[S-CG61] 海洋底地球科学

[SCG61-05] 化学組成及び同位体比に基づく南鳥島周辺EEZ内堆積物の起源の変遷

*田中 えりか¹、安川 和孝^1,2、中村 謙太郎¹、宮崎 隆³、Bogdan Vaglarov³、藤永 公一郎^2,1、岩森 光^3,4、加藤 泰浩^1,2,3 (1.東京大学工学系研究科、2.千葉工業大学、3.海洋研究開発機構、4.東京工業大学)

キーワード：Sr同位体、端成分、深海堆積物、南鳥島EEZ、レアアース泥

Recently, deep-sea sediments containing a high concentration of rare-earth elements and yttrium (REY), which is called “REY-rich mud”, were discovered in the Pacific Ocean [1]. Moreover, the presence of “extremely REY-rich mud” was confirmed within the Japanese exclusive economic zone (EEZ) surrounding Minamitorishima Island [2]. Although previous studies have shown that the main host phase of REY in these sediments is biogenic calcium phosphate based on bulk and in situ geochemical analyses [2,3], the contribution of other components constituting the REY-rich mud have not been completely understood yet.

One of the most effective ways to constrain the origin(s) of the deep-sea sediments, including REY-rich mud, is to use isotopic ratios of the sediments, because each possible geochemical end-member has characteristic isotopic ratios reflecting source materials and genetic processes [4].

Here, to clarify the origin of deep-sea sediments within the Minamitorishima EEZ, we modeled and quantified the contribution ratios of a few, representative geochemical end-members based on Sr isotopic ratio and major-/trace-element contents. The reconstructed downhole variation of the contribution ratios indicates a transition of end-members along with the change of geological settings due to the motion of the Pacific plate.



References
[1] Kato et al. (2011) Nature Geoscience 4, 535-539.
[2] Iijima et al. (2016) Geochemical Journal 50, 557-573.
[3] Kon et al. (2014) Resource Geology 64, 47-57.
[4] Capo et al. (1998) Geoderma 82, 197 – 225.