著者
Mayu KAKEFUDA Tatsuki TSUJIMORI Katsuyuki YAMASHITA Yoshiyuki IIZUKA Kennet E. FLORES
出版者
Japan Association of Mineralogical Sciences
雑誌
Journal of Mineralogical and Petrological Sciences (ISSN:13456296)
巻号頁・発行日
pp.190731a, (Released:2020-03-04)

Awaruite (Ni2–3Fe) is a natural occurring Ni–Fe alloy in serpentinite, which represents a better candidate to assess Pb isotope signatures in the mantle wedge since the concentration of Pb in awaruite is almost ten times higher than that in serpentine minerals. Revisiting so–called josephinite from the Josephine Ophiolite confirmed that josephinite is characterized by aggregates of awaruite with minor Ni–arsenide. The Raman spectrum obtained from the josephinite–hosting serpentinite shows diagnostic peaks of antigorite, suggesting josephinite might have formed under stability field of antigorite. Using a stepwise leaching and partial dissolution method, we obtained Pb isotope ratios of josephinite by TIMS. Since all ratios converged to a homogeneous value towards the later steps of the partial dissolution, this allowed to calculate weighted mean values that give precise Pb isotope ratios: 206Pb/204Pb = 18.3283 ± 0.0020 (MSWD = 0.49), 207Pb/204Pb = 15.5645 ± 0.0020 (MSWD = 0.36), and 208Pb/204Pb = 38.0723 ± 0.0061 (MSWD = 0.50); these values can be evaluated as one of the reference Pb isotope ratios in serpentinites from supra–subduction zone ophiolite. The newly obtained Pb isotope ratios of josephinite are consistent with the previous reported isotope ratios, which are characterized by enriched 207Pb/204Pb ratio with MORB–source like 206Pb/204Pb and 208Pb/204Pb ratios. Although these Pb isotope features interpreted as a reflection of arc magmatism in the previous study, the presence of Ni–arsenide and enriched 207Pb/204Pb ratios may indicate an involvement of As–rich fluids derived from slab sediments.

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東北大PRG論文早期公開。Josephinite中awaruiteのPb同位体比の特徴とNi–As鉱物の存在から、その形成には堆積物由来のスラブ流体が関与している可能性が示唆された。スラブ流体に関する理解を深めるために、josephiniteの同位体研究は今後とも重要。 Kakefuda et al. (2020) https://t.co/ErZapUuiVj

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