Here we present in situ 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 in situ isotope measurements, using ‘chemical resolution’ of 87Rb+ and 204Hg+ isobaric interferences on 87Sr+ and 204Pb+, achieved with SF6 and NH3 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, n = 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 in situ dating, which indicates a means to help screen for reliable ages.

中文翻译：

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碎屑 K-长石作为大陆地壳演化的新档案，使用原位 Rb[sbnd]Sr 测年和 Pb 同位素分析进行分析


在这里，我们对来自 Shap 花岗岩（英国坎布里亚郡）的 K-长石和来自相关 Shap Wells 砾岩组的碎屑 K-长石进行了原位 RbSr 和 Pb 同位素分析，以研究碎屑 K-长石记录作为地壳组成档案的潜力。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原位同位素测量，使用 SF6 和 NH3 反应气体分别实现 87Sr+ 和 204Pb+ 上 87Rb+ 和 204Hg+ 等量异位素干涉的“化学分辨率”。使用这种技术，我们成功地证明了来自 Shap Wells 砾岩的大多数碎屑 K-长石 RbSr 年龄以及初始 Sr 和 Pb 同位素比值与母体 Shap 花岗岩 K-长石 （398 ± 1 马， n = 6） 的年龄在不确定性范围内。一些碎屑 K-长石颗粒记录了扰动的 RbSr 年龄，反映了沉积后的蚀变事件。在原位测年之前，大多数 RbSr 年龄受干扰的样品在 SEM 成像中都带有明显的岩相特征，这表明这是一种帮助筛选可靠年龄的方法。