Abstract

Electrical impedance measurements were performed on deforming fine-grained (c. 300 µm) synthetic halite rocks containing small quantities of water in order to study the distribution of intercrystalline brine. The experimental conditions were 125 °C and 50 MPa confining pressure. The resistivity at the predeformational, heated and hydrostatically pressurized state suggests that brine is interconnected in halite. The resistivity progressively increases with deformation, reflecting the change in distribution. In this paper we applied a simple tube model to the resistivity change, and found that the change must be caused by deformation of a thin fluid path with an initial aspect ratio of less than 2×10⁻⁴. Brine must, therefore, exist on grain boundaries as a thin fluid film. Previous studies on dihedral angles, however, showed that brine cannot be interconnected under our experimental conditions. The variation in grain-boundary energy cannot explain the coexistence of grain-boundary brine with a positive dihedral angle. The observed resistivity change requires grain-boundary brine to be very thin (<100 nm). Such a thin fluid film might have properties distinct from the bulk fluid, and coexist with brine pores at grain corners and grain faces.