LATTICE PREFERRED ORIENTATION AND WATER CONTENT OF OLIVINE IN PERIDOTITES FROM ALMKLOVDALEN IN WESTERN GNEISS REGION, SW NORWAY

Almklovdalen is a part of Norwegian Western Gneiss Region, located in SW Norway. Six garnet peridotites from Almklovdalen were studied to understand deformation processes and seismic anisotropy in the upper mantle. These peridotites were metamorphosed at high pressure and high temperature and contained chlorite up to ~20 %. Lattice preferred orientation (LPO) of olivine was determined by using electron backscattered diffraction (EBSD) in SEM. Water content of olivine was measured using the Nicolet 6700 Fourier transformation infrared (FTIR) spectroscopy.

Six samples showed various LPOs of olivine. The garnet peridotite with the highest garnet content (19 %) showed that [100] axes of olivine are aligned subparallel to the lineation and [010] axes aligned normal to the foliation, which is known as A-type LPO. Two samples showed that [001] axes are aligned subparallel to the lineation and [010] axes aligned normal to the foliation, which is known as B-type LPO. One sample showed that [100] axes are aligned subparallel to the lineation and [001] axes aligned normal to the foliation, which is known as E-type LPO. Another sample showed that [001] axes are aligned subparallel to the lineation and [100] axes aligned normal to the foliation, which is known as C-type LPO. Water content of olivine obtained from FTIR analysis was in the range of 250 – 660 ppm H/Si. The garnet peridotite with the highest garnet content (19 %) showed a small amount (250 ppm H/Si) of water in olivine. Samples with olivine LPOs of B-, C-, and E-type showed high water contents in olivine. In contrast, samples with olivine A-type LPO showed low water content which is consistent with the result of previous experimental studies at high pressure and high temperature. Seismic anisotropy of different LPOs of olivine was calculated and will be presented.