T019-07
Interrupt and resurgence of subduction: switch of subducting plate from the Pacific to the Philippine Sea Plates in the Miocene SW Japan margin

Wednesday, 9 December 2020: 07:24
Virtual
Gaku Kimura, Tokyo University of Marine Science and Technology, Tokyo, Japan, Yoshitaka Hashimoto, Kochi University, Kochi, Japan, Asuka Yamaguchi, University of Tokyo, Kashiwa, Japan, Hiroaki Koge, Tsukuba, Ibaraki, Japan, Mari Hamahashi, Kobe University, Ocean bottom exploration center, Kobe, Japan, Yohei Hamada, JAMSTEC, Kochi Institute for Core Sample Research, Nankoku, Japan and Yujin Kitamura, Kagoshima University, Kagoshima, Japan
Recorded Presentation
Abstract:
Geological and geophysical investigations have been intensively conducted in the Nankai Trough and southwest Japan. Recent plate reconstructions infer a major reorganization during the Neogene. The timing and events, however, remain elusive, especially regarding the interaction of the Philippine Sea Plate (PSP) with the Pacific plate, the collision of the proto-Izu arc, and the formation of the TTT (trench-trench-trench) triple junction. In this study, we give an overview of recent progress in drilling, systematic dating of rocks and sediments, and geophysical studies in this margin, and reevaluate the hypotheses for the Miocene tectonics in southwest Japan.

Three hypotheses have been proposed for the Neogene Nankai subduction zone;

1) continuous subduction of the PSP without break since ~17 or ~15 Ma,

2) immediate switch of subduction from the Pacific (or other micro-oceanic plate) to the PSP at ~10Ma, ~8Ma or ~5Ma,

or

3) a break of subduction of the PSP after the proto-Izu arc arrival near to the east of the present TTT triple junction at ~12Ma and resurgence of subduction since ~6 Ma.

Recent drilling campaign into the Nankai forearc by IODP NanTroSEIZE project suggests that the current accretion started at ~6 Ma. The result is consistent with the third hypothesis. This inference is also able to explain a tomographic image for the PSP slab several hundred km long beneath the SW Japan and Ryukyu arc assuming relative convergence of NNR-MORVEL56 model between the PSP and overriding plates.

Age data acquired in the past decade suggests that the PSP subduction along the Nankai margin ceased at ~13Ma, which is close to the third hypothesis if it was a switch of subduction from Pacific to PSP as suggested.

The driving mechanism for this plate kinematics is a matter of debate. The force balance acting along the plate boundaries surrounding PSP during ~15 Ma requires examination.

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