HR: 1340h
AN: T53A-1402    [Abstracts]
TI: The petrological study on the dredged volcanic rocks from forearc seamount along Ogasawara-Mariana forearc
AU: * Yibing, L
EM: liyibing@ori.u-tokyo.ac.jp
AF: Ocean Reseach Institute, University of Tokyo, 1-15-1 Minamidai,Nakanoku,Tokyo,Japan, Tokyo, 164
AU: Teruaki, I
EM: ishii@ori.u-tokyo.ac.jp
AF: Ocean Reseach Institute, University of Tokyo, 1-15-1 Minamidai,Nakanoku,Tokyo,Japan, Tokyo, 164
AU: Yuki, Y
EM: geoishw@kenroku.kanazawa-u.ac.jp
AF: Department of Earth Science,Kanazawa University, Kakuma,Kanazawa, Japan, Kanazawa, 920
AU: Akira, I
EM: geoishw@kenroku.kanazawa-u.ac.jp
AF: Department of Earth Science,Kanazawa University, Kakuma,Kanazawa, Japan, Kanazawa, 920
AB: Hahajima Seamount is one of forearc seamount located at about 20 km west of Ogasawara Trench, and about 110 km southeast of Ogasawara Islands.Serpentinized ultramafic rocks, mafic rocks, metamorphic rocks, and volcanic rocks were dredged from this large seamount. The dredged volcanic rocks during KH03-3 and KT04-28 can be subdivided into two types: boninitic series and tholeiitic series. The boninitic rocks include boninite, boninitic andesite-dacite and rhyolite. Some boninitic andesites show typical adakitic or bajaitic chemical characteristics, TiO2=0.3; FeO*/MgO=0.5; Sr 500-600 ppm; Y 7-8 ppm. The boninitic rocks are similar to the nearby Chichijima Island type volcanic rocks. The tholeiitic series include aphyric basalt and phyric basaltic andesite, bulk compositions of these rocks are similar to anther neaby Hahajiam Island type island arc tholeiitic rocks :TiO2=0.5; SiO2 = 50-55, and a few basalts show chemical characteristics similarly to MORBs. There is no petrological evidence to show any relation between these two types of magma in Hahajiam Seamount. To explain the association of boninitic and tholeiitic volcanic rocks in the Hahajima Seamount, it is anticipated that there had been two distinct magma sources at different time interval in this area. At an early stage of subduction, may be the mantle wedge was so much hot that the subducted oceanic crust and wadge mantle were partly melted at a shallower depth, and thus adakitic and boninitic magmas were derived in this special geo-tectonic environment,respectively. After the formation of boninitic magma stage, the subducted oceanic crust became cold, the tholeiitic magma was derived at a deeper depth where low temperature mantle wedge produce common island arc magmatism. The dredged volcanic rocks from other forearc seamount in Mariana during KH05-1-5 will be also discussed.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
SC: Tectonophysics [T]
MN: Fall Meeting 2005