U-Pb-Hf zircon data from Wilkes/Queen Mary lands

This dataset file is unpublished. Details of analytical methods: U-Pb from Daczko et al. (2018) and Lu-Hf from Halpin et al. (2020). U-Pb analysis was via SHRIMP following procedure outlined in Daczko et al. (2018). Zircon grains were hand-picked and mounted into a 25-mm diameter epoxy resin disc along with grains of reference zircons BR266 (559 Ma, 909 ppm U; Stern and Amelin, 2003) and OGC-1 (3465 Ma; Stern et al., 2009) and a fragment of NBS610 glass (used to center the 204Pb peak). The mount was polished to expose the zircon grains and reference materials, then carbon-coated for cathodoluminescence imaging on a TESCAN Mira 3 scanning electron microscope in the John de Laeter Centre, Curtin University. The carbon coat was removed and the mount gold-coated prior to U-Pb isotope analysis on the SHRIMP II sensitive high resolution ion microprobe at the John de Laeter Centre, Curtin University.Analytical procedures for the Curtin SHRIMP II facility were described by Kennedy and De Laeter (1994) and De Laeter and Kennedy (1998) and are similar to those described by Compston et al. (1984) and Williams (1998). A mass-filtered primary beam of O2– ions at 10 keV with 25–30 μm diameter was used to sputter secondary ions from the target material. The primary beam current measured at the mount surface was ~2.0 nA, and the beam was rastered over each analysis site for 3–4 minutes to remove surface contamination before secondary ions were collected in 6 scans through the following masses: 196 (90Zr216O+, 2 seconds), 204 (204Pb+, 10 seconds), 205.5 (background, 10 seconds), 206 (206Pb+, 20 seconds), 207 (207Pb+, 30 seconds), 238 (238U+, 3 seconds), 248 (232Th16O+, 2 seconds) and 254 (238U16O+, 3 seconds). Values of 206Pb/238U in zircons from 8628–5807 and 8628–6006 were calibrated using analyses of reference zircon BR266, assuming a power law relationship between 206Pb+/238U+ and 238U16O+/238U+ and a fixed exponent of 2 (Claoué-Long et al., 1995). External spot-to-spot uncertainty (1σ) in 238U/206Pb values in BR266 over the analytical session was 1.03%. Values of 207Pb/206Pb were monitored using the OGC-1 reference zircon which yielded an error-weighted mean 207Pb/206Pb date (95% confidence) of 3466.3 ± 4.8 Ma for the analytical session, within uncertainty of the reference value (3465.4 Ma). Data were processed and displayed using the Excel add-ins SQUID 2.50.09.08.06 (Ludwig, 2009) and Isoplot 3.76.12.02.24 (Ludwig, 2012). All analyses were corrected for common Pb based on measured 204Pb (Compston et al., 1984) and common Pb isotope ratios appropriate for the approximate age of zircon crystallization according to the Stacey and Kramers (1975) model of Pb isotope evolution. Lu-H analysis was via LAM-ICPMS following procedure in Halpin et al. (2020). Hf isotope analyses were performed in situ on the same grains analysed for U-Pb using a Photon Machines Excimer 193 nm Ar-F laser ablation micro-probe attached to a Nu Plasma multi- collector (MC)-ICPMS system at Macquarie University GeoAnalytical (MQGA)(see Griffin et al., 2004 for a detailed methodology). A gas blank was analysed for 30 s followed by up to 120 s of ablation at a beam diameter of 40–50 μm, 5 Hz and ~7.5 J/cm2. Zircon CL images were used to ensure that Hf isotope analyses overlapped the same domain analysed for U-Pb. The Mud Tank and Temora-2 zircon standards were used as a reference standard for Hf analysis; our weighted average 176Hf/177Hf values for these standards are 0.282525 ± 07 (n = 11, MSWD = 1.09) and 0.282649 ± 20 (n = 2), respectively, within error of the published values of 0.282523 ± 43 (Mud Tank; Griffin et al., 2006) and 0.282680 ± 24 (Temora-2; Woodhead et al., 2004). Uncertainties quoted are the internal measured uncertainty and do not include any propagation of error from the reference standard. The initial 176Hf/177Hf value (Hfi) in zircon is calculated using the measured 176Lu/177Hf, 176Hf/177Hf and apparent 207Pb/206Pb age and the 176Lu decay constant of Scherer et al. (2001) of 1.865 x 10-11. Model age calculations (TDM) are based on a depleted-mantle source with Hfi = 0.279718 and 176Lu/177Hf = 0.0384. This provides a value of 176Hf/177Hf (0.28325) similar to that of average mid-ocean ridge basalt over 4.56 Ga. The calculated TDM ages use the measured 176Lu/177Hf of the zircon and give a minimum age for the source material of the magma from which the zircon crystallised. Two-stage model ages (TDM2) are calculated assuming that the parental magma was derived from the average continental crust (176Lu/177Hf = 0.015), which in turn was originally derived from the depleted mantle.

本数据集文件尚未公开。分析方法详情如下：U-Pb同位素定年数据源自Daczko等人（2018）的研究，Lu-Hf同位素数据源自Halpin等人（2020）的研究。
U-Pb定年采用SHRIMP（Sensitive High Resolution Ion Microprobe，高灵敏度高分辨率离子探针），实验流程遵循Daczko等人（2018）的描述。锆石颗粒经人工挑选后，与标准锆石BR266（年龄559 Ma，铀含量909 ppm；Stern与Amelin，2003）、OGC-1（年龄3465 Ma；Stern等人，2009）以及NBS610玻璃碎片（用于校准204Pb峰位）一同封装于直径25 mm的环氧树脂靶盘中。随后对靶盘进行抛光以暴露锆石颗粒与标准物质，随后在科廷大学约翰·德莱特中心（John de Laeter Centre, Curtin University）的TESCAN Mira 3型扫描电子显微镜上进行阴极发光成像，成像前需对靶盘进行碳涂层处理。完成成像后，去除碳涂层并对靶盘镀金，随后在科廷大学约翰·德莱特中心的SHRIMP II型高灵敏度高分辨率离子探针上开展U-Pb同位素分析。
科廷大学SHRIMP II装置的分析流程由Kennedy与De Laeter（1994）及De Laeter与Kennedy（1998）详述，其原理与Compston等人（1984）及Williams（1998）描述的方法类似。实验采用能量为10 keV的O2–离子作为质量过滤后的原束流，束斑直径25~30 μm。靶面处的原束流电流约为2.0 nA，在采集二次离子前，需对每个分析点位进行3~4分钟的束流扫描以去除表面污染。随后依次采集6轮扫描的二次离子信号，对应质量及积分时间分别为：196（90Zr216O+，2 s）、204（204Pb+，10 s）、205.5（背景，10 s）、206（206Pb+，20 s）、207（207Pb+，30 s）、238（238U+，3 s）、248（232Th16O+，2 s）及254（238U16O+，3 s）。
对于8628–5807与8628–6006号样品中的锆石，其206Pb/238U比值通过标准锆石BR266的分析结果进行校准，校准假设206Pb+/238U+与238U16O+/238U+之间满足幂律关系，且固定指数为2（Claoué-Long等人，1995）。本次分析批次中，标准锆石BR266的238U/206Pb比值的外部点间不确定度（1σ）为1.03%。207Pb/206Pb比值通过标准锆石OGC-1进行监控，本次分析批次得到的误差加权平均207Pb/206Pb年龄（95%置信度）为3466.3 ± 4.8 Ma，与标准参考值（3465.4 Ma）在不确定度范围内一致。数据处理与可视化采用Excel插件SQUID 2.50.09.08.06（Ludwig，2009）与Isoplot 3.76.12.02.24（Ludwig，2012）完成。所有分析均基于实测204Pb含量（Compston等人，1984）以及Stacey与Kramers（1975）的Pb同位素演化模型，根据锆石结晶的近似年龄校正普通Pb同位素比值。
Lu-Hf同位素分析采用LAM-ICPMS（激光剥蚀电感耦合等离子体质谱），实验流程遵循Halpin等人（2020）的描述。Hf同位素分析在与U-Pb定年相同的锆石颗粒上进行，实验使用安装于麦考瑞大学地质分析实验室（Macquarie University GeoAnalytical, MQGA）的Nu Plasma多接收器（MC）-ICPMS系统，配套Photon Machines公司的Excimer 193 nm Ar-F准分子激光剥蚀探针（详细方法参见Griffin等人，2004）。实验前先采集30 s的气体本底信号，随后以40~50 μm的束斑直径、5 Hz重复频率、约7.5 J/cm2的能量密度进行激光剥蚀，剥蚀时长最长可达120 s。通过锆石阴极发光图像确保Hf同位素分析点位与U-Pb定年的分析点位位于同一锆石结构域内。本实验采用Mud Tank与Temora-2锆石作为Hf分析的标准物质；本次分析得到的这两种标准物质的加权平均176Hf/177Hf比值分别为0.282525 ± 07（n=11，MSWD=1.09）与0.282649 ± 20（n=2），与已发表的参考值（Mud Tank：0.282523 ± 43，Griffin等人，2006；Temora-2：0.282680 ±24，Woodhead等人，2004）在误差范围内一致。文中给出的不确定度为内部测量不确定度，未包含由标准物质引入的误差传递。锆石初始176Hf/177Hf比值（Hfi）通过实测的176Lu/177Hf比值、176Hf/177Hf比值以及表观207Pb/206Pb年龄，结合Scherer等人（2001）给出的176Lu衰变常数1.865×10-11计算得到。亏损地幔模式年龄（TDM）基于亏损地幔端元Hfi=0.279718、176Lu/177Hf=0.0384计算得到，该端元在4.56 Ga内的176Hf/177Hf比值（0.28325）与全球平均洋中脊玄武岩的数值相近。计算得到的TDM年龄采用锆石实测的176Lu/177Hf比值，代表锆石结晶所在岩浆的源区物质的最小形成年龄。两阶段模式年龄（TDM2）假设母岩浆源自平均大陆地壳（176Lu/177Hf=0.015），而平均大陆地壳最初源自亏损地幔。