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Further constraint of the in situ cosmogenic 10Be production rate in pyroxene and a viability test for late Quaternary exposure dating

Eaves, Shaun R.; Collins, Julia A.; Jones, R. Selwyn; Norton, Kevin P.; Tims, Stephen G.; Mackintosh, Andrew N.

Further constraint of the in situ cosmogenic 10Be production rate in pyroxene and a viability test for late Quaternary exposure dating Thumbnail


Authors

Shaun R. Eaves

Julia A. Collins

R. Selwyn Jones

Kevin P. Norton

Stephen G. Tims

Andrew N. Mackintosh



Abstract

Beryllium-10 (10Be) in quartz represents the most common in situ cosmogenic nuclide used for quantifying Earth-surface processes, primarily due to the prevalence of quartz in the Earth's crust. However many landscapes lack quartz-bearing rocks, thus other nuclide-mineral pairs are required for geochronometric and geomorphic applications. Here we describe the successful isolation and measurement of in situ10Be concentrations in pyroxene from two mafic sample sets: (i) andesite boulders of the Murimotu Formation debris avalanche on Mt. Ruapehu, New Zealand, and (ii) dolerite cobbles deposited in a ∼100 m vertical transect at Mt. Gran by Mackay Glacier, Antarctica. Precise radiocarbon age constraint of the New Zealand site provides further geological constraint of the reference (at sea level and high latitude) 10Be production rate in pyroxene, which we find to be indistinguishable from a previous estimate. Combining our results with previous data yields a reference production rate of 3.2 ± 0.8 at. g−1 yr−1 (n=5; ‘Lm’ scaling). Application of this rate to the glacial cobbles at Mackay Glacier yields a relatively coherent chronology of ice surface lowering between ∼14 and 6 ka, which is broadly consistent with a well-constrained quartz-based 10Be chronology from nearby nunataks. Improving the viability of in situ10Be for geological applications in mafic domains requires increased analytical precision beyond current levels. This improvement may be best achieved by further modification of the quartz-based methodologies for 10Be purification, in order to better handle the high cationic contaminant loads of ferromagnesian minerals. In addition, further 10Be measurements from suitable mafic sedimentary deposits with independent age control (e.g. existing cosmogenic 3He calibration sites) will help to refine estimates of the reference production rate.

Journal Article Type Article
Acceptance Date Sep 24, 2018
Online Publication Date Sep 28, 2018
Publication Date Sep 28, 2018
Deposit Date Nov 1, 2018
Publicly Available Date Sep 28, 2019
Journal Quaternary Geochronology
Print ISSN 1871-1014
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 48
Pages 121-132
DOI https://doi.org/10.1016/j.quageo.2018.09.006
Public URL https://durham-repository.worktribe.com/output/1314362

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