[S-IT22] Innovation through the Integration of Solid Earth Science and Materials Science

[SIT22-P01] First-principles investigations of the polysomatism of antigorite under pressure

*Jun Tsuchiya¹, Taiga Mizoguchi¹, Sayako Inoue¹ (1.Geodynamics Research Center, Ehime University)

Keywords:ab initio calculation, serpentine

Serpentine is hydrous phyllosilicate known to be formed in the mantle wedge by a reaction between
mantle peridotit and upwelling water released by the decomposition of hydrous minerals in the
subducting slab [e.g. Schmidt and Poli,1998]. Partially serpentinized peridotite may be a significant
reservoir of water in the mantle wedge and the dehydration of serpentine is considered to have an
important contribution to the generation of arc magmatism. This was also extensively investigated in
connection with intermediate and deep earthquakes [e.g. Irifune et al. , 1996].
In order to investigate the transporting processes of water into the Earth’s interior, the thermodynamic
stabilities and the elastic properties of antigorite should be clarified. Antigorite is the high-temperature
polymorph of serpentine and thus the relevant phase in the subduction zone. This phase has been
reported to show polysomatism depending on the pressure and temperature conditions. Previous TEM
study reported that m value (m = number of SiO4 tetrahedra in a wavelength along the a axis)
increases/decreases with pressure/temperature [e.g. Wunder et al. 2001]. However, there is no sufficient
structural and thermodynamic corroboration regarding the stable polysome of antigorite along the
pressure and temperature conditions of the subducting oceanic plate.
In the present study, we investigated the structure and elasticity of antigorite with several different m
values by ab intio calculation and discuss the stable polysome of antigorite in the subducting oceanic
plate.