Abstract: In order to discuss the formation conditions of coesite, the authors use biotite gneiss from Archean Fuping Group in Xibaipo, Pingshan county, Hebei Province to conduct the deformation experiments under high temperatures and pressures. Under experimental temperature of 800 ℃ and confining pressure at 0.2 GPa, the stress degree is 10% and the stress rate is 10^-5/s. Experimental results indicate that the laser Raman spectra of quartz grains in different sites of the deformed sample show obvious changes compared with that of standard quartz, suggesting that differential stress may change crystal lattice of quartz.

Key words: ultra high pressure metamorphic rock, differential stress, Raman spectra, quartz fabrics