[S-CG61] Ocean Floor Geoscience

[SCG61-05] Origin of deep-sea sediments within the Minamitorishima EEZ based on downhole variation of bulk chemical composition and isotopic ratios

*Erika Tanaka¹, Kazutaka Yasukawa^1,2, Kentaro Nakamura¹, Takashi Miyazaki³, Bogdan Vaglarov³, Koichiro Fujinaga^2,1, Hikaru Iwamori^3,4, Yasuhiro Kato^1,2,3 (1.School of Engineering, The University of Tokyo, 2.Chiba Institute of Technology, 3.JAMSTEC, 4.Tokyo Institute of Technology)

Keywords:Sr isotopic ratio, end-members, deep-sea sediments, Minamitorishima EEZ, REY-rich mud

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.