EXPERIMENTAL CALIBRATION OF FRACTIONATION OF SILICON ISOTOPES BETWEEN QUARTZ AND WATER

Silicon isotopes have been investigated as potential indicators of such things as paleoenvironment, biologic processes, sediment provenance and hydrothermal interactions. However, interpretation of measured silicon isotope values has been encumbered by the lack of experimentally determined fractionation factors for the quartz-fluid system. Previously published fractionation factors have been dominated by amorphous silica, or empirical calibrations due to the challenging nature of low-temperature mineral precipitation experiments. In this presentation we will show data from the first measurements of silicon isotope ratios of experimentally grown quartz and corresponding dissolved silica and provide an estimate for the equilibrium fractionation of silicon between quartz and fluid. We will also discuss the apparently significant role of non-equilibrium fractionation in natural samples and some low-temperature experiments. The new fractionation factor calculated from our experiments, and associated interpretation of equilibrium vs. non-equilibrium fractionation, can be applied to studies of silica precipitation, particularly at low-temperatures.