High precision 176Hf/177Hf measurements in zircons by LA-MC-ICP-MS

Importance of the topic

High precision determination of 176Hf/177Hf in zircon is essential for reconstructing crustal evolution and mantle differentiation processes. Zircon hosts both U-Pb and Hf chronometers, offering complementary age and source information. Improving in situ Hf isotope measurements enhances geochronological workflows and expands insights into Earth history.

Objectives and overview of the study

This study evaluates the performance of the Thermo Scientific Neoma MC-ICP-MS coupled with laser ablation for high‐precision in situ 176Hf/177Hf analysis in zircons. It demonstrates the integration of the Neoma system with Qtegra ISDS Software to streamline data acquisition, tuning, and real‐time data reduction.

Methodology and instrumentation

• Instrument setup

• Laser ablation system: ESL NWR 193 UC with TwoVol 2 cell
• Mass spectrometer: Neoma MC-ICP-MS with Jet interface, X-skimmer and Jet sampler cones
• Gas flows: He at 0.8 L/min and N2 at 4 mL/min

• Tuning and calibration

• Raster ablation on NIST SRM 610 for cup configuration and sensitivity tuning
• Optimization of U/Th ratio and oxide formation rates

• Sample analysis

• Spot ablation of zircons: 35 µm diameter, 30 s, 4 J/cm2, 10 Hz
• Four reference zircons and 14 detrital samples from Bengal Basin, two to four spots per grain

• Data processing

• Qtegra transient signal region selection for background correction
• Interference corrections: 176Yb via 173Yb/171Yb, 176Lu via 175Lu/179Hf
• Mass bias correction using 179Hf/177Hf

Main results and discussion

The Neoma MC-ICP-MS yielded total Hf signals of 12 to 23 V and achieved 176Hf/177Hf reproducibility better than 50 ppm RSD on four reference zircons. Mean ratios fell within accepted values, confirming accuracy. Detrital zircons from the Bengal Basin displayed a 176Hf/177Hf range of 0.2822 to 0.2832, highlighting source heterogeneity and complex geological histories.

Benefits and practical applications

The integrated LA-MC-ICP-MS approach offers:

• Fully automated tuning and data reduction without third-party software
• Real-time isotopic ratio calculation and mass bias correction
• High throughput and ease of use for geochronology labs
• Enhanced capability for crustal evolution and provenance studies

Future trends and potential applications

Emerging developments may include:

• Advanced algorithms and machine learning for transient signal interpretation
• Broader compatibility with diverse laser systems
• Combined in situ Hf and U-Pb dating workflows for single‐session analyses
• Extension to other isotope systems such as Nd, Pb, and Sr

Conclusion

The Thermo Scientific Neoma MC-ICP-MS, combined with Qtegra ISDS Software and modern laser ablation, delivers robust, accurate and precise in situ 176Hf/177Hf measurements in zircons. This integration significantly streamlines geochronological workflows and expands the potential for high‐resolution crustal studies.

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