TERRAPUB Geochemical Journal

Geochemical Journal, Vol. 55 (No. 4), pp. 283-287, 2021


An effect of variations in relative sensitivity factors on Al-Mg systematics of Ca-Al-rich inclusions in meteorites with secondary ion mass spectrometry

Noriyuki Kawasaki,1* Changkun Park,2 Shigeyuki Wakaki,3 Hwayoung Kim,2 Sunyoung Park,2 Toshihiro Yoshimura,4 Kazuya Nagaishi,5 Hyun Na Kim,6 Naoya Sakamoto7 and Hisayoshi Yurimoto1,7

1Department of Natural History Sciences, Hokkaido University, Sapporo 060-0810, Japan
2Division of Earth-System Sciences, Korea Polar Research Institute, Incheon 21990, Republic of Korea
3Kochi Institute for Core Sample Research, Japan Agency of Marine-Earth Science and Technology, 200 Monobe-Otsu, Nankoku 783-8502, Japan
4Biogeochemistry Research Center, Japan Agency for Marine-Earth Science and Technology, 2-15, Natsushima-cho, Yokosuka 237-0061, Japan
5Marine Works Japan Ltd., 200 Monobe-Otsu, Nankoku 783-8502, Japan
6Department of Geoenvironmental Sciences, Kongju National University, Chungcheongnam-do 32588, Republic of Korea
7Isotope Imaging Laboratory, Creative Research Institution, Hokkaido University, Sapporo 001-0021, Japan

(Received March 16, 2021; Accepted May 16, 2021)

Abstract: Instrumental mass fractionation of Mg-isotopes and the relative sensitivity factor (RSF) for 27Al/24Mg ratios for in situ analysis by secondary ion mass spectrometry were investigated for minerals in Ca-Al-rich inclusions (CAIs) of meteorites, to verify systematic errors in Al-Mg chronological systematics of CAIs. We synthesized seventeen glasses with different chemical compositions that imitate those for CAI minerals and measured their Al-Mg isotopic compositions. In particular, the variation range of RSFs for six melilite glasses almost covering chemical compositions of CAI melilite is 2.0 ± 0.3%, indicating that systematic error for 27Al/24Mg for melilite is less than 2.0 ± 0.3% and likely corresponds to that of an 26Al-26Mg relative age of ∼0.01 Myr for melilite-rich CAIs. Our data strongly support the robustness of variations in initial 26Al/27Al ratios among CAIs, corresponding to a formation age spread of ∼0.4 Myr at the very beginning of the Solar System formation.
Key words: Ca-Al-rich inclusions, Al-Mg systematics, secondary ion mass spectrometry, instrumental mass fractionation, relative sensitivity factor

*Corresponding author E-mail: kawasaki@ep.sci.hokudai.ac.jp

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