日本地球惑星科学連合2018年大会

講演情報

[EE] Eveningポスター発表

セッション記号 S (固体地球科学) » S-IT 地球内部科学・地球惑星テクトニクス

[S-IT22] 核-マントルの相互作用と共進化

2018年5月22日(火) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:飯塚 毅(東京大学)、渋谷 秀敏(熊本大学大学院先端科学研究部基礎科学部門地球環境科学分野)、土屋 卓久(愛媛大学地球深部ダイナミクス研究センター、共同)、太田 健二(東京工業大学大学院理工学研究科地球惑星科学専攻)

[SIT22-P23] Recycled Archean sulfur in the mantle wedge of the Mariana Forearc

*青山 慎之介1西澤 学2宮崎 淳一2渋谷 岳造2上野 雄一郎3高井 研2 (1.新潟大学、2.海洋研究開発機構、3.東京工業大学)

キーワード:多種硫黄同位体、マントル不均質、蛇紋岩海山、マリアナ前弧

Non-mass dependent (NMD) sulfur isotopes in rock record is found in the Archean (>2.5 Ga) period, probably owing to the low oxygen concentration in atmosphere at that time (e.g., Farquhar et al., 2000). Recent studies reported NMD sulfur isotopes in sulfide inclusions in olivine within OIB, suggesting recycling of Archean materials in the mantle (Cabral et al., 2013; Delavault et al., 2016). However, sulfur isotopes in the mantle wedge is poorly constrained. In order to evaluate sulfur cycle in the mantle and incorporation of surface materials through subduction, we analyzed quadruple sulfur isotopes of dissolved sulfate in upwelling seepage fluids collected as deep as 202 mbsf (meters below the seafloor) in a cased hole near the summit of the South Chamorro serpentinite seamount in the Mariana Forearc.
Sulfate in the upwelling fluids show NMD (D33S ranging from −0.2‰ to −0.3‰ with analytical errors of ±0.01‰). These are unlikely to originate in typical sulfur components in the subducting plate, which is a mixture of sulfide in the MORB (D33S ≈ 0‰; Labidi et al., 2013) and sulfide produced by reduction of seawater sulfate (D33S > +0.05‰). Instead, it is comparable if Archean materials or the plume-related OIB is present in the mantle wedge beneath Mariana Forearc. Because NMD sulfur primarily originates in Archean sulfur, our results may extend the potential presence of recycled Archean materials in the upper mantle due to subduction of oceanic crusts in the Archean period or ongoing subduction of OIB seamounts abundantly exist in the Pacific Plate.

References
Farquhar, J., Bao, H.M., Thiemens, M., 2000. Atmospheric influence of Earth's earliest sulfur cycle. Science 289, 756-758.

Cabral, R.A., Jackson, M.G., Rose-Koga, E.F., Koga, K.T., Whitehouse, M.J., Antonelli, M.A., Farquhar, J., Day, J.M.D., Hauri, E.H., 2013. Anomalous sulphur isotopes in plume lavas reveal deep mantle storage of Archaean crust. Nature 496, 490-+.

Delavault, H., Chauvel, C., Thomassot, E., Devey, C.W., Dazas, B., 2016. Sulfur and lead isotopic evidence of relic Archean sediments in the Pitcairn mantle plume. Proceedings of the National Academy of Sciences of the United States of America 113, 12952-12956.

Labidi, J., Cartigny, P., Moreira, M., 2013. Non-chondritic sulphur isotope composition of the terrestrial mantle. Nature 501, 208-+.