[S-CG66] Ocean Floor Geoscience

[SCG66-18] Statistic and isotopic characterization of deep-sea sediments in the western North Pacific Ocean

*Kazutaka Yasukawa^1,2, Erika Tanaka¹, Takashi Miyazaki³, Bogdan Stefanov Vaglarov³, Qing Chang³, Junichiro Ohta^1,2, Kentaro Nakamura¹, Koichiro Fujinaga^2,1, Shiki Machida^2,1, Hikaru Iwamori^4,3,5, Yasuhiro Kato^1,2 (1.School of Engineering, The University of Tokyo, 2.ORCeNG, Chiba Institute of Technology, 3.JAMSTEC, 4.Earthquake Research Institute, The Universityof Tokyo, 5.Department of Earth and Planetary Sciences, Tokyo Institute of Technology)

Keywords:deep-sea sediment, seafloor mineral resources, REY-rich mud, multivariate analysis, isotopes, rare-earth elements

Deep-sea sediments highly enriched in rare-earth elements and yttrium (REY), lying in the Japanese exclusive economic zone around Minamitorishima Island in the western North Pacific Ocean, are expected as a promising new resource for the industrially critical metals [1-4]. In recent years, we have constructed a comprehensive geochemical dataset (1,646 samples x 41 element contents) of the deep-sea sediments including the extremely REY-rich mud, and statistically analyzed the huge dataset by an integrated method using k-means cluster analysis and independent component analysis [5]. The extracted 10 data clusters are systematically aligned from the seafloor to depth in a specific order and thus constitute stratigraphic units defined by multi-elemental geochemical features. Moreover, this characteristic alignment can also be recognized in a certain linear subspace spanned by extracted independent components.
To further characterize the data clusters statistically extracted from the high-dimensional dataset, we implemented Sr–Nd–Pb isotope analyses on a set of representative samples of each cluster. Here we regarded samples closest to each cluster centroid (calculated center of each cluster) as the representatives of each cluster. The representative bulk sediment samples were pre-treated to isolate detrital silicate fraction, and isotopic compositions of the silicate fractions were analyzed. In the presentation, by integrating the statistic and isotopic information, we will discuss the origin(s) of deep-sea sediments including REY-rich mud in the western North Pacific Ocean.

[1] Kato et al. (2011) Nat. Geosci. 4, 535-539.
[2] Iijima et al. (2016) Geochem. J. 50, 557-573.
[3] Takaya et al. (2018) Sci. Rep. 8, 5763.
[4] Tanaka et al. (2020) Ore Geol. Rev. doi.org/10.1016/j.oregeorev.2020.103392
[5] Yasukawa et al. JpGU2019.