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<p>The paucity of rocks from Earth’s first billion years (4.5–3.5 Ga) limits understanding of early felsic (continental) crust formation and craton development. We present zircon U–Pb, O- and Hf-isotope and whole-rock geochemical data from deformed and metamorphosed (ultra)mafic and felsic rocks of the Archaean Lewisian Gneiss Complex, NW Scotland. The felsic, MgO-rich hornblende-bearing tonalite gneisses contain magmatic zircon populations at c. 3.6, 3.5, and 2.8 Ga, as do enclosed hornblendite pods (&gt;95 vol.% hornblende). Zircons from hbl-tonalite preserve median δ¹<sup>8</sup>O<sub>(zircon)</sub> of ~5.8‰, indicating limited supracrustal input. The hornblendites have high-MgO (~18 wt%), Cr (up to 5500 µg/g), and Ni (up to 2800 µg/g) concentrations and record slightly higher δ¹<sup>8</sup>O<sub>(zircon)</sub> median values (~6.3‰). Zircon εHf<sub>(zircon)</sub> from both lithologies implies a Hadean to early Archaean (c. 4.1–3.9 Ga) depleted mantle source variably modified by low-temperature surface-derived fluids and/or incorporation of Hadean continental crust. We argue that the hornblendites represent vestiges of a hydrated (proto)crust that contributed to the growth of the earliest Archaean continental nuclei.</p>

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Insights into early continental crust formation from the most ancient heart of Scotland

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年4月21日

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  • Silvia Volante,
  • Fernanda Torres-Mancinelli,
  • Jonas Kaempf,
  • Vitor Barrote,
  • Tim Johnson,
  • Christopher Kirkland,
  • Maria Rosa Scicchitano,
  • Lorenzo Tavazzani,
  • Sampriti Basak,
  • Anne-Sophie Bouvier,
  • Annika Dziggel,
  • Axel Gerdes

摘要

The paucity of rocks from Earth’s first billion years (4.5–3.5 Ga) limits understanding of early felsic (continental) crust formation and craton development. We present zircon U–Pb, O- and Hf-isotope and whole-rock geochemical data from deformed and metamorphosed (ultra)mafic and felsic rocks of the Archaean Lewisian Gneiss Complex, NW Scotland. The felsic, MgO-rich hornblende-bearing tonalite gneisses contain magmatic zircon populations at c. 3.6, 3.5, and 2.8 Ga, as do enclosed hornblendite pods (>95 vol.% hornblende). Zircons from hbl-tonalite preserve median δ¹8O(zircon) of ~5.8‰, indicating limited supracrustal input. The hornblendites have high-MgO (~18 wt%), Cr (up to 5500 µg/g), and Ni (up to 2800 µg/g) concentrations and record slightly higher δ¹8O(zircon) median values (~6.3‰). Zircon εHf(zircon) from both lithologies implies a Hadean to early Archaean (c. 4.1–3.9 Ga) depleted mantle source variably modified by low-temperature surface-derived fluids and/or incorporation of Hadean continental crust. We argue that the hornblendites represent vestiges of a hydrated (proto)crust that contributed to the growth of the earliest Archaean continental nuclei.