[Study on the FTIR spectra of OH in olivines from mengyin kimberlite]

The results of FTIR spectra study of OH in olivines from Mengyin kimberlite show that there are more than 60 OH absorption peaks in the range of 3800-3000 cm(-1). We identified four major spectral features in the OH absorption bands of kimberlitic olivines. One is with nuOH in the range of 3800-3700 cm(-1), which is caused by the vapour of the room circumstance, and can not be regarded as intrinsic or non-intrinsic nuOH of the olivines. Another one is with nuOH in the range of 3710-3620 cm(-1), which belongs to three "water"-bearing minerals including serpentine, talc and Mg-bearing amphiboles, which is the non-intrinsic nuOH of the olivines. There is the possibility that H in hydrous minerals mainly entered into olivines during post-emplacement processes of the kimberlite magma. The third one is with nuOH in the range of 3620-3425 cm(-1), which originated from H occupying the Si-defect in the olivine structure, forming humite-like defects, and/or the defects that H occupies (Mg,Fe)-depletion, which is certainly attributed to the intrinsic nuOH of the olivines. In this case, H possibly entered into olivines following its immersion in the high temperature and rich fluid kimberlite magma in the mantle circumstance. The last one is with nuOH in the range of 3425-3000 cm(-1). In this area, nuOH is assigned to fluid inclusions of the olivines, and is the non-intrinsic nuOH of olivines. Fluid inclusions can enter into the olivines either during post-emplacement processes of the kimberlite magma or during the periods that olivines were formed in the mantle.