Dislocation recovery experiment of hydrous olivine as a function of water content and crystallographic orientation

• Applicant: Professor Dr. Tomoo Katsura
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2012 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 229061489

Deformation experiments suggested that dislocation mobility should be enhanced by water incorporation, and the water-content dependence of dislocation mobility in the [100](010) (Type-A), [100](001) (Type-E) and [001](100) (Type-C)slips should be higher in this order. The overall water-content exponent of dislocation mobility should be 1.2. In order to examine these results, the applicant conducted dislocation recovery experiment in the preceding project and obtained the following results. (1) In spite of at least four reported fabric types (Type A, B, C and E), there are only two kinds of dislocations. Dislocations for Type A and E fabrics are edge dislocations with a [100] Burgers vector (a-dislocations), whereas those for Type B and C fabrics are screw dislocations with a [001] Burgers vector (c-dislocations).(2) The activation energies and volumes of annihilation-rate constants of a- and c-dislocations are identical, and are also comparable with those of the Si diffusions. These facts suggest that motions of these two dislocations are diffusion-controlled. (3) The water-content exponents of annihilation-rate constants of a- and c-dislocations are 0.2±0.4 and -0.5±0.2, respectively. Namely, their water content dependences are zero with in uncertainty and negative, respectively.Although these striking results were thus obtained, there are insufficient Points.(1) Uncertainties of the annihilation-rate constants of a-dislocations by the [100](010) slip are very large.(2) Data points of the annihilation-rate constants of c-dislocations by the [001](010) slip are too few.(3) It is not clear whether dislocations accounting for Type-E fabric are really absent under any condition.(4) It is not clear whether c-dislocations responsible for Type-B and Type-C fabrics are identical or not. For these reasons, the following experiments will be conducted in this project.(1) Data points of water-content dependence of annihilation-rate constants of a-dislocations will be reinvestigated by means of more precise techniques.(2) More data points will be produced for water-content dependence of annihilation-rate constants of c-dislocations.(3) Olivine single crystals will be sheared in the [100] direction on the (001) plane under various pressure, temperature, strain-rate and water-content conditions to examine their dislocation textures.(4) Pressure and temperature dependence of c-dislocations by the [001](100) slip and water-content dependence of those by the [001](010) slip will be obtained.

• DFG Programme: Research Grants