Laser ablation split stream (LASS) between three ICP-MS for zircon petrochronology

Significance of the Topic

Zircon petrochronology combining U-Pb ages, Hf isotopes and rare earth element distributions provides detailed insights into magma sources and crustal evolution. Simultaneous measurements at a single laser ablation site reduce errors from sample heterogeneity and improve throughput.

Objectives and Study Overview

• Evaluate laser ablation split stream (LASS) configuration splitting output to three ICP-MS devices for zircon geochronology
• Test performance on four reference zircons to assess precision, accuracy and reproducibility of U-Pb ages, Hf isotope ratios and REE concentrations

Methodology and Instrumentation

Laser ablation was carried out on a Photon Machines Analyte G2 excimer laser at 50 micrometer spot size and 10 Hz repetition under helium carrier. Two KNF Neuberger diaphragm pumps controlled aerosol splits of approximately 50, 20 and 30 percent to three instruments. The instruments included:

• Thermo Scientific Neptune Plus MC-ICP-MS for high precision 176Hf/177Hf isotopes
• Thermo Scientific Element XR high resolution ICP-MS for U-Pb isotopic ratios
• Thermo Scientific iCAP RQ quadrupole ICP-MS for REE concentration patterns

Data processing employed Iolite software with custom data reduction schemes for Hf and built-in schemes for U-Pb and trace elements.

Main Results and Discussion

176Hf/177Hf ratios in Plesovice, GJ-1 and Mud Tank yielded repeatabilities of 47, 76 and 101 ppm 1 sigma RSD and were generally within reference uncertainties. U-Pb ages based on 206Pb/238U ratios matched known values of 337, 609 and 732 Ma within 2 sigma confidence. REE patterns normalized to chondrite agreed with published data but lower signal on the iCAP RQ limited detection of elements below 0.1 ppm.

Benefits and Practical Applications

• Simultaneous multi-isotope and elemental analyses on a single ablation spot
• Reduced risk of misalignment between separate analyses and insights into sample heterogeneity
• Cost efficient routine operation using widely available pumps and software

Future Trends and Potential Applications

Further improvements in split stream control and instrument sensitivity could extend simultaneous analysis to additional isotope systems. Integration with novel microbeam lasers and advanced data reduction may enhance spatial resolution. Applications may expand to monazite, titanite and other accessory minerals for comprehensive petrochronology.

Conclusion

The LASS setup using variable diaphragm pumps to split a laser aerosol stream to three ICP-MS units achieved reliable simultaneous U-Pb dating, Hf isotope ratio determination and REE profiling in zircon. Precision and accuracy were comparable to conventional sequential measurements, demonstrating suitability for routine petrochronology.

Used Instrumentation

• Photon Machines Analyte G2 excimer laser with HelEx II two volume cell
• KNF Neuberger NMP 09S and NMP 05S diaphragm pumps for aerosol splitting
• Thermo Scientific Neptune Plus MC-ICP-MS, Element XR HR-ICP-MS and iCAP RQ ICP-MS

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