Nanoscale characterisation of crystal zoning

Advances in analytical techniques are fundamental to the enhanced understandings of many geological processes. This study investigates zoned volcanic crystals analyzed by low kV field emission gun electron probe micro-analyser (FEG-EPMA) and NanoSIMS to obtain sub-micrometre chemical profiles compared to time-of-flight SIMS (TOF-SIMS) and high kV EPMA profiles. Plagioclase and orthopyroxene crystals were examined using FEG-EPMA at 5 kV, achieving spatial resolutions of ≤350 nm for orthopyroxene and ca. 750 nm for plagioclase crystals. The step sizes employed are comparable to interaction volumes, allowing for the acquisition of quantitative major and minor element compositions with similar accuracy to traditional EPMA analyses at higher voltages. Additionally, NanoSIMS provided greater spatial resolution of up to 200 nm, enabling Li measurements, although its profiles currently lack quantification. Overall, combining these analytical approaches demonstrates strong agreement between FEG-EPMA, NanoSIMS, conventional EPMA, and TOF-SIMS data, showcasing their potential applications in petrology, particularly in analyzing small crystals and assessing crystal zoning at high spatial resolutions that are critical for studies in crystal forensics and diffusion chronometry.