Zircon separates from the contact aureole of the syn-tectonic Dawros–Currywongaun–Doughruagh Complex, western Ireland, are studied to constrain the nature and timing of magmatism associated with the early stages of the Grampian Orogeny. The samples analysed come from the uppermost part of the Dalradian Supergroup in northern Connemara (the Ben Levy Grit Formation), where a laterally extensive (>10 km) package of metamorphosed siliciclastic sedimentary rocks containing heavy mineral seams crops out. The seams mainly comprise magnetite, but zircon is also present in greater than accessory quantities. The seams have been locally reworked at granulite-facies metamorphic conditions during intrusion of the Dawros–Currywongaun–Doughruagh Complex magmas. Here we combine in situ mineral chemical and U–Pb geochronological analyses of zircons from samples of these heavy mineral seams collected at different locations in the Dawros–Currywongaun–Doughruagh Complex thermal aureole. An important finding is that the zircons studied have magmatic trace-element compositions, interpreted here as a function of their growth during contact metamorphic-induced partial melting. The zircons yield a range of U–Pb spot ages whose uncertainties suggest a maximum duration of zircon growth of ˜11 Ma, between 477.1 and 466.1 Ma, though it is likely that zircon growth occurred much more quickly than this. The age constraints revealed here match well with the range of 475 to 463 Ma previously proposed for the Grampian Orogeny overall in Connemara and lend useful support to models that argue for high-intensity, relatively short-lived Grampian orogenesis in the Connemara Caledonides.

中文翻译：

---

Connemara Caledonides 岩浆作用和变质作用的时间尺度：来自爱尔兰西部 Dawros-Currywongaun-Doughruagh 复合体的热光环的见解

研究了爱尔兰西部同构造 Dawros-Currywongaun-Doughruagh 复合体的接触光环中分离出的锆石，以限制与格兰屏造山运动早期阶段相关的岩浆作用的性质和时间。分析的样品来自康尼马拉北部的 Dalradian 超群（Ben Levy Grit 组）的最上部，那里有一个横向广泛（> 10 公里）的变质硅质碎屑沉积岩包，其中含有重矿物层。接缝主要由磁铁矿组成，但锆石的含量也高于副产品。在 Dawros-Currywongaun-Doughruagh 复合岩浆侵入过程中，这些煤层在麻粒岩相变质条件下进行了局部改造。这里我们结合原位在 Dawros-Currywongaun-Doughruagh 复合体热光环的不同位置收集的这些重矿物层样品中的锆石的矿物化学和 U-Pb 地质年代学分析。一个重要的发现是，所研究的锆石具有岩浆微量元素成分，在此解释为它们在接触变质诱导的部分熔融过程中的生长函数。锆石产生了一系列 U-Pb 斑点年龄，其不确定性表明锆石生长的最大持续时间约为 11 Ma，介于 477.1 和 466.1 Ma 之间，尽管锆石的生长可能比这快得多。这里揭示的年龄限制与之前为康尼马拉的格兰屏造山运动提出的 475 到 463 Ma 的范围非常匹配，并为主张高强度的模型提供了有用的支持，