日本地球惑星科学連合2019年大会

講演情報

[J] ポスター発表

セッション記号 M (領域外・複数領域) » M-GI 地球科学一般・情報地球科学

[M-GI34] 海底マンガン鉱床の環境,開発,地球史

2019年5月28日(火) 13:45 〜 15:15 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:臼井 朗(高知大学海洋コア総合研究センター)、高橋 嘉夫(東京大学大学院理学系研究科地球惑星科学専攻)、鈴木 勝彦(国立研究開発法人海洋研究開発機構・海底資源研究開発センター)、伊藤 孝(茨城大学教育学部)

[MGI34-P04] 北西太平洋産マンガンノジュールの切断面に対するマイクロ蛍光X線マッピング

*町田 嗣樹1,2下村 遼2堀之内 航一2中村 謙太郎2小木曽 哲3加藤 泰浩2,1 (1.千葉工業大学 次世代海洋資源研究センター、2.東京大学、3.京都大学)

キーワード:マンガンノジュール、マイクロX線分析、南鳥島EEZ

A dense field of hydrogenous ferromanganese nodules was discovered on a small seamount approximately 300 km east of Minamitorishima (Marcus) Island, in the western North Pacific [1]. Previous study [1] defined two fundamental features on structure and geochemistry of nodules, as follows. The large nodules generally consist of three concentric layers: the outermost mottled (sediment-filled) layer L0; the massive black layer L1; and the innermost porous (sediment-filled) layer L2. Elements including Fe, Ti, and Co are concentrated in the nodule rim rather than the center. In contrast, Mn, Al, P, Ca, Ni, and Zn are concentrated in the center, and decrease toward the rim.

To further investigate the relationship between structure of oxide layers and its geochemical features, we conducted mapping analysis for polished slab of nodules including nuclei and whole layers of oxide by a microfocus X-ray fluorescence analytical microscope (XGT-7000; HORIBA) at Kyoto University. Analysis was conducted in vacuo, and the intensity of Si, Al, P, Ca, K, Mn, Fe, Ti, Ni, Cu, and Y were determined by an energy-dispersive spectrometer at an accelerating voltage of 50 kV, 100 µm beam, and intervals of approximately 160 µm.

We identified that L2 is further sub-divided into three layers, which correspond to layers obtained by X-ray CT [2]. The most inner part of L2 (around nuclei) is characterized by high intensity of Ti and Fe. In contrast, outer part of L2 is characterized by higher intensity of Mn than that of the inner part. Many spots of high intensity of P, Ca, and Y, indicating particles of calcium phosphate including highly amount of Y (and probably rare-earth elements), are observed in the entire area of L2. We found that L1 is clearly characterized by low Si. Furthermore, we observed thin layers showing high intensity of Cu and Ni at the sediment-filled boundaries between L1 and L2, and L1 and L0. Existence of such thin layers suggests that nodules were fully covered by pelagic sediment at the intervals before formation of L1 and L0.

References: [1] Machida et al. (2016) Geochem. J.50, 539-555. [2] Shimomura et al. (2018) Goldschmidt Conference 2018.