Japan Geoscience Union Meeting 2019

Presentation information

[J] Oral

M (Multidisciplinary and Interdisciplinary) » M-GI General Geosciences, Information Geosciences & Simulations

[M-GI34] Marine Manganese Minerals

Tue. May 28, 2019 3:30 PM - 5:00 PM A09 (TOKYO BAY MAKUHARI HALL)

convener:Akira Usui(Marine Core Research Center, Kochi University), Yoshio Takahashi(Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo), Katsuhiko Suzuki(Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology), Takashi Ito(Faculty of Education, Ibaraki University), Chairperson:takashi ito(Ibaraki Univ.), Yoshio Takahashi(東京大学), Katsuhiko Suzuki(JAMSTEC)

4:45 PM - 5:00 PM

[MGI34-06] Mineralogical and geochemical characteristics of ferromanganese nodules in the Minamitorishima EEZ

*Kentaro Nakamura1, Koichi Horinouchi1, Ryo Shimomura1, Shiki Machida2, Kazutaka Yasukawa1,2, Koichiro Fujinaga1,2, Yasuhiro Kato1,2 (1.Department of Systems Innovation, School of Engineering, University of Tokyo, 2.ORCeNG, Chiba Institute of Technology)

Keywords:ferromanganese nodules, ferromanganese mineral, bulk chemical compositions, formation environment, Minamitorishima EEZ

Ferromanganese nodules are spherical material mainly composed of manganese, iron, and other transition metal (oxyhydro)oxides, which are widely distributed on the deep seafloor around the world [1]. It has been widely accepted that ferromanganese nodules can be classified into three types: hydrogenetic, diagenetic and hydrothermal types [1]. Among them, hydrogenetic nodules are composed of Fe–Mn (oxyhydr)oxides that precipitated from seawater and thus, this type of nodules can be expected to provide proxy paleoceanographic records [2, 3, 4, 5].
In this study, we investigated mineralogy and geochemistry of ferromanganese nodules sampled from the Minamitorishima EEZ for the purpose of elucidating formation environment of the nodules. Both the ferromanganese mineral phase and bulk chemical compositions clearly show that these nodules are hydrogenetic in origin. Based on X-ray CT and micro X-ray mapping analyses, oxide layer of the nodules can be subdivided into five layers [6. 7]. Although ferromanganese mineral is common to all the oxide layers, we found that Mn/Fe and Ni content systematically changed from inner layer to outer layer. The result implies that bottom water of the Minamitorishima EEZ has gradually been oxygenated toward the present.