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GZ7 and GZ8 – Two Zircon Reference Materials for SIMS U-Pb Geochronology

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Year:
2018
Type of Publication:
Article
Keywords:
zircon, reference material, SIMS, U-Pb geochronology, Ti-in-zircon geothermometry
Authors:
Nasdala, Lutz; Corfu, Fernando; Schoene, Blair; Tapster, Simon R.; Wall, Corey J.; Schmitz, Mark D.; Ovtcharova, Maria; Schaltegger, Urs; Kennedy, Allen K.; Kronz, Andreas; Reiners, Peter W.; Yang, Yue-Heng; Wu, Fu-Yuan; Gain, Sarah E. M.; Griffin, William L.; Szymanowski, Dawid; N., Chutimun Chanmuang; Ende, Martin; Valley, John W.; Spicuzza, Michael J.; Wanthanachaisaeng, Bhuwadol; Giester, Gerald
Journal:
Geostandards and Geoanalytical Research
Volume:
42
Number:
4
Pages:
431-457
BibTex:
Abstract:
Here, we document a detailed characterisation of two zircon gemstones, GZ7 and GZ8. Both stones had the same mass at 19.2 carats (3.84 g) each; both came from placer deposits in the Ratnapura district, Sri Lanka. The U-Pb data are in both cases concordant within the uncertainties of decay constants and yield weighted mean 206Pb/238U ages (95\% confidence uncertainty) of 530.26 Ma ± 0.05 Ma (GZ7) and 543.92 Ma ± 0.06 Ma (GZ8). Neither GZ7 nor GZ8 have been subjected to any gem enhancement by heating. Structure-related parameters correspond well with the calculated alpha doses of 1.48 × 1018 g−1 (GZ7) and 2.53 × 1018 g−1 (GZ8), respectively, and the (U-Th)/He ages of 438 Ma ± 3 Ma (2s) for GZ7 and 426 Ma ± 9 Ma (2s) for GZ8 are typical of unheated zircon from Sri Lanka. The mean U mass fractions are 680 μg g−1 (GZ7) and 1305 μg g−1 (GZ8). The two zircon samples are proposed as reference materials for SIMS (secondary ion mass spectrometry) U-Pb geochronology. In addition, GZ7 (Ti mass fractions 25.08 μg g−1 ± 0.18 μg g−1; 95\% confidence uncertainty) may prove useful as reference material for Ti-in-zircon temperature estimates.

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