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Isobar-free neon isotope measurements of flux-fused potential reference minerals on a Helix-MC-Plus^(10K) mass spectrometer

Farley, K. A. and Treffkorn, J. and Hamilton, D. (2020) Isobar-free neon isotope measurements of flux-fused potential reference minerals on a Helix-MC-Plus^(10K) mass spectrometer. Chemical Geology, 537 . Art. No. 119487. ISSN 0009-2541. https://resolver.caltech.edu/CaltechAUTHORS:20200203-092720795

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Abstract

This work presents new analytical techniques for extraction and analysis of neon from a suite of different mineral phases, including quartz, pyroxene, hematite, apatite, zircon, topaz, and fluorite. Neon was quantitatively extracted at 1100 °C from all of these minerals using an in-vacuum lithium borate-flux fusion technique. Evolved neon was purified using a cryogenic method capable of separating Ne from He present in abundances ~8 orders of magnitude higher, typical of samples carrying nucleogenic/radiogenic noble gases. The purified neon was measured on a Helix-MC-Plus^(10K) mass spectrometer that permits isobar-free measurement of all three neon isotopes. When operated at its highest mass resolving power (MRP) of ~10,300, the shoulder representing solely ²²Ne on the low mass-side of the ²²Ne-CO₂⁺² doublet is wide enough to permit measurement of isobar free ²²Ne. Operating in this mode comes with the penalty of a 50% reduction in neon sensitivity. Coupled with a mathematical isobar-stripping method, this approach excludes 99.5% of the CO₂⁺² while still collecting >99% of the ²²Ne beam. Routine edge-centering on the dynamic CO₂⁺² peak prior to introduction of a sample permits rapid and robust relocation of the desired measure point in the mass spectrum. Cosmogenic ²¹Ne and ²²Ne concentrations obtained using these methods on the Cronus-A quartz and Cronus-P pyroxene international reference materials are in excellent agreement with previous work or expectations. Similarly, the concentration of nucleogenic ²¹Ne and ²²Ne in Durango apatite and the CIT hematite standard agree well with previous work. Durango apatite has notable heterogeneity in neon concentrations, consistent with previous observations of heterogeneous He, U and Th concentrations in this apatite. Nucleogenic neon concentrations are also presented for previously unstudied minerals including a Sri Lanka zircon (SLC), a topaz from the Imperial Topaz mine in Brazil (ITP1), and a fluorite (W-90) from New Hampshire. Taken together this set of potential reference minerals and the associated dataset provide a starting point for intercalibration among multiple mineral phases carrying ²¹Ne and ²²Ne of cosmogenic or nucleogenic origin.


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https://doi.org/10.1016/j.chemgeo.2020.119487DOIArticle
ORCID:
AuthorORCID
Farley, K. A.0000-0002-7846-7546
Additional Information:© 2020 Elsevier. Received 4 September 2019, Revised 12 January 2020, Accepted 31 January 2020, Available online 1 February 2020. The authors thank Dan Barfod and two anonymous reviewers for helpful comments on this manuscript. The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Author Doug Hamilton is employed by ThermoFisher the manufacturer of the mass spectrometer described in this manuscript.
Record Number:CaltechAUTHORS:20200203-092720795
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200203-092720795
Official Citation:K.A. Farley, J. Treffkorn, D. Hamilton, Isobar-free neon isotope measurements of flux-fused potential reference minerals on a Helix-MC-Plus10K mass spectrometer, Chemical Geology, Volume 537, 2020, 119487, ISSN 0009-2541, https://doi.org/10.1016/j.chemgeo.2020.119487. (http://www.sciencedirect.com/science/article/pii/S0009254120300267)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101056
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:03 Feb 2020 18:50
Last Modified:14 Feb 2020 21:59

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