Japan Geoscience Union Meeting 2015

Presentation information

International Session (Oral)

Symbol S (Solid Earth Sciences) » S-IT Science of the Earth's Interior & Techtonophysics

[S-IT05] Hard-Rock Drilling: Oceanic Lithosphere to Island Arc Formation and Beyond

Wed. May 27, 2015 11:00 AM - 12:45 PM 303 (3F)

Convener:*Yoshihiko Tamura(R & D Center for Ocean Drilling Science, Japan Agency for Maine-Earth Science and Technology), Yildirim Dilek(Department of Geology & Environmental Earth Science Miami University), Tomoaki Morishita(School of Natural System, Colleage of Science and Technology, Kanazawa University), Takashi Sano(Department of Geology and Paleontology, National Museum of Nature and Science), Natsue Abe(R&D Center for Ocean Drilling Science Japan Agency for Marine-Earth Science and Technology), Susumu Umino(Department of Earth Sciences, Kanazawa University), Eiichi TAKAZAWA(Department of Geology, Faculty of Science, Niigata University), Shigeaki Ono(Japan Agency for Marine-Earth Science and Technology), Katsuyoshi Michibayashi(Institute of Geosciences, Shizuoka University), Chair:Natsue Abe(R&D Center for Ocean Drilling Science), Shigeaki Ono(Japan Agency for Marine-Earth Science and Technology), Katsuyoshi Michibayashi(Institute of Geosciences, Shizuoka University)

11:15 AM - 11:30 AM

[SIT05-13] Ultradepleted olivine and spinel sands in Challenger Deep, Mariana Trench

Yuka SHIMADA1, *Katsuyoshi MICHIBAYASHI1, Naonobu TERUMINE1, Shigeki UEHARA1, Shoma OYA1, Yasuhiko OHARA2, Teruaki ISHII3, Yumiko HARIGANE4, Takuro NUNOURA5, Junichi MIYAZAKI5, Ken TAKAI5, Kazutaka MANNEN6 (1.Institute of Geosciences, Shizuoka University, 2.Hydrographic and Oceanographic Department of Japan, 3.Fukada Geological Insitute, 4.AIST/GSJ, 5.JAMSTEC, 6.Hot Springs Institute of Kanagawa Prefecture)

Peridotite has been studied extensively as a clue to understand the uppermost mantle structure. Abysal peridotite is known to be exposed to the plate spreading axes such as mid-ocean ridges and the plate convergence margin such as trenches. Many studies have had interested in peridotites outcropped at the landside slope in the southern Mariana Trench. Challenger Deep (10,911 m depth) of Mariana Trench is the deepest in the Earth. However, it is difficult even today to sample rocks exposed at deeper slopes than 7,000 m depth due to technical problem. In 2008, JAMSTEC (Japan Agency for Marine-Earth Science and Technology) sampled a sediment core at 10,350 m in Challenger Deep by ABISMO (Automatic Bottom Inspection and Sediment Mobile). Mafic minerals such as olivine and spinel have been identified in this core. They may be derived from peridotites that could be exposed at deeper slopes than 7,000 m below the sea surface. Therefore, these mafic minerals may give us an opportunity to explore mantle peridotite at the bottom of Challenger Deep. We have chosen relatively coarse mineral grains from this core. These grains were analysed their chemical compositions by EPMA (Electron Probe Micro Analyzer). As a result, olivine, spinel, pyroxene, plagioclase, quartz and magnetite were identified. The olivine CaO are less than 0.07 wt%. Moreover, assuming that both spinel and olivine grains were derived from the same peridotites, spinel Cr# and olivine Mg# indicated that the peridotite could be in the mantle origin. The spinel Cr# are highly depleted up to 0.8, suggesting their origin from the forearc mantle. Olivine Mg# in the sediment core have been compared with those in peridotites occurred at the landside slope. It shows that olivine Mg# increase toward deeper slopes from 3,500 m depth. As a result, it suggests that these olivine and spinel grains could be derived from peridotites exposed at the deeper slopes than 7,000 m depth, possibly at very bottom of Challenger Deep, where unknown peridotites could have been highly depleted.