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

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

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Beryllium-10 ( 10 Be) 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 situ 10 Be 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) 10 Be 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 10 Be chronology from nearby nunataks. Improving the viability of in situ 10 Be 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 10 Be purification, in order to better handle the high cationic contaminant loads of ferromagnesian minerals. In addition, further 10 Be measurements from suitable mafic sedimentary deposits with independent age control (e.g. existing cosmogenic 3 He calibration sites) will help to refine estimates of the reference production rate.

Original languageEnglish
Pages (from-to)121-132
Number of pages12
JournalQuaternary Geochronology
Volume48
DOIs
Publication statusPublished - 1 Oct 2018
Externally publishedYes

Keywords

  • Be
  • Cosmogenic nuclides
  • Production rate calibration
  • Pyroxene
  • Sequential leaching

Cite this

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 10 Be production rate in pyroxene and a viability test for late Quaternary exposure dating. In: Quaternary Geochronology. 2018 ; Vol. 48. pp. 121-132.
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abstract = "Beryllium-10 ( 10 Be) 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 situ 10 Be 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) 10 Be 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 10 Be chronology from nearby nunataks. Improving the viability of in situ 10 Be 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 10 Be purification, in order to better handle the high cationic contaminant loads of ferromagnesian minerals. In addition, further 10 Be measurements from suitable mafic sedimentary deposits with independent age control (e.g. existing cosmogenic 3 He calibration sites) will help to refine estimates of the reference production rate.",
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Further constraint of the in situ cosmogenic 10 Be 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.

In: Quaternary Geochronology, Vol. 48, 01.10.2018, p. 121-132.

Research output: Contribution to journalArticleResearchpeer-review

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AB - Beryllium-10 ( 10 Be) 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 situ 10 Be 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) 10 Be 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 10 Be chronology from nearby nunataks. Improving the viability of in situ 10 Be 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 10 Be purification, in order to better handle the high cationic contaminant loads of ferromagnesian minerals. In addition, further 10 Be measurements from suitable mafic sedimentary deposits with independent age control (e.g. existing cosmogenic 3 He calibration sites) will help to refine estimates of the reference production rate.

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