Deep-sea submersible survey in the Suruga, Sagami and Japan Trenches: preliminary results of the 1985 Kaiko cruise, Leg 2 |
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| Authors: | Guy Pautot Kazuaki Nakamura Philippe Huchon Jacques Angelier Jacques Bourgois Kantaro Fujioka Toshihiko Kanazawa Yasuo Nakamura Yujiro Ogawa Michel Sguret Akira Takeuchi |
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| Institution: | Guy Pautot, Kazuaki Nakamura, Philippe Huchon, Jacques Angelier, Jacques Bourgois, Kantaro Fujioka, Toshihiko Kanazawa, Yasuo Nakamura, Yujiro Ogawa, Michel Séguret,Akira Takeuchi |
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| Abstract: | Nine submersible dives were made in three trenches off central Japan, between 2990 and 5900 m of water depth. Our observations confirm the interpretation that Daiichi-Kashima Seamount is a Cretaceous guyot formed on the Pacific plate that has traveled into the Japan Trench. We also confirmed the previous interpretation of a large normal fault that splits the seamount in two halves, the lower one being now subducting beneath the Japan margin. Compressional deformation was identified within the lower part of the inner slope in front of the seamount. The pattern of deformation that affects Quaternary sediments is in agreement with the present kinematics of the convergence between the Pacific plate and Japan. Deep-water (5700 m) clam colonies are associated with advection of fluids, driven by the subduction-related overpressures. In the northern slope of the Boso Canyon, along the Sagami Trough system (Philippine Sea plate-Japan boundary), the deformation affecting a thick upper Miocene to lower Pliocene sequence indicates two directions of shortening: a N175°E direction which is consistent with the present relative motion along the Sagami Trough (N285–N300°E) and a N30°E direction which could be related to a more northerly direction of convergence that occured during the early Quaternary and earlier. |
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