| Co-Investigator(Kenkyū-buntansha) |
MASUDA Toshiaki Univ. of Shizuoka Faculty of Sci., Associate Professor, 理学部, 助教授 (30126164)
KATO Yasuhiro Univ. of Yamaguchi Faculty of Sci., Associate, 理学部, 助手 (40221882)
ISOZAKI Yukio Univ. of Tokyo Dept. Earth Sci. & Astronomy Associate Professor, 大学院・総合文化研究科, 助教授 (90144914)
HIRATA Daiji History Museum of Kanagawa Prefecture, Researcher, 学芸部, 主任学芸員(研究職) (70132917)
TERABAYASHI Masaru Kagawa University Faculty of Engineer Associate Professor, 工学部, 助教授 (40243745)
EBIHARA Mitsuru Tokyo Metropolitan Univ. Faculty of Sci., Associate Professor, 理学部, 助教授 (10152000)
KUNUGIZA Keitaro Univ. of Toyama, Dept. of Geology, Associate Professor, 教育学部, 助教授 (30225180)
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| Research Abstract |
The sampling Group has mapped the following areas to collect samples systematically over the world. Those are the orogenic belts from (1) 3.9-3.6Ga Isua, SW Greenland, (2) 3.5-3.3 Ga Pilbara, 2.7-1.9Ga Hamersley and adjacent regions, W. Australia, and 3.5 Ga Barberton region of S. Africa and 2.7 Ga Zimbabwe, (3) 1.0-0.6 Ga Russian Altai-Sayan region, and (4) Permo-Triassic cherts in Inuyama, Japan.
These field researches are planned to decode the first-class geologic events of the evolving Earth, namely, at boundaries of (1) Hadean/Archean, (2) Archean/Proterozoic, (3) Proterozoic/Phanerozoic, and (4) Permian/Triassic. All samples collected were preliminary described in terms of petrography, rock-forming mineralogy and major-trace element geochemistry.
The followings are the brief summary of our results. (1) Origin of life goes back to 3.9Ga and born at hydrothermal system of mid-oceanic ridge. (2) Depth of seawater was 1600m above ridge crest at 3.5 Ga. XCO2 was ca. 100 times higher than that of modern mid-oceanic ridge. (3) Plate tectonics goes back to 3.9Ga, when modern-stype consuming plate boundary process has already operated by the presence of rigid plate. (4) Potential mantle temperature was 150 C higher than that of modern mid-oceanic ridge. The source mantle was richer in FeO (10wt%) than that of modern MORB (8wt%). (5) Superanoxic event was identified in both deep-sea and off-shore of oceanic islands at Permo-Triassic boundary. Moreover, it was proposed that the Proterozoic-Phanerozoic boundary has been a fate of initiation of return flow of seawater into mantle at 750Ma, based on the extensive compilation of regional metamorphic belts over the world, and a new phase diagram of (MORB+Water) established by new multi-anvil experiments. The mass extinction at Permo-Triassic boundary was speculated to be caused by kimberlitic explosive magmatism and related temporary stop of photo-synthesis. This may be associated with superplume activity.
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