LAUSR

Abstract To better understand the effect of water on the plasticity of garnet, the water content and dislocation structures in 10 deformed garnet grains from 8 ultrahigh pressure (UHP) eclogite samples collected at Shuanghe, Dabie orogen, China, were investigated by Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM). The FTIR results show that the mean water content in these garnet grains range from 66 to 2256 wt. ppm H2O. The TEM observations show that dislocations and subgrain boundaries (e.g. dislocation array, network, and wall) are widely distributed in all garnet grains. The dislocation density and subgrain boundary density ranges are 1.22 × 106 to 1.56 × 107 cm−2 and 1.61 × 105 to 2.43 × 106 cm−2, respectively. Our data suggest that the water content is independent of dislocation density but shows a positive correlation with subgrain boundary density. This correlation suggests that the water contents preserved in our garnets represent the initial ones at the peak metamorphism stage and had played a role in their dislocation creep. Our results indicate that water could enhance the velocity and multiplication of dislocation, which in turn could promote the formation of subgrain boundaries and reduce the rheological strength of garnet.