Zircon Megacrysts from the Kawisigamuwa Carbonatite, Sri Lanka – A Potential Reference Material for In Situ U-Pb and Hf Isotope Measurement

Daniela Gallhofer, Etienne Skrzypek, Christoph Hauzenberger, Walter Kurz, Andreas Möller, Joseph Andrew, Luis A. Parra-Avila, Laure Martin, Anthony Kemp, G. W.A.R. Fernando, Dengfeng He

Research output: Contribution to journalArticlepeer-review

Abstract

We characterise zircon megacrysts from the Kawisigamuwa carbonatite as a new potential reference material for laser ablation-inductively coupled plasma-mass spectrometry U-Pb and Hf isotope measurement. We studied ten 0.5–4 cm long, brown megacrysts that consist of oscillatory zoned (OZ) and nearly featureless cathodoluminescence-bright recrystallised (RX) zircon domains. The zircons have low to moderate radiation damage (total α-dose < 0.5 x 1018 events g-1), tested by the measured FWHM of the ν3 (SiO4) Raman band < 5 cm-1. An ID-TIMS weighted mean 206Pb/238U age of 532.39 ± 0.66 Ma (2s uncertainty) was determined for OZ zircon domains of three grains. While hafnium content varies within and between crystals (6630–9960 μg g-1) the in situ mean 176Hf/177Hf ratios of ten crystals overlap within uncertainty. We recommend a mean 176Hf/177Hf ratio of 0.282003 ± 0.000020 (2s) as preliminary working value for OZ domains. Two OZ megacrysts yield indistinguishable δ18OVSMOW of 12.1 ± 0.4‰ and 12.2 ± 0.4‰ (2s). Elevated Th/U (> 1.5), Zr/Hf (59–75) and low hafnium contents in OZ domains are similar to those of zircons from carbonatites of mantle origin, while high δ18O and low εHfi (-15.8 to -17.1) indicate a crustal contribution. The zircons probably grew from crustal-derived carbonate melts under high grade metamorphic conditions.

Original languageEnglish
Pages (from-to)749-771
Number of pages23
JournalGeostandards and Geoanalytical Research
Volume47
Issue number4
Early online date3 Aug 2023
DOIs
Publication statusPublished - Dec 2023

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