In Situ Trace Element Microanalysis

We define in situ trace element microanalysis as the measurement of concentrations of trace elements (< 1000 ppm) in individual mineral phases in polished sections, analogous to electron microprobe analysis for major elements. It is our opinion that such measurements are important and can provide a new dimension to petrology and geochemistry. This article is both a review of work already done and a summary of potential advances in the future. The advantages of in situ analyses, as opposed to methods involving physical and/or chemical mineral separations, are that the trace element data can be interpreted in a petrographic context and that ambiguities associated with the purity of the mineral separates can be avoided. With data on individual grains, comparisons of intergrain and intragrain (zoning) variations between major and trace elements can be made, and the importance of inclusions can be assessed, within the spatial resolution of the microanalysis technique.