Fig. 9. Lower-hemisphere equal-area projections of poles to olivine. XZ is the sample section, X is the lineation, and Z is normal to the foliation. N is the number of analyzed grains. The color coding represents the data density. A half width of 20° was used to construct the figures.
6. Olivine water contents
Most nominally anhydrous minerals (e.g., olivine and orthopyroxene) contain a small amount of lattice-bound water more or less, which has a significant role in the deformation of such minerals (Jung & Karato, 2001; Wang, 2010). As such, we measured the olivine water contents by FTIR to assess the effects of water on the olivine fabrics in the garnet lherzolites.
FTIR absorbance spectra of olivine from different stages (M1 and M2) are shown in Fig. 10a–b. The wavenumbers 3400–3800 cm–1 are shown because this region is dominated by the stretching vibrations of O–H bonds (Paterson, 1982). The dominant absorption peaks are at 3639, 3635, 3624, 3616, 3608, 3574, and 3555 cm−1, and represent structurally bound water in olivine (Bell et al., 2003; Hans & Joseph, 2006). The water contents of the coarse-grained (M1) and fine-grained (M2) olivine were calculated using the method of Bell et al. (2003), which yielded values of 183–213 ppm H/Si and 93–139 ppm H/Si, respectively. The coarse- and fine-grained olivine mostly have lower water contents (<200 ppm H/Si), and a few coarse-grained olivine grains have higher water contents (~278 ppm H/Si), perhaps due to later serpentinization or the presence of amphibole inclusions. The FTIR peaks at 3699, 3688, 3683 cm–1 and 3677, 3663, 3662 cm−1can be attributed to serpentine (Wang et al., 2007; Jung, 2009b) and amphibole (Hans & Joseph, 2006; Wang et al., 2007), respectively.