Japan Geoscience Union Meeting 2015

Presentation information


Symbol H (Human Geosciences) » H-CG Complex & General

[H-CG35] Interdisciplinary approach to earth's changing surface

Wed. May 27, 2015 9:15 AM - 10:45 AM 105 (1F)

Convener:*Naofumi Yamaguchi(Center for Water Environment Studies, Ibaraki University), Hajime Naruse(Department of Geology and Mineralogy, Graduate School of Science, Kyoto University), Koji Seike(Atmosphere and Ocean Research Institute, University of Tokyo), Hideko Takayanagi(Institute of Geology and Paleontology, Graduate School of Science, Tohoku University), Masayuki Ikeda(Shizuoka University), Chair:Naofumi Yamaguchi(Center for Water Environment Studies, Ibaraki University)

9:45 AM - 10:00 AM

[HCG35-03] Lead isotopic variations of fine particles discharged from rivers of Tokai area, Central Japan

*Yu SAITOH1, Masaharu TANIMIZU2, Tsuyoshi ISHIKAWA2 (1.Center for Advanced Marine Core Research, Kochi University, 2.Kochi Institute for Core Sample Research, JAMSTEC)

Keywords:Pb isotope ratios, Sr-Nd isotope ratios, river sediments, hemipelagic sediments, Shikoku Basin

We report lead isotopic variations of fine fraction of river sediments of the Tonankai area in order to provide the reference data in resolving the provenance of hemipelagic sediment distributed in the Shikoku Basin. We targeted smaller particles than 10 μm. This grain size is important because they constitute the majority of hemipelagic sediments distributed on seafloor of the Shikoku Basin (Saitoh, 2014).
Lead isotope ratios widely differ by rivers. The most prominent contrast is recognized between the rivers draining the Izu-Honshu collision zone and the others. Isotopic ratios of the former, the Sagami, Sakawa, and Kano rivers are low (206Pb/204Pb: 18.15-18.3; 207Pb/204Pb: 15.55-15.59; 208Pb/204Pb: 38.1-38.4), while those of the latter are higher (206Pb/204Pb: 18.46-18.66; 207Pb/204Pb: 15.59-15.63; 208Pb/204Pb: 38.6-38.9) (Figure). The low ratios of the former are supposed to be the results of the contribution from the mafic rocks distributed around the collision zone. Contribution from the sedimentary rocks of accretionary complexes distributed in the watersheds must increase the isotopic ratios of the other rivers. Minor isotopic differences are supposed to be dependent on the age of accretionary comprex and types of other rocks distributed in watershed of each river. Isotopic comparison with these river sediments suggests that the sediments of the Shikou Basin deposited after 3Ma are mainly contributed from the Fuji, Abe, and Tenryu rivers.
Sr-Nd isotope ratios of river sediments will be also shown and discussed.

Saitoh, Y., 2014. Data report: grain size distribution of the late Cenozoic hemipelagic mud from Site C0011. In Henry, P., Kanamatsu, T., Moe, K., and the Expedition 333 Scientists, Proceedings of the Integrated Ocean Drilling Program 333: Tokyo (Integrated Ocean Drilling Program Management International, Inc.).