Here we present RbSr and Pb isotopic analysis of K-feldspar from the Shap Granite, (Cumbria, UK) and detrital K-feldspar from the associated Shap Wells Conglomerate Formation, to investigate the potential of the detrital K-feldspar record as an archive of crustal composition. We use a unique, collision cell – multi collector inductively coupled plasma tandem mass spectrometer to make the isotope measurements, using ‘chemical resolution’ of Rb and Hg isobaric interferences on Sr and Pb, achieved with SF and NH reaction gases, respectively. Using this technique, we successfully demonstrate that the majority of detrital K-feldspar RbSr ages, as well as initial Sr and Pb isotope ratios, from the Shap Wells Conglomerate are within uncertainty of those for parental Shap Granite K-feldspar (398 ± 1 Ma, = 6). Some detrital K-feldspar grains record perturbed RbSr ages, reflecting post depositional alteration events. The majority of samples with disturbed RbSr ages carry distinct petrographic features evident in SEM imaging, prior to dating, which indicates a means to help screen for reliable ages.

中文翻译：

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使用耦合原位 Rb[sbnd]Sr 测年和 Pb 同位素分析将碎屑钾长石作为大陆地壳演化的新档案


在这里，我们对来自 Shap 花岗岩（英国坎布里亚）的钾长石和来自相关 Shap Wells 砾岩地层的碎屑钾长石进行了 RbSr 和 Pb 同位素分析，以研究碎屑钾长石记录作为地壳组成。我们使用独特的碰撞池 - 多收集器电感耦合等离子体串联质谱仪进行同位素测量，利用 SF 和 NH 反应气体分别对 Sr 和 Pb 上的 Rb 和 Hg 同量异位素干扰进行“化学分辨率”。使用这项技术，我们成功地证明了来自 Shap Wells 砾岩的大多数碎屑钾长石 RbSr 年龄以及初始 Sr 和 Pb 同位素比与母体 Shap 花岗岩钾长石的不确定性 (398 ± 1 Ma , = 6)。一些碎屑钾长石颗粒记录了扰动的铷锶年龄，反映了沉积后的蚀变事件。大多数 RbSr 年龄受到干扰的样品在测年之前在 SEM 成像中具有明显的明显岩相特征，这表明有一种方法可以帮助筛选可靠的年龄。