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首页> 外文期刊>Contributions to Mineralogy and Petrology >Alpha-recoil in U–Pb geochronology: effective sample size matters
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Alpha-recoil in U–Pb geochronology: effective sample size matters

机译：U–Pb年代学中的α反冲：有效样本量很重要

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Displacement of the daughter isotope by α-recoil results in an open system on the nanoscale. For a heterogeneous distribution of U and Th, this redistribution of intermediate and stable daughter isotopes results in subvolumes with a deficit of Pb and others with an excess of Pb. Whether such heterogeneities affect the analyzed U–Pb system depends on: (1) the volume of the analyzed sample, (2) the degree and scale of heterogeneity in the U and Th distribution, and (3) the analytical procedure. Spatial separation of parent and daughter through α-recoil affects the U–Pb systematics of leached samples, where leaching gives access to domains less than 1 μm wide. Anomalous data patterns originating from recoil induced parent-to-daughter fractionation are more important if there are strong heterogeneities in the U and Th distribution, whereby Pb excess appears more pronounced than Pb deficit. Fractionation of parent and daughter elements through selective dissolution of U-REE-rich growth zones in zircon and U-inclusions in columbite, as well as the presence of U–Th-rich micro-inclusions in silicates dated using a step-leaching scheme, may result in anomalous 207Pbrad/206Pbrad, scattered 206Pbrad/238U and 207Pbrad/235U, and reverse discordance. The accumulated structural damage controls the leaching and dissolution behavior, but may also influence the non-stoichiometric element mobilization during sputtering or ablation in the analysis of U-rich samples by SHRIMP and LA-MC-ICP-MS.
机译：α-反冲对子同位素的置换导致纳米级的开放系统。对于U和Th的异质分布，中间和稳定子同位素的这种重新分布会导致子体积中的Pb不足，而其他体积中的Pb过多。这种异质性是否会影响所分析的U–Pb系统取决于：（1）被分析样品的体积，（2）U和Th分布中异质性的程度和规模，以及（3）分析程序。母体和子体通过α-反冲空间分离会影响浸出样品的U-Pb系统，浸出可以进入小于1μm宽的区域。如果U和Th分布中存在很强的异质性，则由反冲作用引起的母婴分离所产生的异常数据模式更为重要，从而铅的过量比铅的缺乏更为明显。通过选择性溶解锆石中富含U-REE的生长区和哥伦比中的U-夹杂物，以及通过分步浸出法测得的硅酸盐中富含U-Th的微夹杂物，可以分离母体和子元素。可能会导致207 Pbrad / 206 Pbrad 异常，散落的206 Pbrad / 238 U和207 Pbrad / 235 U，然后反向不一致。累积的结构损伤控制了浸出和溶解行为，但在通过SHRIMP和LA-MC-ICP-MS分析富铀样品时，也可能影响溅射或烧蚀过程中的非化学计量元素迁移。

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