A FLOW LAW FOR DISLOCATION CREEP OF QUARTZ AGGREGATES DETERMINED WITHTHE MOLTEN-SALT CELL

We have used the molten salt cell to conduct an experimental study on the theology of a natural quartzite containing similar to 0.15 wt. % w ater. Co-axial deformation experiments were conducted at constant pist on displacement rates, approximating constant strain rates at low stra in. The strengths of our natural quartzite measured in the molten salt cell are approximately half those measured at the same conditions in solid media because, unlike solid confining media, molten salt does no t contribute to the strength of the sample; it reduces the friction on the moving piston, and it allows clear identification of the 'hit' po int. We have limited the experimental conditions to those required for dislocation creep, and have used only steady-state flow stresses meas ured during climb-accommodated dislocation creep to calculate the flow law parameters. Two flow laws were determined, one for samples contai ning minor amounts of melt (1-2%) and one for melt-free samples. In bo th cases, the power law stress exponent, n, is 4.0 +/- 0.9, which is g reater than that previously reported in flow laws for dislocation cree p of quartz aggregates determined in solid media. The activation energ y, Q, is 137 +/- 34 kJ mol(-1) for samples with melt and 223 +/- 56 kJ mol(-1) for those without, within the range of previously determined values for quartz aggregates containing similar to 0.1 wt. % water. Th e pre-exponential term, A, is 1.1 X 10((-4+/-2)) Mpa(-n)s(-1) for samp les without melt and 1.8 X 10((-8+/-2)) MPa(-n)s(-1) for those with me lt. The lower strengths measured in the molten salt cell indicate that previous piezometer relations for quartz experimentally determined in solid media are not correct. Extrapolation of the flow law for melt-f ree aggregates to natural strain rates predicts higher strengths than most previous quartz flow laws. However, accurate extrapolation requir es determining the dependence of flow stress on f(H2O) and/or a(H+).