High-temperature And High-pressure Investigation On Crystal Chemistry Of Hydrous Minerals In Al₂O₃-SiO₂-H₂O System In Subduction Zones

The concentration and distribution of water in Earth's interior controls the evolution and dynamics process of the planet.Hydrous minerals are main carriers of water in subducting slabs,and water can be transported from Earth's surface to its deep interior or even to the core-mantle boundary.Compared with the lithospheric mantle,the sediments and oceanic crust layers are rich in aluminum and silicon,which could be simplified by Al₂O₃-SiO₂-H₂O ternary system under hydration conditions.The hydrous minerals formed in this system are potential carriers of water and can be stable at warm subduction zones or along the normal mantle geotherm.We have investigated the P-V-T equation of state of phase egg and topaz using the synchrotron-based single-crystal X-ray diffraction and obtained their thermoelastic parameters.And we have conducted high-pressure IR absorption spectra and Raman spectra of Phase egg,?-AlOOH and?-AlOOH to understand the occurrence states of hydrogen in deep Earth.Based on the high-pressure single crystal X-ray diffraction results,the F/(F+OH)in topaz corresponded positively to its bulk modulus.Fluorine content also presents significant effects on the anisotropic compressibility of topaz,the linear modulus of a-axis increases and c-axis decreases with increasing of F content.The parameters of P-V-T equation of state of topaz are as follows:K₀=166(1)GPa,K'=3.0(1),((?)K₀/(?)T)_P=-0.015(9)GPa/K,?₀=3.9(5)×10^-5 K^-1.The density and bulk velocity of toapz are greater than those of preliminary reference Earth model at subduction zone conditions.The thermal expansivity is an important thermodynamic parameter,which is closely related to the physical properties of samples and experimental P-T ranges.The thermal expansivity obtained from single crystal X-ray diffraction at high-pressure and high-temperature will be more suitable for deep Earth research.The proton flips its position at?14 GPa in phase egg and the hydrogen bonding configuration changes fromO4-H···O3 toO4···H-O3 according to the high-pressure single crystal X-ray diffraction experiments.The bulk modulus and linear modulus of b-axis and c-axis of phase egg increase and the anisotropic compressibility decrease for the reason of hydrogen-bond structure transition.The IR absorption peak attributed toOH stretching vibration increases by?20 cm^-1 and a new Raman peak at?487 cm^-1observed along with the changes of hydrogen-bond.The parameters of P-V-T equation of state of phase egg are as follows:K₀=167(8)GPa,K'=5.5(10),((?)K₀/(?)T)_P=-0.023(5)GPa/K,?₀=4.2(11)×10^-5 K^-1.However,this behavior is smeared out because of thermal disordering of hydrogen atom at high temperatures,and accordingly its influence on bulk modulus would be cancelled out.Along the cold and warm subducting slab geotherms,the density and bulk velocity of phase egg are greater than those of preliminary reference Earth model in the mantle transition zone,presenting negative buoyancy force for deep-water transportation.These results are useful for identifying the potential presence of phase egg and may provide a constraint on the fine velocity structures in subduction zones.Hydrogen-bond symmetry of?-AlOOH occurs at?12 GPa by high-pressure IR absorption spectra.The relative intensity of Raman shifts would be changed at high pressure because of the strength or transformation of hydrogen-bond in?-AlOOH,?-AlOOH and Phase egg,which will provide more implications for the occurrence states of hydrogen in hydrous minerals in Earth's interior.