[S-IT21] Innovation through the Integration of Solid Earth Science and Materials Science

[SIT21-03] Ab initio modeling of antigorite transported by subducting oceanic plates

*Jun Tsuchiya¹, 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.