HR: 0800h
AN: V21D-0761    [Abstracts]
TI: Archean hydrothermal sea-floor surface environment: Australia VS South Africa
AU: * Kiyokawa, S
EM: kiyokawa@geo.kyushu-u.ac.jp
AF: Kyushu Univ. Earth and Planet., 6-10-1 Hakozaki Higashiku Fukuoka, Fukuoka, 813-8581, Japan
AU: Ito, T
EM: tito@mx.ibaraki.ac.jp
AF: Ibaraki Univ., 2-1-1 Bunkyou Mito, Ibaraki, 310-8512, Japan
AU: Koge, S
EM: kohge@geo.kyushu-u.ac.jp
AF: Kyushu Univ. Earth and Planet., 6-10-1 Hakozaki Higashiku Fukuoka, Fukuoka, 813-8581, Japan
AU: Inamoto, Y
EM: inamoto@geo.kyushu-u.ac.jp
AF: Kyushu Univ. Earth and Planet., 6-10-1 Hakozaki Higashiku Fukuoka, Fukuoka, 813-8581, Japan
AU: Ikehara, M
EM: ikehara@cc.kochi-u.ac.jp
AF: Kochi Univ. Core center, 200Monobe otu Nankoku, Kochi, 783-8502, Japan
AU: Kitajima, F
EM: kitajima@geo.kyushu-u.ac.jp
AF: Kyushu Univ. Earth and Planet., 6-10-1 Hakozaki Higashiku Fukuoka, Fukuoka, 813-8581, Japan
AU: Yamaguchi, K
EM: kosei@jamstec.go.jp
AF: JAMATEC IFREE, 2-15 Natsushima, Yokosuka, Kanazawa, 237-0061, Japan
AB: Archean greenstone belt typically contains chemical sedimentary sequences such as cherts and BIFs and underlying thick volcanics. These sequences may be used to extract information on hydrothermal activity and potential biological activity on early Earth. We compare the geological and geochemical characteristics of such chemical sediments in the 3.2 Ga Cleaverville Group and 3.4 Ga Warrawoona Group (Marble Bar Chert) in the Pilbara district and coeval Onverwacht Group (Masauri River Chert) and Komati River Formation in the Barberton Greenstone Belt. The Cleaverville Group formed by bimodal volcanism in an immature island arc. The Dixon Island Formation of the Cleaverville Group is one of the best-preserved sequences of Archean hydrothermal activity. The Dixon Island Formation is composed of Komatiite-Rhyolite Tuff, Black Chert, and Varicolored Chert Members to the top. The Komatiite-Rhyolite Tuff Member contains highly altered volcanic rocks with black chert veins. The thick Black Chert Member is characterized by low organic carbon contents (<0.5 percent) and low carbon isotope compositions (- 28 to -40 per mil). It contains fossil-like carbonaceous materials. The Masauri River Chert is also a hydrothermal sequence that is quite similar to the Dixon Island Formation. It contains highly altered volcanic rocks with numerous quartz swarms and black chert dikes, which are covered by volcanic tuff and well-stratified black/white cherts. Its upper sequence contains Fe- rich black/white cherts. Black chert of the Masauri River Chert is also characterized by low organic carbon content (<0.5 percent) and relatively high carbon isotope compositions (-20 to -30 per mil). Similarity in the petrographical and geochemical characteristics of black chert veins and massive black chert beds in the Australian and South African sections suggest that the depositional environments for those rocks were also similar. These evidences strong suggest that Archean hydrothermal system contains organic matter which is blowout from the see-floor surface. Early life exuberate (such as bacteria) on these organic rich see-floor along the vent system.
DE: 8135 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8424)
DE: 8427 Subaqueous volcanism
DE: 9305 Africa
DE: 9330 Australia
DE: 9623 Archean
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting