EXPERIMENTAL PRESSURE SOLUTION IN HALITE - THE EFFECT OF GRAIN INTERPHASE BOUNDARY STRUCTURE

To investigate the mechanisms and kinetics of pressure solution, we measured deformation at contacts between polished convex lenses of halite and polished flat lenses of either halite or fused silica in saturated brine at 50.2 +/- 0.2-degrees-C and fluid pressures of 0.1 MPa. Loads, applied using small springs, ranged from 0.1-4.2 N; mean effective normal stresses within the contact zone ranged from 1-14 MPa. The geometry and diametric growth rate of the contact spot (neck growth) and the rate at which the lenses approached one another (convergence) were monitored during deformation using transmitted and reflected light photomicrography. Time-dependent convergence did not occur at measurable rates when two halite lenses were pressed together in saturated brine but did occur when halite and fused silica lenses were pressed together in brine. Convergence rates in the halite/silica experiments were 0.01-0.05-mu-m/day. Although the initial deformation during loading involved elastic and plastic processes, control experiments without brine showed no time-dependent convergence, indicating that dislocation creep did not contribute to the observed rates. No undercutting or cataclasis was observed in any experiments. Residual fluid inclusions were formed along grain boundaries between two halite lenses loaded in brine, indicating non-zero wetting angles.