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    An impact melt origin for Earth’s oldest known evolved rocks

    272144.pdf (4.072Mb)
    Access Status
    Open access
    Authors
    Johnson, Tim
    Gardiner, Nicholas
    Miljkovic, Katarina
    Spencer, Christopher
    Kirkland, Chris
    Bland, Phil
    Smithies, H.
    Date
    2018
    Type
    Journal Article
    
    Metadata
    Show full item record
    Citation
    Johnson, T. and Gardiner, N. and Miljkovic, K. and Spencer, C. and Kirkland, C. and Bland, P. and Smithies, H. 2018. An impact melt origin for Earth’s oldest known evolved rocks. Nature Geoscience. 11 (10): pp. 795-799.
    Source Title
    Nature Geoscience
    DOI
    10.1038/s41561-018-0206-5
    ISSN
    1752-0894
    School
    School of Earth and Planetary Sciences (EPS)
    Funding and Sponsorship
    http://purl.org/au-research/grants/arc/DP170102529
    URI
    http://hdl.handle.net/20.500.11937/71426
    Collection
    • Curtin Research Publications
    Abstract

    Earth’s oldest evolved (felsic) rocks, the 4.02-billion-year-old Idiwhaa gneisses of the Acasta Gneiss Complex, northwest Canada, have compositions that are distinct from the felsic rocks that typify Earth’s ancient continental nuclei, implying that they formed through a different process. Using phase equilibria and trace element modelling, we show that the Idiwhaa gneisses were produced by partial melting of iron-rich hydrated basaltic rocks (amphibolites) at very low pressures, equating to the uppermost ~3 km of a Hadean crust that was dominantly mafic in composition. The heat required for partial melting at such shallow levels is most easily explained through meteorite impacts. Hydrodynamic impact modelling shows not only that this scenario is physically plausible, but also that the region of shallow partial melting appropriate to formation of the Idiwhaa gneisses would have been widespread. Given the predicted high flux of meteorites in the late Hadean, impact melting may have been the predominant mechanism that generated Hadean felsic rocks.

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