[S-CG61] Ocean Floor Geoscience

[SCG61-P03] Re-mesasurement of the basement of the Shikoku Basin recovered by DSDP Leg 58 Sites 442~444 and ODP Leg 131 Site 808, and the characteristics of data.

*Satoru Haraguchi¹, Koichiro Fujinaga², Kentaro Nakamura³, Asuka Yamaguchi⁴, Teruaki Ishii⁵ (1.Japan Agency for Marine-Earth Science and Technology, 2.Ocean Resources Research Center for Next Generation, Chiba Institute of Technology, 3.Faculty of Engineering, University of Tokyo, 4.Atmosphere and Ocean Research Institute, University of Tokyo, 5.Center for Integrated Research and Education of Natural Hazards, Sizuoka University)

Keywords:Shikoku Basin, Back-arc basin basalt, geochemical measurement, Archive samples

The Shikoku Basin basement rocks are recovered by the DSDP Leg 58 Sites 442~444 in the central Shikoku Basin and the ODP Leg 131 Site 808 in the Nankai Trough subduction zone. The bulk chemical data of these rocks are reported by the initial report and proceeding volume of DSDP and ODP. However, these data are analyzed at 1980 of Site 442 to 444 and 1990 of site 808. Therefore, from technical limitation of the then analysis technique, precision is low in low-concentrated parts less than 10ppm of the trace element in particular, and there are many problems to compare it with the analysis level by the latest analysis technique at the present. A dominant value may not be provided in particular when comparing "element ratio" because of low significant figures of the data. We reported alteration processes in the basements of the Shikoku Basin provided in the IODP Exp. 333 Site C0012 in the JPGU 2016. In this study, we used Sites 442~444 and 808 rocks as a target for comparison. At this chance because there was not the report of new analysis, and data included a problem such as the above after a report of the DSDP, ODP. We obtained an archived DSDP and ODP samples kept by the Texas A&M university, and chemical analysis data performed a re-analysis by analysis technique same as a sample of Exp. 333. In this report, we have reported a chemical characteristic of the Shikoku Basin basements which data analyzed again show and "the significance" of the re-analysis.