Atomic Spectroscopy

Water is perhaps the most important molecule in the solar system, and determining its origin and distribution in planetary interiors has significant implications for understanding the formation and evolution of planetary bodies.Zircon (present in both extraterrestrial and terrestrial samples) is a resistant and versatile accessory mineral, and its water content has the potential to characterize the hydrous status of zircon-crystallizing magma.However, the hydrous status can be altered by magma fractionation, mixing, or degassing.Although hydrogen isotopes of zircon can help to trace these processes, the lack of relevant microanalytical technology and reference materials has hindered significant breakthroughs in this area.In this study, we employed an analytical technique of secondary ion mass spectrometry (SIMS) to simultaneously measure the hydrogen isotopes of zircon and their H2O content.The homogeneity test of hydrogen isotope and the H2O content of the potential reference materials (D15395, D15814, and Temora 2) were conducted by measuring the 16 OD and 16 O 1 H signals (using SIMS) in a conventional peak-hopping mono-collector mode with electron-multiplier (EM) detectors.SIMS results show that the apparent external precision (1SD) of hydrogen isotope of large grains D15395 and D15814 are 16‰ and 22‰, which is comparable with their internal error and theoretical precision according to counting statistics, indicating that they are sufficiently homogenous at the micrometer sampling level in terms of hydrogen isotopes.However, zircon Temora 2 shows a much worse external precision (83‰, 1SD) and an obvious negative correlation between hydrogen isotope and H2O content, hence it is not suitable to be used as reference material for hydrogen isotope.Both hydrogen isotope and H2O content of three samples were also measured using a continuous-flow thermal conversion elemental analyzer operating online with a mass spectrometer (TC/EA-MS).The homogeneous samples zircon D15395 and D15814 yielded recommended δD values of -87 ± 9‰ and -68 ± 2‰ (1SD) and H2O content of ~478 ppm and ~332 ppm, respectively.Additionally, H2O contents acquired by TC/EA-MS and SIMS (calibrated by FTIR determined standards) were consistent within a 10% error range, demonstrating the reliability of the SIMS H2O content calibration curve for zircon and the FTIR absorption coefficient used before.