Abstract Detrital apatite deposited before, during and after Grampian-Taconic arc accretion in western Ireland reveals dramatic changes in source provenance and provides a detailed detrital petrochronological record of a Wilson Cycle sited on the Laurentian margin. These determinations are made possible by recent improvements in source rock type diagnosis by apatite trace element analysis. In addition, by interrogating the proportion of apatite derived from peraluminous vs metaluminous melt and felsic vs mafic melt in detritus, temporal changes can be seen in the relative proportions of these magma compositions over time. We present combined trace element and U-Pb age data for detrital apatite in clastic formations from the South Mayo Trough, a uniquely well-preserved fore-arc basin accreted to the Laurentian margin during the Grampian-Taconic orogeny (∼ 475 – 460 Ma), which records the early phase of closing of the Iapetus Ocean. Apatite deposited before collision is derived from the Laurentian margin and mafic igneous rocks of the Central Iapetus Magmatic Province associated with the Neoproterozoic break-up of Rodinia / Pannotia leading to the birth of the Iapteus Ocean. Following the onset of ocean closure in the Cambrian, igneous apatite derived from the nascent Grampian-Taconic arc is detected. Apatite derived from felsic and peraluminous melts becomes progressively more dominant over apatite from more mafic and metaluminous sources as the arc evolves from an intra-oceanic to continental arc setting after collision. The subsequent Grampian-Taconic unroofing history recorded by detrital apatite records the transition from ancient Laurentian margin- and intra-oceanic arc-derived detritus, to the exhumation of the high-grade metamorphic core of the Grampian-Taconic orogen and the exposure of post-collisional continental-arc granitoids. Our results are in broad agreement with both the Grampian fore-arc provenance record (heavy mineral analysis, detrital zircon U-Pb and white mica Ar-Ar) and the Laurentian crustal reworking record derived from the geochemistry of volcaniclastic units in the South Mayo Trough. However, we also obtain novel provenance information undetected by detrital zircon in the South Mayo Trough, such as apatite derived from the Central Iapetus Magmatic Province. Critically this information is obtained from a single mineral system, which eliminates the need to consider differing mineral stabilities during weathering, transport and diagenesis. The high preservation potential for apatite in similar tectonic environments illustrates the potential to employ detrital apatite as a record of Earth's lithological composition in deep time.

中文翻译：

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威尔逊旋回的碎屑记录：来自 Grampian-Taconic 前弧碎屑磷灰石岩石年代学的证据

摘要 在爱尔兰西部 Grampian-Taconic 弧增生之前、期间和之后沉积的碎屑磷灰石揭示了源来源的巨大变化，并提供了位于 Laurentian 边缘的威尔逊旋回的详细碎屑岩石年代学记录。通过磷灰石微量元素分析在烃源岩类型诊断方面的最新改进使这些确定成为可能。此外，通过询问碎屑中来自过铝质熔体与金属铝熔体以及长英质与镁铁质熔体的磷灰石的比例，可以看到这些岩浆成分的相对比例随时间的时间变化。我们提供了来自南梅奥海槽的碎屑岩地层中碎屑磷灰石的微量元素和 U-Pb 年龄数据，一个独特的保存完好的前弧盆地，在格兰坪-塔康造山运动（~ 475 - 460 Ma）期间增生到劳伦大陆边缘，记录了土卫八洋闭合的早期阶段。碰撞前沉积的磷灰石来自中央岩浆区的劳伦边缘和镁铁质火成岩，与罗迪尼亚 / Pannotia 的新元古代分裂导致岩浆洋的诞生有关。在寒武纪海洋闭合开始后，检测到来自新生的格兰屏-塔康弧的火成磷灰石。随着弧在碰撞后从大洋内弧演化为大陆弧，来自长英质和过铝质熔体的磷灰石逐渐变得比来自更多基性和金属铝质来源的磷灰石更具优势。随后由碎屑磷灰石记录的 Grampian-Taconic 开顶历史记录了从古劳伦边缘和洋内弧衍生碎屑到 Grampian-Taconic 造山带高等级变质核的挖掘和后碰撞大陆弧花岗岩。我们的结果与格兰坪前弧物源记录（重矿物分析、碎屑锆石 U-Pb 和白云母 Ar-Ar）和源自南梅奥海槽火山碎屑单元地球化学的劳伦地壳改造记录广泛一致. 然而，我们也获得了在南梅奥海槽中未被碎屑锆石检测到的新物源信息，例如来自中央 Iapetus 岩浆省的磷灰石。至关重要的是，这些信息是从单一矿物系统中获得的，这消除了在风化、运输和成岩过程中考虑不同矿物稳定性的需要。在类似的构造环境中磷灰石的高保存潜力说明了使用碎屑磷灰石作为地球岩性组成的深层记录的潜力。