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<p>Fluid-flux melting is increasingly recognised as a key mechanism for continental crust growth and recycling, but the abundance and sources of the external fluids involved in this process are typically uncertain. Here we use zircon and garnet oxygen isotope data, geochronology, and petrological analysis of mid- to lower-crustal rocks from the Georgetown Inlier, Australia, to explore the composition and origin of anatexis-triggering fluids. Tonalite veins and garnetite residues show higher zircon δ<sup>18</sup>O values (~6‰) than their amphibolite source (~2–3‰), whereas sediment-derived granites show lower values (6‰) than those of typical siliciclastic sources (10–20‰). Mass balance modelling suggests that these isotopic shifts result from the interaction with mantle-derived fluids. Asthenospheric mantle upwelling beneath the Georgetown crust during slab rollback or break-off provided heat and fluids, generating hydrous mafic underplates that exsolved mantle-derived water, promoting crustal anatexis. This process may have been key in shaping Earth’s early buoyant sodic continental crust.</p>

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Oxygen isotope shifts reveal fluid-fluxed melting in continental anatexis

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年4月11日

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  • Silvia Volante,
  • Amaury Pourteau,
  • Zheng-Xiang Li,
  • William J. Collins,
  • Luc S. Doucet,
  • Hugo K. H. Olierook,
  • Laure Martin,
  • Matthijs A. Smit

摘要

Fluid-flux melting is increasingly recognised as a key mechanism for continental crust growth and recycling, but the abundance and sources of the external fluids involved in this process are typically uncertain. Here we use zircon and garnet oxygen isotope data, geochronology, and petrological analysis of mid- to lower-crustal rocks from the Georgetown Inlier, Australia, to explore the composition and origin of anatexis-triggering fluids. Tonalite veins and garnetite residues show higher zircon δ18O values (~6‰) than their amphibolite source (~2–3‰), whereas sediment-derived granites show lower values (6‰) than those of typical siliciclastic sources (10–20‰). Mass balance modelling suggests that these isotopic shifts result from the interaction with mantle-derived fluids. Asthenospheric mantle upwelling beneath the Georgetown crust during slab rollback or break-off provided heat and fluids, generating hydrous mafic underplates that exsolved mantle-derived water, promoting crustal anatexis. This process may have been key in shaping Earth’s early buoyant sodic continental crust.