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<p>The Sept-Iles Intrusive Suite, Quebec, Canada, comprises several components, including the third largest mafic layered intrusion in the world. Until now, the age of the whole suite was estimated at 565 ± 4&#xa0;Ma based on zircon U-Pb dating from a single sample. However, the Layered Series component consists of three Mega Cyclic Units (MCU) which may record distinct magmatic events. This study uses apatite and zircon U-Pb and Lu-Hf geochronology to constrain the emplacement age of samples from the top of MCU I and II. Apatite from MCU I yields U-Pb dates of ca. 620&#xa0;Ma. Samples from MCU II, stratigraphically above MCU I, yield a homogeneous U-Pb apatite date of ca. 565&#xa0;Ma, overlapping the Lu-Hf apatite date of 567 ± 14&#xa0;Ma, and the U-Pb zircon crystallization age of 564 ± 2&#xa0;Ma. Based on these new ages and geochemical signatures, we propose a revised nomenclature for the Layered Series of the Sept-Iles Intrusive Suite. The ca. 620&#xa0;Ma unit is divided into the Rivière Sainte-Marguerite unit (RSM; former MCU I) and Rivière des Rapides unit (RdR; former MCU III), the high (Gd/Yb)<sub>N</sub> ratios in RSM cumulus apatite indicating partial melting at depth related to the Central Iapetus Magmatic Province mantle plume. The Lac au Castor unit (LC; former MCU II) was injected as a sill at ca. 565&#xa0;Ma, with lower (Gd/Yb)<sub>N</sub> ratios in cumulus apatite reflecting decompression melting of shallow asthenospheric mantle during subsequent rifting and opening of the Iapetus Ocean some 55 Myrs later.</p>

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Apatite geochronology of the Sept-Iles Intrusive Suite (Grenville province, Canada) reveals two magmatic episodes 55 Myrs apart related to plume arrival and subsequent rifting

  • 期刊论文

  • 发表日期：

    2026年4月11日

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  • Hélène Legros,
  • Marie A. Kieffer,
  • Sarah A. S. Dare,
  • Olivier Namur,
  • Michael D. Higgins,
  • Dany Savard,
  • Stijn Glorie

摘要

The Sept-Iles Intrusive Suite, Quebec, Canada, comprises several components, including the third largest mafic layered intrusion in the world. Until now, the age of the whole suite was estimated at 565 ± 4 Ma based on zircon U-Pb dating from a single sample. However, the Layered Series component consists of three Mega Cyclic Units (MCU) which may record distinct magmatic events. This study uses apatite and zircon U-Pb and Lu-Hf geochronology to constrain the emplacement age of samples from the top of MCU I and II. Apatite from MCU I yields U-Pb dates of ca. 620 Ma. Samples from MCU II, stratigraphically above MCU I, yield a homogeneous U-Pb apatite date of ca. 565 Ma, overlapping the Lu-Hf apatite date of 567 ± 14 Ma, and the U-Pb zircon crystallization age of 564 ± 2 Ma. Based on these new ages and geochemical signatures, we propose a revised nomenclature for the Layered Series of the Sept-Iles Intrusive Suite. The ca. 620 Ma unit is divided into the Rivière Sainte-Marguerite unit (RSM; former MCU I) and Rivière des Rapides unit (RdR; former MCU III), the high (Gd/Yb)N ratios in RSM cumulus apatite indicating partial melting at depth related to the Central Iapetus Magmatic Province mantle plume. The Lac au Castor unit (LC; former MCU II) was injected as a sill at ca. 565 Ma, with lower (Gd/Yb)N ratios in cumulus apatite reflecting decompression melting of shallow asthenospheric mantle during subsequent rifting and opening of the Iapetus Ocean some 55 Myrs later.