Titanium isotope constraints on the mafic sources and geodynamic origins of Archean crust
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The timing and formation of Earth’s first continents during the Archean are subjects of significant debate. By examining titanium isotope variations in Archean Tonalite-Trondhjemite-Granodiorite (TTG) rocks and using advanced thermodynamic modelling, we can narrow down the processes involved and emphasise the role of mafic precursor compositions. In our study of Eoarchean Isua metabasalts and Itsaq tonalites in southern West Greenland, we observed a pattern of increasing Ti isotope enrichment with higher SiO2 content, resembling the compositions found in modern subduction zone rocks. Our modelling suggests that the Ti isotope variations in TTGs can be best explained by a combination of partial melting of low TiO2 metabasalts and subsequent crystallisation of tonalitic magmas, resulting in heavier Ti isotopes. This means that Ti isotopes help us distinguish the contributions of various mafic sources and fractional crystallisation during TTG formation. In the case of Itsaq tonalites and many other Eoarchean TTGs, low TiO2 tholeiitic metabasalts with arc-like characteristics likely represent the mafic source rocks, suggesting the formation of some of Earth’s earliest continental crust within a proto-subduction zone setting.
Originalsprog | Engelsk |
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Tidsskrift | Geochemical Perspectives Letters |
Vol/bind | 28 |
Sider (fra-til) | 37-42 |
Antal sider | 6 |
ISSN | 2410-339X |
DOI | |
Status | Udgivet - 2023 |
Bibliografisk note
Funding Information:
LH, ROCF, and JEH acknowledge funding from Deutsche Forschungsgemeinschaft (DFG) Grant FO 698/14-1 and HO4794/4-1. ROC further thanks the DFG for funding of a Heisenberg Professorship (Grant FO 698/13-1). We thank Regina Friese and Michael Bode for managing the clean lab at the Deutches Bergbau Museum, and Edward Inglis for managing the clean lab at Cardiff University. We also thank Philipp Gleißner, Ninja Braukmüller and Guillaume Florin for assistance and advice with the Neoma MC-ICP-MS at Freie Universität Berlin. We are grateful to Silvia Volante and Capucine Albert for helpful discussions. The authors would also like to acknowledge detailed and constructive reviews by two anonymous referees which greatly improved the manuscript. Furthermore, we would like to thank Anat Shahar for expert editorial handling.
Publisher Copyright:
© 2023 The Authors Published by the European Association of Geochemistry.
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