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 δ¹⁸O_VSMOW 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 εHf_i (-15.8 to -17.1) indicate a crustal contribution. The zircons probably grew from crustal-derived carbonate melts under high grade metamorphic conditions.

中文翻译：

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斯里兰卡 Kawisigamuwa 碳酸岩中的锆石巨晶体——原位 U-Pb 和 Hf 同位素测量的潜在参考材料

我们将 Kawisigamuwa 碳酸岩中的锆石巨晶描述为激光烧蚀电感耦合等离子体质谱 U-Pb 和 Hf 同位素测量的新潜在参考材料。我们研究了十个 0.5-4 厘米长的棕色巨晶体，它们由振荡分区 (OZ) 和几乎无特征的阴极发光-明亮重结晶 (RX) 锆石域组成。锆石具有低至中度辐射损伤（总α剂量< 0.5 x 10 ¹⁸事件g ^-1），通过测量ν ₃ (SiO ₄ ) 拉曼波段的FWHM < 5 cm ^-1进行测试。确定三种颗粒的 OZ 锆石域的ID-TIMS 加权平均²⁰⁶ Pb/ ²³⁸ U 年龄为 532.39 ± 0.66 Ma（2 s不确定性）。虽然晶体内部和晶体之间的铪含量有所不同 (6630–9960 µg g ^-1 )，但十个晶体的原位平均¹⁷⁶ Hf/ ¹⁷⁷ Hf 比率在不确定性范围内重叠。我们建议将平均¹⁷⁶ Hf/ ¹⁷⁷ Hf 比率为 0.282003 ± 0.000020 (2 s ) 作为 OZ 域的初步工作值。两个 OZ 巨晶产生难以区分的 δ ¹⁸ O _VSMOW，分别为 12.1 ± 0.4 ‰ 和 12.2 ± 0.4 ‰ (2 s )。OZ 区域中 Th/U (> 1.5)、Zr/Hf (59–75) 和低铪含量与地幔来源碳酸岩中的锆石相似，而高 δ ¹⁸ O 和低 εHf _i (-15.8 至 - 17.1）表明地壳的贡献。锆石可能是在高级变质条件下从地壳衍生的碳酸盐熔体中生长出来的。