Silicon isotope fractionation during abiotic silica precipitation at low temperatures: Inferences from flow-through experiments

Silicon isotopes have considerable potential as proxy for (near-) surface processes and environmental conditions. However, unambiguous interpretations of isotope signatures in natural silica deposits are often hampered by a lack of independent quantitative information on isotopic fractionations operating under the environmental conditions of interest. We performed seeded silica precipitation experiments using flow-through reactors in the 10-60. °C temperature range to alleviate this problem. The principal objective was to quantify the silicon isotope fractionations during controlled precipitation of amorphous silica from a flowing aqueous solution. The experiments were designed to simulate silica deposition induced by a temperature drop, with particular relevance for (near-) surface hydrothermal systems associated with steep temperature gradients. Monitored differences in silicon isotope ratios (