In situ X-ray observation of dehydration and EoS of chlorite under high pressure and temperature

Abstract:

Water in hydrous minerals has been transported to deep Earth’s interior by subducting slab, which dehydrate at certain pressure and temperature. The existence of deep Earth’s water affects the physical properties of Earth’s mantle minerals. Therefore it is important to study the effect of water for the subducting slab materials. Serpentine ((Mg,Fe)₆Si₄O₁₀(OH)₈) is major hydrous mineral in subducting slab, and chlorite ((Mg,Fe,Al)₆(Si,Al)₄O₁₀(OH)₈) should be also important hydrous mineral in the subducting slab because Al is included in slab materials. In this study, the dehydration reactions and P-V-T EoS of chlorite were determined by time-resolved X-ray diffraction analysis under high pressure and temperature using MAX80, PF-AR, KEK. We found that chlorite was quickly dehydrated to forsterite + pyrope + fluid within 1 hour at 3 - 7 GPa when across the phase equilibrium boundary. On the other hand, the kinetic boundary was observed above 7 GPa because of low temperature phase equilibrium boundary, and the dehydration product was Mg-sursassite + unknown + fluid. In the EoS study, we observed compressibility change, i.e. elastic softening behavior in chlorite at around 4 GPa. This behavior is consistent with the case of antigorite (serpentine) (e.g. Yang et al., 2014). The details of P-V-T results will be presented.