Japan Geoscience Union Meeting 2015

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Symbol S (Solid Earth Sciences) » S-CG Complex & General

[S-CG57] Structure, evolution and dynamics of mobile belts

Wed. May 27, 2015 4:15 PM - 6:00 PM A06 (APA HOTEL&RESORT TOKYO BAY MAKUHARI)

Convener:*Toru Takeshita(Department of Natural History Sciences, Graduate School of Science, Hokkaido University), Hiroshi Sato(Earthquake Prediction Research Center, Earthquake Research Institute, The University of Tokyo), Koichiro Obana(Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology), Takuya NISHIMURA(Disaster Prevention Research Institute, Kyoto University), Yukitoshi Fukahata(Disaster Prevention Research Institute, Kyoto University), Aitaro Kato(Graduate School of Environmental Studies, Nagoya University), Jun Muto(Department of Earth Sciences, Tohoku University), Katsushi Sato(Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University), Shuichi Kodaira(Institute for Research on Earth Evolution Japan Agency for Marine-Earth Science and Technology), Takeshi Sagiya(Disaster Mitigation Research Center, Nagoya University), Tatsuya Ishiyama(Earthquake Research Institute, University of Tokyo), Makoto MATSUBARA(National Research Institute for Earth Science and Disaster Prevention), Yasutaka Ikeda(Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo), Chair:Bunichiro Shibazaki(International Institute of Seismology and Earthquake Engineering, Building Research Institute)

5:00 PM - 5:15 PM

[SCG57-09] Geodynamics of subducting slab under Izu collision zone

*Masahiro ISHIKAWA1, Yumiko TSUBOKAWA1, Satoko HONDA1 (1.Yokohama National University)

Keywords:Izu collision zone, Philippine Sea slab, geodynamics

The Philippine Sea plate subducts northward under the Honshu arc, Japan. The existence of relatively thick crust of the intraoceanic arc, Izu-Bonin arc, along the western margin of the Philippine Sea plate causes a complex tectonic environment. In the south Kanto area, an accretionary wedge composed of late Cenozoic sediments overlies the downgoing Philippine Sea plate. In western part of the south Kanto area, the Izu-Bonin arc has collided with the Honshu crust; remnant pieces of the Izu-Bonin arc such as the Tanzawa block were accreted to the Honshu crust. In order to interpret the geodynamics of the subducting slab under the izu collision zone, we examine mineral assemblages and dehydration process of the subducting lower crust of the Izu arc. Previous study infers that hornblende gabbro is a main constituent rock of the lower crust of the Izu-Bonin arc. Here mineral assemblages within the gabbroic composition from the Tanzawa gabbroic rocks was calculated by Theriak-Domino software, and stability fields of minerals and dehydration process are discussed. The estimated dehydration process and calculated stability fields of amphibole and garnet expects that phase change of gabbroic rocks to garnet-bearing rocks is an important process to explain the geodynamics of the subducting slab under the Izu collision zone. In this study, we propose a new hypothesis that the microearthquakes under the Izu collision zone may be triggered by phase change of gabbroic rocks to garnet-bearing rocks which seems to enhance stress concentration by volume change in the subducting lower crust.