4:45 PM - 5:00 PM
[SCG44-06] Modeling of olivine-spinel phase transformation of germanate olivine (Mg2GeO4) by using the phase-field method
★Invited Papers
Keywords:phase transformation, phase field method, germanate olivine, deep-focus earthquakes
Olivine-Spinel phase transformation under differential stress affects the rheology of subducting slabs and the mechanisms for deep-focus earthquakes (e.g., Rubie, 1984; Green and Burnley, 1989). To investigate the effect of differential stress and microstructural properties such as grain boundary energy and plastic strain on the kinetics of phase transformation, we conducted phase-field simulations using germanate olivine, an analog of silicate olivine. We conducted simulations under various confining pressures of 1–5 GPa, temperatures of 1000 and 1200 K, with and without plastic strain, and various grain boundary energies. The volume fraction of spinel decreases as the overpressure (confining pressure) increases because the elastic strain energy owing to the large overpressure decreases the growth rate of spinel grains. The shape of grown spinel has two types: “spinel needle” parallel to the maximum compression direction and “spinel platelet” perpendicular to the maximum compression direction. The spinel needles constantly grow owing to the interface mobility controlled by the grain boundary diffusivity, whereas the spinel platelets rapidly grow owing to the plastic strain caused by phase transformation and deformation. The spinel growth produces further plastic strain; thus, the spinel growth progresses by this positive feedback between the transformation and deformation (Sawa et al., 2023). This positive feedback would be crucial for the deformation localization required for deep-focus earthquakes.