Tectonics of the Ogasawara Plateau in the western Pacific Ocean.
The Ogasawara Plateau in an about 220×160 km semicircle shaped high, situates at the Junction of the N-S trending Izu Ogasawara -Mariana trenches and the E-W trending Michelson Ridge. The vessel "Takuyo” of the Maritime Safety Agency surveyed the plateau in December 1987 and January 1988 with her narrow multi beam echo sounder, single-and multichannel seismic reflection profiler, magnetometer and gravity meter. The survey revealed the details of geomorphology and geology of the plateau and the adjacent area. The geomorphological features are clearly indicating that the plateau is composed of four seamount blocks and three grabens. The seamount blocks are composed of volcanoes with thick reef limestone on the top. The features further suggest that several individual seamounts, arranged in E-W direction in line with the Michelson Ridge, drifted westward by the plate motion, came close to the trench and reduced the drift speed, backed up each other. A large number of NW-SE to NNW-SSE trending typical reverse faults were identified in the most part of the plateau. The faults, which cut the surface and underlying layers in the plateau, are showing recent compression. On the other hand, typical normal faults, associated with tension in the surface of the subducting Pacific Plate, are recognized in the ocean-ward slope of the trench around the plateau. The dredged samples from the seamounts in the land ward trench slope west of the plateau indicate that the seamounts are composed of forarc ophiolite and boninite formed by Tertiary volcanism, probably associated with subduction of the large seamounts beneath Philippine Sea Plate. These facts do not support the idea of Pacific Plate obduction, but suggest the recent slower speed subduction of the Ogasawara Plateau compared with that of the adjacent Pacific Plate. The partial speed down of the movement of the plate surface caused congestion of seamounts near the trench, which formed the Ogasawara Plateau
| Main Authors: | , , , , , , |
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| Format: | Journal Contribution biblioteca |
| Language: | Japanese |
| Published: |
1989
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| Online Access: | http://hdl.handle.net/1834/16074 |
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