Evaluation and calibration of matrix effects during SIMS silicon isotope analysis in silicate glasses†

Abstract

Silicon is one of the most abundant elements in rocks, and its isotopic composition can be traced back to various geological processes. In situ high-precision silicon isotope analysis requires matrix-matched standards as reference materials for mass fractionation calibration. However, finding completely matrix-matched standards is impractical for minerals or glasses with complex matrices or a wide range of chemical compositions. For instance, the major component variation in lunar glasses can reach 30%, making it impossible to find matrix-matched standards for each glass bead. In this study, SIMS silicon isotope analyses on eleven glass standards ranging from basaltic to rhyolitic compositions were conducted to evaluate the relationship between instrumental mass fractionation and the major components. We established a calibration model highly correlated with instrumental mass fractionation based on the contents of Si, Ca, Al and Mg (R² = 0.997, SCAM model) in glass samples. This model can accurately calibrate the instrumental mass fractionation of silicon isotopes in glass samples within the compositional range covered by the standards, providing insights and methods for accurately determining various isotope compositions in glass samples with varying compositions.