Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Oral

S (Solid Earth Sciences) » S-CG Complex & General

[S-CG61] Ocean Floor Geoscience

Wed. May 23, 2018 1:45 PM - 3:15 PM 302 (3F International Conference Hall, Makuhari Messe)

convener:Kyoko Okino(Atmosphere and Ocean Research Institute, The University of Tokyo), Chairperson:Sato Yuki, Fujinaga Koichiro

2:45 PM - 3:00 PM

[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 Yasukawa1,2, Kentaro Nakamura1, Takashi Miyazaki3, Bogdan Vaglarov3, Koichiro Fujinaga2,1, Hikaru Iwamori3,4, Yasuhiro Kato1,2,3 (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.

[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.