Overcoming Vertical Spatial Resolution Limitations in Coupled Zircon U-Pb-Hf Analysis by Laser Ablation Split Stream...

Spatial resolution has long limited the coupled in situ determination of zircon U-Pb ages and Hf isotopic compositions, particularly in grains with thin growth rims and complex core-rim zoning. We present a laser ablation split stream (LASS) depth profiling approach that enables simultaneous, spatially matched U-Pb-Hf analyses along a single continuous ablation trajectory. During one uninterrupted laser ablation sequence, the aerosol is split and introduced concurrently into a Q-ICP-MS and an MC-ICP-MS, allowing direct pairing of U-Pb ages and Hf isotopic ratios from the same ablation volume and eliminating spatial mismatch. Multiple zircon reference materials yield U-Pb ages, trace element concentrations, and Hf isotopic ratios consistent with published values, verifying the accuracy and reliability of this approach. Uncertainty assessment shows that with a signal integration time of at least 5 s, precisions of ≤6% for U-Pb ages and ≤0.000060 for 176Hf/177Hf ratios are achieved, corresponding to a vertical spatial resolution better than 3 μm. Application of this approach to natural zircon grains recording complex crust-mantle interactions produces age spectra comparable to those obtained by conventional depth profiling techniques and delivers a high proportion of valid Hf isotopic data (93%). This LASS depth profiling strategy successfully characterizes rim growth domains as thin as 1.8 μm in zircon grains, thereby enhancing vertical spatial resolution in coupled zircon U-Pb-Hf analyses without sacrificing analytical precision. The method provides a robust tool for high-resolution age-isotope investigations of complex geological processes recorded in zircon.