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Expanding the toolbox for dating basaltic lava sequences: 40Ar–39Ar dating of silicic volcanic glass from interbeds

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posted on 16.12.2020, 16:24 by Simone Cogliati, Sarah C Sherlock, Alison M Halton, Alena Ebinghaus, Simon P Kelley, David W Jolley, Tiffany L Barry
40Ar–39Ar dating of glass shards from silicic tuffs of the Ellensburg Formation (NW, USA) interbedding basaltic lavas yielded accurate, precise, reproducible plateau and isochron ages that are within error at the 2σ level. The age-spectra have flat plateaus and the inverse isochrons have atmospheric 40Ar/36Ar at the 2σ level. Ages of 12.00 ± 0.24, 11.37 ± 0.15, 10.67 ± 0.21 and 10.70 ± 0.18 Ma are consistent with the stratigraphy of four of the dated layers; the age of 10.77 ± 0.18 Ma for a fifth layer is at odds with the stratigraphy. This discrepancy arises due to the effect of glass alteration that induced K- and Ar-loss. There is no evidence of excess 40Ar or 39Ar recoil. The new ages indirectly constrain the timing of eruption of the lavas above and below the ash beds. This demonstrates that volcanic glass from interbeds can be used as an additional tool for indirectly dating basaltic lava sequences, which is independent of the lavas and complementary to other materials. Considering the numerous studies in which volcanic glass failed to provide reliable 40Ar–39Ar ages, additional and supportive constraints are still needed to assess the validity of the ages from glass shards.

History

Citation

Journal of the Geological Society (2021) 178 (1): jgs2019-207. https://doi.org/10.1144/jgs2019-207

Author affiliation

School of Geography, Geology and the Environment

Version

AM (Accepted Manuscript)

Published in

Journal of the Geological Society

Volume

178

Issue

1

Pagination

jgs2019 - 207

Publisher

Geological Society of London

issn

0016-7649

eissn

2041-479X

Acceptance date

23/07/2020

Copyright date

2020

Available date

15/09/2021

Language

en

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