Titanium isotope constraints on the mafic sources and geodynamic origins of Archean crust

Hoare, Liam, Rzehak, Laura J. A., Kommescher, Sebastian, Jansenm, Moritz, Rosing, Minik T., Thorsten, Nagel, Millet, Marc-Alban ORCID: https://orcid.org/0000-0003-2710-5374, Hoffmann, J. Elis and Fonseca, Raul O. C. 2023. Titanium isotope constraints on the mafic sources and geodynamic origins of Archean crust. Geochemical Perspectives Letters 28 , pp. 37-42. 10.7185/geochemlet.2342

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Abstract

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.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Earth and Environmental Sciences
Publisher:	European Association of Geochemistry
ISSN:	2410-339X
Date of First Compliant Deposit:	10 November 2023
Date of Acceptance:	6 November 2023
Last Modified:	25 Jan 2024 13:43
URI:	https://orca.cardiff.ac.uk/id/eprint/163820

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