Characteristics Of Raman Spectra Of Nature Clinochlore At High Temperature And High Pressure

Raman spectra of nature clinochlore, augite and andesine in chlorite rock were in situ measured with the diamond anvil cell (DAC) and micro-Raman spectrograph at 200℃up to 7.7 GPa, and the seismogeological application was discussed based on the experimental data. The following remarkable results were obtained:(1)The 481 cm-1 and 786 cm-1 peaks shift towards high-frequency linearly with increasing pressure at 200℃. The linear relations between Raman shift(N, cm-1) and pressure(P, GPa) for the two peaks are: N=11.136P+482.6 (R2=0.9874) and N=5.055P+785.7 (R2=0.9837), respectively. The 865 cm-1 peak arising from the stretching mode of the Si-Onb of clinochlore shifts slightly because of the strong repulsion between T cations at the tetrahedral sites and M cations at the octahedral sites in the TOT layer. Raman shift of 481 cm-1 and 786 cm-1 mean the shortening of the length of M-Obr and Si-Obr bonds since the peaks are contributed by the stretching mode of the M-Obr and Si- Obr of clinochlore, respectively.(2)The 695 cm-1 peak arising from the stretching mode of the Si-Obr-Si of augite shifts toward high-frequency linearly with increasing pressure, the linear relation is: N=6.5559P+698.7(R2=0.97).(3)The 1262 cm-1 peak arising from bending mode of the Si-Obr-Si of andesine shifts slightly with increasing pressure.(4)No phase transition of clinochlore, augite and andesine under the experimental condition was found. The results indicate that chlorite minerals may be stable at least at a depth of 70~80 km in the cold subduction zones, and the fluid derived from chlorite dehydration may be an important fact for earthquake occurrence in the subduction zones.