattice of partial dislocations with Burgers' vector (1/12) [013] dragging stacking faults equivalent to spinel layers. The main assumptions used in this model are:
(1)|Dislocation sources are in grain boundaries.
(2)|Dislocation velocity depends on the effective stress on the partial dislocation through a power law with exponent m.
(3)|The effective stress is the sum of the mechanical shear stress, a chemical stress and a thermally-activated friction stress.
The kinetics are found to be first-order with a reaction rate constant dependent on temperature and grain size.
The depth at which the transition is completed in a sinking lithospheric slab is calculated using the Hsui and Toksöz (1979) temperature profile, a grain size of 1.5 cm and an activation energy of 62 000 cal mol-1. Other parameters are fitted on experimental results of Kasahara and Tsukahara (1971) on Ni2SiO4 and of Lacam et al. (1980) on Fe2SiO4. It is found that the olivine-spinel transition cannot take place above 350 km and is completed at depths ranging from 350 to 420 km according to the value of m.
The model is sensitive to the temperature profile in the slab and to the activation parameters of the transformation.

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