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

Area of Science:

• Geochemistry
• Isotope Geology
• Analytical Chemistry

Background:

• Coupled in situ determination of zircon U-Pb ages and Hf isotopic compositions is crucial for geological studies.
• Limited spatial resolution of existing methods hinders analysis of fine growth rims and complex zoning in zircon grains.

Purpose of the Study:

• To develop and validate a laser ablation split stream (LASS) depth profiling approach for simultaneous, spatially matched U-Pb-Hf analyses in zircon.
• To enhance vertical spatial resolution in coupled zircon U-Pb-Hf analyses without compromising analytical precision.

Main Methods:

• A novel LASS depth profiling technique was employed, splitting aerosol into Q-ICP-MS and MC-ICP-MS for concurrent U-Pb and Hf isotope analysis along a single ablation trajectory.
• Zircon reference materials were analyzed to verify accuracy, precision, and reliability of the method.
• The approach was applied to natural zircon grains to assess its performance in complex geological settings.

Main Results:

• The LASS depth profiling method achieved simultaneous, spatially matched U-Pb ages and Hf isotopic ratios with precisions of ≤6% for U-Pb ages and ≤0.000060 for 176Hf/177Hf ratios.
• A vertical spatial resolution better than 3 μm was achieved, enabling characterization of rim domains as thin as 1.8 μm.
• Analysis of natural zircons yielded comparable age spectra to conventional methods and a high proportion (93%) of valid Hf isotopic data.

Conclusions:

• The developed LASS depth profiling approach significantly enhances vertical spatial resolution for coupled zircon U-Pb-Hf analyses.
• This method provides a robust tool for high-resolution age-isotope investigations of complex geological processes recorded in zircon.
• The technique overcomes previous limitations in analyzing fine-scale features within zircon grains.