Abstract Zircons from three distinct granites within the Samphire Pluton, South Australia, are characterised at the micron- to nanoscale. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon dating generated 207Pb/206Pb weighted average ages of 1586 ± 9.3 Ma, 1583.2 ± 8.5 Ma and 1578 ± 9.5 Ma, respectively. Although zircons from all three granites display evidence of hydrothermal overprinting, this is most strongly expressed in a distinct, red-colored granite referred to here as Granite C. Alteration is expressed as variation in the concentrations of HREE + Y, Th and Pb, whereby grain margins are relatively enriched in these elements and both Zr and Si are depleted. Altered zircon cores have high U contents relative to grain margins, which are appreciably poorer in this element, whereas Th is strongly enriched within crosscutting microfractures. Coupled with the relative enrichment in non-formula elements and marked disturbance of U-Th-Pb isotope ratios, the nanoscale observations of Pb-bearing nanoparticles (galena?) implying mobility of Pb and other elements, nanofractures and structural defects demonstrate that zircon in Granite C has undergone multi-stage alteration impacting upon accurate dating. Importantly, and with implications for analogous systems elsewhere, our results confirm nanoscale open system U-Pb behaviour in Hiltaba Suite zircon. SHRIMP U-Pb zircon geochronology cannot confidently resolve any statistical differences in the age of the three granites, despite their distinct appearance suggesting they might represent temporally distinct phases of a larger magmatic system. Zircons within the most altered Granite (C), directly underlying the Blackbush uranium prospect contain convincing micron- to nanoscale evidence for an alteration event that triggered a remobilisation of uranium from granite into the cover sequence.

中文翻译：

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南澳大利亚 Samphire Pluton 花岗岩中锆石的微米到纳米级表征和 U-Pb 年代学

摘要 来自南澳大利亚 Samphire Pluton 内三种不同花岗岩的锆石具有微米到纳米级的特征。敏感高分辨率离子微探针 (SHRIMP) U-Pb 锆石测年产生的 207Pb/206Pb 加权平均年龄分别为 1586 ± 9.3 Ma、1583.2 ± 8.5 Ma 和 1578 ± 9.5 Ma。尽管来自所有三种花岗岩的锆石都显示出热液叠印的证据，但在此处称为花岗岩 C 的独特红色花岗岩中表现得最为强烈。变化表现为 HREE + Y、Th 和 Pb 浓度的变化，由此这些元素的晶粒边缘相对富集，而 Zr 和 Si 均被耗尽。变质锆石核的 U 含量相对于晶粒边缘较高，在该元素中明显较差，而 Th 在横切微裂缝中强烈富集。再加上非分子式元素的相对富集和 U-Th-Pb 同位素比的显着扰动，含铅纳米粒子（方铅矿？）的纳米级观察表明 Pb 和其他元素、纳米裂缝和结构缺陷的迁移表明锆石在花岗岩 C 经历了影响准确年代的多阶段变化。重要的是，对于其他地方的类似系统，我们的结果证实了 Hiltaba Suite 锆石中的纳米级开放系统 U-Pb 行为。SHRIMP U-Pb 锆石年代学不能自信地解决这三种花岗岩年龄的任何统计差异，尽管它们的不同外观表明它们可能代表更大岩浆系统的时间不同阶段。