The Strcture Of Albite And Andesine At High Pressure

In order to understand the circulation process of crust and mantle material in subduction zone,Albite and Andesine have been studied using Electron Probe Microanalysis（EPMA）,Fourier Transform Infrared Spectrometer（FTIR-spectrometer）,laser Raman spectrometer and X-ray diffractometer（XRD）.The lattice parameters,phase transition,P-V equation,lattice vibration and volume modulus of two plagioclase were discussed.It can be calculated from the EPMA data that samples’formulae are Na_1.178Ca0.04（Mn0.003Al0.983Si2.960O8）of Albite and Na0.593K0.033Ca0.429Mg0.005（Fe0.016Mn0.003Ti0.005Al1.411Si2.545O8）of Andesine,respectively.The in situ high-pressure XRD（HPXRD）experiment of Albite was done in 13BMC beamline of Advanced Photon Souce.Several phase transitions were observed up to 50.2 GPa,which is around 5.0,9.6 and 19.0 GPa.The phase transition is not reversible.The HPXRD experiments of Andesine were carried out up to 11.6 GPa at BL15U of SSRF.There are phase transitions around 2.4 GPa,4.5 GPa and 9.2 GPa,which can be deduced from the appearance and disappearance of peaks.The situ HP-Raman Spectra of Albite and Andesine were also studied by DAC.Raman peaks of Albite(478 cm^-1and 506 cm^-1),which belong to the flexural vibration of the Si-O-Si and Al-O-Si,merged at about 5.8 GPa.Meanwhile,the 762cm^-1peak（the Al-O stretching vibration）split into two peaks at first,and merged with 816cm^-1 at about 8.8GPa.These processes show there are two phase transitions in Albite and the transformation is reversible.The HP-Raman results of Andesine indicate there are two phase transitions near 4.6 GPa and 9.0 GPa（up to 19.4 GPa）.The first transition is deduced from the merge of 480 cm^-1 and 507 cm^-1 peak at about 4.6 GPa,and the second can be seen from the sharp increasement of its intensityaround 9.0 GPa.The phase transition of Andesine is not reversible.