Japan Geoscience Union Meeting 2016

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International Session (Poster)

Symbol S (Solid Earth Sciences) » S-IT Science of the Earth's Interior & Techtonophysics

[S-IT11] Geodynamic evolution of northeast Asia and western Pacific

Tue. May 24, 2016 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL6)

Convener:*Gaku Kimura(Department of Earth and Planetary Science of the Graduate School of Science, The University of Tokyo), Jonny Wu(Department of Geosciences, National Taiwan University), Timothy Byrne(University of Connecticut), Kyoko Okino(Ocean Research Institute, University of Tokyo)

5:15 PM - 6:30 PM

[SIT11-P02] Major variations in vitrinite reflectance and consolidation characteristics within a post-middle Miocene forearc basin, central Japan

*Nana Kamiya1,2, Yuzuru Yamamoto2, Qian Wang3, Yuhei Kurimoto3, Feng Zhang3, Takato Takemura1 (1.Nihon University, 2.JAMSTEC, 3.Nagoya Institute of Technology)

Keywords:Forearc basin, Boso Peninsula, Vitrinite reflectance, Consolidation test

Forearc basin sediments near the oceanward margin preserve tectonic information related to plate subduction. The post-middle Miocene Boso forearc basin, central Japan, records major differences in structure, paleo-maximum temperature, and consolidation state between below (Miura Group) and above (Kazusa Group) the Kurotaki Unconformity, which formed at ca. 3 Ma. Many fault systems below the unconformity are characterized by a disaggregation-band-like inner fabric that apparently formed soon after sedimentation, whereas there are few of this type of fault system above the unconformity. Vitrinite reflectance values (Ro) are 0.38%–0.44% and 0.16%–0.22% below and above the unconformity, respectively. The consolidation yield stress (pc) in the Miura Group (23.7 MPa in the Anno Formation; 31.0 MPa in the Amatsu Formation) is much greater than that in the Kazusa Group (7.5 MPa in the Umegase Formation; 7.6 MPa in the Ohtadai Formation). These clear differences in vitrinite reflectance and consolidation characteristics above and below the unconformity are attributed to a change in the convergence direction of the Philippine Sea Plate, which resulted in the Miura Group being uplifted and eroded by ~2000 m before sedimentation of the Kazusa Group. The forearc basin, especially near the trench-slope break, records structural and physical properties reflecting the plate-tectonic environment and the development of the trench-slope.