TERRAPUB Geochemical Journal

Geochemical Journal, Vol. 52, 2018


High-precision in situ analysis of Pb isotopes in melt inclusions by LA-ICP-MS and application of Independent Component Analysis

Morihisa Hamada1*, Jun-Ichi Kimura1, Qing Chang1, Takeshi Hanyu1, Takayuki Ushikubo2, Kenji Shimizu2, Motoo Ito2, Takahiro Ozawa3 and Hikaru Iwamori1, 3

1Department of Solid Earth Geochemistry, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan
2Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 200 Monobe-otsu, Nankoku, Kochi 783-8502, Japan
3Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Meguro-ku, Tokyo 152-8551, Japan

(Received April 13, 2017; Accepted July 28, 2017)

Abstract: We report a high-precision 206Pb-based lead isotope composition of olivine-hosted melt inclusions in basaltic rocks from Rarotonga Island, Polynesia, in the southern Pacific, using femtosecond laser ablation (FsLA)-multiple Faraday collector-inductively coupled plasma-mass spectrometry (MFC-ICP-MS). This improved method enables high-precision analysis of Pb isotopes from low-Pb (≤10 ppm) melt inclusions with a crater size of ∼30 μm in diameter and depth. The small crater size allows for further analysis of major and trace elements from the same melt inclusions using FsLA-sector field (SF)-ICP-MS. Using Pb isotope ratios of two olivine-hosted melt inclusions, we suggest that the mantle source beneath Rarotonga Island is heterogeneous. Such identification becomes possible owing to high-precision in situ analysis of Pb isotopes in melt inclusions and application of statistical approaches such as Independent Component Analysis to the analytical data.
Key words: Rarotonga Island, Ocean island basalt, Pb isotope, Laser ablation ICP-MS, Independent Component Analysis

*Corresponding author E-mail: mhamada@jamstec.go.jp

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