Insights into early continental crust formation from the most ancient heart of Scotland
- 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
2026-04-21
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 δ¹ 8 O (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 δ¹ 8 O (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.