HR: 1340h
AN: V33A-1175    [Abstracts]
TI: Geochemical study on the seamounts along the Japan Trench: implications for the origin of HIMU magmas
AU: * Shimoda, G
EM: h-shimoda@aist.go.jp
AF: Geological Survey of Japan, AIST, Higashi 1-1-1, Tsukuba, 305-8567, Japan
AU: Ishizuka, O
EM: o-ishizuka@aist.go.jp
AF: Geological Survey of Japan, AIST, Higashi 1-1-1, Tsukuba, 305-8567, Japan
AU: Yamashita, K
EM: kty@misasa.okayama-u.ac.jp
AF: Institute for Study of the Earthfs Interior, Okayama University, Yamada 827, Misasa, 682- 0193, Japan
AU: Yamashita, M
EM: miwa@kobe-u.ac.jp
AF: Department of Earth and Planetary Sciences, Faculty of Science, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe, 657-8501, Japan
AU: Ogasawara, M
EM: masa.ogasawara@aist.go.jp
AF: Geological Survey of Japan, AIST, Higashi 1-1-1, Tsukuba, 305-8567, Japan
AU: Yuasa, M
EM: yuasa-m@aist.go.jp
AF: Geological Survey of Japan, AIST, Higashi 1-1-1, Tsukuba, 305-8567, Japan
AB: The Northwestern Pacific plate is characterized by existence of a large number of seamounts that is defined as Western Pacific Seamount Province (WPSP) (Koppers et al., 1998). These seamounts are considered to be produced by large-scale mantle upwelling (superplume) that is now active in the South Pacific region. As the magmatism in Cretaceous is much more active than that in present, research on the past magmatism in South Pacific region could provide a key constraint on the large-scale mantle upwelling. The seamounts that are situated along the Japan trench (Takuyo, Erimo and Ryofu-Daini Seamounts, and Joban Seamount Chain) are old seamounts in WPSP of which ages are Early to Late Cretaceous (Ozima et al. 1970; Takagi et al., 1989; Masalu et al., 1997; Nakanishi and Winterner 1998; Kobayashi et al., 1998), suggesting that these seamount would be suitable examples to study the past superplume activity. However, only a few geochemical studies have been made for the seamounts near the NE Japan (e.g., Izu, 1985). In order to evaluate the origin of seamounts near Japan trench, we collected samples during Geological Survey of Japan (GSJ) Daini-Hakureimaru cruise 05GH. Drilling was conducted at 10 sites, i.e., Smetanin seamounts (4 sites), Joban Seamount chain (6 site) including; Bousei seamount (2 sites), Daisan-Kahisma Northwest seamount (3 site) and Daisan Kashima seamount (1 site). The samples from the Hotta seamountt were also collected by dredging (2 sites). Among these sites, fresh samples were recovered from Bousei, Hotta and Smetanin seamounts. These samples are alkali basalts and andesites that are porphyritic and poorly to moderately vesiculated. The phenocrysts are mainly plagioclase and pyroxene with/without hornblende. The geochemical character of the rocks from the Bosei and Hottat is HIMU-type. However, those from the Smetanin show less HIMU signature. In this presentation, we will discuss the origin of Seamounts along Japan Trench and constrain the origin of HIMU-type magmas
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1030 Geochemical cycles (0330)
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1065 Major and trace element geochemistry
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting