Magnesium isotope analysis of olivine and pyroxene by SIMS: Evaluation of matrix effects

Kohei Fukuda; Brian L. Beard; Daniel R. Dunlap; Michael J. Spicuzza; John H. Fournelle; Meenakshi Wadhwa; Noriko T. Kita

doi:10.1016/j.chemgeo.2020.119482

Magnesium isotope analysis of olivine and pyroxene by SIMS: Evaluation of matrix effects

Kohei Fukuda, Brian L. Beard, Daniel R. Dunlap, Michael J. Spicuzza, John H. Fournelle, Meenakshi Wadhwa, Noriko T. Kita

Research output: Contribution to journal › Article › peer-review

22 Scopus citations

Abstract

The performance of multi-collector secondary ion mass spectrometry (MC-SIMS) for Mg isotope ratio analysis was evaluated using 17 olivine and 5 pyroxene reference materials (RMs). The Mg isotope composition of these RMs was accurately and precisely determined by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), and these measured isotope ratios were used to evaluate SIMS instrumental mass bias as a function of the forsterite (Fo) content of olivine. The magnitude of the Mg isotope matrix effects were ~3‰ in δ²⁵Mg, and are a complex function of olivine Fo content, that ranged from Fo_59.3 to Fo₁₀₀. In addition to these Mg isotope matrix effects, Si⁺ ion yields and Mg⁺/Si⁺ ion ratios varied as a complex function of the Fo content of the olivine RMs. For example, Si⁺ ion yields varied by ~33%. Based on the observations, we propose instrumental bias correction procedures for SIMS Mg isotope analysis of olivine using a combination of Mg⁺/Si⁺ ratios and Fo content of olivine. Using this correction method, the accuracy of δ²⁵Mg analyses is 0.3‰, except for analysis of olivine with Fo₈₆ _– ₈₈ where instrumental biases and Mg⁺/Si⁺ ratios change dramatically with Fo content, making it more difficult to assess the accuracy of Mg isotope ratio measurements by SIMS over this narrow range of Fo content. Five pyroxene RMs (3 orthopyroxenes and 2 clinopyroxenes) show smaller ranges of instrumental bias (~1.4‰ in δ²⁵Mg) as compared to the olivine RMs. The instrumental bias for the 3 orthopyroxene RMs do not define a linear relationship with respect to enstatite (En) content, that ranged from En₈ ₅ _. ₅ _– _96.3. The clinopyroxene RMs have similar En and wollastonite (Wo) contents but have δ²⁵Mg values that differ by 0.5‰ relative to their δ²⁵Mg values determined by MC-ICP-MS. These results indicate that additional factors (e.g., minor element abundances) likely contribute to SIMS instrumental mass fractionation. In order to better correct for these SIMS matrix effects, additional pyroxene RMs with various chemical compositions and known Mg isotope ratios are needed.

Original language	English
Article number	119482
Journal	Chemical Geology
Volume	540
DOIs	https://doi.org/10.1016/j.chemgeo.2020.119482
State	Published - May 5 2020
Externally published	Yes

Funding

We are grateful to Kouki Kitajima for his valuable comments and developments of SIMS operation and data reduction procedures. We thank Timothy McCoy and Julie Hoskin (Smithsonian Institution) for allocating Winona, Kenna, and Springwater meteorites for the study. We thank Katsuyuki Yamashita, Cyrena Goodrich, Alexander Sobolev, Shichun Huang, and Fang-Zhen Teng for generously providing meteorite and rock samples (ALH77257, NWA7325, Weltevreden komatiite, and CL09 series). Several WiscSIMS oxygen standards used in this work were provided by John Valley. We thank Guillaume Siron for assistance with electron microprobe analyses. We are grateful to Steve Romaniello and Rebekah Hines for their invaluable assistance in the IGCL at ASU. We also thank Kazuhide Nagashima and an anonymous reviewer for constructive comments that improved the quality of the paper and Balz Kamber for prompt editorial handling of this paper. This work is supported by the NASA program (NNX16AG80G to NK and NNX15AH41G to MW). WiscSIMS is partly supported by NSF (EAR 1658823). We are grateful to Kouki Kitajima for his valuable comments and developments of SIMS operation and data reduction procedures. We thank Timothy McCoy and Julie Hoskin (Smithsonian Institution) for allocating Winona, Kenna, and Springwater meteorites for the study. We thank Katsuyuki Yamashita, Cyrena Goodrich, Alexander Sobolev, Shichun Huang, and Fang-Zhen Teng for generously providing meteorite and rock samples (ALH77257, NWA7325, Weltevreden komatiite, and CL09 series). Several WiscSIMS oxygen standards used in this work were provided by John Valley. We thank Guillaume Siron for assistance with electron microprobe analyses. We are grateful to Steve Romaniello and Rebekah Hines for their invaluable assistance in the IGCL at ASU. We also thank Kazuhide Nagashima and an anonymous reviewer for constructive comments that improved the quality of the paper and Balz Kamber for prompt editorial handling of this paper. This work is supported by the NASA program ( NNX16AG80G to NK and NNX15AH41G to MW). WiscSIMS is partly supported by NSF (EAR 1658823 ).

Funders	Funder number
John Valley
Julie Hoskin
National Science Foundation	EAR 1658823, 2004618, 1658823
Smithsonian Institution	ALH77257, NWA7325
National Aeronautics and Space Administration	NNX16AG80G, NNX15AH41G

Keywords

Inductively coupled plasma mass spectrometry
Magnesium isotopes
Matrix effects
Olivine and pyroxene
Secondary ion mass spectrometry

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10.1016/j.chemgeo.2020.119482

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title = "Magnesium isotope analysis of olivine and pyroxene by SIMS: Evaluation of matrix effects",

abstract = "The performance of multi-collector secondary ion mass spectrometry (MC-SIMS) for Mg isotope ratio analysis was evaluated using 17 olivine and 5 pyroxene reference materials (RMs). The Mg isotope composition of these RMs was accurately and precisely determined by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), and these measured isotope ratios were used to evaluate SIMS instrumental mass bias as a function of the forsterite (Fo) content of olivine. The magnitude of the Mg isotope matrix effects were ~3‰ in δ25Mg, and are a complex function of olivine Fo content, that ranged from Fo59.3 to Fo100. In addition to these Mg isotope matrix effects, Si+ ion yields and Mg+/Si+ ion ratios varied as a complex function of the Fo content of the olivine RMs. For example, Si+ ion yields varied by ~33%. Based on the observations, we propose instrumental bias correction procedures for SIMS Mg isotope analysis of olivine using a combination of Mg+/Si+ ratios and Fo content of olivine. Using this correction method, the accuracy of δ25Mg analyses is 0.3‰, except for analysis of olivine with Fo86 – 88 where instrumental biases and Mg+/Si+ ratios change dramatically with Fo content, making it more difficult to assess the accuracy of Mg isotope ratio measurements by SIMS over this narrow range of Fo content. Five pyroxene RMs (3 orthopyroxenes and 2 clinopyroxenes) show smaller ranges of instrumental bias (~1.4‰ in δ25Mg) as compared to the olivine RMs. The instrumental bias for the 3 orthopyroxene RMs do not define a linear relationship with respect to enstatite (En) content, that ranged from En8 5 . 5 – 96.3. The clinopyroxene RMs have similar En and wollastonite (Wo) contents but have δ25Mg values that differ by 0.5‰ relative to their δ25Mg values determined by MC-ICP-MS. These results indicate that additional factors (e.g., minor element abundances) likely contribute to SIMS instrumental mass fractionation. In order to better correct for these SIMS matrix effects, additional pyroxene RMs with various chemical compositions and known Mg isotope ratios are needed.",

keywords = "Inductively coupled plasma mass spectrometry, Magnesium isotopes, Matrix effects, Olivine and pyroxene, Secondary ion mass spectrometry",

author = "Kohei Fukuda and Beard, {Brian L.} and Dunlap, {Daniel R.} and Spicuzza, {Michael J.} and Fournelle, {John H.} and Meenakshi Wadhwa and Kita, {Noriko T.}",

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doi = "10.1016/j.chemgeo.2020.119482",

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T1 - Magnesium isotope analysis of olivine and pyroxene by SIMS

T2 - Evaluation of matrix effects

AU - Fukuda, Kohei

AU - Beard, Brian L.

AU - Dunlap, Daniel R.

AU - Spicuzza, Michael J.

AU - Fournelle, John H.

AU - Wadhwa, Meenakshi

AU - Kita, Noriko T.

PY - 2020/5/5

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N2 - The performance of multi-collector secondary ion mass spectrometry (MC-SIMS) for Mg isotope ratio analysis was evaluated using 17 olivine and 5 pyroxene reference materials (RMs). The Mg isotope composition of these RMs was accurately and precisely determined by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), and these measured isotope ratios were used to evaluate SIMS instrumental mass bias as a function of the forsterite (Fo) content of olivine. The magnitude of the Mg isotope matrix effects were ~3‰ in δ25Mg, and are a complex function of olivine Fo content, that ranged from Fo59.3 to Fo100. In addition to these Mg isotope matrix effects, Si+ ion yields and Mg+/Si+ ion ratios varied as a complex function of the Fo content of the olivine RMs. For example, Si+ ion yields varied by ~33%. Based on the observations, we propose instrumental bias correction procedures for SIMS Mg isotope analysis of olivine using a combination of Mg+/Si+ ratios and Fo content of olivine. Using this correction method, the accuracy of δ25Mg analyses is 0.3‰, except for analysis of olivine with Fo86 – 88 where instrumental biases and Mg+/Si+ ratios change dramatically with Fo content, making it more difficult to assess the accuracy of Mg isotope ratio measurements by SIMS over this narrow range of Fo content. Five pyroxene RMs (3 orthopyroxenes and 2 clinopyroxenes) show smaller ranges of instrumental bias (~1.4‰ in δ25Mg) as compared to the olivine RMs. The instrumental bias for the 3 orthopyroxene RMs do not define a linear relationship with respect to enstatite (En) content, that ranged from En8 5 . 5 – 96.3. The clinopyroxene RMs have similar En and wollastonite (Wo) contents but have δ25Mg values that differ by 0.5‰ relative to their δ25Mg values determined by MC-ICP-MS. These results indicate that additional factors (e.g., minor element abundances) likely contribute to SIMS instrumental mass fractionation. In order to better correct for these SIMS matrix effects, additional pyroxene RMs with various chemical compositions and known Mg isotope ratios are needed.

AB - The performance of multi-collector secondary ion mass spectrometry (MC-SIMS) for Mg isotope ratio analysis was evaluated using 17 olivine and 5 pyroxene reference materials (RMs). The Mg isotope composition of these RMs was accurately and precisely determined by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), and these measured isotope ratios were used to evaluate SIMS instrumental mass bias as a function of the forsterite (Fo) content of olivine. The magnitude of the Mg isotope matrix effects were ~3‰ in δ25Mg, and are a complex function of olivine Fo content, that ranged from Fo59.3 to Fo100. In addition to these Mg isotope matrix effects, Si+ ion yields and Mg+/Si+ ion ratios varied as a complex function of the Fo content of the olivine RMs. For example, Si+ ion yields varied by ~33%. Based on the observations, we propose instrumental bias correction procedures for SIMS Mg isotope analysis of olivine using a combination of Mg+/Si+ ratios and Fo content of olivine. Using this correction method, the accuracy of δ25Mg analyses is 0.3‰, except for analysis of olivine with Fo86 – 88 where instrumental biases and Mg+/Si+ ratios change dramatically with Fo content, making it more difficult to assess the accuracy of Mg isotope ratio measurements by SIMS over this narrow range of Fo content. Five pyroxene RMs (3 orthopyroxenes and 2 clinopyroxenes) show smaller ranges of instrumental bias (~1.4‰ in δ25Mg) as compared to the olivine RMs. The instrumental bias for the 3 orthopyroxene RMs do not define a linear relationship with respect to enstatite (En) content, that ranged from En8 5 . 5 – 96.3. The clinopyroxene RMs have similar En and wollastonite (Wo) contents but have δ25Mg values that differ by 0.5‰ relative to their δ25Mg values determined by MC-ICP-MS. These results indicate that additional factors (e.g., minor element abundances) likely contribute to SIMS instrumental mass fractionation. In order to better correct for these SIMS matrix effects, additional pyroxene RMs with various chemical compositions and known Mg isotope ratios are needed.

KW - Inductively coupled plasma mass spectrometry

KW - Magnesium isotopes

KW - Matrix effects

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KW - Secondary ion mass spectrometry

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DO - 10.1016/j.chemgeo.2020.119482

M3 - Article

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SN - 0009-2541

VL - 540

JO - Chemical Geology

JF - Chemical Geology

M1 - 119482

ER -

Magnesium isotope analysis of olivine and pyroxene by SIMS: Evaluation of matrix effects

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