[J05-P] Poster

[J05-P-16] Influence of water on rheological properties of feldspar aggregates under the lower crustal temperature and pressure

^○Masanori Kido¹, Jun Muto¹, Sanae Koizumi², Hiroyuki Nagahama¹ (1.Tohoku University, Sendai, Japan, 2.Earthquake Research Institute, The University of Tokyo, Tokyo, Japan)

Fluids in deep part of the crust have an important role in deformation and seismicity of the crust. However, experimental data of crustal materials under the lower crustal conditions are insufficient. In this study, we performed high temperature and high pressure deformation experiments to reveal rheological properties of feldspars under hydrous conditions. Axial compression tests on synthetic polycrystalline anorthite with 0.5 wt% of water were performed in a Griggs-type solid medium apparatus at temperature of 900 deg C and various confining pressures of 0.8-1.4 GPa. Times were changed to investigate the reduction of strength by volume and grain boundary diffusion of water into samples. Water contents in samples were measured by an FTIR method. As a result, strengths of wet anorthite tended to decrease with increasing time or strain magnitude. It was suggested that anorthite samples were still not saturated with water in time range of this study. Strengths of wet anorthite also decreased with increasing confining pressures. Differential stresses were significantly lower than predicted values by previous flow laws for wet anorthite obtained by low pressure experiments (<0.5 GPa). This implies that the effect of fugacity of water on strength in higher pressure might be larger than those predicted by lower pressure experiments. Our experiments show that the strength of hydrous regions in the lower crust becomes lower than that predicted by previous studies.