The enigmatic occurrence of Neoarchean- and Proterozoic-aged zircon grains in some samples of metasedimentary rocks from the Jack Hills, Western Australia, that otherwise appear to have been deposited before 3.0 Ga is explained by contamination with embedded zircon grains sourced from transported regolith. Zircon U-Pb age spectra obtained by laser ablation–inductively coupled plasma mass spectrometry (LA-ICPMS) analysis of modern alluvium in creek beds draining the metasedimentary belts of Mount Narryer and Jack Hills are dominated by these exotically sourced younger components, as is the red soil that partly covers and infiltrates fractures in the exposed Hadean zircon-bearing bedrock at Jack Hills. The consistency of the age patterns found in superficial deposits sampled over some 100 km implies a dominance of colluvium transported from the wider Yilgarn craton, adjacent Capricorn orogen, and more distal sources rather than material produced from the local (Mesoarchean and older) bedrocks. The potential for similar cases of “environmental contamination” of surface rocks by exogenous zircons needs to be considered more widely, particularly in situations where interpreted maximum deposition ages are based on only a small number of outlying youngest analyzed grains.

中文翻译：

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杰克山变质沉积物到底有多古老？：运输的风化层中锆石颗粒污染基岩的案例

来自西澳大利亚杰克山的一些变沉积岩样品中的新太古代和元古代锆石颗粒的神秘出现，这些样品似乎在 3.0 Ga 之前沉积，这是由来自运输的风化层的嵌入锆石颗粒的污染解释的。通过激光烧蚀-电感耦合等离子体质谱 (LA-ICPMS) 分析现代冲积层中的锆石 U-Pb 年龄光谱，这些河床排干了 Mount Narryer 和 Jack Hills 的变质沉积带，主要由这些外来来源的年轻成分组成，正如部分覆盖并渗入 Jack Hills 裸露的 Hadean 含锆基岩中的裂缝的红土。在超过 100 公里取样的表层沉积物中发现的年龄模式的一致性意味着从更广泛的 Yilgarn 克拉通、邻近的摩羯座造山带和更远的来源输送的崩积岩占主导地位，而不是从当地（中太古宙和更老的）基岩产生的物质。需要更广泛地考虑外源锆石对地表岩石“环境污染”的类似情况的可能性，特别是在解释的最大沉积年龄仅基于少数外围最年轻的分析晶粒的情况下。