[S-CG49] Innovation through the Integration of Solid Earth Science and Materials Science

[SCG49-03] A molecular dynamics study of phase transformation from Olivine under high pressure and high temperature

*Kobayashi Ryo¹, Eito Date¹ (1.Nagoya Institute of Technology)

Keywords:deep earthquakes, molecular dynamics, structural transformation

Deep earthquakes are the earthquakes that occur at the transition zone between upper and lower mantles at depths of 410 and 660 km. Since the condition of pressure and temperature at the transition zone is much different from those at shallow or intermediate depths where most of earthquakes take place, the mechanism or trigger of the deep earthquakes is also considered to be different from that of shallow earthquakes. However, it is more difficult to study the mechanism of the deep earthquakes than the shallower earthquakes because of its harsh condition of pressure and temperature. Transformation of super pressured olivine is considered as a candidate mechanism of triggering the deep earthquakes, but it is not clear which structure appears as a consequence of the transformation and whether the transformation can cause an earthquake in much larger length-scale. We have conducted molecular dynamics (MD) simulations to investigate the transformation from olivine under high pressure and high temperature condition, and to study the consequences of the transformation.
Focusing on ternary Mg-Si-O system having an olivine structure under a moderate pressure-temperature condition and spinel structure under high pressure, we produced an interatomic potential of the ternary system by optimizing the potetial parameters by using a meta-heuristic approach. The potential was shown to reproduce not only olivine and spinel structures, but also reproduce the intermediate structure suggested in a previous study of ab-initio calculations. We conducted several MD simulation runs with different puressure conditions at high temperature and found different resulting transformed structures with different microstructures such as 1D needle shape and 2D plate shape. We have also conducted large-scale MD simulation of one case within obtained several transformations, to investigate the speed of the transformation front, emission of shockwaves from the front, and the stability of the front by analogy to the crack-front instability. We will discuss in details at the presentation.