Concurrent Determination of U-Pb Age and REE Mass Fractions of Zircon by High Mass Resolution SIMS

Abstract

A combined geochronological and geochemical investigation for the same domain of zircon provides valuable information on timing and genesis, particularly in the case of multi-growth metamorphic zircon. A high spatial resolution concurrent analytical method for zircon U-Pb age and rare earth element content was successfully achieved in this study, using a multi-collector secondary ion mass spectrometer (SIMS) at a ~ 8 μm diameter scale. Special instrument parameters were employed, including a high mass resolution of approximately 15000 applied to replace the previous energy filter method, and a dynamic multi-collector mode used to reduce the measurement time to 18 min per analysis. Six zircon reference materials yielded precise and accurate 206Pb/238U ages, which are comparable to those obtained by the ordinary mono-collector method, but with 2–3 times higher spatial resolution. All zircon grains measured in this study showed enriched heavy-REE (HREE) contents consistent with previously reported values determined by LA and solution ICP-MS methods. The light-REE (LREE) mass fractions measured using both SIMS and LA-ICP-MS methods in this study, although with quite different volume, show consistent results within uncertainties.