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
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An ID-TIMS weighted mean <sup>206</sup>Pb/<sup>238</sup>U age of 532.39 ± 0.66 Ma (2<i>s</i> uncertainty) was determined for OZ zircon domains of three grains. While hafnium content varies within and between crystals (6630–9960 μg g<sup>-1</sup>) the <i>in situ</i> mean <sup>176</sup>Hf/<sup>177</sup>Hf ratios of ten crystals overlap within uncertainty. We recommend a mean <sup>176</sup>Hf/<sup>177</sup>Hf ratio of 0.282003 ± 0.000020 (2<i>s</i>) as preliminary working value for OZ domains. Two OZ megacrysts yield indistinguishable δ<sup>18</sup>O<sub>VSMOW</sub> of 12.1 ± 0.4‰ and 12.2 ± 0.4‰ (2<i>s</i>). 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 δ<sup>18</sup>O and low εHf<sub>i</sub> (-15.8 to -17.1) indicate a crustal contribution. 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引用次数: 0
摘要
我们将Kawisigamuwa碳酸盐岩中的锆石巨晶作为激光烧蚀-电感耦合等离子体质谱法测量U-Pb和Hf同位素的新潜在参考物质。我们研究了10个0.5-4厘米长的棕色巨型晶体,它们由振荡带(OZ)和几乎没有特征的阴极发光明亮的再结晶(RX)锆石域组成。锆石具有中低辐射损伤(总α-剂量<0.5 x 1018个事件g-1),通过测量的ν3 (SiO4)拉曼波段的FWHM < 5 cm-1进行测试。3粒OZ锆石结构域的ID-TIMS加权平均206Pb/238U年龄为532.39±0.66 Ma (2s不确定度)。虽然晶体内部和晶体之间的铪含量不同(6630-9960 μg -1),但10个晶体的原位平均176Hf/177Hf比值在不确定度内重叠。我们推荐平均176Hf/177Hf比值为0.282003±0.000020 (2s)作为OZ域的初步工作值。两种OZ巨型晶体的δ18OVSMOW分别为12.1±0.4‰和12.2±0.4‰(2s)。高架Th/U (>锆石的δ18O值高,εHfi值低(-15.8 ~ -17.1),与地幔碳酸盐锆石的δ18O值相似。锆石可能来自高变质条件下的地壳源碳酸盐熔体。
Zircon Megacrysts from the Kawisigamuwa Carbonatite, Sri Lanka – A Potential Reference Material for In Situ U-Pb and Hf Isotope Measurement
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.
期刊介绍:
Geostandards & Geoanalytical Research is an international journal dedicated to advancing the science of reference materials, analytical techniques and data quality relevant to the chemical analysis of geological and environmental samples. Papers are accepted for publication following peer review.