Liu, Z.,1 Lager, G.A.,2 Hemley, R.J.,1 and Ross, N.L.3
1Geophysical Laboratory,
Washington, D.C. 20015
2 University of Louisville, Louisville, KY 40292
3 Virginia Tech, Blacksburg, VA 24061
NSLS-U2A
Humites are models for the OH-defect structure of olivine and may be important phases involved in the storage, transport and recycling of water in the mantle. High-pressure synchrotron infrared (IR) absorption spectra were collected at ambient temperature for OH-chondrodite and OH-clinohumite up to 38 and 29 GPa, respectively, using argon as the pressure-transmitting medium. The crystal structures of both clinohumite and chondrodite are preserved up to the maximum pressure. However, disordering of the silicate framework appears to become more pronounced at high pressure based on the significant broadening of the IR bands with increasing pressure. All three OH bands in both structures shift linearly to higher frequency with pressure up to 18 GPa. Above 18 GPa, the variation of OH frequency with pressure remains linear; however, the slopes for the three OH bands are significantly different as a result of different degrees of H bonding. This result differs from that obtained by Raman spectroscopy in which one of the OH bands in clinohumite shows a mode softening at ~13 GPa followed by a splitting of this band at ~18 GPa. Based on recent high-pressure neutron powder data, the positive pressure dependence of the OH bands may reflect changes in the O-H...O angle due to rotation of the O-H vector.