High-pressure recovery of olivine: implications for creep mechanisms and creep activation volume

Details High-pressure recovery of olivine: implications for creep mechanisms and creep activation volume High-pressure recovery of olivine: implications for creep mechanisms and creep activation volume

May 1982

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982pepi...28..102k&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 28, Issue 2, p. 102-117.

Physics

28

Scientific paper

High-temperature and high-pressure recovery experiments were made on experimentally deformed olivines at temperatures of 1613-1788 K and pressures of 0.1 MPa to 2.0 GPa. In the high-pressure experiments, a piston cylinder apparatus was used with BN and NaCl powder as the pressure medium, and the hydrostatic condition of the pressure was checked by test runs with low dislocation density samples. No dislocation multiplication was observed. The kinetics of the dislocation annihilation process were examined by different initial dislocation density runs and shown to be of second order, i.e. dρ/dt= -p2K0exp[-(E*+PV*/RT] where ρ is the dislocation density, k0 is a constant, E* and V* are the activation energy and volume respectively, and P, R and T are pressure, gas constant and temperature, respectively. Activation energy and volume were estimated from the temperature and pressure dependence of the dislocation annihilation rate as E*=389+/-59 kJ mol-1 and V*=14+/-2 cm3 mol-1, respectively.
The diffusion constants relevant to the dislocation annihilation process were estimated from a theoretical relation k=αD where k=k0 exp[-(E* + PV*)/RT], D is the diffusion constant and α is a non-dimensional constant of ca. 300. The results agree well with the self-diffusion constant of oxygen in olivine. This suggests that the dislocation annihilation is rate-controlled by the (oxygen) diffusion-controlled dislocation climb.
The mechanisms of creep in olivine and dry dunite are examined by using the experimental data of static recovery. It is suggested that the creep of dry dunite is rate-controlled by recovery at cell walls or at grain boundaries which is rate-controlled by oxygen diffusion. Creep activation volume is estimated to be 16+/-3 cm3 mol-1.

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