HR: 0800h
AN: T21A-0508    [Abstracts]
TI: Accretionary Complex Origin of the Mafic-ultramafic Bodies of the Sanbagawa Belt, Central Shikoku, Japan
AU: * Terabayashi, M
EM: tera@eng.kagawa-u.ac.jp
AF: Kagawa University, Dept. of Safety Systems Construction Engineering, Kagawa, 761 Japan
AU: Okamoto, K
EM: kazu@earth.sinica.edu.tw
AF: Tokyo Institute of Technology, Dept. of Earth and Planetary Sciences, Tokyo, 152 Japan
AU: Yamamoto, H
AF: Kagoshima University, Dept. of Earth & Environmental Sciences, Kagoshima, 890 Japan
AU: Kaneko, Y
AF: Tokyo Institute of Technology, Dept. of Earth and Planetary Sciences, Tokyo, 152 Japan
AU: Ota, T
AF: Tokyo Institute of Technology, Dept. of Earth and Planetary Sciences, Tokyo, 152 Japan
AU: Maruyama, S
AF: Tokyo Institute of Technology, Dept. of Earth and Planetary Sciences, Tokyo, 152 Japan
AU: Katayama, I
AF: Tokyo Institute of Technology, Dept. of Earth and Planetary Sciences, Tokyo, 152 Japan
AU: Komiya, T
AF: Tokyo Institute of Technology, Dept. of Earth and Planetary Sciences, Tokyo, 152 Japan
AU: Anma, R
AF: University of Tsukuba, Institute of Geoscience, Ibaraki, 305 Japan
AU: Ozawa, H
AF: Naruto University of Education, Dept. of Geology, Tokushima, 772 Japan
AU: Windley, B F
EM: brian.windley@btinternet.com
AF: Leicester University, Dept. of Geology, Leicester, LE1 7RH United Kingdom
AU: Liou, J G
EM: liou@pangea.stanford.edu
AF: Stanford University, Dept. of Geological & Environmental Sciences, Stanford, 94306 United States
AB: In the high-grade Cretaceous Sanbagawa high pressure (HP) metamorphic belt our new 1:5000 scale mapping of the eclogitic mafic-ultramafic bodies and their surrounding epidote-amphibolite-facies schists, has revealed a duplex structure formed by the subduction of the Izanagi-Pacific oceanic plate. Lithologies of the two largest mafic-ultramafic bodies in the Sanbagawa belt, the Iratsu eclogite and the Higashi-Akaishi peridotite, strike WNW-ESE and dip N; the upper boundary with the surrounding schist is a normal fault, whereas the lower boundary is a thrust. The Iratsu body is subdivided into at least two tectonic units; the unit boundary is sub-parallel to a lithological boundary. The protoliths of the upper unit are gabbro, basalt, minor quartz rock and pelite, and those of the lower unit are pyroxenite, gabbro, basalt, chert and marble, in ascending order. The lower unit is characterized by layers of alternating eclogitic metagabbro and pyroxenite. The layers are extensive at the bottom of the Iratsu eclogite, and transient towards the Higashi-Akaishi body. Eclogite-facies metapsammite is intercalated between the Iratsu and Higashi-Akaishi bodies. Our mapping has revealed the following; (1) a duplex structure of the mafic-ultramafic bodies indicating their accretionary complex origin. (2) Reconstructed oceanic plate stratigraphy in ascending order of peridotite, gabbro, basalt, limestone, minor chert and pelite suggests that different parts of the protolith were derived from a mid-oceanic topographic high, an oceanic island or plateau, and an overlying trench turbidite. (3) The convergent motion of the oceanic plate changed from NW to NE during the accretion of the large oceanic island or plateau.
DE: 8000 STRUCTURAL GEOLOGY (New field, replaces single entry 8165)
DE: 8109 Continental tectonics--extensional (0905)
DE: 3660 Metamorphic petrology
DE: 1744 Tectonophysics
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting