Production of 21Ne in depth-profiled olivine from a 54 Ma basalt sequence, Eastern Highlands (37° S), Australia

Erin L. Matchan*, Masahiko Honda, Timothy T. Barrows, David Phillips, Allan R. Chivas, Keith Fifield, Derek Fabel

*Corresponding author for this work

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    Abstract

    In this study we investigate the cosmogenic neon component in olivine samples from a vertical profile in order to quantify muogenic 21Ne production in this mineral. Samples were collected from an 11 m thick Eocene basalt profile in the Eastern Highlands of southeastern Australia. An eruption age of 54.15 ± 0.36 Ma (2σ) was determined from 40Ar/39Ar step-heating experiments (n = 6) on three whole-rock samples. A 36Cl profile on the section indicated an apparent steady state erosion rate of 4.7 ± 0.5 m Ma−1. The eruption age was used to calculate in situ produced radiogenic 4He and nucleogenic 3He and 21Ne concentrations in olivine. Olivine mineral separates (n = 4), extracted from the upper two metres of the studied profile, reveal cosmogenic 21Ne concentrations that attenuate exponentially with depth. However, olivine (Fo68) extracted from below 2 m does not contain discernible 21Ne aside from magmatic and nucleogenic components, with the exception of one sample that apparently contained equal proportions of nucleogenic and muogenic neon. Modelling results suggest a muogenic neon sea-level high-latitude production rate of 0.02 ± 0.04 to 0.9 ± 1.3 atoms g−1 a−1 (1σ), or <2.5% of spallogenic cosmogenic 21Ne production at Earth's surface. These data support a key implicit assumption in the literature that accumulation of muogenic 21Ne in olivine in surface samples is likely to be negligible/minimal compared to spallogenic 21Ne.

    Original languageEnglish
    Pages (from-to)276-290
    Number of pages15
    JournalGeochimica et Cosmochimica Acta
    Volume220
    Early online date28 Sep 2017
    DOIs
    Publication statusPublished - 1 Jan 2018

    Keywords

    • Cosmogenic Ne
    • Cosmogenic Cl
    • Muons
    • Noble gases
    • Olivine

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